Dormancy and germination of seeds are determined by various factors such as vitality, genotype, hardness, and other environmental cues, such as moisture, air, temperature, and light. Metabolic activity of seeds varies between the quiescent and imbibition state. In the dry state, longevity of a seed is determined by the reactive oxygen species (ROS) such as lipid peroxyl radical (LOO•) and lipid hydroperoxide (LOOH) that are generated nonenzymatically due to lipid peroxidation (LPO). During rehydration phase, enormous amount of ROS, such as superoxide (O2−), hydrogen peroxide (H2O2) and hydroxyl (•OH) radicals, are generated from the metabolically active compartments such as mitochondria, chloroplasts, and peroxisomes. The progressive conditional, temporal, and spatial distribution of ROS is tightly controlled by the effective antioxidant system that leads to the successful germination of seeds and this phenomenon is defined as ‘oxidation window.’ Gibberellins (GAs) and abscisic acid (ABA) are the key phytohormones involved in the germination/dormancy. Former promotes germination, whereas the latter induces dormancy. Genes involved in the synthesis and signaling of GA, such as gibberellin 3-β-dioxygenase (GA3ox), GA20ox, and GA-insensitive dwarf (GID), are responsible for the conversion of GA from an inactive to a bioactive form. On the other hand, DELLA, an important protein family acting as the repressors for GA-regulating genes, is activated by ABA. Function of genes, such as SLEEPY, PICKLE, SPINDLY, SECRET AGENT, AMYLASE, GAMYB, and LEAFY, are interrelated with the GA/ABA metabolism. By inducing the ubiquitin-26S proteolysis pathway, GA overcomes the DELLA-mediated effects on germination. The E3 ubiquitin ligase SCFSLY1 (skp1-cullin-F-box-Rbx1SLY1) complex was reported to be involved in the degradation of DELLA proteins. Additionally, cell differentiation and elongation process sustained by the ROS were also linked with the ethylene, brassinosteroids, and auxins. Hence, this chapter provides the heuristic framework on the phenomenon of systemic cross-talk between the ROS and phytohormones during the transition period of quiescent seeds into the metabolically active organisms.
Part of the book: New Challenges in Seed Biology