CC BY
143
Journal of Stress Physiology & Biochemistry, Vol. 19, No. 1, 2023, pp. 5-17 ISSN 1997-0838 Original Text Copyright © 2022 by Korgaonkar and Bhandari
REVIEW
OPEN/J) ACCESS
Drought Stress in Plants: Effects and Tolerance
Shravani Korgaonkar, Rupali Bhandari*
1 Department of Botany, Goa University, Goa, India
*E-Mail: rupali. bhandari@unigoa. ac. in
Received August 7, 2022
Water is the catalyst of life and plays a profound role in plant physiological processes ranging from photosynthesis to intermolecular interactions through a hydrophobic bond. Because of the alterations due to changing environmental conditions, the plants are continuously exposed to a lack of optimum water availability, leading to impaired growth and disturbance in water transport and uptake. Drought is a prominent environmental factor that triggers various plant processes from morphological, physiological, biochemical, and molecular. Plants portray an array of drought tolerance mechanisms; these responses differ based on the type of plant species and may involve the functions of various stress genes. Reduction in plant growth and productivity due to stomatal closure affects photosynthetic efficiency, altering membrane integrity and several enzymes involved in adenosine triphosphate synthesis. Plants exhibit a range of drought tolerance mechanisms and undergo several phenological, morphological, physiological, biochemical, and molecular adaptations at the cellular, subcellular and whole plant levels. Also, drought stress induces the production of reactive oxygen species at the cellular level and is strongly protected by the increase in the enzymatic and non-enzymatic antioxidative system. This chapter/ review provides a glimpse of the effects and tolerance strategies adapted by the plant under drought stress.
Key words: Abiotic stress, drought, phytohormone, reactive oxygen species, antioxidants
By 2050, it is hypothesized that the world's population will overdo 9.7 billion, and over 65% will solely rely on agriculture (Castañeda et al., 2016). Consequently, food supply and also nation's financial system will be influenced mainly by agronomy. On the other hand, agronomic practices combat hurdles such as inadequate irrigation systems, scarcity of good trait seeds, the excessive course of chemical pesticides and fertilizers leading to unsuitable soils, and soil erosions (Dev 2012). Besides the above constraints, plants both in the natural and agricultural environment are exposed to a wide array of biotic (insects, bacteria, viruses, fungi) and abiotic (temperature, water, salinity, chilling, freezing) stresses, which will affect their growth and development, thereby hampering crop productivity (Seki et al., 2003), in extreme cases, leads to the death of the plant. Due to changing climatic conditions, water scarcity is one of the most severe threats to food security for the rapidly increasing population (Farooq et al., 2009a). As a result, a 30% downfall in global crop production is estimated by 2025 compared to current productivity as per World economic forum Q2 (Hasanuzzaman et al., 2013).
From an agricultural point of view, alterations in rainfall, light and temperature are the factors to induce water deficit in plants. Also, a shortfall in meteorological drought coupled with an increased evapotranspiration rate leads to a lack of optimum soil moisture required for plant's average growth and development, leading to agricultural drought (Mishra and Cherkauer 2010 Manivannan et al., 2008). As a result, plant growth, yield, water relations, membrane integrity, pigment composition, and photosynthetic efficiency is drastically affected by drought (Praba et al., 2009). The water content's downturn characterizes the leaf water potential, causing stomatal closure, thereby decreasing cell growth and elongation (Anjum et al., 2011a). Lowered water content affects the entire physiological and biochemical mechanisms such as ion uptake and its translocation, photosynthesis, respiration, and nutrient metabolism, thus reducing plant growth (Farooq et al., 2009a) and causing the death of the plant (Jaleel et al., 2008). Hence, the production of drought-tolerant crop
plants may help meet the food demands. On the other hand, several drought-tolerant traits are used to assess the plant tolerance to drought stress, such as root-leaf traits, the ability for osmotic adjustment, water potential, synthesis of abscisic acid and cell membrane stability (Ha et al., 2012). In addition, several molecular mechanisms, including signal transduction, also help the plant in response to drought stress (Nishiyama et al., 2013; Osakabe et al., 2014). It is of utmost significance to comprehend the effects of drought on plant's morphological, anatomical, physiological and biochemical adaptations to cope with changing climatic challenges. This review is an overview of plant responses and tolerance mechanisms to drought stress and suggests some management strategies and possibilities to cope with drought effects, especially regarding field crops.
DAMAGING EFFECTS OF DROUGHT STRESS
Plants being sessile need to respond and adapt to various unfavourable environmental conditions. Under normal conditions, there is an irreversible increase in size, weight or volume, which comprises cell division, elongation and differentiation, causing plant growth and establishing an optimum crop stand, which is crucial for producing maximum yield (Farooq et al., 2012). Global climatic change is the leading cause of the increase in temperatures and atmospheric CO2 levels, increasing the rate of soil water evaporation, thereby altering the rainfall patterns, ultimately triggering drought stress worldwide (Dai 2011; Mishra and Singh 2011), exposing the plants to water stress. The severity of the stress depends entirely on the intensity, duration of stress, onset time, soil physicochemical conditions and the degree of plant susceptibility. The imbalance in water absorption and water loss rate is mainly due to lower soil water potential than plant roots, primarily due to the atmospheric conditions causing continuous water deficit by transpiration or evaporation (Mafakheri et al., 2010). Hence, meteorological drought is followed by agricultural drought (Dai 2011). However, in specific conditions, there is ample soil water content, but various edaphic factors, such as low soil temperatures, salinity, and flooding, decrease the water uptake by roots. Subsequently, inducing water stress in plants defined as
pseudo-drought or physiological drought wherein altered atmospheric conditions are not the decisive factors (Arbona et al., 2013; Lisar et al., 2012).
Drought, a multidimensional stress factor, affects plants from morphological, physiological, and biochemical levels and is apparent at all plant growth phenological phases (Korgaonker and Bhandari 2021; Anjum et al., 2011a). Under severe water deficit, plants exhibit a loss in leaf turgor, making it flaccid, leading to chlorosis and premature senescence (Akhtar and Nazir 2013; Sapeta et al., 2013). A few uncommon water deficit symptoms include irregular stunted growth, necrosis, cracks in twigs or bark, thinning of shrub and tree canopy, and extreme situations causing plant death (Arbona et al., 2013; Sapeta et al., 2013). During the early drought, germination and establishment are affected mainly due to reduced water uptake during the imbibition phase, seed germination, eased energy supply, distorted enzymatic activities and downregulated energy supply from photosynthesis (Okcu et al., 2005; Taiz and Zeiger 2010; Bhargava and Sawant 2013; Ding et al., 2013). Plant growth is reduced when soil water availability is restrained, wherein shoot development is more stunted than root growth (Anithakumari et al., 2012). Avramova et al. (2015) observed that water deficit reduces leaf expansion and photosynthesis due to impaired cell mitosis, elongation, proliferation, and differentiation (Potopova et al., 2016).
The chief response to drought stress is stomatal closure that disrupts leaf gas exchange, phloem loading, assimilate translocation and dry matter partitioning causing a severe deterioration in plant traits (Farooq et al., 2009b; Akram 2011). The drought stress also reduced leaf area due to loss of turgor, cut short the number of leaves, and suppressed leaf expansion and tillering (Farooq et al., 2010; Kramer and Boyer 1995; Nooden, 1988). All these constituents lowered the accumulation of dry matter and grain yield.
Drought is also associated to alterations in several aspects of morphological and anatomical features, such as the leaf anatomy, crop phenology and its ultrastructure (Hirt and Shinozaki 2003; Rao et al., 2006). It is also reported that the early plant development from the vegetative to reproductive phase
is suppressed due to limited water supply (Desclaux and Roumet 1996), leading to a substantial decrease in economic yield in the flowering stage (Hussain et al., 2008). An elaborative account of various effects of drought stress concerning their responses and adaptational aspects is conferred below.
ADAPTATIONS: PLANT RESPONSES TO DROUGHT STRESS
Plants undergo several phenological, morphological, physiological, biochemical, and molecular adaptations to cope with stress at the cellular, subcellular, and whole plant levels.
MORPHOLOGICAL RESPONSE
Plant resistance to stress conditions is divided into two primary strategies: stress avoidance and stress tolerance (Bhargava and Sawant 2013; Khan et al., 2011; Nezhadahmadi et al., 2013). These plant responses to withstand drought stress can range from molecular to entire plant level by escape, avoidance and tolerance, which is further explained:
Drought Escape: The drought escape shortens the life cycle or grows seasonally and allows the plants to reproduce in the presence of water (Akhtar and Nazir 2013; Bray 2007). A plant's life cycle mainly depends on the individual's genotype and environmental conditions. The synchrony of the plant phenological growth and development with soil moisture availability helps the plant escape drought conditions. A shortened life cycle can lead to drought escape as the plant matures and flowers early, although the yield is negatively affected (Akhtar and Nazir 2013; Farooq et al., 2009b).
Drought Avoidance: The principal objective used by the plant is to maintain higher water potential by reducing loss of water and preserving the water uptake by developing an extensive and prolific rooting system (Dai 2011; Farooq et al., 2009b), enabling the plant to absorb water from a considerable soil depth and far away distance from the plant. The xeromorphic trait such as hairy leaves and thick cuticle layers will assist the plant in maintaining high tissue water potential, but producing such xeromorphic structures consumes high energy and leads to decreased yield. Consequently, plants which use this strategy to uphold an optimum
water potential are generally small because of their adaptation to harsh environments (Khan et al., 2011; Lisar et al., 2012; Farooq et al., 2009b).
Drought Tolerance: The plants that adapt tolerance strategy restrict the number of leaves and leaf area in response to drought stress and thus decrease the yield (Akhtar and Nazir 2013; Bray 2007). Also, these plants show some xeromorphic characteristics, such as the presence of trichomes on the adaxial and abaxial surface of leaves, thereby reducing the leaf temperature and minimizing the loss of water by creating a layer of resistance to the movement of water away from the leaf surface (Lisar et al., 2012; Farooq et al., 2009d, Bray 2007). The root growth rate, size, density and proliferation are the key features of a plant's response to drought stress. However, other mechanisms involved in plant tolerance are the accumulation of compatible solutes, osmotic adjustments, activation of antioxidant systems, modifications in metabolic pathways, increased plant biomass, and stomatal closure (Bray 2007).
PHYSIOLOGICAL RESPONSE
Inadequate water availability alters crop growth and throughput due to declined water status and turgor. The drought-tolerant plants maintain their metabolic activities at low tissue water potential by adapting effective strategies such as osmotic adjustments, antioxidant defence system and changes in concentration of phytohormones (Kiani et al., 2007; Hussain et al., 2009). The increased accumulation of organic and inorganic solutes under stress aids in lowering water potential without decreasing actual water contents and is defined as osmotic adjustment or osmoregulation (Serraj and Sinclair 2002) and is one of the dynamic routes in plant adaptation to drought stress, minimizing the effects of drought-induced damage (Blum 2005). Osmo-protectants are compatible solutes with low molecular weight, are highly soluble and non-toxic even at higher concentrations, and confer protection to plants under oxidative damage by stabilizing membranes and maintaining primary structures of enzymes and proteins (Farooq et al., 2008). Compatible solutes involve soluble sugars such as fructans, sucrose, sugar alcohols, amino acids that include proline, aspartic acid, glutamic acid,
glycine betaine (GB), organic acids, trehalose, cyclitols such as mannitol and pinitol (Kiani et al., 2007; Kaur and Asthir 2015). Synthesis of osmotic compounds helps maintain leaf turgor, improves stomatal conductance for efficient carbon dioxide intake (Kiani et al., 2007), and promotes the root's ability for water uptake (Chimenti et al., 2006). As a result, an upsurge in water influx, turgor, and cell wall elasticity is obtained to maintain the physiological activity at an average pace helping the plant to attain growth from the vegetative stage until the reproductive stage during the drought phase (Kramer and Boyer 1995; Ludlow and Muchow 1990; Subbarao et al, 2000).
The synthesis of proline, a crucial compatible solute at low water potential in plants, is combined with enhanced biosynthesis and ceasing oxidation in mitochondria (Zhu 2002). Proline is seen to accumulate in bacteria, algae and animals to lower water potential, exposed to dehydration stress having a physiological role in stabilizing macromolecules (proteins), maintaining membrane integrity and quenching reactive oxygen species (Perez-Perez et al., 2009; Wahid and Close, 2007; Verbruggen and Hermans 2008; Verslues and Sharma 2010; Kaur and Asthir 2015). During post-drought, proline also serves as energy for carbon and nitrogen source (Szabados and Savouré 2009). Transgenic plants, resistant to osmotic stress, accumulate proline due to overexpression of the pyrroline-5-carboxylase synthase (P5CS) gene (Khan et al., 2015). Glycinebetaine (N, N, N-trimethyl glycine), an amphoteric quaternary amine, is yet another widely studied compatible solute in plants, animals and bacteria (Wahid et al., 2007). Glycinebetaine is critical in strengthening plant growth under various abiotic stresses by participating in the signal transduction pathway. Further, it safeguards the plant cells either by depositing hydration shells or by directly interacting with the macromolecules, thereby preventing them from unfolding and denaturation (Giri 2011; Quan et al., 2004; Subbarao et al., 2000). According to findings by Nuccio et al. (2015), Trehalose, a non-reducing glucose disaccharide, plays a significant role in plant growth and development by effectively preserving the biological structures and stabilizing enzymes, proteins and lipid
bilayer rather than adjusting the water potential under desiccation stress (Goddijn et al., 1997; Wingler, 2002; Lee et al., 2003). It is reported that the expression of heterologous genes from some eukaryotic species, such as Escherichia coli and Saccharomyces cerevisiae leads to trehalose synthesis and develops tolerance to drought stress in various species of plants (Iordachescu and Imai 2008). Li et al. (2011) observed that the overexpression of multiple isoforms of trehalose- 6-phosphate synthase aids in boosting drought tolerance in rice. Akram et al. (2016) emphasized the enhanced expression of SOD and POX in radish due to trehalose synthesis under drought stress. Turner et al. (2001) highlighted the maintenance of high tissue water potential by synthesizing abscisic acid and the generation of dehydrins that may confer protection to the plant against drought injuries.
BIOCHEMICAL RESPONSE
The first biochemical response of plants on exposure to any environmental stress that causes a shift from normal ecological conditions such as drought leads to the generation of reactive oxygen species (ROS), also known as oxidative burst, thereby acting as a secondary messenger to induce successive defense responses in plants (Apel and Hirt 2004). ROS radicals such as superoxide radical (O2-), hydroxyl radical (OH.), hydrogen peroxide (H2O2), alkoxy radicals (RO), and singlet oxygen causes oxidative stress in plant cell compartments such as chloroplasts, mitochondria, peroxisomes. On the other hand, under normal metabolism, ROS is formed as a natural byproduct having an essential role in cell signalling. However, ROS being highly reactive, denatures the structure and function of macromolecules such as nucleic acid, oxidation of amino acids, protein, and photosynthetic pigments, and boosts up malondialdehyde (MDA) content, which is a crucial marker for oxidative damage (Labudda and Safiul 2014; Osakabe et al., 2014; Farooq et al., 2009c; Nezhadahmadi et al., 2013, Moller et al., 2007). Thus, to deal with continuous oxidative bursts under stress, plants have an internal protective enzymatic and non-enzymatic cleanup system, which is enough to deflect injuries, ensuring normal functioning of the plant cell (Horvath et al., 2007). The non-enzymatic
antioxidants are low molecular mass, water and lipid-soluble compounds such as glutathione, ascorbic acid, carotenoids, and a-tocopherol. The enzymatic ROS scavenging defense system includes superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX), and glutathione reductase (GR) (Apel and Hirt 2004; Lisar et al., 2012; Hasegawa et al., 2000). During the oxidative burst the non-enzymatic defense system upholds the integrity of the photosynthetic membrane, whereas the enzymatic system may scavenge ROS directly, being the most effective mechanism (Farooq et al., 2008). According to the preceding literature, an upregulated antioxidant activity was noticed under water deficit conditions (Chugh et al., 2011; Chakraborty and Pradhan 2012; Marok et al., 2013). Marok et al. (2013) observed higher activity of CAT and SOD in drought-tolerant barley genotypes on exposure to drought compared to its drought-sensitive genotype. Carotenoids and other non-enzymatic compounds form vital components of the plant's antioxidant defense system (Havaux, 1998; Wahid 2007), scavenging singlet oxygen and lipid peroxy radicals inhibiting superoxide generation and lipid peroxidation under dehydrative forces (Deltoro et al., 1998). Ascorbate peroxidase is a crucial antioxidant enzyme in plants, whereas the fundamental role of preserving the glutathione pool is carried out by glutathione reductase under stress (Orvar and Ellis 1997; Pastori et al., 2000). Superoxide radicals with a half-life of less than one second are rapidly dismutased into H2O2 by SOD, a moderate stable product eliminated by catalase and peroxidase (Apel and Hirt 2004; Farooq et al., 2009b). SOD, a metalloenzyme, is clubbed up as the main line of defense against generating free superoxide radicals under drought conditions. Thus, increased superoxide dismutase activity confers tolerance against oxidative stress (Pan et al, 2006).
MOLECULAR MECHANISMS
Plants exposed to drought undergo several adaptive mechanisms at molecular levels that include signal transduction resulting in the expression of drought-responsive genes and adaptation to drought to curb the water balance (Nishiyama et al., 2013;
Osakabe et al., 2014; Kaur and Asthir 2017). Sensing stress and activation of defense and acclimation pathways are associated with complex signalling events involving ABA, Ca2+ and calcium-regulated proteins, ROS, phosphoglycerol, diacylglycerols, and signal transduction pathways (Kovtun et al., 2000; Kaur and Asthir 2017). These ROS, calcium, and phytohormones are the chemical indicators involved in inducing stress tolerance via transduction cascade and activating genomic reprogramming (Joyce et al., 2003). Recent research shows that drought-responsive genes primarily encode proteins involved in transcriptional regulation (mitogen-activated protein kinase cascades, protein phosphatases and cross-talk between diverse transcription factors), signalling cascades and functional proteins that aid the protection to cellular membranes, late embryogenesis abundant (LEA) proteins, antioxidants, proteins related to water uptake such as aquaporins and sugar transporters (Chen et al., 2002; Nakashima et al., 2014).
Aquaporins are present in the plasma membrane, and vacuoles are a group of crucial intrinsic membrane proteins that assist the passive water exchange across the membranes; their structural analysis reveals the familiar mechanism of protein-mediated water movement (Tyerman et al., 2002). These can potentiate a 10 to 20-fold upsurge in water permeability by regulating the hydraulic conductivity of the membranes (Maurel and Chrispeels 2001). Aquaporin activity is significantly controlled by phosphorylation (Johansson et al., 1998), calcium and pH (Tournaire- Roux et al., 2003). The function of aquaporins is expressed primarily in roots, where they mediate soil water uptake controlled by transcellular water transport (Javot and Maurel 2002).
Production of ABA is triggered in roots under water deficit and transported to shoot, causing restricted growth due to stomatal closure (Mittler and Blumwald 2015). Horvath et al. (2014) indicated that ABA compartmentalization and expanse of ABA reaching the stomata are influenced by xylem/apoplastic pH. Underwater deficit condition, xylem/apoplast pH being alkaline results in alkaline ABA trapping; that is, there is a decline in ABA exclusion from xylem and leaf apoplast to symplast, due to which added ABA on reaching guard
cells, enables stomatal aperture modulation in response to various stress factors (Shatil- Cohen et al., 2011). It was also observed by Le Gall et al. (2015) in drought-stressed plants that translocation of sugars through xylem exerts a significant impact on the sensitivity of stomata to ABA.
Many dehydration-responsive element-binding genes are involved in signalling pathways in response to drought and other abiotic stresses (Agarwal et al., 2006). The dehydration-responsive element/C-repeat (DRE/CRT) cis-acting element and its DNA-binding protein constitute a significant transcription system modulating ABA-independent gene expression in response to drought and includes dehydration-responsive element-binding proteins (DREB)/C-repeat binding factors (CBF) family of proteins. DREB2 subclass of DREB/CBF family proteins is expressed under drought to articulate genes involved in stress tolerance (Seki et al., 2003). Also, an early warning response mechanism exists in plant roots to activate the hydrogen pump ATPase protein (H+-ATPase) on the plasma membrane of root hairs before a substantial decline in plant RWC. The activation further triggers amplified biosynthesis of leaf proline and GB, the key osmolytes that maintain the water budget of plants (Gong et al., 2010). Poly Amines (PA) have been associated with the drought response of plants via signalling and are also involved in playing a role in other stresses (Bae et al., 2008). In addition, upregulation and downregulation of various gene transcripts and stress protein accumulation are crucial, and stress-driven forces, secondary stress signals, and plant response to injury may trigger gene expression (Kavar et al., 2008).
IMPROVING DROUGHT TOLERANCE AND MANAGEMENT STRATEGY
The cultivation of drought-tolerant crops is one of the options to meet the needs of the escalating world population. The production of transgenic plants is one of the well-known approaches for tolerance as a wide range of genes in the plant genome has opened up excellent prospects for crop improvement (Lisar et al., 2012; Xoconostle-Cazares et al., 2010). On the other hand, the generation of transgenic plants cannot be
entirely operative for producing drought-tolerant crop plants as it requires detailed and expensive protocol, and the success rate is primarily low (Nezhadahmadi et al., 2013; Nakashima et al., 2014). In the traditional breeding method, two plant individuals with desirable traits are selected and crossed to exchange genetic material; therefore, the offspring result from a new genetic combination (Khan et al., 2011; Nezhadahmadi et al., 2013). Some crucial traits used in plant breeding include water use efficiency, hydraulic conductance, osmotic and elastic adjustments, and variation in leaf area (Bhargava and Sawant 2013; Farooq et al., 2009b; Ding et al., 2013). Genetic data can improve plant breeding efficiency by using suitable tags for the target gene, known as polymorphisms, based on the naturally present sequence in DNA (Xoconostle-Cazares et al., 2010). The unique approaches are employed to distinguish linked markers, including restriction fragment length polymorphisms (RFLPs), sequence characteristic amplified regions (SCARs), random amplified polymorphic DNA (RAPDs), simple sequence repeats (SSRs), amplified fragment length polymorphism (AFLPs), and others (Khan et al., 2013; Xoconostle-Cazares et al., 2010).
Plant breeding methods have a massive potential to fasten the production of drought-tolerant plants, which helps in drought management. However, there are various strategies for managing drought in agricultural fields at different levels, such as irrigation at low soil moisture during germination and crop stand establishment, mulch to maintain the soil moisture level, eliminating attacks by insects and herbivores, appropriate planting practices, native plant individual based on the edaphic conditions, and plant inoculation by symbiotic microorganisms such as AM fungi (Nezhadahmadi et al., 2013; Khan et al., 2011; Farooq et al, 2009b).
Foliar application of assorted PGRs and osmoprotectants can also enhance the drought tolerance of crop plants. The exogenous application of plant hormones and osmoprotectants such as gibberellins (GA3), cytokinin (Ck), abscisic acid (ABA), proline, glycine betaine (GB), brassinolide, polyamine (PA), and salicylic acid (SA) has been recognized to
ameliorate stress effects, with high osmotic adjustment to maintain turgor and antioxidants accumulation to detoxify ROS to preserve the stability of membrane structures, enzymes, and other macromolecules (Manivannan et al., 2008; Farooq et al., 2009b, c; Yuan et al., 2010; Alcázar et al., 2010; Anjum et al., 2011b). Salicylic acid is a secondary metabolite that promotes plant drought tolerance by regulating several physiological processes through signalling (Senaratna et al., 2000; Singh and Usha 2003). The foliar application of methyl salicylic acid in water-stressed plants promotes leaf senescence, which contributes to nutrient remobilization, profiting the rest of the plant from the accumulated nutrients of the leaf from its life span (Abreu and Munne-Bosch 2008). Also, exogenously applied glycine betaine involved in osmoregulation acts as an osmoprotectant to protect membranes and enzymes from oxidative stress under drought stress (Ma et al, 2006).
CONCLUSION
Under the impact of ongoing global climate change intensifying greenhouse gas emissions, drought onset, frequency, and severity have been foreseen to increase shortly, affecting plant growth, development, and metabolism. The low rainfall, salinity, high temperature, and high light intensity are some of the main causal factors of the drought. Drought as a multidimensional stress factor negatively affects a plant at the molecular level up to the whole plant level. The plant has adopted strategies by shortening its life cycle and yield penalty to withstand drought. Also, the plants respond to drought by maintaining metabolic activities at low tissue water potential. Plants show physiological adaptation to dehydration tolerance by osmotic adjustments such as increased accumulation of proline, glycine betaine, sugars, inducing antioxidant activities (enzymatic and non-enzymatic systems) by scavenging ROS, maintaining cell membrane stability, expression of aquaporins, and altered growth regulators are vital mechanisms of drought tolerance. To curtail the effects of water stress, plants exhibit various signaling pathways and respond by upregulating antioxidant activity, accumulation of osmolytes and changing the growth pattern by producing chaperones and stress
proteins. The production of drought-tolerant transgenic plants by combining traditional breeding methods and gene manipulation is helpful to curtail the adverse effects of drought on plants. Also, several other strategies in agricultural fields for drought management
CONFLICTS OF INTEREST
The authors declare that they have no potential
conflicts of interest.
REFERENCES
Abreu M., and Munne-Bosch, S. (2008). Salicylic acid may be involved in the regulation of drought-induced leaf senescence in perennials: A case study in field-grown Salvia officinalis L. plants. Environ. Exp. Bot. 64, 105-112.
Agarwal P.K., Agarwal P., Reddy M.K. and Sopory S.K. (2006). Role of DREB transcription factors in abiotic and biotic stress tolerance in plants. Plant Cell Rep. 25, 1263-1274.
Akhtar I., and Nazir N. (2013). Effect of waterlogging and drought stress in plants. IJWRAE. 2, 34-40.
Akram M. (2011). Growth and yield components of wheat under water stress of different growth stages. Bangladesh J. Agric. Res. 36, 455-468.
Akram N.A., Waseem M., Ameen R. and Ashraf M. (2016). Trehalose pretreatment induces drought tolerance in radish (Raphanus sativus L.) plants: some key physio-biochemical traits. Acta Physiol. Plant. 38, 1-10.
Andresa Z., Perez-Hormaechea J., Leidia E.O., Schlucking K., Leonie S., McLachlanc D.H., Schumacher K., Hetherington A.M., Kudlab J., Cuberoa B. and Pardo J.M. (2014). Control of vacuolar dynamics and regulation of stomatal aperture by tonoplast potassium uptake. PNAS USA 111, 1806-1814.
Anithakumari A.M., Nataraja K.N., Visser R.G. and Van der Linden C.G. (2012). Genetic dissection of drought tolerance and recovery potential by quantitative trait locus mapping of a diploid potato population. Mol. Breed. 30,1413-1429.
Anjum S.A., Wang L.C., Farooq M., Hussain M., Xue L.L. and Zou C.M. (2011a). Brassinolide application improves the drought tolerance in maize through modulation of enzymatic antioxidants and leaf gas exchange. J Agron Crop Sci. 197,177-185.
Anjum S.A., Xie X.Y., Wang L.C., Saleem M.F., Man C. and Lei W. (2011b). Morphological, physiological and biochemical responses of plants to drought stress. Afr. J. Agric. Res. 6, 2026-2032.
Apel K., and Hirt H. (2004). Reactive oxygen species: metabolism, oxidative stress, and signal transduction. Annu. Rev. Plant Biol. 55, 373-399.
Arbona V., Manzi M., Ollas C.D. and Gómez-Cadenas A. (2013). Metabolomics as a tool to investigate abiotic stress tolerance in plants. Int. J. Mol. Sci. 14, 4885-4911.
Avramova V., Abd Elgawad H., Zhang Z., Fotschki B., Casadevall R., Vergauwen L. and Beemster G.T. (2015). Drought induces distinct growth response, protection, and recovery mechanisms in the maize leaf growth zone. Plant Physiol. 169, 1382-1396.
Bae H., Kim S.H., Kim M.S., Sicher R.C., Lary D., Strem M.D. and Bailey B.A. (2008). The drought response of Theobroma cacao (cacao) and the regulation of genes involved in polyamine biosynthesis by drought and other stresses. Plant Physiol. Biochem. 46,174-188.
Bhargava S. and Sawant K. (2013). Drought stress adaptation: metabolic adjustment and regulation of gene expression. Plant Breed. 132,21-32.
Blum A. (2005). Drought resistance, water-use efficiency, and yield potential—are they compatible, dissonant, or mutually exclusive?. Aust. J. Agric. Res. 56,1159-1168.
Bray E.A. (2007). Plant Response to Water-deficit Stress. eLS. , John Wiley & Sons, Ltd
Castaneda R., Doan D., Newhouse D.L., Nguyen M., Uematsu H. and Azevedo J.P. (2016). Who are the poor in the developing world?. World Bank Policy Research Working Paper, (7844).
Chakraborty U. and Pradhan B. (2012). Oxidative stress in five wheat varieties (Triticum aestivum L.)
on multiple levels can be effective.
exposed to water stress and study of their antioxidant enzyme defense system, water stress responsive metabolites and H2O2 accumulation. Braz. J. Plant Physiol. 24, 117-130.
Chen W., Provart, N.J., Glazebrook J., Katagiri F., Chang H.S., Eulgem T. and Zhu T. (2002). Expression profile matrix of Arabidopsis transcription factor genes suggests their putative functions in response to environmental stresses. The Plant Cell. 14, 559-574.
Chimenti C.A., Marcantonio M. and Hall A.J. (2006). Divergent selection for osmotic adjustment results in improved drought tolerance in maize (Zea mays L.) in both early growth and flowering phases. Field Crops Res. 95, 305-315.
Chugh V., Kaur N. and Gupta A. (2011). Evolution of oxidative stress tolerance in maize (Zea mays L.) seedlings in response to drought. Indian J Biochem Biophys. 48, 47-53.
Dai A. (2011). Drought under global warming: a review. Wiley Interdisciplinary Reviews: Clim Change 2, 4565.
Deltoro V.I., Calatayud A., Gimeno C., Abadía A., and Barreno E. (1998). Changes in chlorophyll a fluorescence, photosynthetic CO2 assimilation and xanthophyll cycle interconversions during dehydration in desiccation-tolerant and intolerant liverworts. Planta. 207, 224-228.
Desclaux D., and Roumet P. (1996). Impact of drought stress on the phenology of two soybean (Glycine max L. Merr) cultivars. Field Crops Res. 46, 61-70.
Dev S.M. (2012). Small Farmers in India: Challenges and Opportunities. WP-2012-014, Indira Gandhi Institute of Development Research, Mumbai. http://www.igidr.ac.in/pdf/publication/WP-2012-014.pdf
Ding Y., Tao Y. and Zhu C. (2013). Emerging roles of microRNAs in the mediation of drought stress response in plants. J. Exp. Bot. 64, 3077-3086.
Farooq M., Aziz T., Basra S.M.A., Cheema M.A. and Rehman H. (2008). Chilling tolerance in hybrid maize induced by seed priming with salicylic acid. J Agron Crop Sci. 194, 161-168. -188.
Farooq M., Basra S.M.A., Wahid A., Ahmad N. and Saleem B.A. (2009b). Improving the drought tolerance in rice (Oryza sativa L.) by exogenous application of salicylic acid. J Agron Crop Sci. 195, 237-246.
Farooq M., Hussain M., Wahid A. and Siddique K.H.M. (2012). Drought stress in plants: an overview. in Plant responses to drought stress. 1-33.
Farooq M., Kobayashi N., Ito O., Wahid A. and Serraj R. (2010). Broader leaves result in better performance of indica rice under drought stress. J. Plant Physiol. 167, 1066-1075.
Farooq M., Wahid A. and Lee D.J. (2009c). Exogenously applied polyamines increase drought tolerance of rice by improving leaf water status, photosynthesis and membrane properties. Acta Physiol. Plant. 31, 937-945.
Farooq M., Wahid A., Kobayashi N.S.M.A., Fujita D.B.S.M.A. and Basra S.M.A. (2009a). Plant drought stress: effects, mechanisms and management. Sustain. Agric. 153.
Farooq M., Wahid A., Lee D.J., Ito O. and Siddique K.H. (2009d). Advances in drought resistance of rice. Crit Rev Plant Sci. 28, 199-217.
Giri J. (2011). Glycinebetaine and abiotic stress tolerance in plants. Plant Signal. Behav. 6, 17461751.
Goddijn O.J., Verwoerd T.C., Voogd E., Krutwagen R.W., De Graff P.T.H.M., Poels J. and Pen J. (1997). Inhibition of trehalase activity enhances trehalose accumulation in transgenic plants. Plant physiol. 113, 181-190.
Gong D.S., Xiong Y.C., Ma,B.L., Wang T.M., Ge J.P., Qin X.L. and Li F.M. (2010). Early activation of plasma membrane H+-ATPase and its relation to drought adaptation in two contrasting oat (Avena sativa L.) genotypes. Environ. Exp. Bot. 69, 1-8.
Ha S., Vankova R., Yamaguchi-Shinozaki K., Shinozaki K. and Tran L.S.P. (2012). Cytokinins: metabolism and function in plant adaptation to environmental stresses. Trends Plant Sci. 17, 172-179.
Hasanuzzaman M., Nahar K. and Fujita M. (2013). Plant response to salt stress and role of exogenous
protectants to mitigate salt-induced damages. In Ecophysiology and responses of plants under salt stress. Springer, New York, NY 25-87.
Hasegawa P.M., Bressan R.A., Zhu J.K. and Bohnert H.J. (2000). Plant cellular and molecular responses to high salinity. Annu. Rev. Plant Biol. 51, 463-499.
Havaux M. (1998). Carotenoids as membrane stabilizers in chloroplasts. Trends Plant Sci. 3, 147-151.
Hirt H. and Shinozaki K. (2003). Plant responses to abiotic stress (Vol. 4). Springer Science & Business Media.
Horvath E., Pal M., Szalai G., Paldi E. and Janda T. (2007). Exogenous 4-hydroxybenzoic acid and salicylic acid modulate the effect of short-term drought and freezing stress on wheat plants. Biol. Plant. 51, 480-487.
Hussain M., Malik M.A., Farooq M., Ashraf M.Y. and Cheema M.A. (2008). Improving drought tolerance by exogenous application of glycinebetaine and salicylic acid in sunflower. J Agron Crop Sci. 194, 193-199.
Hussain M., Malik M.A., Farooq M., Khan M.B., Akram M. and Saleem M.F. (2009). Exogenous glycinebetaine and salicylic acid application improves water relations, allometry and quality of hybrid sunflower under water deficit conditions. J Agron Crop Sci. 195, 98-109.
Iordachescu M. and Imai R. (2008). Trehalose biosynthesis in response to abiotic stresses. J Integr Plant Biol. 50, 1223-1229.
Jaleel C. A., Gopi R., Sankar B., Gomathinayagam M., & Panneerselvam R. (2008). Differential responses in water use efficiency in two varieties of Catharanthus roseus under drought stress. Comptes Rendus Biologies, 331(1), 42-47.
Javot H. and Maurel C. (2002). The role of aquaporins in root water uptake. Ann. Bot. 90, 301-313.
Johansson I., Karlsson M., Shukla V.K., Chrispeels M.J., Larsson C. and Kjellbom P. (1998). Water transport activity of the plasma membrane aquaporin PM28A is regulated by phosphorylation. Plant Cell. 10, 451459.
Joyce S.M., Cassells A.C. and Jain S.M. (2003). Stress and aberrant phenotypes in vitro culture. PCTOC. 74, 103-121.
Kaur G. and Asthir B. (2015). Proline: a key player in plant abiotic stress tolerance. Biol. Plant. 59, 609619.
Kaur G. and Asthir B. (2017). Molecular responses to drought stress in plants. Biol. Plant. 61, 201-209.
Kavar T., Maras M., Kidric M., Sustar-Vozlic J. and Meglic V. (2008). Identification of genes involved in the response of leaves of Phaseolus vulgaris to drought stress. Mol. Breed. 21, 159-172.
Khan M. A., Iqbal M., Akram M., Ahmad M., Hassan M. W., & Jamil M. (2013). Recent advances in molecular tool development for drought tolerance breeding in cereal crops: a review. Zemdirbyste-Agriculture, 100(3), 325-334.
Khan M.A., Iqbal M., Jameel M., Nazeer W., Shakir S., Aslam M.T. and Iqbal B. (2011). Potentials of molecular based breeding to enhance drought tolerance in wheat (Triticum aestivum L.). Afr. J. Biotechnol. 10, 11340-11344.
Khan M.S., Ahmad D. and Khan M.A. (2015). Utilization of genes encoding osmoprotectants in transgenic plants for enhanced abiotic stress tolerance. Electron. J. Biotechnol. 18, 257-266.
Kiani S.P., Talia P., Maury P., Grieu P., Heinz R., Perrault A. and Sarrafi A. (2007). Genetic analysis of plant water status and osmotic adjustment in recombinant inbred lines of sunflower under two water treatments. Plant Sci. 172, 773-787.
Korgaonker S. and Bhandari R. (2021). Response of Oryza sativa L. To the interactive effect of drought and salicylic acid. J. stress physiol. biochem. 17, 95-104.
Kovtun Y., Chiu W.L., Tena G. and Sheen J. (2000). Functional analysis of oxidative stress-activated mitogen-activated protein kinase cascade in plants. PNAS USA 97, 2940-2945.
Kramer P.J. and Boyer J.S. (1995). Water relations of plants and soils. Academic press.
Labudda, M., & Azam, F. M. S. (2014). Glutathione-dependent responses of plants to drought: a review. Acta Societatis Botanicorum Poloniae, 83(1). 3-12
Le Gall H., Philippe F., Domon J.M., Françoise G., Jérôme P. and Rayon C. (2015). Cell wall metabolism in response to abiotic stress. Plants. 4, 112-166.
Lee S.B., Kwon H.B., Kwon S.J., Park S.C., Jeong M.J., Han S.E. and Daniell H. (2003). Accumulation of trehalose within transgenic chloroplasts confers drought tolerance. Mol Breed. 11, 1-13.
Li H.W., Zang B.S., Deng X.W. and Wang X.P. (2011). Overexpression of the trehalose-6-phosphate synthase gene OsTPS1 enhances abiotic stress tolerance in rice. Planta. 234, 1007-1018.
Lisar S. Y., Motafakkerazad R., Hossain M. M., & Rahman I. M. (2012). Causes, effects and responses. Water stress, 25(1), 33.
Ludlow M.M. and Muchow R.C. (1990). A critical evaluation of traits for improving crop yields in water-limited environments. Adv. Agron. 43, 107153.
Ma Q.Q., Wang W., Li Y.H., Li D.Q. and Zou Q. (2006). Alleviation of photoinhibition in drought-stressed wheat (Triticum aestivum) by foliar-applied glycinebetaine. J. Plant Physiol. 163, 165-175.
Mafakheri A., Siosemardeh A.F., Bahramnejad B., Struik P.C. and Sohrabi Y. (2010). Effect of drought stress on yield, proline and chlorophyll contents in three chickpea cultivars. Aust. J. Crop Sci. 4, 580-585.
Manivannan P., Jaleel C.A., Somasundaram R. and Panneerselvam R. (2008). Osmoregulation and antioxidant metabolism in drought-stressed Helianthus annuus under triadimefon drenching. C. R. Biol. 331, 418-425.
Marok M., Tarrago L., Ksas B., Henri P., Abrous-Belbachir O., Havaux M., Rey P. (2013). A drought-sensitive barley variety displays oxidative stress and strongly increased contents in low-molecular weight antioxidant compounds during water deficit compared to a tolerant variety. J. Plant Physiol. 170, 633-645.
Maurel C. and Chrispeels M.J. (2001). Aquaporins. A molecular entry into plant water relations. Plant physiol. 125, 135-138.
Mishra A.K. and Singh V.P. (2011). Drought modeling-A review. J. Hydrol. 403, 157-175.
Mishra V. and Cherkauer K.A. (2010). Retrospective droughts in the crop growing season: Implications to corn and soybean yield in the Midwestern United States. Agric For Meteorol. 150, 1030-1045.
Mittler R., Blumwald E. (2015). The roles of ROS and ABA in systemic acquired acclimation. Plant Cell. 27, 64-70.
M0ller I.M., Jensen P.E. and Hansson A. (2007). Oxidative modifications to cellular components in plants. Annu. Rev. Plant Biol. 58, 459-481.
Nakashima K., Yamaguchi-Shinozaki K. and Shinozaki K. (2014). The transcriptional regulatory network in the drought response and its crosstalk in abiotic stress responses including drought, cold, and heat. Front. Plant Sci. 5, 170.
Nezhadahmadi A., Prodhan Z.H. and Faruq G. (2013). Drought tolerance in wheat. The Scientific World Journal. 2013, Article ID 610721
Nishiyama R., Watanabe Y., Leyva-Gonzalez M.A., Van Ha C., Fujita Y., Tanaka M. and Tran L.S.P. (2013). Arabidopsis AHP2, AHP3, and AHP5 histidine phosphotransfer proteins function as redundant negative regulators of drought stress response. PNAS USA. 110, 4840-4845.
Nooden L.D. (1988). The phenomenon of senescence and aging. Senescence and aging in plants. 2-50.
Nuccio M.L., Wu J., Mowers R., Zhou H.P., Meghji M., Primavesi L.F., Paul M.J., Chen X., Gao Y., Haque E., Basu S.S. and Lagrimini L.M (2015). Expression of trehalose-6- phosphate phosphatase in maize ears improves yield in well-watered and drought conditions. Nat. Biotechnol. 33, 862- 869.
Ok?u G., Kaya M.D. and Atak M. (2005). Effects of salt and drought stresses on germination and seedling growth of pea (Pisum sativum L.). Turk J Agric For. 29, 237-242.
Orvar B.L. and Ellis B.E. (1997). Transgenic tobacco plants expressing antisense RNA for cytosolic
ascorbate peroxidase show increased susceptibility to ozone injury. Plant J. 11, 1297-1305.
Osakabe Y., Osakabe K., Shinozaki K. and Tran L.S.P. (2014). Response of plants to water stress. Front. Plant Sci. 5, 86.
Pan Y., Wu L.J. and Yu Z.L. (2006). Effect of salt and drought stress on antioxidant enzymes activities and SOD isoenzymes of liquorice (Glycyrrhiza uralensis Fisch). Plant Growth Regul. 49, 157-165.
Pastori G., Foyer C.H. and Mullineaux P. (2000). Low temperature-induced changes in the distribution of H2O2 and antioxidants between the bundle sheath and mesophyll cells of maize leaves. J. Exp. Bot. 51, 107-113.
Pérez-Pérez J.G., Robles J.M., Tovar J.C. and Botia P. (2009). Response to drought and salt stress of lemon 'Fino 49'under field conditions: water relations, osmotic adjustment and gas exchange. Sci. Hortic. 122, 83-90.
Potopova V., Boroneant; C., Boincean B. and Soukup J. (2016). Impact of agricultural drought on main crop yields in the Republic of Moldova. Int. J. Climatol. 36, 2063-2082.
Praba M.L., Cairns J.E., Babu R.C. and Lafitte H.R. (2009). Identification of physiological traits underlying cultivar differences in drought tolerance in rice and wheat. J Agron Crop Sci. 195, 30-46.
Quan R., Shang M., Zhang H., Zhao Y. and Zhang J. (2004). Improved chilling tolerance by transformation with betA gene for the enhancement of glycinebetaine synthesis in maize. Plant Sci. 166, 141-149.
Rao K.M., Raghavendra A.S. and Reddy K.J. (Eds.). (2006). Physiology and molecular biology of stress tolerance in plants. Springer Science & Business Media.
Sapeta H., Costa J.M., Lourenco T., Maroco J., Van der Linde P. and Oliveira M.M. (2013). Drought stress response in Jatropha curcas: growth and physiology. Environ. Exp. Bot. 85, 76-84.
Seki M., Kamei A., Yamaguchi-Shinozaki K. and Shinozaki K. (2003). Molecular responses to
drought, salinity and frost: common and different paths for plant protection. Curr. Opin. Biotechnol. 14, 194-199.
Senaratna T., Touchell D., Bunn E. and Dixon K. (2000). Acetyl salicylic acid (Aspirin) and salicylic acid induce multiple stress tolerance in bean and tomato plants. Plant Growth Regul. 30, 157-161.
Serraj R. and Sinclair T.R. (2002). Osmolyte accumulation: can it really help increase crop yield under drought conditions?. Plant Cell Environ. 25, 333-341.
Shatil-Cohen A., Attia Z. and Moshelion M. (2011). Bundle-sheath cell regulation of xylem-mesophyll water transport via aquaporins under drought stress: a target of xylem-borne ABA? Plant J. 67, 72-80.
Singh B. and Usha K. (2003). Salicylic acid induced physiological and biochemical changes in wheat seedlings under water stress. Plant Growth Regul. 39, 137-141.
Subbarao G.V., Nam N.H., Chauhan Y.S. and Johansen C. (2000). Osmotic adjustment, water relations and carbohydrate remobilization in pigeonpea under water deficits. J. Plant Physiol. 157, 651-659.
Taiz L. and Zeiger E. (2010). Plant physiology. 5th edn (Sinauer Associates: Sunderland, MA, USA).
Tournaire-Roux C., Sutka M., Javot H., Gout E., Gerbeau P., Luu D.T. and Maurel C. (2003). Cytosolic pH regulates root water transport during anoxic stress through gating of aquaporins. Nature. 425, 393-397.
Turner N.C., Wright G.C. and Siddique K.H.M. (2001). Adaptation of grain legumes (pulses) to water-limited environments. Adv. Agron. 71, 193-231.
Tyerman S.D., Niemietz C.M. and Bramley H. (2002). Plant aquaporins: multifunctional water and solute channels with expanding roles. Plant Cell Environ. 25, 173-194.
Verbruggen N. and Hermans C. (2008). Proline accumulation in plants: a review. Amino Acids. 35, 753-759.
Verslues P.E. and Sharma S. (2010). Proline metabolism and its implications for plant-environment interaction. Arabidopsis Book. 8, 140.
Wahid A. (2007). Physiological implications of metabolite biosynthesis for net assimilation and heat-stress tolerance of sugarcane (Saccharum officinarum) sprouts. J. Plant Res. 120, 219-228.
Wahid A. and Close T.J. (2007). Expression of dehydrins under heat stress and their relationship with water relations of sugarcane leaves. Biol. Plant. 51, 104-109.
Wahid A., Gelani S., Ashraf M., & Foolad M. R. (2007). Heat tolerance in plants: an overview. Environmental and experimental botany, 61(3), 199-223.
Wingler A. (2002). The function of trehalose biosynthesis in plants. Phytochemistry. 60, 437440.
Xoconostle-Cazares B., Ramirez-Ortega F.A., Flores-Elenes L. and Ruiz-Medrano R. (2010). Drought tolerance in crop plants. Am. J. Plant Physiol. 5, 241-256.
Yuan G.F., Jia C.G., Li Z., Sun B., Zhang L.P., Liu N. and Wang Q.M. (2010). Effect of brassinosteroids on drought resistance and abscisic acid concentration in tomato under water stress. Sci. Hortic. 126:103-108.
Zhu J.K. (2002). Salt and drought stress signal transduction in plants. Annu. Rev. Plant Biol. 53, 247-273.
