Drought Tolerance In Crop Plants Research Articles

Developing Drought Tolerance in Field Crops towards Current Century: An Integrated Bio-Molecular Approach

Drought stresses are foremost threat to plant growth, productivity as well as sustainability towards agriculture through worldwide. Some of the classical breeding approaches have been attempted to develop crop performance towards stress without significant success and so therefore, recently genetic engineering in crop plants is recognized as an alternative strategy to generate drought tolerant crop plants. Various integrated biological approaches have been undertaken to overcome such drought hurdles in achieving the full potentiality of the plant growth and production as well as improving the drought tolerance in different field crops. Some approaches are commonly used to identify genes related to drought tolerance and genes to be identified which are involved in processes known to be critical for drought tolerance; whose expression is regulated by drought stress and that consists in the identification of drought tolerance determinants based on functionality. Plant researchers have developed several spurts of biological novel ‘Omics’ technologies viz. genomics, transcriptomics, proteomics and metabolomics etc to engineer plant stress tolerance. In this review, an attempt has been made to summarize the current information based on recent literature towards recent understanding as well as latest advancement related to the adverse effect of plant under drought and their adaptations or tolerance towards such abiotic stress with a focus on the identification of drought tolerance mechanisms by soil management practices, crop establishment and exogenous application of growth regulators by regulating an appropriate level of water due to osmotic adjustment and stomatal performance etc at an integrated biological level of approach.

Expression Patterns and Molecular Mechanisms Regulating Drought Tolerance of Soybean [Glycine max (L.) Merr.] Conferred by Transcription Factor Gene GmNAC19.

NAC transcription factors are commonly involved in the plant response to drought stress. A transcriptome analysis of root samples of the soybean variety 'Jiyu47' under drought stress revealed the evidently up-regulated expression of GmNAC19, consistent with the expression pattern revealed by quantitative real-time PCR analysis. The overexpression of GmNAC19 enhanced drought tolerance in Saccharomyces cerevisiae INVSc1. The seed germination percentage and root growth of transgenic Arabidopsis thaliana were improved in comparison with those of the wild type, while the transgenic soybean composite line showed improved chlorophyll content. The altered contents of physiological and biochemical indices (i.e., soluble protein, soluble sugar, proline, and malondialdehyde) related to drought stress and the activities of three antioxidant enzymes (i.e., superoxide dismutase, peroxidase, and catalase) revealed enhanced drought tolerance in both transgenic Arabidopsis and soybean. The expressions of three genes (i.e., P5CS, OAT, and P5CR) involved in proline synthesis were decreased in the transgenic soybean hairy roots, while the expression of ProDH involved in the breakdown of proline was increased. This study revealed the molecular mechanisms underlying drought tolerance enhanced by GmNAC19 via regulation of the contents of soluble protein and soluble sugar and the activities of antioxidant enzymes, providing a candidate gene for the molecular breeding of drought-tolerant crop plants.

ZmC2H2-149 negatively regulates drought tolerance by repressing ZmHSD1 in maize.

Drought is a major abiotic stress that limits maize production worldwide. Therefore, it is of great importance to improve drought tolerance in crop plants for sustainable agriculture. In this study, we examined the roles of Cys2 /His2 zinc-finger-proteins (C2H2-ZFPs) in maize's drought tolerance as C2H2-ZFPs have been implicated for plant stress tolerance. By subjecting 150 Ac/Ds mutant lines to drought stress, we successfully identified a Ds-insertion mutant, zmc2h2-149, which shows increased tolerance to drought stress. Overexpression of ZmC2H2-149 in maize led to a decrease in both drought tolerance and crop yield. DAP-Seq, RNA-Seq, Y1H and LUC assays additionally showed that ZmC2H2-149 directly suppresses the expression of a positive drought tolerance regulator, ZmHSD1 (hydroxysteroid dehydrogenase 1). Consistently, the zmhsd1 mutants exhibited decreased drought tolerance and grain yield under water deficit conditions compared to their respective wild-type plants. Our findings thus demonstrated that ZmC2H2-149 can regulate ZmHSD1 for drought stress tolerance in maize, offering valuable theoretical and genetic resources for maize breeding programmes that aim for improving drought tolerance.

Differentially expressed genes in Jojoba (Simmondsia chinensis) when subjected to water-stress

Jojoba (Simmondsia chinensis) is a desert shrub with an ability to survive in extremely arid environments. The exceptional drought tolerance of jojoba includes traits that could be useful in developing drought tolerant crop plants. This study characterized changes in gene expression in jojoba under water-stress during a controlled-environment experiment. A large number of transcripts (10,936) were identified as differentially expressed under contrasting water stress conditions. These included transcripts corresponding to antioxidant activity-related genes such as superoxide dismutase, defense response genes such as Pathogenesis-Related 4 (PR4), water molecule bio-channels such as aquaporins, cell membrane protectants such as Late Embryogenesis Abundant (LEA), and growth regulators such as 1-aminocyclopropane-1-carboxylic acid (ACC). A total of 880 novel transcripts were identified as representing possible novel genes associated with jojoba subjected to water stress. There were also many transcripts linked to transcriptional regulation that were expressed in response to water-stress in jojoba. Many male-specific transcripts corresponding to stress-related genes and transcription regulators were differentially expressed under water-stress with 1928 differentially expressed transcripts that aligned to the two Y chromosome-specific regions Y1 and Y2. The water-stress related genes detected may help explain the drought tolerance of jojoba and provide a valuable source of genes for exploitation in providing tolerance to water stress in other species.

Maize GOLDEN2-LIKE proteins enhance drought tolerance in rice by promoting stomatal closure.

Drought has become one of the most severe abiotic stresses experienced in agricultural production across the world. Plants respond to water deficit via stomatal movements in the leaves, which are mainly regulated by abscisic acid (ABA). A previous study from our lab showed that constitutive expression of maize (Zea mays L.) GOLDEN2-LIKE (GLK) transcription factors in rice (Oryza sativa L.) can improve stomatal conductance and plant photosynthetic capacity under field conditions. In the present study, we uncovered a function of ZmGLK regulation of stomatal movement in rice during drought stress. We found that elevated drought tolerance in rice plants overexpressing ZmGLK1 or GOLDEN2 (ZmG2) was conferred by rapid ABA-mediated stomatal closure. Comparative analysis of RNA-sequencing (RNA-seq) data from the rice leaves and DNA affinity purification sequencing (DAP-seq) results obtained in vitro revealed that ZmGLKs played roles in regulating ABA-related and stress-responsive pathways. Four upregulated genes closely functioning in abiotic stress tolerance with strong binding peaks in the DAP-seq data were identified as putative target genes of ZmGLK1 and ZmG2 in rice. These results demonstrated that maize GLKs play an important role in regulating stomatal movements to coordinate photosynthesis and stress tolerance. This trait is a valuable target for breeding drought-tolerant crop plants without compromising photosynthetic capacity.

The genomic regions and candidate genes associated with drought tolerance and yield-related traits in foxtail millet: an integrative meta-analysis approach

Drought stress is one of the most significant limiting factors limiting crop productions. Foxtail millet (Setaria italica) is among the most drought-tolerant crop plants, with a high degree of collinearity with other staple cereals. The present study used a meta-analysis approach to identify genomic regions and candidate genes associated with drought tolerance and yield-related traits in foxtail millet. A meta-analysis employing all 448 collected original quantitative trait loci (QTL) identified 41 meta-QTL (MQTL) on the nine foxtail millet chromosomes. The confidence interval (CI) of the identified MQTL was determined to be 0.31–14.47 cM (5.23 cM average), which was 3.5 times narrower than the mean CI of the original QTL. Based on the available RNA-seq and microarray data, 1631 differentially expressed genes (DEGs) were detected in 41 MQTL. Furthermore, through synteny analysis, 8, 4, and 2 ortho-MQTL were recognized within co-linear regions of foxtail millet with rice (Oryza sativa), barley (Hordeum vulgare), and maize (Zea mays), respectively. To detect the most significant genome regions involved in the genetic control of drought tolerance and yield maintenance in foxtail millet, 10 MQTL with physical intervals of less than 1 Mb and seven hotspot regions with a high QTL-overview index were identified. Several candidate genes involved in foxtail millet sensing and signaling, transcription regulation, ROS inhibition, and adaptation to abiotic stress were detected by seeking drought-responsive genes in MQTL regions with a CI < 1 Mb. We hope that the achieved results would aid in developing new high-yielding drought-tolerant genotypes.

Silicon Nutrition in Plants under Water-Deficit Conditions: Overview and Prospects

Drought is one of the major constraints for sustainable crop production worldwide, especially in arid and semiarid regions. The global warming and climate change scenario has worsened the dilemma of water scarcity, creating an immediate threat to food security. Conserving water resources and exploiting various strategies that enable plants to withstand water deficits need to be urgently addressed. Drought adversely affects plant growth by modulating a range of physio-chemical, metabolic, and molecular processes inside the plant body, which ultimately reduces crop productivity. Besides developing drought-tolerant cultivars, better nutrient management could be a promising strategy to enhance drought tolerance in crop plants. Silicon, a quasi-essential element, is known to play a vital role in improving crop performance under a range of biotic and abiotic stresses. This review discusses the potential of Si application in attenuating the adverse effects of water-deficit stress. Silicon enhances plant growth by improving seed germination, cell membrane stability, carbon assimilation, plant–water relations and osmotic adjustment (by accumulating soluble sugars, proline and glycine betaine). It triggers the activity of antioxidants, promotes the biosynthesis of phytohormones, enhances nutrient acquisition and regulates the activity of vital enzymes in plants under drought stress. Silicon also induces anatomical changes in the plant cell wall through the deposition of polymerized amorphous silica (SiO2-nH2O), thereby improving stem and leaf erectness and reducing lodging. Further, Si-mediated physiological, biochemical and molecular mechanisms associated with drought tolerance in plants and future research prospects have been elucidated.

Corn (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench) yield and nutritional quality affected by drought stress

Comparison of drought tolerance of crop plants is important for planning efficient cropping strategies and increasing yield production. The objective was to investigate the effects of drought stress including control (S1), 80 (moderate, S2) and 60% (severe, S3) of crop essential irrigation (determined by evaporation from the Class A evaporation pan) on grain yield and nutritional quality of different corn (Zea mays L.) (Maxima (sensitive) and 704 (tolerant)) and sorghum (Sorghum bicolor (L.) Moench) (Kimia (sensitive) and Payam (tolerant)) genotypes. The experiment, conducted in 2019, was a split plot based on randomized complete block design with three replicates. Plants yields and nutritional quality including relative water content (RW), fiber, protein, starch, tannin, and chlorophyll were measured. Although water stress did not significantly affect RW in corn, it significantly affected RW in sorghum. Fiber concentration was the highest at the severe stress in both corn genotypes (9.36% in 704 and 10.35% in Maxima), and sorghum Payam genotype (14.54%). The lowest (13.29%) and the highest (14.35%) corn protein content were obtained for Maxima in the medium and control level of stress, and for 704 genotype it ranged from 13.51 to 13.77%. Sorghum protein was the highest in the sensitive and tolerant genotypes in control and severe stress, respectively. Treatments S3 and S2 resulted in the highest (14.58%) and the lowest (12.47%) protein content for sorghum Kimia genotype. Although sorghum plants were tolerant in stress conditions, corn plants could also tolerate the stress up to some level by adjusting their physiological characteristics.

Is Endophytic Colonization of Host Plants a Method of Alleviating Drought Stress? Conceptualizing the Hidden World of Endophytes.

In the wake of changing climatic conditions, plants are frequently exposed to a wide range of biotic and abiotic stresses at various stages of their development, all of which negatively affect their growth, development, and productivity. Drought is one of the most devastating abiotic stresses for most cultivated crops, particularly in arid and semiarid environments. Conventional breeding and biotechnological approaches are used to generate drought-tolerant crop plants. However, these techniques are costly and time-consuming. Plant-colonizing microbes, notably, endophytic fungi, have received increasing attention in recent years since they can boost plant growth and yield and can strengthen plant responses to abiotic stress. In this review, we describe these microorganisms and their relationship with host plants, summarize the current knowledge on how they “reprogram” the plants to promote their growth, productivity, and drought tolerance, and explain why they are promising agents in modern agriculture.

Initial Description of the Genome of Aeluropus littoralis, a Halophile Grass.

The use of wild plant species or their halophytic relatives has been considered in plant breeding programs to improve salt and drought tolerance in crop plants. Aeluropus littoralis serves as halophyte model for identification and isolation of novel stress adaptation genes. A. littoralis, a perennial monocot grass, grows in damp or arid areas, often salt-impregnated places and wasteland in cultivated areas, can survive periodically high water salinity, and tolerate high salt concentrations in the soil up to 1,100 mM sodium chloride. Therefore, it serves as valuable genetic resource to understand molecular mechanisms of stress-responses in monocots. The knowledge can potentially be used for improving tolerance to abiotic stresses in economically important crops. Several morphological, anatomical, ecological, and physiological traits of A. littoralis have been investigated so far. After watering with salt water the grass is able to excrete salt via its salt glands. Meanwhile, a number of ESTs (expressed sequence tag), genes and promoters induced by the salt and drought stresses were isolated, sequenced and annotated at a molecular level. Transfer of stress related genes to other species resulted in enhanced stress resistance. Here we describe the genome sequence and structure of A. littoralis analyzed by whole genome sequencing and histological analysis. The chromosome number was determined to be 20 (2n = 2x = 20). The genome size was calculated to be 354 Mb. This genomic information provided here, will support the functional investigation and application of novel genes improving salt stress resistance in crop plants. The utility of the sequence information is exemplified by the analysis of the DREB-transcription factor family.

Growth, Nutrient Accumulation, and Drought Tolerance in Crop Plants with Silicon Application: A Review

Plants take up silicon (Si) from the soil which impacts their growth and nutrient accumulation. It increases plant resistance to abiotic and biotic stresses such as drought, salinity, and heavy metal, diseases, and pest infestation. However, until recently, research of Si application on the crop is limited. This article reviews the recent progress of research on Si application on crop growth and yield, nutrient availability in soil and accumulation, and drought tolerance of crop plants. The review’s findings show that Si improves crop development and output under stressful environmental conditions. Silicon increases the availability and accumulation of both macronutrients (nitrogen, potassium, calcium, and sulphur) and micronutrients (iron and manganese). It improves drought resistance by increasing plant water usage efficiency and reducing water loss during transportation. Silicon application is a crucial aspect of crop productivity because of all of these favorable attributes. The gaps in current understandings are identified. Based on the outcome of the present research, future scopes of research on this field are proposed.

Identification of resurrection genes from the transcriptome of dehydrated and rehydrated Selaginella tamariscina

ABSTRACT Selaginella tamariscina is a lycophyta species that survives under extremely dry conditions via the mechanism of resurrection. This phenomenon involves the regulation of numerous genes that play vital roles in desiccation tolerance and subsequent rehydration. To identify resurrection-related genes, we analyzed the transcriptome between dehydration conditions and rehydration conditions of S. tamariscina. The de novo assembly generated 124,417 transcripts with an average size of 1,000 bp and 87,754 unigenes. Among these genes, 1,267 genes and 634 genes were up and down regulated by rehydration compared to dehydration. To understand gene function, we annotated Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG). The unigenes encoding early light-inducible protein (ELIP) were down-regulated, whereas pentatricopeptide repeat-containing protein (PPR), late embryogenesis abundant proteins (LEA), sucrose nonfermenting protein (SNF), trehalose phosphate phosphatase (TPP), trehalose phosphate synthase (TPS), and ABC transporter G family (ABCG) were significantly up-regulated in response to rehydration conditions by differentially expressed genes (DEGs) analysis. Several studies provide evidence that these genes play a role in stress environment. The ELIP and PPR genes are involved in chloroplast protection during dehydration and rehydration. LEA, SNF, and trehalose genes are known to be oxidant scavengers that protect the cell structure from the deleterious effect of drought. TPP and TPS genes were found in the starch and sucrose metabolism pathways, which are essential sugar-signaling metabolites regulating plant metabolism and other biological processes. ABC-G gene interacts with abscisic acid (ABA) phytohormone in the stomata opening during stress conditions. Our findings provide valuable information and candidate resurrection genes for future functional analysis aimed at improving the drought tolerance of crop plants.

Targeted mutation of transcription factor genes alters metaxylem vessel size and number in rice roots

Root metaxylem vessels are responsible for axial water transport and contribute to hydraulic architecture. Variation in metaxylem vessel size and number can impact drought tolerance in crop plants, including rice, a crop that is particularly sensitive to drought. Identifying and validating candidate genes for metaxylem development would aid breeding efforts for improved varieties for drought tolerance. We identified three transcription factor candidate genes that potentially regulate metaxylem vessel size and number in rice based on orthologous annotations, published expression data, and available root and drought‐related QTL data. Single gene knockout mutants were generated for each candidate using CRISPR‐Cas9 genome editing. Root metaxylem vessel area and number were analyzed in 6‐week‐old knockout mutants and wild‐type plants under well‐watered and drought conditions in the greenhouse. Compared with wild type, LONESOME HIGHWAY (OsLHW) mutants had fewer, smaller metaxylem vessels in shallow roots and more, larger vessels in deep roots in drought conditions, indicating that OsLHW may be a repressor of drought‐induced metaxylem plasticity. The AUXIN RESPONSE FACTOR 15 mutants showed fewer but larger metaxylem vessel area in well‐watered conditions, but phenotypes were inconsistent under drought treatment. ORYZA SATIVA HOMEBOX 6 (OSH6) mutants had fewer, smaller metaxylem vessels in well‐watered conditions with greater effects on xylem number than size. OSH6 mutants had larger shoots and more, deeper roots than the wild type in well‐watered conditions, but there were no differences in performance under drought between mutants and wild type. Though these candidate gene mutants did not exhibit large phenotypic effects, the identification and investigation of candidate genes related to metaxylem traits in rice deepen our understanding of metaxylem development and are needed to facilitate incorporation of favorable alleles into breeding populations to improve drought stress tolerance.

Silicon Induced Drought Tolerance in Crop Plants: Physiological Adaptation Strategies

Silicon Induced Drought Tolerance in Crop Plants: Physiological Adaptation Strategies

Copper Nanoparticle Application Enhances Plant Growth and Grain Yield in Maize Under Drought Stress Conditions

Abiotic stresses, including drought, detrimentally affect the growth and productivity of many economically important crop plants, leading to significant yield losses, which can result in food shortages and threaten the sustainability of agriculture. Balancing plant growth and stress responses is one of the most important functions of agricultural application to optimize plant production. In this study, we initially report that copper nanoparticle priming positively regulates drought stress responses in maize. The copper nanoparticle priming plants displayed enhanced drought tolerance indicated by their higher leaf water content and plant biomass under drought as compared with water-treated plants. Moreover, our data showed that the treatment of copper nanoparticle on plants increased anthocyanin, chlorophyll and carotenoid contents compared to water-treated plants under drought stress conditions. Additionally, histochemical analyses with nitro blue tetrazolium and 3,3′-diaminobenzidine revealed that reactive oxygen species accumulation of priming plants was decreased as a result of enhancement of reactive oxygen species scavenging enzyme activities under drought. Furthermore, our comparative yield analysis data indicated applying copper nanoparticles to the plant increased total seed number and grain yield under drought stress conditions. Our data suggest that copper nanoparticle regulates plant protective mechanisms associated with drought tolerance, which is a promising approach for the production of drought-tolerant crop plants.

Plant aquaporins alleviate drought tolerance in plants by modulating cellular biochemistry, root-architecture, and photosynthesis.

Water is a vital resource for plants to grow, thrive, and complete their life cycle. In recent years, drastic changes in the climate, especially drought frequency and severity, have increased, which reduces agricultural productivity worldwide. Aquaporins are membrane channels belonging to the major intrinsic protein superfamily, which play an essential role in cellular water and osmotic homeostasis of plants under both control and water deficit conditions. A genome-wide search reveals the vast availability of aquaporin isoforms, phylogenetic relationships, different families, conserved residues, chromosomal locations, and gene structure of aquaporins. Furthermore, aquaporins gating and subcellular trafficking are commonly controlled by phosphorylation, cytosolic pH, divalent cations, reactive oxygen species, and stoichiometry. Researchers have identified their involvement in regulating hydraulic conductance, root system architecture, modulation of abiotic stress-related genes, seed viability and germination, phloem loading, xylem water exit, photosynthetic parameters, and post-drought recovery. Remarkable effects following the change in aquaporin activity and/or gene expression have been observed on root water transport properties, nutrient acquisition, physiology, transpiration, stomatal aperture, gas exchange, and water use efficiency. The present review highlights the role of different aquaporin homologs under water-deficit stress condition in model and crop plants. Moreover, the opportunity and challenges encountered to explore aquaporins for engineering drought-tolerant crop plants are also discussed here.

An overview of recent advancement in phytohormones-mediated stress management and drought tolerance in crop plants

Plants face a continuous threat of abiotic stresses under the changing environment. Because of climate change, water scarcity has been shown to be a significant environmental constraint on plant productivity. Droughts in particular have been shown to affect plant growth and development, lead to alteration in quality and quantity of crop production, and result in global food insecurity. Phytohormones are known to play critical roles in regulating diverse processes of plant adaption to a drought environment. They regulate cellular functions at molecular levels via various cell signaling. Among various phytohormones, abscisic acid (ABA) is known for its role in drought-stress tolerance in plants. Other phytohormones such as auxins, brassinosteroids (BRs), cytokinins (CK), ethylene (ET), gibberellins (GA), jasmonic acid (JA), and salicylic acid (SA) are also crucial in plant drought tolerance. Several plant growth-promoting microbes have been reported to enhance the phytohormone levels in plants to mitigate the negative effect of drought. However, the transgenic approach appears to be a boon to engineering the genes responsible for regulating phytohormones to develop a drought-tolerant trait. Expression analyses have revealed that genes encoding transcription factors such as bZIP11, DREB2, MYB14, MYB48, WRKY2, WRKY56, WRKY108715, and RD22 play a very crucial role in phytohormone mediated drought response. Furthermore, exogenous applications of phytohormones are shown to enhance endogenous phytohormones. This review highlights the most recent advancements in phytohormone-mediated drought tolerance in major crop plants.

Harnessing High-throughput Phenotyping and Genotyping for Enhanced Drought Tolerance in Crop Plants

Development of drought-tolerant cultivars is one of the challenging tasks for the plant breeders due to its complex inheritance and polygenic regulation. Evaluating genetic material for drought tolerance is a complex process due to its spatiotemporal interactions with environmental factors. The conventional breeding approaches are costly, lengthy, and inefficient to achieve the expected gain in drought tolerance. In this regard, genomics-assisted breeding (GAB) offers promise to develop cultivars with improved drought tolerance in a more efficient, quicker, and cost-effective manner. The success of GAB depends upon the precision in marker-trait association and estimation of genomic estimated breeding values (GEBVs), which mostly depends on coverage and precision of genotyping and phenotyping. A wide gap between the discovery and practical use of quantitative trait loci (QTL) for crop improvement has been observed for many important agronomical traits. Such a limitation could be due to the low accuracy in QTL detection, mainly resulting from low marker density and manually collected phenotypes of complex agronomic traits. Increasing marker density using the high-throughput genotyping (HTG), and accurate and precise phenotyping using high-throughput digital phenotyping (HTP) platforms can improve the precision and power of QTL detection. Therefore, both HTG and HTP can enhance the practical utility of GAB along with a faster characterization of germplasm and breeding material. In the present review, we discussed how the recent innovations in HTG and HTP would assist in the breeding of improved drought-tolerant varieties. We have also discussed strategies, tools, and analytical advances made on the HTG and HTP along with their pros and cons.

Physio-morphological, biochemical, and anatomical traits of drought-tolerant and susceptible sorghum cultivars under pre- and post-anthesis drought.

Understanding the physiological mechanisms that control drought tolerance in crop plants is vital for effective breeding. In this study, we characterized drought stress responses in four sorghum cultivars exhibiting differential levels of drought tolerance at pre- and post-anthesis. Greenhouse-grown plants were subjected to two types of drought treatment, water stress (WS) and desiccant-induced water stress (DA), timed to occur at pre- and post-anthesis. Multiple physiological measurements were then made revealing varying responses among the experimental cultivars. The pre- and post-flowering drought-tolerant cultivar P898012 showed a significantly higher net photosynthetic rate, higher transpiration rate, and greater stomatal conductance compared to the drought-susceptible cultivars at both pre- and post-anthesis. A significantly greater stomatal size was also detected in P898012, while the highest stomatal density was found in the drought-susceptible cultivar P721Q. Meanwhile, the two post-flowering drought-tolerant cultivars P898082 and B35 had a higher starch content and exhibited greater osmotic potential under post-anthesis water stress. Compared to WS and well-watered control plants, a greater increase in root biomass was observed in P898012 under DA at pre-anthesis. This finding suggests that plants invested more assimilates into the roots under severe DA at pre-anthesis. Overall, our results show good conformity between drought tolerance in sorghum and key physiological mechanisms of stomatal conductance, root growth patterns, and starch accumulation, all of which act as coping mechanisms during critical drought-sensitive growth stages.

Seed Priming: A Feasible Strategy to Enhance Drought Tolerance in Crop Plants.

Drought is a serious threat to the farming community, biasing the crop productivity in arid and semi-arid regions of the world. Drought adversely affects seed germination, plant growth, and development via non-normal physiological processes. Plants generally acclimatize to drought stress through various tolerance mechanisms, but the changes in global climate and modern agricultural systems have further worsened the crop productivity. In order to increase the production and productivity, several strategies such as the breeding of tolerant varieties and exogenous application of growth regulators, osmoprotectants, and plant mineral nutrients are followed to mitigate the effects of drought stress. Nevertheless, the complex nature of drought stress makes these strategies ineffective in benefiting the farming community. Seed priming is an alternative, low-cost, and feasible technique, which can improve drought stress tolerance through enhanced and advanced seed germination. Primed seeds can retain the memory of previous stress and enable protection against oxidative stress through earlier activation of the cellular defense mechanism, reduced imbibition time, upsurge of germination promoters, and osmotic regulation. However, a better understanding of the metabolic events during the priming treatment is needed to use this technology in a more efficient way. Interestingly, the review highlights the morphological, physiological, biochemical, and molecular responses of seed priming for enhancing the drought tolerance in crop plants. Furthermore, the challenges and opportunities associated with various priming methods are also addressed side-by-side to enable the use of this simple and cost-efficient technique in a more efficient manner.