Climate Change and Abiotic Stresses in Plants

Abstract

Any altered physiological conditions which can hamper the growth and development of crop plants that is denoted as stress. The challenges of abiotic stress on plant growth and development are evident among the emerging ecological impacts of climate change. In a compatible environment for one genotype may not be fitable for another. The field of plant abiotic stress encompasses all studies on abiotic factors or stresses from the environment that can impose stress on a variety of species. Abiotic stress induces redox imbalance during reproductive growth. These studies indicate that stress induced over accumulation of ROS leads to pollen abortion and programmed cell death of microspores in developing anthers consequently resulting in male sterility. With these changing climatic conditions climate resilient crops and crop varieties have been recommended as a way for farmers to cope with or adopt to climate change. Integrated physiological and molecular approaches are important for combating multiple abiotic stresses.

1. Introduction

Plants encounter changing environments during their entire life cycle, from seedling to reproductive stage, that are often unfavourable to their growth and developmental processes, and they create unique mechanisms to cope with these challenges. There are primarily two types of negative environmental variables. The first are biotic variables, such as disease and herbivore attacks, and the second are abiotic factors, such as drought, heat, cold, nutrient inadequacy, and heavy metal build-up in the soil. Salt, drought, and temperature, for example, have an impact on the geographical distribution of plant species and disturb plant metabolism. As a result, they reduce the quality and quantity of food production in agriculture, lowering the food supply for a growing population, and tolerance mechanisms in plants have been thoroughly explored to overcome these negative impacts. Various environmental variables (biotic and abiotic) activate stress tolerance genes in plants, causing them to become resistant.

2. Heat stress

The average temperature has been determined to be increasing by 0.2°C per year, and it will have to grow by 1.8°C 4°C by the end of the year 2100, making temperature one of the most damaging stresses [1]. Temperature-related climate change is a global concern that has affected plant physiological and biochemical activity, lowering crop output [1, 2]. Plants are subjected to heat stress as a result of rising temperatures, which is dependent on the quality, intensity, and duration of light.

All environmental conditions (biotic and abiotic) contribute to the production of reactive oxygen species (ROS), including heat stress, which damages macromolecules such as DNA, proteins, and lipids [3], and plants are under oxidative stress. Heat stress also changed the expression of genes involved in the creation of osmo-protectants, detoxifying enzymes, transporters, and regulatory proteins [4]. Heat stress, on the other hand, inhibits protein folding, alters membrane (lipid bilayer) fluidity and cytoskeleton arrangement, and has an impact on vegetative and reproductive tissue [5, 6]. A rise in temperature up to a certain point is helpful to plants, since it governs plant circadian rhythms, plant movements (corolla opening/closing), and impacts the geographical dispersion of plants in nature [7]. High temperatures increased the susceptibility of plants to pathogens. When the ambient temperature rose, the infection capability of tobacco mosaic and tomato-spotted wilt viruses increased, causing viral illnesses in tobacco (Nicotiana tabacum) and pepper (Capsicum annuum), respectively [8]. Wheat genotypes were shown to be more sensitive to Cochliobolus sativus (which causes spot blotch) when night time temperatures rose (Figure 1) [10].

Figure 1.

Effect of low and high-temperature stress in plants. Source: Tiwary et al. [9].

3. Cold stress

Apart from heat stress, a drop in ambient temperature causes chilling stress in plants, which has a significant effect on cell physiology. Chilling, according to Ruelland et al. [5], promotes cell death by suppressing enzymatic activities, rigidifying biological membranes, stabilising nucleic acids, generating reactive oxygen species (ROS), and impairing photosynthesis. Low temperature causes flowering in plants, which is known as vernalization [11], and upregulates metabolic processes that confer the tolerance strategy of plants, known as the cold-hardening process [12], which results in the accumulation of compatible solutes (sugar), membrane composition changes, and increased synthesis of dehydrin-like proteins [13]. Plants had long- and short-term responses to temperature stress (heat or cold stress). Long-term effects included morphological and phenological adaptations, whereas short-term effects included leaf orientation changes, increased transpiration, and changes in membrane lipid content.

Heat stress causes a reduction in water loss by closing the stomata, as well as increased stomatal densities and larger xylem vessels [14], allowing plants to thrive in these harsh conditions. ROS production is an unavoidable by-product of aerobic activity, and its toxicity is determined by its concentration. It functions as a signalling molecule at low concentrations, but at greater concentrations, it becomes poisonous and causes cell death [15]. Under various stress situations, particularly heat stress, ROS such as H₂O₂, O₂, and ¹O₂ are produced [16]. Every plant contains an assortment of antioxidant systems to deal with the detrimental effects of ROS. These systems help to lessen the negative effects. Enzymatic antioxidants such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione S-transferase (GST), as well as non-enzymatic antioxidants such as cysteine, proline, non-protein thiols, and the synthesis of molecular chaperones known as heat-shock proteins (HSPs), are part of the antioxidant system [17]. HSPs are important proteins that are activated by heat stress and target HS-responsive transcription factors, which regulate protein quality by re-energising proteins [18].

4. Salt stress

The impact of salt stress in plants has become an important issue in modern agricultural development, climate change and global food crisis. Survival of plants under adverse environmental conditions relies on integration of stress adaptive metabolic and structural changes into endogenous developmental programs. Almost all crops are sensitive to high salt (NaCl) levels [19], however the degree of sensitivity varies substantially between species and marginally between cultivar types within a species [19]. The plant response to high salt concentrations is complex. The effect of excessive NaCl concentrations on plants results in osmotic stress and creates an ionic imbalance due to accumulation of toxic ions like Na⁺ and Cl⁻. The plant’s developmental growth stage [20] as well as external environmental elements influence the plant’s sensitivity to salinity [21]. Salt stress is a major issue for agriculture systems since it reduces crop yield potential [22]. Excess salt in the soil affects plant growth by lowering seed germination, plant height, root length, and fructification [19], and it has also negative impact on mineral homeostasis, in particular Ca²⁺ and K⁺. But it also has indirect impacts on the food web segment that depends on that host plant [22]. Salinity induced imbalance of cellular ion homeostasis is coped with regulated ion influx and effect at plasma membrane and vacuoler ion sequestration [23]. All of this occurs as a result of salt-induced oxidative stress [24], ion toxicity, and decreased photosynthetic rate in plants, all of which led to a considerable reduction in overall crop production [25].

Despite this, plants may naturally live and complete their life cycle under extreme salt stress [26]. They have well-developed biological, chemical, and physiological mechanisms [19], which could result in the synthesis of products and the start of processes that improve plant resistance to soluble salts [26]. Depending on the types of modifications they must perform in response to plant salt stress, these systems could be complex or simple [26]. Plant stress sensing and signalling machinery are critical components of their salt stress tolerance network, according to several studies [27]. The most common salt tolerance systems in plants are salt excessively sensitive (SOS) signalling pathways, hyperosmotic sensors, gene regulation in roots, and plant membrane Na⁺ and K⁺ transporters [27]. Plants’ biological salt tolerance adaptations include osmoregulation and hormonal alterations. Other options for improving plant tolerance to salt stress include the use of plant growth-promoting rhizobacteria (PGPR), plant fungal associations, and the application of organic and inorganic amendments [28]. To address this problem, scientists used salt tolerant engineered plants or transgenic salt resistant cultivars, as well as a potential physiological method [27]. However, because the salt tolerance mechanism in plants is genetically complex, it was not very successful [19].

5. Drought stress

Drought is one of the key factors affecting crop output around the world, as crop growth and yield are both influenced by this stress [29]. Drought stress is caused by a lack of rainfall, salt buildup in the soil, significant temperature swings, and excessive light intensity. Due to climate change, climate simulation models that take previous year data and estimate the future have indicated that this stress would become more severe in the near future. Drought stress affects plant growth, water retention, and water efficiency [30, 31], as well as causing changes in physiological, biochemical, morphological, and molecular features [30, 31]. Drought-tolerant/resistant plants have evolved a more efficient drought resilience mechanism to withstand drought stress, however these mechanisms are not well-organised or investigated. Plants, in general, have a mechanism for maintaining cell homeostasis that involves increased water transport into the plant cell. Drought resistance is a cellular defence mechanism that allows cells to survive long periods of drought [32]. Plants, in addition to drought tolerance, tend to undergo a number of metabolic changes in response to drought stress, including decreased ribulose bisphosphate (RuBP) and adenosine triphosphate (ATP) levels, as well as reduced Rubisco activity. Plants reduce substomatal CO₂ conductivity and close stomata to avoid water loss up to their maximum capacity during drought. Water stress reduces the light saturation rate, decarboxylation velocity, ribulose 1,5-bisphosphate regeneration ability, photosystem II (PS-II) efficiency, and stomatal conductance in plants [33]. Drought has a negative impact on amino acids in plants, such as asparagine and glutamic acid, although plants can respond by boosting amino acids and soluble levels to temporarily relieve stress and manage osmotic potential [34].

6. Conclusions

Daily environmental fluctuations can have dramatic effects on plant vegetative growth at multiple levels, resulting in molecular, cellular, physiological and morphological changes. Environmental stress factors such as drought, elevated temperature, salinity and rising CO₂ affect to sustainable agriculture. Plants are even more sensitive to environmental changes during reproductive stages. Changing climate condition imposes different abiotic stresses to plant growth and development. This chapter will provide how different stress condition affects the plant growth and development and how they acclimatised with changing environment.

With this conclusion, there are some future scopes of research. Changing climate and Yield reduction in the late sown crop may be minimised with appropriate hormonal and nutritional interventions. Hormonal boosting may invigorate the plants under stress [35]. The stimulatory effect of hormones does not sustain for a long period when applied externally. Hormone based stimulatory physiology may be enhanced internally through nutritional treatment with boron and zinc which either enhances auxin stimulation or auxin biosynthesis. Smooth and healthy reproductive development is a precondition for the realisation of the yield potential of the crop.