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Molecular Mechanisms Controlling Dormancy and Germination in Barley

Written By

Santosh Kumar, Arvind H. Hirani, Muhammad Asif and Aakash Goyal

Submitted: 05 November 2012 Published: 03 July 2013

DOI: 10.5772/55473

From the Edited Volume

Crop Production

Edited by Aakash Goyal and Muhammad Asif

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1. Introduction

1.1. History of barley

Barley (Hordeum vulgare L.) is amongst the oldest crops within cereals. Archaeological remains of this crop have been discovered at different locations in the Fertile Crescent (Zohary & Hopf, 1993) indicating that barley is being cultivated since 8,000 BC. The wild relatives of barley were recognized as Hordeum spontaneum C. Koch. However, in the recent literature of taxonomy, H. spontaneum C. Koch, H. vulgare L., as well as H. agriocrithon Åberg, are believed to be the subspecies of H. vulgare (Bothmer & Jacobsen, 1985). Studies with molecular markers have confirmed that barley was brought into cultivation in the Isreal-Jordan area but barley diversification occurred in Indo-Himalayan regions (Badr et al., 2000).

1.2. Importance of barley in Canada

Barley, a gladiator’s food in Athens and the only crop to be used as a form of money in early Sumerian and Babylonian cultures, is the fourth largest cultivated crop in the world after wheat, rice and maize. Barley is one of the most fundamental plants in human nutrition and it is one of the most widely cultivated cereal grown in various climatic regions of world; starting from sub-Arctic to subtropical (Zohary & Hopf, 1993). Depending on the physical arrangement of the kernels on the plant, it is categorized into two different types as six-row and two-row barley. Based on the presence or absence of covering on the kernels, it is also classified as hulled or hull-less.

In Canada, it was first cultivated in Port Royal in 1606. Today, Canada is the 4th biggest barley producer after the European Union, Russia and Ukraine (Taylor et al., 2009). Most farmers grow barley for sale as malting barley. If the grain does not meet malting quality, it is sold as feed barley. Malting quality is somewhat subjective and depends upon the supply of good malting barley and its price. In the past couple of years, barley crops have suffered great loss in yield and quality due to lower germination potential and water sensitivity (Statistics Canada, 2007). Despite significant losses in barley production and yield in the year 2006-2007 (9.5 million tonnes (Mt)), the total production of barley increased (11.8 Mt) in 2007-2008 due to larger cropping area at the expense of wheat acerage (Statistics Canada, 2007).

Total barley production decreased by 10% and the harvested area by 1.5% in 2009 compared to 2008. Domestic use has increased by 4% due to a decline in corn imports. Total exports have increased by 12.5% in 2009 after a drastic decline of 47% in 2008 from the previous year (USDA Report, 2009). Average price for malt barley has gone down significantly from $208 to $179 per tonne (Agric. & Agri-Food Canada, 2009).

1.3. Challenges related to barley production

Malting quality characteristics (beta-glucan content, protein breakdown, fermentability, hull adherence and even germination) are extremely important aspects for barley improvement. While considerable progress has been achieved, much remains to be done in terms of improving the quality and production of malting barley. Quality of barley significantly affects its end utilization. Statistical data indicate that approximately 19% of total barley produced is used in malting process, 8% is consumed as food, 2% in industrial processes and about 73% is used for animal feed due to inadequate malting quality (, 2007). The issues linked with germination of malting barley have acquired substantial global attention for the last few years. It is evident from the literature that storage conditions and pre-harvest sprouting have major consequences on germination. The underlying causes for varietal differences in these characteristics is still unclear. Secondary dormancy greatly reduces the germination and marketability of grains used for malting purposes. Therefore, there is dire need to address this issue that malting barley sustains its germination without prolonged dormancy and pre-harvest sprouting.


2. Seed dormancy

2.1. Seed dormancy: Definition

Seed dormancy is a common characteristic of wild plants which ensures their continued existence/survival under unfavourable conditions, decreases competition with other species and prevents damage to seedlings from out-of-season germination of the seed. Domesticated species, on the other hand, are selected for uniform germination and rapid seedling establishment often leading to selection of genotypes with less dormancy. This can lead to pre-harvest sprouting (PHS), a phenomenon in which the seed germinates on the parent plant causing extensive loss of grain quality to crops like wheat, barley and maize (Bewley & Black, 1994).

Seed dormancy is defined as “inhibition of germination of an intact viable seed under favourable conditions” (Hilhorst, 1995; Li & Foley, 1997; Bewley, 1997). The germination block has developed in a different way from one species to another depending upon their habitat and conditions of growth. These dormancy mechanisms have evolved because these germination blocks have been operated in a variety of climates and habits. In light of these complex nature of germination blocks, another definition of dormancy has been defined as, a “dormant seed cannot germinate in a specified period of time under any combination of conditions that are otherwise sufficient for its germination” (Baskin & Baskin, 2004). It is reported that dormancy must not be linked with lack of germination, but dormancy is the combination of characteristics of the seed which decide physical and environmental circumstances needed for germination (Finch-Savage & Leubner-Metzger, 2006). Germination can be defined as appearance of radicle from seed coat. The requirement of germination may include one or more of the processes like mobilization of stored food, overcoming the physical barrier by activation of cell wall degrading enzymes followed by resumption of active growth by cell elongation and division (Finkelstein et al., 2008).

2.2. Classification of seed dormancy

Although almost all kinds of dormancy cause delay in germination, the principal of this delay may vary from species to species. The variation can be due to embryonic immaturity or due to the existence of physical or physiological constraints caused by the presence of a hard seed coat or some inhibitory chemicals that interfere with embryo growth (Finch-Savage & Leubner-Metzger, 2006). Dormancy can be primary dormancy that is acquired in the later developmental phases of embryo development and seed maturity. There are also conditions in which after-ripened, imbibed seeds enter into secondary dormancy when exposed to unfavourable temperature, light or low moisture conditions (Bewley, 1997).

Despite the progress in understanding the mechanisms controlling dormancy, it can be treated as the least recognized event (Finch-Savage & Leubner-Metzger, 2006). Both physiologists and ecologists have studied the factors controlling dormancy but the outcome is far from clear due to the fact that dormancy is affected by numerous environmental conditions (an ecologist’s dilemma) and the model species like Arabidopsis studied by molecular physiologists and geneticists tend to have a very shallow dormancy (Walck et al., 2005). The molecular controls that regulate dormancy can be of two different components i.e., an embryo or a seed coat. However, dormancy is a entire seed trait and on this basis, can be classified into the five classes namely physiological, morphological, morpho-physiological, physical and combinatorial dormancy (Nikolaeva, 1969; Baskin & Baskin, 2004; Finch-Savage & Leubner-Metzger, 2006).

2.3. Factors affecting dormancy

Dormancy is affected by various factors and the potential regulators are identified by their effect on depth of dormancy or by analysis of genetic lines that have varying levels of dormancy. The factors that affect dormancy are classified into two broad categories, embryo- and seed coat imposed dormancy. A hard seed coat manifests its effect on dormancy by prevention of water uptake during imbibition (waxy or lignified tissues in legume seeds), mechanical constraint due to hard seed coat (nuts) or endosperm (lettuce) causing inhibition of radicle protrusion, interference with gas exchange (cocklebur) and retention of inhibitors (Xanthium) and production of inhibitors like abscisic acid (ABA). Genetic variation in seed coat components such as testa layer, pericarp and pigmentation also cause altered dormancy and seed longevity (Debeaujon et al., 2000; Groos et al., 2002; Sweeney et al., 2006). Pigmented seeds are generally more dormant although hormone levels and their sensitivity to them may increase dormancy of non-pigmented seeds (Gale et al., 2002; Walker-Simmons, 1987; Flintham, 2000). Many nitrogenous compounds like nitrite (NO2-), nitric oxide (NO), and nitrate (NO3-) cause dormancy release. NO could promote germination by cell wall weakening and instigating vacuolation (Bethke et al., 2007). Genomic studies in rice to identify loci controlling seed colour, dormancy and shattering resistance show a tight linkage between the responsible genes and single locus can also control these traits (Ji et al., 2006).

Embryo dormancy is controlled by inherent characteristics of the embryo. The presence or absence of embryo dormancy has mainly been attributed to the content and sensitivity of phytohormones ABA and gibberellic acid (GA) (Bewley, 1997). Dormancy and germination are also affected by environmental factors such as light, moisture and temperature (Borthwick et al., 1952; Gutterman et al., 1996). The intensity of dormancy in the mature seed and its onset during seed development vary considerably due to genotype by environmental interaction during the entire process of seed development (Corbineau et al., 2000; Crome et al., 1984; Bewley, 1997;).

2.4. Hormonal control of dormancy

The plant hormone abscisic acid is required for setting dormancy during embryo maturation and its deposition associate with the commencement of primary dormancy (Kermode, 2005). Another plant hormone, gibberellic acid is antagonistic in action to ABA. Gibberellins promote post-germinative growth by activating hydrolyzing enzymes that break cell walls, mobilize seed storage reserves and stimulate embryo cell expansion (Bewley, 1997). Ethylene also promotes germination by antagonizing ABA signalling. Ethylene receptor mutants have higher ABA content and are hypersensitive to ABA (Ghassemian et al., 2000; Beaudoin et al., 2000; Chiwocha et al., 2005). Plant steroidal hormones, brassinosteroids, enhance the germination potential of embryos in a GA-independent manner (Leubner-Metzger, 2001). The germination completion and establishment of seedling is accomplished by Auxin (Carrera et al., 2007; Ogawa et al., 2003; Liu et al., 2007a). Auxin accumulates at the radicle tip during embryo development and in seeds after imbibition (Liu et al., 2007a). Although various hormones may affect dormancy and germination, the general consensus is that ABA is the primary mediator of dormancy (Koornneef et al., 2002; Holdsworth et al., 2008; Finkelstein et al., 2008).

2.5. ABA and GA regulate dormancy and germination

The functions of ABA in dormancy maintenance and initiation are firmly established and widely reviewed (Koornneef et al., 2002; Finch-Savage & Leubner-Metzger, 2006; Finkelstein et al., 2008). In cereals like wheat, barley and sorghum, ABA controls the onset of dormancy (Walker-Simmons, 1987; Jacobsen et al., 2002). Genetic studies show that the de novo synthesis of ABA in embryo or endosperm is required to induce dormancy (Nambara & Marion-Poll, 2003). Other studies with ABA-deficient mutants have suggested that ABA in the embryos and not the maternal ABA is crucial for induction of dormancy (Karssen et al., 1983). Dormancy may be maintained by renewed post-imbibition synthesis of ABA (LePage-Degivry & Garello, 1992; Ali-Rachedi et al., 2004). The reduction in seed dormancy has been seen for ABA biosynthetic enzymes, that have ABA sequestration with expressed antibodies in the seeds and in seeds that are treated with chemicals for inhibition of ABA biosynthesis (Nambara & Marion-Poll, 2003; Lin et al., 2007). The content of ABA and resulting dormancy are controlled by interaction of ABA biosynthetic and ABA catalyzing enzymes. The most critical enzyme in ABA biosynthesis is the 9-cis-epoxycarotenoid dioxygenase (NCED) that is essential for ABA synthesis in endosperm and embryo (Lefebvre et al., 2006). Rate-limiting enzyme during ABA biosynthesis, NCED regulates ABA biosynthesis during induction of secondary dormancy (Leymarie et al., 2008). During the transition from embryo maturation to germination, ABA is catabolised by ABA 8’-hydroxylases which are encoded by cytochrome P450 CYP707A gene family causing a decline in dormancy (Okamoto et al., 2006). Imbibition of embryos in water also causes leaching of ABA resulting in reduced dormancy (Suzuki et al., 2000). After-ripening, which is occurring during dry storage of seeds, causes a decline in embryo ABA content and sensitivity (Grappin et al., 2000). In a study conducted on pre-harvest sprouting (PHS) in susceptible and resistant wheat cultivars, after-ripening occured prior to harvest ripeness in the majority of PHS-susceptible cultivars, whereas it was slowest in cultivars that were most PHS-resistant. However, no direct relationship could be found between timing of caryopsis after-ripening and dormancy or ABA responsiveness in wheat (Gerjets et al., 2009).

ABA content as well as ABA sensitivity are critical components of embryo dormancy. ABA-insensitive mutants that are deficient in ABA perception or signalling have lower dormancy and exhibit viviparous germination (Koornneef et al., 1984; Robichaud & Sussex, 1986; Koornneef et al., 1989). Analysis of sprouting-susceptible and sprouting-resistant cultivars of wheat for ABA content and ABA sensitivity showed larger differences in ABA sensitivity than ABA content measured by capability of ABA to block embryo germination (Walker-Simmons, 1987).

The role of GA in modulating dormancy is highly debated (Finkelstein et al., 2008). The treatment with GA may not direct germination in few species or in fully dormant seeds of Arabidopsis. The decline of ABA content is usually needed prior to embryo GA content or sensitivity to the hormone increases (Ali-Rachedi et al., 2004; Jacobsen et al., 2002). After-ripening, which leads to a decline in ABA content and ABA sensitivity, results in increased sensitivity to GA and light in Arabidopsis (Derkx & Karssen, 1993). So the ratio of ABA to GA seems to be critical, where a higher content of ABA overrides the growth-promoting effect of GA. In cereals, although the GA signalling components seem to be similar to dicots, redundant GA signalling pathways may exist. This is evident from the fact that in rice, the mutation in the only known receptor of GA, Gibberellin-Insensitive Dwarf 1 (GID1) leads to decreased α-amylase production (Ueguchi-Tanaka et al., 2005); however mutating all three homologues of GID1 in Arabidopsis inhibits germination (Willige et al., 2007). Therefore, it can be concluded that the embryo dormancy in case of cereals, for the most part, is controlled by ABA content and sensitivity.

2.6. Effect of light on dormancy occurs through ABA and GA metabolism

The role of light in regulation of dormancy was first identified when germination was induced by exposing the dark-imbibed seeds with red (R) light pulse and the successive far-red (FR) light pulse cancelled the effect of red light (Borthwick et al., 1952). This response is mediated by the R/FR phytochromes, UV-A/blue light receptor cryptochromes, the phototropins and the recently identified blue light receptor zeitlupes (Bae & Choi, 2008).

The induction of germination by red light can be substituted by the application of GA (Kahn et al., 1957), whereas red light application do not induce germination in mutants deficient in GA (Oh et al., 2006). Toyomasu et al., (1998) reported that the GA biosynthetic gene’s expression encoding GA3ox (LsGA3ox1 in lettuce and AtGA3ox1 and AtGA3ox2 in Arabidopsis) is generated by R light and its activation is inhibited by FR light. On the other hand, transcripts of a GA-deactivating gene GA2ox (LsGA2ox2 in lettuce and AtGA2ox2 in Arabidopsis) are reduced by R light (Yamauchi et al., 2007; Oh et al., 2006; Nakaminami et al., 2003; Seo et al., 2006).

Similar to modulation of GA content, ABA biosynthetic and deactivating enzymes are also regulated by light. Genes encoding ABA biosynthetic enzymes NCED (LsNCED2 and LsNCED4 in lettuce and the Arabidopsis AtNCED6 and AtNCED9) and zeaxanthin epoxidase (AtZEP/AtABA1 in Arabidopsis) are reduced by R light treatment (Seo et al., 2006; Sawada et al., 2008; Oh et al., 2007) whereas, transcript levels of ABA-deactivating genes encoding CYP707A (LsABA8ox4 in lettuce and CYP707A2 in Arabidopsis) are elevated by R light (Sawada et al., 2008; Oh et al., 2007; Seo et al., 2006).

The phytochromes regulate the levels of ABA and GA by one of the interrelating proteins PHYTOCHROME INTERACTING FACTOR3-LIKE 5 (PIL5) which belongs to a family of helix-loop-helix (bHLH) family of proteins containing 15 members (Yamashino et al., 2003; Toledo-Ortiz et al., 2003;). Studies of PIL5 over-expressing and mutant lines show that it regulates ABA and GA content by regulating their metabolic genes (Oh et al., 2006).


3. Molecular networks regulating dormancy

3.1. Perception and transduction of ABA signal

3.1.1. ABA receptors

Physiological studies in different plant species indicate that accumulation of ABA is required for induction and maintenance of dormancy (Finkelstein et al., 2008). The perception of ABA and its downstream signalling to inigtiate ABA-regulated responses is an area of active research. Various lines of evidence suggest multiple sites of ABA perception, thus, multiple ABA receptors (Allan & Trewavas, 1994; Gilroy & Jones, 1994; Huang et al., 2007). The first ABA-specific binding protein, a 42 kDa ABAR, was identified and isolated from Vicia faba leaves and the pretreatment of their guard cell protoplasts with a monoclonal antibody against the 42 kDa protein reduced ABA induced phospholipase D activity in a manner that was dose-dependent (Zhang et al., 2002). Another 52kDa protein, ABAP1 was shown to bind ABA and was up-regulated by ABA in barley aleurone layer tissue (Razem et al., 2004). The ABA “receptor”, Flowering Time Control Locus A (FCA) in Arabidopsis was identified based on its high sequence similarity to barley ABAP1 and was shown to bind ABA and affect flowering (Razem et al., 2006). Another ABA receptor from Arabidopsis, the Magnesium Protoporphyrin-IX Chelatase H subunit (CHLH) regulates classical ABA-regulated processes like stomatal movements, post germination growth and seed germination (Shen et al., 2006).The CHLH also shared very high sequence similarity to ABAR (Shen et al., 2006). In 2008, questions about FCA being a receptor for ABA arose in both the laboratory of the original authors and, independently, in laboratories in New Zealand and Japan. This culminated in the simultaneous publication of a letter questioning the original results (Risk et al. 2008) and a retraction of the claim that FCA was an ABA receptor (Razem et al., 2006). Subsequent studies have confirmed that the findings of Razem et al., (2006) were not reproducible (Risk et al., 2009; Jang et al., 2008). Questions have also been raised regarding CHLH and its effect on feedback regulation of ABA synthesis and the apparent lack of a mechanism for its ABA receptor function (Shen et al., 2006; Verslues & Zhu, 2007). CHLH binding to ABA was proven using more than one method (Wu et al., 2009). Yet the barley homologue of CHLC (magnesium chelatase 150 kD subunit) does not bind ABA (Muller & Hansson, 2009). Two classes of plasmamembrane ABA receptor, a G-protein-coupled receptor (GPCR), the GCR2, and a novel class of GPCR, the GTG1 and the GTG2 have been discovered. They regulate major ABA responses such as seed germination, seedling growth and stomatal movement (Liu et al., 2007b; Pandey et al., 2009). However, the GCR2 mediation of ABA-controlled seed germination and post-germination growth are controversial as the ABA-related phenotypes are lacking or weak in gcr2 mutants (Gao et al., 2007; Guo et al., 2008). GTGs regulate ABA signalling positively and interact with the only Arabidopsis G-protein α-subunit, GPA1, which can negatively regulate ABA signalling by nullyfying the activity of GTG-ABA binding (Pandey et al., 2009). The ABA insensitive mutants abi1 and abi2 belong to Mg2+- and Mn2+-dependent serine-threonine phosphatases type 2C (PP2Cs) and are known to be negative regulators of ABA signalling (Merlot et al., 2001; Gosti et al., 1999; Rodriguez et al., 1998; Meyer et al., 1994). The 14 member gene family of Regulatory Components of ABA Receptor (RCARs), which interact with ABI1 and ABI2, bind ABA, mediate ABA-dependent inactivation of ABI1 and ABI2 in vitro and antagonize PP2C action in planta (Ma et al., 2009). PYRABACTIN RESISTANCE 1 (PYR/PYL family of START proteins) were shown to inhibit the PP2C mediated ABA signaling (Park, 2009). In Arabidopsis, the PYR/PYL/RCAR family proteins constitute the major in vivo phosphatase 2C-interacting proteins (Noriyuki et al., 2010). The crystal structure of Arabidopsis PYR1 indicated that the molecule existed as a dimer, and the mechanism of its binding to ABA in one of the PYR1 subunits was recently established (Nishimura et al., 2009; Santiago et al., 2009). Finally, the whole ABA signalling cascade that includes PYR1, PP2C, the serine/threonine protein kinase SnRK2.6/OST1 and the transcription factor ABF2/AREB1 was reconstituted in vitro in plant protoplasts resulting in ABA responsive gene expression (Fujii et al., 2009).

3.1.2. ABA signalling components

To identify the different ABA signalling components, various Arabidopsis mutants were screened for insensitivity to ABA for germination and were termed ABA insensitive (abi) (Koornneef et al., 1984; Finkelstein, 1994). The ABI1 and ABI2 encoded protein phosphatase 2C (type 2C phosphatases, PP2C) regulate ABA signalling ( Leung et al., 1997). ABI3, ABI4 and ABI5 control mainly seed related ABA responses (Parcy et al., 1994; Finkelstein & Lynch, 2000).

The process of dormancy initiates during early seed maturation and continues until the seed matures completely (Raz et al., 2001). In Arabidopsis, the seed maturation and induction of dormancy is mainly controlled by four transcription factors namely FUSCA3 (FUS3), ABSCISIC ACID INSENSITIVE 3 (ABI3), LEAFY COTYLEDON 1 (LEC 1) and LEC 2 (Stone et al., 2001; Baumlein et al., 1994; Giraudat et al., 1992; Lotan et al., 1998). The plant specific transcription factors with the conserved B3-binding domain include ABI3, FUS3 and LEC2 (Stone et al., 2001). LEC1 encodes the HAP3 subunit of a CCAAT-binding transcription factor CBF (Lotan et al., 1998). Common mutant phenotypes such as decreased dormancy at maturation occur due to abi3, lec1, lec2 and fus3 and they affect seed maturation severely (Raz et al., 2001) as well as cause reduced expression of seed storage proteins (Gutierrez et al., 2007). A study, using Arabidopsis cultivars that differed in dormancy, showed no correlation between LEC1, FUS3, ABI3 and Em expression and dormancy (Baumbusch et al., 2004). Although all four genes affect embryo maturation, they also play a unique role in regulating each other’s functionality and expression pattern (Holdsworth et al., 2008). FUS3 controls formation of epidermal cell identity and embryo derived dormancy (Tiedemann et al., 2008). Loss of LEC1 causes germination of excised embryos similar to lec2 and fus3 mutants (Raz et al., 2001). LEC2 controls the transcription program during seed maturation and affects DELAY OF GERMINATION 1 (DOG1), the first seed dormancy protein accounting for variation in natural environment as identified by quantitative trait loci (QTL) analysis (Bentsink et al., 2006; Braybrook et al., 2006). Both LEC1 and LEC2 regulate the expression of FUS3 and ABI3 (Kroj et al., 2003; Kagaya et al., 2005). ABI3 and FUS3 positively auto-regulate themselves and each other creating a feedback loop (To et al., 2006). Interestingly, none of these four transcription factors (LEC1, FUS3, ABI3 and LEC2) contains motifs to interact with an ABA response element (ABRE), but do contain a B3 domain that interacts with the RY motif present in the promoters of genes that produce RNA during the late maturation phase of the seed (Ezcurra et al., 1999; Reidt et al., 2000; Monke et al., 2004; Braybrook et al., 2006). The transcription factor ABSCISIC ACID INSENSITIVE 5 (ABI5) is a basic leucine zipper (bZIP) domain-containing protein that interacts with ABRE and activats ABA-mediated transcription in seeds (Finkelstein & Lynch, 2000; Carles et al., 2002). ABI3 activates RY elements, physically interacts with ABI5 and this physical interaction seems to be necessary for ABA-dependent gene expression (Nakamura et al., 2001).

Although much information on dormancy regulation is available for dicots like Arabidopsis, the molecular control of dormancy in cereals is not very clear. One of the key genes in regulating seed maturation, dormancy and desiccation in maize is Viviparous1 (VP1), an ortholog to ABI3 in Arabidopsis (McCarty et al., 1989; McCarty et al., 1991; Giraudat et al., 1992). It is also responsible for transcriptional control of the LATE EMBRYOGENESIS ABUNDANT (LEA) class of proteins (Nambara et al., 1995; Nambara et al., 2000). VP1 is involved in root growth-related interaction between ABA and auxin (Suzuki et al., 2001). QTL analysis showed VP1 to be responsible for seed dormancy and PHS (Flintham et al., 2002; Lohwasser et al., 2005). VP1 is responsible for controlling embryo maturation and dormancy as well as inhibition of germination (McCarty & Carson, 1991; Hoecker et al., 1995). Like ABI3, ABI5 and VP1 interac to regulate embryonic gene expression and sensitivity of seed to ABA (Lopez-Molina et al., 2002). VP1/ABI3 has been cloned from various dicot and monocot species (Hattori et al., 1994; Jones et al., 1997; Rohde et al., 2002) and contains three basic domains designated B1, B2 and B3 and a N-terminal acidic domain (A1) (Giraudat et al., 1992). The A1 domain is responsible for ABA-mediated transcriptional activation, B2 for ABRE-mediated transcriptional activation and B3 for RY/G-box interaction (Hoecker et al., 1995; Ezcurra et al., 1999). VP1/ABI3 is also alternatively spliced in various plant species and its mis-splicing causes PHS in wheat (McKibbin et al., 2002; Wilkinson et al., 2005; Gagete et al., 2009). ABI5 undergoes alternative splicing forming two variants which interact with each other and each having distinct binding affinity to VP1/ABI3 (Zou et al., 2007). In barley, ABA-dependent up-regulation of ABI5 is positively regulated by a feed-forward mechanism that involves ABI5 itself and VP1 (Casaretto & Ho, 2005).

Our work on FCA and FY, two key components in regulation of flowering, suggest that commonalities exist in germination and flowering pathways. The transcript levels of barley FCA are positively correlated to dormant state of the embryos and are involved in regulation of VP1 and Em gene promoters (Kumar et al., 2011). The Arabidopsis FY, which regulates the autonomous floral transition pathway through its interaction with FCA, is also involved in seed germination in Arabidopsis (Jiang et al., 2012). The fy-1 mutant has lower ABA sensitivity and may be involved in development of dormancy (Jiang et al., 2012). These reports suggest a very prominent role of transcriptional regulation in fine tuning ABA responses.

3.2. Inhibition of GA signalling by DELLA proteins

Components of GA signalling regulate seed germination (Peng & Harberd, 2002). Nuclear transcriptional regulators, the DELLA proteins, control GA signalling (Itoh et al., 2002; Richards et al., 2000; Wen & Chang, 2002; Dill et al., 2001). DELLA proteins are negative regulators of GA signalling (Wen & Chang, 2002). Arabidopsis has five DELLA proteins (GA-INSENSITIVE [GAI], REPRESSOR OF GA1-3 [RGA], RGA-LIKE1 [RGL1], RGL2, and RGL3), while rice SLENDER1 (SLR1) and other species such as barley SLENDER1 (SLN1), maize, and wheat have only one DELLA protein (Dill et al., 2001; Chandler et al., 2002; Itoh et al., 2002; Peng & Harberd, 2002). Downstream of the DELLA proteins, GA regulates Myb-like (GAmyb) transcription factor binding to promoter of α-amylase genes (Gubler et al., 1995). The GA-signal is recepted by a soluble GA receptor which has homology to GA-INSENSITIVE DWARF1 (GID1), a human hormone-sensitive lipase (Ueguchi-Tanaka et al., 2005). The bioactive GAs bind to GID1 which in turn promotes interaction between GID1 and the DELLA-domain of DELLA protein (Willige et al., 2007; Ueguchi-Tanaka et al., 2007). This interaction enhances the affinity between DELLA-GID1-GA complex and a specific SCF E3 ubiquitin–ligase complex, SCFSLY1/GID2 which involves the F-box proteins AtSLY1 and OsGID2 in Arabidopsis and rice, respectively (Sasaki et al., 2003; McGinnis et al., 2003; Willige et al., 2007; Griffiths et al., 2006). The ubiquitinylation and subsequent destruction of DELLAs is promoted by SCFSLY1/ GID2 through the 26S proteasome (Fu et al., 2002; McGinnis et al., 2003; Sasaki et al., 2003). The DELLA genes are transcriptionally controlled by the light-labile transcription factor PIL5 which increases the transcription of GAI and RGA genes by binding to its promoters on the G-Box (Oh et al., 2007).

DELLA degradation is GA-dependent and is inhibited by ABA in barley and by both ABA and salt (NaCl) in Arabidopsis (Gubler et al., 2002; Achard et al., 2006). Plant development through the two independent salt-activated hormone signalling pathways (ABA and ethylene) integrates at the level of DELLA function (Achard et al., 2006). DELLA also affects flowering in an ABA-dependent manner (Achard et al., 2006); however, its function in regulation of dormancy and germination is not clear. Germination in tomato, soybean and Arabidopsis is not dependent on down-regulation of DELLA genes (Bassel et al., 2004). Despite a high content of RGL2, the DELLA protein that specifically represses seed germination, Arabidopsis sly1 mutant seeds can germinate (Ariizumi & Steber, 2007). Far-red light is known to inhibit germination through DELLA dependent induction of ABI3 activity and ABA biosynthesis while DELLA mediates expansion of cotyledon leading to breaking the coat-imposed dormancy (Penfield et al., 2006; Piskurewicz et al., 2009).


4. Epigenetic regulation of dormancy related genes

Despite the lack of complete information about ABA signalling, it is amply clear that ABA responses are regulated by transcriptional regulation, except for the quick responses in stomatal closure (Wasilewska et al., 2008). Besides transcriptional regulation, ABA mediates epigenetic regulation to control plant responses (Chinnusamy et al., 2008). ABA-mediated epigenetic regulation of gene expression in seeds is now being studied extensively. Polycomb group-based gene imprinting and DNA methylation/demethylation control seed development in plants (Eckardt, 2006). Seed specific physiological processes like dormancy and germination are being studied in the context of epigenetic regulation. A cDNA-AFLP-based study showed epigenetic regulation of transcripts during barley seed dormancy and germination (Leymarie et al., 2007). During seed development and germination inhibition, gene regulation is also regulated by ABA through transcription factors such as ABI3, VP1, LEC2, FUS3 as well as the APETELA2 (ABI4), HAP3 subunit of CCAAT binding factor (LEC1) and the bZIP (ABI5) (Finkelstein et al., 2002). ABA regulates the B3 domain transcription factors through PICKLE (PKL) which encodes putative CHD3 type SWI/SNF-class chromatin-remodeling factor (Ogas et al., 1999). ABA-mediated stress responses occur through Histone Deacetylase (HDACs)-dependent chromatin modifications and ATP-dependent chromatin remodelling complexes that include SWI3-like proteins (Wu et al., 2003; Rios et al., 2007). Stress-related memory is also inherited through epigenetic mechanisms (Boyko et al., 2007). ABA also regulates non-coding small RNAs (siRNA and miRNA) that can regulate DNA methylation resulting in epigenetic changes (Bond & Finnegan, 2007; Yang et al., 2008).


5. Tillering and bud dormancy

Tillering is a key agronomic trait contributing to grain yield. Tillers are formed from axillary buds that grow independent of the main stem. The levels of dormancy in buds determine the timing and extent of tillers in most monocot crops. Various proteins such as MONOCULM 1 (MOC1) (Li et al., 2003) have been implicated in regulation of bud dormancy but recent studies suggest the involvement of autonomous pathway (flowering) genes in regulation of bud dormancy. The first clue regarding the commonality between factors controlling flowering and bud dormancy arose from environmental signals that regulated them (Chouard, 1960). The signalling events responsible for regulation of flowering and bud dormancy converge on FLOWERING LOCUS T (FT) (Bohlenius et al., 2006). Day length is an important determinant in regulation of flowering acting through its photoreceptor PHYTOCHROME A (PHYA). PHYA affects the floral induction pathway through its effect on CONSTANS (CO), a gene involved in flowering pathway, which in turn affects FT(Yanovsky & Kay, 2002). FT is negatively regulated by FLC which regulates temperature-dependent seed germination in Arabidopsis (Helliwell et al., 2006; Chiang et al., 2009). FCA and FVE regulate FT under high and low temperatures in a FLC-dependent manner (Sheldon et al., 2000; Blazquez et al., 2003). The transcript levels of FCA have also been correlated to bud dormancy in poplar (Ruttink et al., 2007). Although limited, the information regarding the intricate network of signalling events that regulate the two most important events, namely the transition from vegetative to reproductive state, and from non-germinated to germinated state suggests some common factors (Horvath, 2009).


6. Breeding for pre-harvest resistance in barely

Seed dormancy is a quantitatively inherited trait in several plant species such as rice, popular, Arabidopsis, wheat and barley (Ullrich et al., 1996; Li et al., 2004). In barley, seed dormancy and germination have been important breeding objectives since its domestication and malt utilization. Malting barley must rapidly germinate upon imbibition. Endosperm starch and proteins hydrolysis within 3 to 4 days is an important characteristic for malting quality in barley. To assure rapid and complete germination for malting industry, barley breeders have stringently selected against seed dormancy resulting in barley varieties that are highly susceptible to pre-harvest spouting after early fall rains or heavy dew, which is an undesirable trait (Prada et al., 2004). A moderate level of seed dormancy is desirable for proper malting. In order to achieve suitable level of seed dormancy, several studies reported seed dormancy QTLs in barley (Edney & Mather, 2004; Zhang et al., 2005), different dormancy genes however responsible in different population of various pedigrees. Levels of seed dormancy that vary in different genetic backgrounds are also affected by environmental factors and their interaction with genetic factors. Various studies have identified the major QTLs (SD1 and SD2) that can be used in combination with other minor QTL of local germplasm to achieve moderate level of seed dormancy for malting barley (Li et al., 2004). Few QTL identified in barley for dormancy and preharvest sprouting are listed in Table 1. In addition hormonal cross talk can be explored for seed dormancy and germination as breeding prospect for better barley values and end utilization.

Chromosome Marker interval Variability (%) References
Cross: Setptoe x Morex
5H Ale - ABC324 50 Ullrich et al., 1993
Obethur et al., 1995
Han et al., 1996
Ullrich et al., 2002
Gao et al., 2003
5H MWG851D - MWG851B 15
7H Amy2 - Ubi1 5
4H WG622 - BCD402B 5
Cross: Chebec x Harrington
5H CDO506 - GMS1 70 Li et al., 2003
Cross: Hordeum spontaneum (Wadi Qilt) x Hordeum vulgare (Mona)
1H1 ABC160-3 13 Zhang et al., 2005
5H2 BMAG812-1 – E35M59mg-4 14
1H2 EMBAC659-3 – EE38M55ob-1 45
7H1 AF22725-3 – BMAG341A-2 13
7H2 BMAG135-4 –
1H1 EMBAC659-3 – EE38M55ob-1 50
Cross: Stirling x Harrington
1Hq Hvglvend – Awbms80 1.6 Li et al., 2003, Bonnardeaux et al., 2008
2Hqa GBMS244 – Emag174 -
3Hqa GBM1043 – Bmag0013 2.2
4Hqa GBM1501 – Bmag741 -
5Hqa Bmag0337 – GBM1399 3.7
5Hqb Scsst09041a – scssr03901 52.2
Cross: Harrington x TR306
1HL iPgd2 – TubA2 10 Ullrich et al., 2009
2HS ABC019 – ABG716 7
2HC MWG865 6
3HL ABG609B – MWG838 13
5HL MWG602 – ABC718 40
7HS dRPG1 – ABG077 6
7HC MWG003 – Ris15 7
Cross: Triumph x Morex
1HS GMS21 10 Ullrich et al., 2009
Prada et al., 2004
3HL E39M49_j – E39M48_c 13
5HC E39M49_f – MWG522 54
7HC E32M48_c – E39M48_p 7
7HL E37M60_g 7
Cross: BCD47 x Baronesse
1H Bmag504 - Bmag032 10 Castro et al., 2010
4H HvSnf2 – HvAmyB 9
5H Bmag222 – GMS001 34.5
6H Bmag500 - Bmag009 9
7H Bmag120 – Ris44 23
Cross: ND24260 x Flagship
3H bPb – 0619 6 Hickey et al., 2012
3H bPb – 2630 4
4H bPb – 9251 4
5H-2 bPb – 9191 15
5H-2 bPb – 5053 31
5H-2 bPb – 1217 35
5H-2 bPb – 1217 28
6H-2 bPb - 1347 4

Table 1.

Dormancy and preharvest sprouting related QTLs in barley.


7. Future perspective

The plethora of information on molecular control of dormancy and germination is ever increasing with studies performed on model plants. Little information is available from agriculturally important crops such as wheat and barley as they are tedious systems due to their genome complexity and ploidy levels. However, these economically important crops do bring out the unique variations of the biological systems that improve our understanding.

The recent pieces of evidence from our studies in barley and Arabidopsis (Kumar et al., 2011; Jiang et al., 2012) lay a foundation for looking deeply into the bigger picture involving flowering and dormancy as connected pathways. Genetic studies in Arabidopsis also identified DOG1, a key component in dormancy pathway, as quantitative trait loci for flowering (Atwell et al., 2010). The improvements in next generation sequencing and its decreasing cost has made it the technology of choice for looking at entire genomes for various transcriptome and epigenetic studies in crop plants. A refocused approach using all interconnected pathways and improved technologies to study them will certainly enhance our understanding of dormancy and germination as well as flowering and in turn promote crop improvement.



ABA Abscisic Acid

ABAP1 ABA Binding Protein 1

ABI3 Abscisic Acid Insensitive 3

ABI5 Abscisic Acid Insensitive 5


FCA Flowering Time Control Protein A

FLC Flowering Control Locus C

FT Flowering Locus T

GA Gibberellic Acid


LEA Late Embryogenesis Abundant


PHS Pre-harvest Sprouting

SLN1 Slender 1 (DELLA protein)

VP1 Viviparous 1

EM Early Methionine



The authors are grateful to Dr. Robert Hill and Dr. Derek Bewley for their expert opinion and advice for preparation of this manuscript. This book chapter has been taken from Dr. Santosh Kumar’s PhD thesis entitled “Molecular and Physiological Characterization of the Flowering Time Control Protein, HvFCA and its Role in ABA Signalling and Seed Germination” submitted to the faculty of graduate studies, University of Manitoba.


  1. 1. AchardPChengHDe GrauweLDecatJSchouttetenHMoritzTVan Der StraetenDPengJ. Rand HarberdN. P2006Integration of plant responses to environmentally activated phytohormonal signals. Science3119194
  2. 2. Ali-rachediSBouinotDWagnerM. HBonnetMSottaBGrappinPand JullienM2004Changes in endogenous abscisic acid levels during dormancy release and maintenance of mature seeds: studies with the Cape Verde Islands ecotype, the dormant model of Arabidopsis thaliana. Planta219479488
  3. 3. AllanA. Cand TrewavasA. J1994Abscisic-acid and gibberellin perception- Inside or out. Plant Physiology10411071108
  4. 4. AriizumiTand SteberC. M2007Seed germination of GA-insensitive sleepy1 mutants does not require RGL2 protein disappearance in Arabidopsis. The Plant Cell19791804
  5. 5. AtwellSHuangY. SVilhjalmssonB. JWillemsGHortonMLiYMengDPlattATaroneA. MHuT. TJiangRMuliyatiN. WZhangXAmerM. ABaxterIBrachiBChoryJDeanCDebieuMDe MeauxJEckerJ. RFaureNKniskernJ. MJonesJ. DMichaelTNemriARouxFSaltD. ETangCTodescoMTrawM. BWeigelDMarjoramPBorevitzJ. OBergelsonJand NordborgM2010Genome-wide association study of 107 phenotypes in Arabidopsis thaliana inbred lines. Nature465627631
  6. 6. BadrAMullerKSchafer-preglRRabeyH. EEffgenSIbrahimH. HPozziCRohdeWand SalaminiF2000On the origin and domestication history of barley (Hordeum vulgare). Molecular Biology and Evolution17499510
  7. 7. BaeGand ChoiG2008Decoding of light signals by plant phytochromes and their interacting proteins. Annual Review of Plant Biology59281311
  8. 8. BaskinJ. Mand BaskinC. C2004A classification system for seed dormancy. Seed Science Research14116
  9. 9. BasselG. WZielinskaEMullenR. Tand BewleyJ. D2004Down-regulation of DELLA genes is not essential for germination of tomato, soybean, and Arabidopsis seeds. Plant Physiology13627822789
  10. 10. BaumbuschL. OHughesD. WGalauG. Aand JakobsenK. S2004LEC1, FUS3, ABI3 and Em expression reveals no correlation with dormancy in Arabidopsis. Journal of Experimental Botany557787
  11. 11. BaumleinHMiseraSLuerssenHKolleKHorstmannCWobusUand MullerA. J1994The Fus3 gene of Arabidopsis Thaliana Is a regulator of gene-expression during late embryogenesis. The Plant Journal6379387
  12. 12. BeaudoinNSerizetCGostiFand GiraudatJ2000Interactions between abscisic acid and ethylene signaling cascades. The Plant Cell1211031115
  13. 13. BentsinkLJowettJHanhartC. Jand KoornneefM2006Cloning of DOG1, a quantitative trait locus controlling seed dormancy in Arabidopsis. Proceedings of the National Academy of Sciences of the United States of America1031704217047
  14. 14. BethkeP. CLibourelI. G. LAoyamaNChungY. YStillD. Wand JonesR. L2007The Arabidopsis aleurone layer responds to nitric oxide, gibberellin, and abscisic acid and is sufficient and necessary for seed dormancy. Plant Physiology14311731188
  15. 15. BewleyJ. D1997Seed germination and dormancy. The Plant Cell, 910551066
  16. 16. BewleyJ. Dand BlackM1994Seeds: Physiology of Development and Germination (Plenum, New York).
  17. 17. BlazquezM. AAhnJ. Hand WeigelD2003A thermosensory pathway controlling flowering time in Arabidopsis thaliana. Nature Genetics33168171
  18. 18. BohleniusHHuangTCharbonnel-campaaLBrunnerA. MJanssonSStraussS. Hand NilssonO2006CO/FT regulatory module controls timing of flowering and seasonal growth cessation in trees. Science31210401043
  19. 19. BondD. Mand FinneganE. J2007Passing the message on: inheritance of epigenetic traits. Trends in Plant Science12211216
  20. 20. BonnardeauxYLiCLanceRZhangXSivasithamparamKand AppelsR2008Seed dormancy in barley: identifying superior genotypes through incorporating epistatic interactions. Australian Journal of Agricultural Research59517526
  21. 21. BorthwickH. AHendricksS. BParkerM. WTooleE. Hand TooleV. K1952A reversible photoreaction controlling seed germination. Proceedings of the National Academy of Sciences of the United States of America38662666
  22. 22. BothmerR. Vand JacobsenN1985Origin, taxonomy, and related species.D. C. Rasmusson, ed. Barley (American Society of Agronomists, Madison, Wisconsin, USA.), 1956
  23. 23. BoykoAKathiriaPZempF. JYaoY. LPogribnyIand KovalchukI2007Transgenerational changes in the genome stability and methylation in pathogen-infected plants (Virus-induced plant genome instability). Nucleic Acids Research3517141725
  24. 24. BraybrookS. AStoneS. LParkSBuiA. QLeB. HFischerR. LGoldbergR. Band HaradaJ. J2006Genes directly regulated by LEAFY COTYLEDON2 provide insight into the control of embryo maturation and somatic embryogenesis. Proceedings of the National Academy of Sciences of the United States of America10334683473
  25. 25. CarlesCBies-etheveNAspartLLeon-kloosterzielK. MKoornneefMEcheverriaMand DelsenyM2002Regulation of Arabidopsis thaliana Em genes: role of ABI5. The Plant Journal30373383
  26. 26. CarreraEHolmanTMedhurstAPeerWSchmuthsHFootittSTheodoulouF. Land HoldsworthM. J2007Gene expression profiling reveals defined functions of the ATP-binding cassette transporter COMATOSE late in phase II of germination. Plant Physiology14316691679
  27. 27. CasarettoJ. Aand HoT. H2005Transcriptional regulation by abscisic acid in barley (Hordeum vulgare L.) seeds involves autoregulation of the transcription factor HvABI5. Plant Molecular Biology572134
  28. 28. CastroA. JBenitezAHayesP. MViegaLand WrightL2010Coincident quantitative trait loci effects for dormancy, water sensitivity and malting quality traits in the BCD47 × Baronesse barley mapping population. Crop and Pasture Science61691699
  29. 29. ChandlerP. MMarion-pollAEllisMand GublerF2002Mutants at the Slender1 locus of barley cv Himalaya. molecular and physiological characterization. Plant Physiology129181190
  30. 30. ChiangG. C. KBaruaDKramerE. MAmasinoR. Mand DonohueK2009Major flowering time gene, FLOWERING LOCUS C, regulates seed germination in Arabidopsis thaliana. Proceedings of the National Academy of Sciences of the United States of America1061166111666
  31. 31. ChinnusamyVGongZ. Zand ZhuJ. K2008Abscisic acid-mediated epigenetic processes in plant development and stress responses. Journal of Integrative Plant Biology5011871195
  32. 32. ChiwochaS. DCutlerA. JAbramsS. RAmbroseS. JYangJRossA. Rand KermodeA. R2005The etr1-2 mutation in Arabidopsis thaliana affects the abscisic acid, auxin, cytokinin and gibberellin metabolic pathways during maintenance of seed dormancy, moist-chilling and germination. The Plant Journal423548
  33. 33. ChouardP1960Vernalization and its relations to dormancy. Annual Review of Plant Physiology and Plant Molecular Biology11191238
  34. 34. CorbineauFPicardM. AFougereuxJ. ALadonneFand ComeD2000Effects of dehydration conditions on desiccation tolerance of developing pea seeds as related to oligosaccharide content and cell membrane properties. Seed Science Research10329339
  35. 35. CromeDLenoirCand CorbineauF1984The dormancy of cereals and its elimination. Seed Science and Technology12629640
  36. 36. DebeaujonILeon-kloosterzielK. Mand KoornneefM2000Influence of the testa on seed dormancy, germination, and longevity in Arabidopsis. Plant Physiology122403413
  37. 37. DerkxM. P. Mand KarssenC. M1993Effects of light and temperature on seed dormancy and gibberellin-stimulated germination in Arabidopsis thaliana- studies with gibberellin-deficient and gibberellin-insensitive mutants. Physiologia Plantarum89360368
  38. 38. DillAJungH. Sand SunT. P2001The DELLA motif is essential for gibberellin-induced degradation of RGA. Proceedings of the National Academy of Sciences of the United States of America981416214167
  39. 39. EckardtN. A2006Genetic and epigenetic regulation of embryogenesis. The Plant Cell18781784
  40. 40. EdneyM. Jand MatherD. E2004Quantitative trait loci affecting germination traits and malt friability in a two-rowed by six-rowed barley cross. Journal of Cereal Science39283290
  41. 41. EzcurraIEllerstromMWycliffePStalbergKand RaskL1999Interaction between composite elements in the napA promoter: both the B-box ABA-responsive complex and the RY/G complex are necessary for seed-specific expression. Plant Molecular Biology40699709
  42. 42. Finch-savageW. Eand Leubner-metzgerG2006Seed dormancy and the control of germination. New Phytologist171501523
  43. 43. FinkelsteinRReevesWAriizumiTand SteberC2008Molecular aspects of seed dormancy. Annual Review of Plant Biology59387415
  44. 44. FinkelsteinR. R1994Mutations at 2 new Arabidopsis ABA response loci are similar to the abi3 mutations. The Plant Journal5765771
  45. 45. FinkelsteinR. Rand LynchT. J2000The arabidopsis abscisic acid response gene ABI5 encodes a basic leucine zipper transcription factor. The plant cell12599609
  46. 46. FinkelsteinR. RGampalaS. S. Land RockC. D2002Abscisic acid signaling in seeds and seedlings. The Plant Cell14S15S45
  47. 47. FinkelsteinR. RWangM. LLynchT. JRaoSand GoodmanH. M1998The Arabidopsis abscisic acid response locus ABI4 encodes an APETALA2 domain protein. The Plant Cell1010431054
  48. 48. FlinthamJAdlamRBassoiMHoldsworthMand GaleM2002Mapping genes for resistance to sprouting damage in wheat. Euphytica1263945
  49. 49. FlinthamJ. E2000Different genetic components control coat-imposed and embryo-imposed dormancy in wheat. Seed Science Research104350
  50. 50. FuXRichardsD. EAit-aliTHynesL. WOughamHPengJand HarberdN. P2002Gibberellin-mediated proteasome-dependent degradation of the barley DELLA protein SLN1 repressor. The Plant Cell1431913200
  51. 51. FujiiHChinnusamyVRodriguesARubioSAntoniRParkS. YCutlerS. RSheenJRodriguezP. Land ZhuJ. K2009In vitro reconstitution of an abscisic acid signalling pathway. Nature462660664
  52. 52. GageteA. PRieraMFrancoLand RodrigoM. I2009Functional analysis of the isoforms of an ABI3-like factor of Pisum sativum generated by alternative splicing. Journal of Experimental Botany6017031714
  53. 53. GaleM. DFlinthamJ. Eand DevosK. M2002Cereal comparative genetics and preharvest sprouting. Euphytica1262125
  54. 54. GaoYZengQGuoJChengJEllisB. Eand ChenJ. G2007Genetic characterization reveals no role for the reported ABA receptor, GCR2, in ABA control of seed germination and early seedling development in Arabidopsis. The Plant Journal5210011013
  55. 55. GaoWClancyJ. AHanFPradaDKleinhofsAUllrichS. E2003Molecular dissection of a dormancy QTL region near the chromosome 7 (5H) L telomere in barley. Theoretical and Applied Genetics107552559
  56. 56. GerjetsTScholefieldDFoulkesM. JLentonJ. Rand HoldsworthM. J2009An analysis of dormancy, ABA responsiveness, after-ripening and pre-harvest sprouting in hexaploid wheat (Triticum aestivum L.) caryopses. Journal of Experimental Botany61597607
  57. 57. GhassemianMNambaraECutlerSKawaideHKamiyaYand MccourtP2000Regulation of abscisic acid signaling by the ethylene response pathway in Arabidopsis. The Plant Cell1211171126
  58. 58. GilroySand JonesR. L1994Perception of gibberellin and abscisic-acid at the external face of the plasma-membrane of barley (Hordeum vulgare L) aleurone protoplasts. Plant Physiology10411851192
  59. 59. GiraudatJHaugeB. MValonCSmalleJParcyFand GoodmanH. M1992Isolation of the arabidopsis-ABI3 gene by positional cloning. The Plant Cell412511261
  60. 60. GostiFBeaudoinNSerizetCWebbA. AVartanianNand GiraudatJ1999ABI1 protein phosphatase 2C is a negative regulator of abscisic acid signaling. The Plant Cell1118971910
  61. 61. GrappinPBouinotDSottaBMiginiacEand JullienM2000Control of seed dormancy in Nicotiana plumbaginifolia: post-imbibition abscisic acid synthesis imposes dormancy maintenance. Planta210279285
  62. 62. GriffithsJMuraseKRieuIZentellaRZhangZ. LPowersS. JGongFPhillipsA. LHeddenPSunT. Pand ThomasS. G2006Genetic characterization and functional analysis of the GID1 gibberellin receptors in Arabidopsis. The Plant Cell1833993414
  63. 63. GroosCGayGPerretantM. RGervaisLBernardMDedryverFand CharmetD2002Study of the relationship between pre-harvest sprouting and grain color by quantitative trait loci analysis in a whitexred grain bread-wheat cross. Theoretical and Applied Genetics1043947
  64. 64. GublerFMillarA. Aand JacobsenJ. V2005Dormancy release, ABA and pre-harvest sprouting. Current Opinion in Plant Biology8183187
  65. 65. GublerFKallaRRobertsJ. Kand JacobsenJ. V1995Gibberellin-regulated expression of a MYB gene in barley aleurone cells- evidence for MYB transactivation of a high-pI alpha-amylase gene promoter. The Plant Cell718791891
  66. 66. GublerFChandlerP. MWhiteR. GLlewellynD. Jand JacobsenJ. V2002Gibberellin signaling in barley aleurone cells. Control of SLN1 and GAMYB expression. Plant Physiology129191200
  67. 67. GuoJZengQEmamiMEllisB. Eand ChenJ. G2008The GCR2 gene family is not required for ABA control of seed germination and early seedling development in Arabidopsis. PLoS ONE3e2982
  68. 68. GutierrezLVan WuytswinkelOCastelainMand BelliniC2007Combined networks regulating seed maturation. Trends in Plant Science12294300
  69. 69. GuttermanYCorbineauFand ComeD1996Dormancy of Hordeum spontaneum caryopses from a population on the Negev Desert Highlands. Journal of Arid Environments33337345
  70. 70. HanFUllrichS. EClancyJ. AJitkovVKilianAand RomagosaI1996Verification of barley seed dormancy loci via linked molecular markers. Theoretical and Applied Genetics928791
  71. 71. HattoriTTeradaTand HamasunaS. T1994Sequence and functional analyses of the rice gene homologous to the maize Vp1. Plant Molecular Biology24805810
  72. 72. HelliwellC. AWoodC. CRobertsonMPeacockW. Jand DennisE. S2006The Arabidopsis FLC protein interacts directly in vivo with SOC1 and FT chromatin and is part of a high-molecular-weight protein complex. The Plant Journal46183192
  73. 73. HickeyL. TLawsonWAriefV. NFoxGFranckowiakJand DietersM. J2012Grain dormancy QTL identified in a doubled haploid barley population derived from two non-dormant parents. Euphytica188113122
  74. 74. HilhorstH. W. M1995A critical update on seed dormancy.1. primary dormancy. Seed Science Research56173
  75. 75. HoeckerUVasilI. Kand MccartyD. R1995Integrated control of seed maturation and germination programs by activator and repressor functions of Viviparous-1 of maize. Genes & Development924592469
  76. 76. HoldsworthM. JBentsinkLand SoppeW. J. J2008Molecular networks regulating Arabidopsis seed maturation, after-ripening, dormancy and germination. New Phytologist1793354
  77. 77. HorvathD2009Common mechanisms regulate flowering and dormancy. Plant Science177523531
  78. 78. HuangD. QJaradatM. RWuW. RAmbroseS. JRossA. RAbramsS. Rand CutlerA. J2007Structural analogs of ABA reveal novel features of ABA perception and signaling in Arabidopsis. The Plant Journal50414428
  79. 79. ItohHUeguchi-tanakaMSatoYAshikariMand MatsuokaM2002The gibberellin signaling pathway is regulated by the appearance and disappearance of SLENDER RICE1 in nuclei. The Plant Cell145770
  80. 80. JacobsenJ. VPearceD. WPooleA. TPharisR. Pand ManderL. N2002Abscisic acid, phaseic acid and gibberellin contents associated with dormancy and germination in barley. Physiologia Plantarum115428441
  81. 81. JangY. HLeeJ. Hand KimJ. K2008Abscisic acid does not disrupt either the Arabidopsis FCA-FY interaction or its rice counterpart in vitro. Plant and Cell Physiology4918981901
  82. 82. JiH. SChuS. HJiangW. ZChoY. IHahnJ. HEunM. YMccouchS. Rand KohH. J2006Characterization and mapping of a shattering mutant in rice that corresponds to a block of domestication genes. Genetics1739951005
  83. 83. JiangSKumarSEuY. JJamiS. KStasollaCand HillR. D2012The Arabidopsis mutant, fy-1, has an ABA-insensitive germination phenotype. Journal of Experimental Botany6326932703
  84. 84. JonesH. DPetersN. C. Band HoldsworthM. J1997Genotype and environment interact to central dormancy and differential expression of the VIVIPAROUS 1 homologue in embryos of Avena fatua. The Plant Journal12911920
  85. 85. KagayaYToyoshimaROkudaRUsuiHYamamotoAand HattoriT2005LEAFY COTYLEDON1 controls seed storage protein genes through its regulation of FUSCA3 and ABSCISIC ACID INSENSITIVE3. Plant and Cell Physiology46399406
  86. 86. KahnAGossJ. Aand SmithD. E1957Effect of gibberellin on germination of lettuce seed. Science125645646
  87. 87. KarssenC. MSwanB. VBreeklandA. Eand KoornneefM1983Induction of dormancy during seed development by endogenous abscisic acid: studies on abscisic acid deficient genotypes of Arabidopsis thaliana (L) Heynh. Planta157158165
  88. 88. KermodeA. R2005Role of abscisic acid in seed dormancy. Journal of Plant Growth Regulation24319344
  89. 89. KoornneefMReulingGand KarssenC. M1984The isolation and characterization of abscisic acid insensitive mutants of Arabidopsis thaliana.. Physiologia Plantarum61377383
  90. 90. KoornneefMBentsinkLand HilhorstH2002Seed dormancy and germination. Current Opinion in Plant Biology53336
  91. 91. KoornneefMHanhartC. JHilhorstH. W. Mand KarssenC. M1989In vivo inhibition of seed development and reserve protein accumulation in recombinants of abscisic-acid biosynthesis and responsiveness mutants in Arabidopsis thaliana. Plant Physiology90463469
  92. 92. KrojTSavinoGValonCGiraudatJand ParcyF2003Regulation of storage protein gene expression in Arabidopsis. Development13060656073
  93. 93. KumarSJiangSJamiS. Kand HillR. D2011Cloning and characterization of barley caryopsis FCA. Physiologia Plantarum14393106
  94. 94. LefebvreVNorthHFreyASottaBSeoMOkamotoMNambaraEand Marion-pollA2006Functional analysis of Arabidopsis NCED6 and NCED9 genes indicates that ABA synthesized in the endosperm is involved in the induction of seed dormancy. The Plant Journal45309319
  95. 95. LePage-DegivryM.T., and Garello, G. (1992In situ abscisic acid synthesis : a requirement for induction of embryo dormancy in Helianthus annuus. Plant Physiology9813861390
  96. 96. Leubner-metzgerG2001Brassinosteroids and gibberellins promote tobacco seed germination by distinct pathways. Planta213758763
  97. 97. LeungJMerlotSand GiraudatJ1997The Arabidopsis ABSCISIC ACID-INSENSITIVE2 (ABI2) and ABI1 genes encode homologous protein phosphatases 2C involved in abscisic acid signal transduction. The Plant Cell9759771
  98. 98. LeymarieJBruneauxEGibot-leclercSand CorbineauF2007Identification of transcripts potentially involved in barley seed germination and dormancy using cDNA-AFLP. Journal of Experimental Botany58425437
  99. 99. LeymarieJRobayo-romeroM. EGendreauEBenech-arnoldR. Land CorbineauF2008Involvement of ABA in induction of secondary dormancy in barley (Hordeum vulgare L.) seeds. Plant and Cell Physiology4918301838
  100. 100. LiC. DTarrALanceR. C. MHarasymowSUhlmannJWestcotSYoungK. JGrimeC. RCakirMBroughtonSand AppelsaR2003A major QTL controlling seed dormancy and pre-harvest sprouting/grain alpha-amylase in two-rowed barley (Hordeum vulgare L.). Australian Journal of Agricultural Research5413031313
  101. 101. LiB. Land FoleyM. E1997Genetic and molecular control of seed dormancy. Trends in Plant Science2384389
  102. 102. LiCNiPFranckiMHunterAZhangYSchibeciDet al2004Genes controlling seed dormancy and pre-harvest sprouting in a rice-wheat-barley comparison. Functional & Integrative Genomics48493
  103. 103. LiXQianQFuZWangYXiongGZengDWangXLiuXTengSHiroshiFYuanMLuoDHanBand LiJ2003Control of tillering in rice. Nature422618621
  104. 104. LinP. CHwangS. GEndoAOkamotoMKoshibaTand ChengW. H2007Ectopic expression of abscisic acid 2/glucose insensitive 1 in arabidopsis promotes seed dormancy and stress tolerance. Plant Physiology143745758
  105. 105. LiuP. PMontgomeryT. AFahlgrenNKasschauK. DNonogakiHand CarringtonJ. C2007aRepression of auxin response factor10 by microrna160 is critical for seed germination and post-germination stages. The Plant Journal52133146
  106. 106. LiuXYueYLiBNieYLiWWuW. Hand MaL2007b). A GProtein-coupledreceptor is a plasma membrane receptor for the plant hormone abscisic acid. Science31517121716
  107. 107. LohwasserURoderM. Sand BornerA2005QTL mapping of the domestication traits pre-harvest sprouting and dormancy in wheat (Triticum aestivum L.). Euphytica143247249
  108. 108. Lopez-molinaLMongrandBMclachlinD. TChaitB. Tand ChuaN. H2002ABI5 acts downstream of ABI3 to execute an ABA-dependent growth arrest during germination. The Plant Journal32317328
  109. 109. LotanTOhtoMYeeK. MWestM. A. LLoRKwongR. WYamagishiKFischerR. LGoldbergR. Band HaradaJ. J1998Arabidopsis LEAFY COTYLEDON1 is sufficient to induce embryo development in vegetative cells. Cell9311951205
  110. 110. LuerssenKKirikVHerrmannPand MiseraS1998FUSCA3 encodes a protein with a conserved VP1/ABI3-like B3 domain which is of functional importance for the regulation of seed maturation in Arabidopsis thaliana. The Plant Journal15755764
  111. 111. OberthurLBlakeT. KDyerW. Eand UllrichS. E1995Genetic analysis of seed dormancy in barley (Hordeum vulgare L.). Journal of Quantitative Trait Loci.
  112. 112. MaYSzostkiewiczIKorteAMoesDYangYChristmannAand GrillE2009Regulators of 2Cphosphatase activity function as abscisic acid sensors. Science324pp. 1064-1068
  113. 113. MccartyD. Rand CarsonC. B1991The molecular-genetics of seed maturation in maize. Physiologia Plantarum81267272
  114. 114. MccartyD. RCarsonC. BStinardP. Sand RobertsonD. S1989Molecular analysis of Viviparous-1- an abscisic acid-insensitive mutant of maize. The Plant Cell1523532
  115. 115. MccartyD. RHattoriTCarsonC. BVasilVLazarMand VasilI. K1991The Viviparous-1 developmental gene of maize encodes a novel transcriptional activator. Cell66895905
  116. 116. McginnisK. MThomasS. GSouleJ. DStraderL. CZaleJ. MSunT. Pand SteberC. M2003The Arabidopsis SLEEPY1 gene encodes a putative F-box subunit of an SCF E3 ubiquitin ligase. The Plant Cell1511201130
  117. 117. MckibbinR. SWilkinsonM. DBaileyP. CFlinthamJ. EAndrewL. MLazzeriP. AGaleM. DLentonJ. Rand HoldsworthM. J2002Transcripts of Vp-1 homeologues are misspliced in modern wheat and ancestral species. Proceedings of the National Academy of Sciences of the United States of America991020310208
  118. 118. MerlotSGostiFGuerrierDVavasseurAand GiraudatJ2001The ABI1 and ABI2 protein phosphatases 2C act in a negative feedback regulatory loop of the abscisic acid signalling pathway. The Plant Journal25295303
  119. 119. MeyerKLeubeM. Pand GrillE1994A Protein Phosphatase 2C involved in ABA signal-transduction in Arabidopsis thaliana. Science26414521455
  120. 120. MonkeGAltschmiedLTewesAReidtWMockH. PBaumleinHand ConradU2004Seed-specific transcription factors ABI3 and FUS3: molecular interaction with DNA. Planta219158166
  121. 121. MullerA. Hand HanssonM2009The barley magnesium chelatase 150-kd subunit is not an abscisic acid receptor. Plant Physiology150157166
  122. 122. NakaminamiKSawadaYSuzukiMKenmokuHKawaideHMitsuhashiWSassaTInoueYKamiyaYand ToyomasuT2003Deactivation of gibberellin by 2-oxidation during germination of photoblastic lettuce seeds. Bioscience Biotechnology Biochemistry6715511558
  123. 123. NakamuraSLynchT. Jand FinkelsteinR. R2001Physical interactions between ABA response loci of Arabidopsis. The Plant Journal26627635
  124. 124. NambaraEand Marion-pollA2003ABA action and interactions in seeds. Trends in Plant Science8213217
  125. 125. NambaraEKeithKMccourtPand NaitoS1995A regulatory role for the ABI3 gene in the establishment of embryo maturation in Arabidopsis thaliana. Development121629636
  126. 126. NambaraEHayamaRTsuchiyaYNishimuraMKawaideHKamiyaYand NaitoS2000The role of ABI3 and FUS3 loci in Arabidopsis thaliana on phase transition from late embryo development to germination. Developmental Biology220412423
  127. 127. NikolaevaM. G1969Physiology of deep dormancy in seeds. National Science Foundation, Washington, DC, USA.
  128. 128. NishimuraNHitomiKArvaiA. SRamboR. PHitomiCCutlerS. RSchroederJ. Iand GetzoffE. D2009Structural mechanism of abscisic acid binding and signaling by dimeric PYR1. Science32613731379
  129. 129. NoriyukiNAliSKazumasaNSang-youlPAngelaWPauloC. CStephenLDanielF. CSeanR. CJoanneCJohnR. Yand JulianI. S2010PYR/PYL/RCAR family members are major in vivo ABI1 protein phosphatase 2C-interacting proteins in Arabidopsis. The Plant Journal61290299
  130. 130. OgasJKaufmannSHendersonJand SomervilleC1999PICKLE is a CHD3 chromatin-remodeling factor that regulates the transition from embryonic to vegetative development in Arabidopsis. Proceedings of the National Academy of Sciences of the United States of America961383913844
  131. 131. OgawaMHanadaAYamauchiYKuwalharaAKamiyaYand YamaguchiS2003Gibberellin biosynthesis and response during Arabidopsis seed germination. The Plant Cell1515911604
  132. 132. OhEYamaguchiSKamiyaYBaeGChungW. Iand ChoiG2006Light activates the degradation of PIL5 protein to promote seed germination through gibberellin in Arabidopsis. The Plant Journal47124139
  133. 133. OhEYamaguchiSHuJ. HYusukeJJungBPaikILeeH. SSunT. PKamiyaYand ChoiG2007PIL5, a phytochrome-interacting bHLH protein, regulates gibberellin responsiveness by binding directly to the GAI and RGA promoters in Arabidopsis seeds. The Plant Cell1911921208
  134. 134. OkamotoMKuwaharaASeoMKushiroTAsamiTHiraiNKamiyaYKoshibaTand NambaraE2006CypAand CypAwhich encode abscisic acid 8’-hydroxylases, are indispensable for proper control of seed dormancy and germination in Arabidopsis. Plant Physiology14197107
  135. 135. PandeySNelsonD. Cand AssmannS. M2009Two novel GPCR-type G proteins are abscisic acid receptors in Arabidopsis. Cell136136148
  136. 136. ParcyFValonCRaynalMGaubiercomellaPDelsenyMand GiraudatJ1994Regulation of gene-expression programs during Arabidopsis seed development- roles of the ABI3 locus and of endogenous abscisic-acid. The Plant Cell615671582
  137. 137. ParkS. Y2009Abscisic acid inhibits type 2C protein phosphatases via the PYR/PYL family of START proteins. Science32410681071
  138. 138. PenfieldSGildayA. DHallidayK. Jand GrahamI. A2006DELLA-mediated cotyledon expansion breaks coat-imposed seed dormancy. Current Biology1623662370
  139. 139. PengJ. Rand HarberdN. P2002The role of GA-mediated signalling in the control of seed germination. Current Opinion in Plant Biology5376381
  140. 140. PiskurewiczUTureckovaVLacombeEand Lopez-molinaL2009Far-red light inhibits germination through DELLA-dependent stimulation of ABA synthesis and ABI3 activity. Embo Journal2822592271
  141. 141. PradaDUllrichS. EMolina-canoJ. LCistuéLClancyJ. Aand RomagosaI2004Genetic control of dormancy in a Triumph/Morex cross in barley. Theoretical and Applied Genetics, 1096270
  142. 142. RazVBergervoetJ. H. Wand KoornneefM2001Sequential steps for developmental arrest in Arabidopsis seeds. Development128243252
  143. 143. RazemF. AEl KereamyAAbramsS. Rand HillR. D2006The RNA-binding protein FCA is an abscisic acid receptor. Nature439290294
  144. 144. RazemF. ALuoMLiuJ. HAbramsS. Rand HillR. D2004Purification and characterization of a barley aleurone abscisic acid-binding protein. Journal of Biological Chemistry27999229929
  145. 145. ReidtWWohlfarthTEllerstromMCzihalATewesAEzcurraIRaskLand BaumleinH2000Gene regulation during late embryogenesis: the RY motif of maturation-specific gene promoters is a direct target of the FUS3 gene product. The Plant Journal21401408
  146. 146. RichardsD. EPengJ. Rand HarberdN. P2000Plant GRAS and metazoan STATs: one family. Bioessays22573577
  147. 147. RiosGGagetelA. PCastilloJBerbelAFrancoLand RodrigoM. I2007Abscisic acid and desiccation-dependent expression of a novel putative SNF5-type chromatin-remodeling gene in Pisum sativum. Plant Physiology and Biochemistry45427435
  148. 148. RiskJ. MDayC. Land MacknightR. C2009Reevaluation of abscisic acid-binding assays shows that G-Protein-Coupled Receptor2 does not bind abscisic acid. Plant Physiology150611
  149. 149. RobichaudCand SussexI. M1986The response of viviparous-1 and wild-type embryos of Zea mays to culture in the presence of abscisic acid. Journal of Plant Physiology126235242
  150. 150. RodriguezP. LLeubeM. Pand GrillE1998Molecular cloning in Arabidopsis thaliana of a new protein phosphatase 2C (2Cwith homology to ABI1 and ABI2. Plant Molecular Biology38pp. 879-883
  151. 151. RohdeAPrinsenEDe RyckeREnglerGVan MontaguMand BoerjanW2002PtABI3 impinges on the growth and differentiation of embryonic leaves during bud set in poplar. The Plant Cell1418851901
  152. 152. RuttinkTArendMMorreelKStormeVRombautsSFrommJBhaleraoR. PBoerjanWand RohdeA2007A molecular timetable for apical bud formation and dormancy induction in poplar. The Plant Cell1923702390
  153. 153. SantiagoJDupeuxFRoundAAntoniRParkS. YJaminMCutlerS. RRodriguezP. Land MarquezJ. A2009The abscisic acid receptor PYR1 in complex with abscisic acid. Nature462665668
  154. 154. SasakiAItohHGomiKUeguchi-tanakaMIshiyamaKKobayashiMJeongD. HAnGKitanoHAshikariMand MatsuokaM2003Accumulation of phosphorylated repressor for gibberellin signaling in an F-box mutant. Science29918961898
  155. 155. SawadaYAokiMNakaminamiKMitsuhashiWTatematsuKKushiroTKoshibaTKamiyaYInoueYNambaraEand ToyomasuT2008Phytochrome- and gibberellin-mediated regulation of abscisic acid metabolism during germination of photoblastic lettuce seeds. Plant Physiology14613861396
  156. 156. SeoMHanadaAKuwaharaAEndoAOkamotoMYamauchiYNorthHMarion-pollASunT. PKoshibaTKamiyaYYamaguchiSand NambaraE2006Regulation of hormone metabolism in Arabidopsis seeds: phytochrome regulation of abscisic acid metabolism and abscisic acid regulation of gibberellin metabolism. The Plant Journal48354366
  157. 157. SheldonC. CRouseD. TFinneganE. JPeacockW. Jand DennisE. S2000The molecular basis of vernalization: The central role of FLOWERING LOCUS C (FLC). Proceedings of the National Academy of Sciences of the United States of America9737533758
  158. 158. ShenY. YWangX. FWuF. QDuS. YCaoZShangYWangX. LPengC. CYuX. CZhuS. YFanR. CXuY. Hand ZhangD. P2006The Mg-chelatase H subunit is an abscisic acid receptor. Nature443823826
  159. 159. StoneS. LKwongL. WYeeK. MPelletierJLepiniecLFischerR. LGoldbergR. Band HaradaJ. J2001LEAFY COTYLEDON2 encodes a B3 domain transcription factor that induces embryo development. Proceedings of the National Academy of Sciences of the United States of America981180611811
  160. 160. SuzukiMKaoC. YCoccioloneSand MccartyD. R2001MaizeV. Pcomplements Arabidopsis abi3 and confers a novel ABA/auxin interaction in roots. The Plant Journal28409418
  161. 161. SuzukiTMatsuuraTKawakamiNand NodaK2000Accumulation and leakage of abscisic acid during embryo development and seed dormancy in wheat. Plant Growth Regulation30253260
  162. 162. SweeneyM. TThomsonM. JPfeilB. Eand MccouchS2006Caught red-handed: Rc encodes a basic helix-loop-helix protein conditioning red pericarp in rice. The Plant Cell18283294
  163. 163. TaylorMBolandMBresterG2009Barley Profile (AgMRC, USDA ).
  164. 164. TiedemannJRuttenTMonkeGVorwiegerARolletschekHMeissnerDMilkowskiCPetereckSMockH. PZankTand BaumleinH2008Dissection of a complex seed phenotype: Novel insights of FUSCA3 regulated developmental processes. Developmental Biology317112
  165. 165. ToAValonCSavinoGGuilleminotJDevicMGiraudatJand ParcyF2006A network of local and redundant gene regulation governs Arabidopsis seed maturation. The Plant Cell1816421651
  166. 166. Toledo-ortizGHuqEand QuailP. H2003The Arabidopsis basic/helix-loop-helix transcription factor family. The Plant Cell1517491770
  167. 167. ToyomasuTKawaideHMitsuhashiWInoueYand KamiyaY1998Phytochrome regulates gibberellin biosynthesis during germination of photoblastic lettuce seeds. Plant Physiology11815171523
  168. 168. Ueguchi-tanakaMAshikariMNakajimaMItohHKatohEKobayashiMChowT. YHsingY. I. CKitanoHYamaguchiIand MatsuokaM2005Gibberellin insensitive dwarf1 encodes a soluble receptor for gibberellin. Nature437693698
  169. 169. Ueguchi-tanakaMNakajimaMKatohEOhmiyaHAsanoKSajiSXiangH. YAshikariMKitanoHYamaguchiI and MatsuokaaM2007Molecular interactions of a soluble gibberellin receptor, GID1, with a rice DELLA protein, SLR1, and gibberellin. The Plant Cell1921402155
  170. 170. UllrichS. EHaysP. MDyerW. EBlackT. KClancyJ. A1993Quantitative trait locus analysis of seed dormancy in Steptoe barley. In: Walker-Simmons MK, Ried JL (eds) Preharvest sprouting in cereals 1992. American Association of Cereal Chemistry, St Paul, 136145
  171. 171. UllrichS. EHanFGaoWPradaDClancyJ. AKleinhofsARomagosaIMolina-canoJ. L2002Summary of QTL analyses of the seed dormancy trait in barley. Barley Newsletter 453941Available at:
  172. 172. UllrichS. EHanFBlakeT. KOberthurL. EDyerW. Eand ClancyJ. A1995Seed dormancy in barley: genetic resolution and relationship to other traits. In: Noda K, Mares DJ, editors. Pre-harvest sprouting in cereals. Osaka: Center for Academic Societies Japan; 1996. 157163
  173. 173. UllrichS. ELeeHClancyJ. Adel Blanco, I.A., Jitkov, V.A., Kleinhofs, A., Han, F., Prada, D., Romagosa, I., and Molina-Cano, J.L. (2009Genetic relationships between preharvest sprouting and dormancy in barley. Euphytica168331345
  174. 174. VersluesP. Eand ZhuJ. K2007New developments in abscisic acid perception and metabolism. Current Opinion in Plant Biology10447452
  175. 175. WalckJ. LBaskinJ. MBaskinC. Cand HidayatiS. N2005Defining transient and persistent seed banks in species with pronounced seasonal dormancy and germination patterns. Seed Science Research15189196
  176. 176. Walker-simmonsM1987B. ALevelsand sensitivity in developing wheat embryos of sprouting resistant and susceptible cultivars. Plant Physiology846166
  177. 177. WasilewskaAVladFSirichandraCRedkoYJammesFValonCFreyN. F. Dand LeungJ2008An update on abscisic acid signaling in plants and more. Molecular Plant1198217
  178. 178. WenC. Kand ChangC2002Arabidopsis RGL1 encodes a negative regulator of gibberellin responses. The Plant Cell1487100
  179. 179. WilkinsonMLentonJand HoldsworthM2005Transcripts of VP-1 homoeologues are alternatively spliced within the Triticeae tribe. Euphytica143243246
  180. 180. WilligeB. CGhoshSNillCZourelidouMDohmannE. M. NMaierAand SchwechheimerC2007The DELLA domain of GA INSENSITIVE mediates the interaction with the GA INSENSITIVE DWARF1A gibberellin receptor of Arabidopsis. The Plant Cell1912091220
  181. 181. WuF. QXinQCaoZLiuZ. QDuS. YMeiCZhaoC. XWangX. FShangYJiangTZhangX. FYanLZhaoRCuiZ. NLiuRSunH. LYangX. LSuZand ZhangD. P2009The magnesium-chelatase H subunit binds abscisic acid and functions in abscisic acid signaling: new evidence in arabidopsis. Plant Physiology15019401954
  182. 182. WuK. QTianL. NZhouC. HBrownDand MikiB2003Repression of gene expression by Arabidopsis HD2 histone deacetylases. The Plant Journal34241247
  183. 183. YamashinoTMatsushikaAFujimoriTSatoSKatoTTabataSand MizunoT2003A link between circadian-controlled bHLH factors and the APRR1/TOC1 quintet in Arabidopsis thaliana. Plant and Cell Physiology44619629
  184. 184. YamauchiYTakeda-kamiyaNHanadaAOgawaMKuwaharaASeoMKamiyaYand YamaguchiS2007Contribution of gibberellin deactivation by AtGA2ox2 to the suppression of germination of dark-imbibed Arabidopsis thaliana seeds. Plant and Cell Physiology48555561
  185. 185. YangJ. HSeoH. HHanS. JYoonE. KYangM. Sand LeeW. S2008Phytohormone abscisic acid control RNA-dependent RNA polymerase 6 gene expression and post-transcriptional gene silencing in rice cells. Nucleic Acids Research3612201226
  186. 186. YanovskyM. Jand KayS. A2002Molecular basis of seasonal time measurement in Arabidopsis. Nature419308312
  187. 187. ZhangD. PWuZ. YLiX. Yand ZhaoZ. X2002Purification and identification of a 42-kilodalton abscisic acid-specific-binding protein from epidermis of broad bean leaves. Plant Physiology128714725
  188. 188. ZhangFChenGHuangQOrionOKrugmanTFahimaTet al2005Genetic basis of barley caryopsis dormancy and seedling desiccation tolerance at the germination stage. Theoretical and Applied Genetics110445453
  189. 189. ZoharyDand HopfM1993Domestication of plants in the Old World. The origin and spread of cultivated plants in West Asia, Europe and the Nile Valley. Clarendon Press, Oxford, England.
  190. 190. ZouMGuanYRenHZhangFand ChenF2007Characterization of alternative splicing products of bZIP transcription factors OsABI5. Biochemical and Biophysical Research Communications360307313

Written By

Santosh Kumar, Arvind H. Hirani, Muhammad Asif and Aakash Goyal

Submitted: 05 November 2012 Published: 03 July 2013