Abiotic stresses are one of the major constraints to crop production and food security worldwide. The situation has aggravated due to the drastic and rapid changes in global climate. Heat and drought are undoubtedly the two most important stresses having huge impact on growth and productivity of the crops. It is very important to understand the physiological, biochemical, and ecological interventions related to these stresses for better management. A wide range of plant responses to these stresses could be generalized into morphological, physiological, and biochemical responses. Interestingly, this review provides a detailed account of plant responses to heat and drought stresses with special focus on highlighting the commonalities and differences. Crop growth and yields are negatively affected by sub-optimal water supply and abnormal temperatures due to physical damages, physiological disruptions, and biochemical changes. Both these stresses have multi-lateral impacts and therefore, complex in mechanistic action. A better understanding of plant responses to these stresses has pragmatic implication for remedies and management. A comprehensive account of conventional as well as modern approaches to deal with heat and drought stresses have also been presented here. A side-by-side critical discussion on salient responses and management strategies for these two important abiotic stresses provides a unique insight into the phenomena. A holistic approach taking into account the different management options to deal with heat and drought stress simultaneously could be a win-win approach in future.

Polyamines (PAs) can improve drought stress tolerance in plants; however, very limited information is available on the mechanism of action of exogenous application by different methods under drought stress in wheat. The present study investigates the mechanism through which seed priming and foliar spraying with PAs protect wheat plants from drought stress. 10 days old wheat seedlings were exposed to drought stress by withholding water alone or with 100 μM PAs solutions (putrescine, Put; spermine, Spm; and mixture of Put and Spm for 10 h seed-priming or three foliar sprays during withholding water. Drought stress impaired the wheat growth and altered the osmoprotectants, endogenous PAs levels, PAs biosynthetic genes expression and weight of 1000 grains compared to the corresponding control values. Exogenously applied PAs improved cell water status, accumulated osmoprotectants and PAs and up-regulated PAs biosynthetic genes, ADC, arginine decarboxylase; DHS, deoxyhypusine synthase; ODC, ornithine decarboxylase and SAMDC, S-adenosyl methionine decarboxylase. Put significantly regulate the endogenous PAs by both methods of application, however, Spm and mixture of Put and Spm could positively regulate the endogenous PAs and the biosynthetic gene expression by foliar spraying rather than seed priming. The data provide evidence that maintenance of water economy through stabilized cellular structure is an important strategy of drought tolerance by PAs in wheat.Copyright © 2017 Elsevier Masson SAS. All rights reserved.

TaRNAC1 is a constitutively and predominantly root-expressed NAC transcription factor. TaRNAC1 overexpression in wheat roots confers increased root length, biomass and drought tolerance and improved grain yield under water limitation. A large and deep root system is an important trait for yield sustainability of dryland cereal crops in drought-prone environments. This study investigated the role of a predominantly root-expressed NAC transcription factor from wheat (TaRNAC1) in the root growth. Expression analysis showed that TaRNAC1 was a constitutively expressed gene with high level expression in the roots and was not drought-upregulated. Overexpression of TaRNAC1 in wheat using a predominantly root-expressed promoter resulted in increased root length and biomass observed at the early growth stage and a marked increase in the maturity root biomass with dry root weight of > 70% higher than that of the wild type plants. Analysis of some root growth-related genes revealed that the expression level of GA3-ox2, which encodes GIBBERELLIN 3-OXIDASE catalysing the conversion of inactive gibberellin (GA) to active GA, was elevated in the roots of transgenic wheat. TaRNAC1 overexpressing transgenic wheat showed more dehydration tolerance under polyethylene glycol (PEG) treatment and produced more aboveground biomass and grain under water-limited conditions than the wild type plants. These data suggest that TaRNAC1 may play a role in root growth and be used as a molecular tool for potential enlargement of root system in wheat.

Polyamines (PAs) are positively charged molecules known to mitigate drought stress; however, little is known about their mechanism of alleviating drought stress. We investigated the effects of PAs exogenously applied as a seed primer and as a foliar spray on the growth, membrane stability (MS), electrolyte leakage (EL), Na and K cations, reactive oxygen species (ROS), catalase (CAT; EC 1.11.1.6) and guaiacol peroxidase (GPX; EC 1.11.1.7) activity and chloroplast ultra-structure in wheat ( L.; cv. Sakha-94) under drought stress. Three PA solutions, namely, putrescine, spermine and a mixture of the two (Mix), were each applied at a concentration of 100 µM. Our study demonstrated that the retardation of chlorophyll loss and elevation of Rubisco levels were involved in PA-enhanced growth under drought stress. These relationships were mainly reflected in elevated fresh weight and dry weight in response to foliar spraying with all PA solutions and seed priming with the Mix solution. The elevated growth seemed to be due to increased photosynthetic pigments, protein and Rubisco. In contrast, drought decreased growth, photosynthetic pigments, protein and Rubisco. MS was enhanced by PAs applied as a seed primer or foliar spray, as shown by clear reductions in EL %, malondialdehyde (MDA) content and the Na/K ratio as well as reduced ROS markers and elevated CAT (but not GPX) activity. Further study showed that the Mix solution of PAs, applied either during seed priming or as a foliar spray, improved chloroplast ultra-structure, suggesting that improvements in Rubisco and photosynthetic pigments were involved in PA maintenance of chloroplast stability. Therefore, the present study showed that elevated CAT activity is the main mechanism through which PAs reduce ROS and MDA, thereby improving MS and protecting mesophyll cells structurally and functionally under drought stress in wheat.© Prof. H.S. Srivastava Foundation for Science and Society 2020.

Here, we explored the mutual regulation of radical oxygen species (ROS) and autophagy in wheat (Triticum aestivum L.) roots under hypoxia stress. We also analyzed differences between the responses of the stele and the cortex in the two wheat cultivars Huamai 8 (waterlogging-tolerant) and Huamai 9 (waterlogging-sensitive) to hypoxia stress. In situ detection and ultracytochemical localization analysis in wheat roots showed that hypoxia stress caused greater increases in ROS levels and the expression levels of alternative oxidase (AOX) and antioxidant enzymes in the stele than in the cortex. The analysis of exogenous ROS addition and the inhibition of its production revealed the pivotal roles played by ROS in autophagy. Moreover, transmission electron microscopy and qRT-PCR analysis indicated that the stele had a higher level of autophagy than the cortex and that the two wheat cultivars primarily differed in the type and number of autophagosomes. Additional research revealed that autophagy could remove excess ROS, as pre-treatment with the autophagy inhibitor 3-methyladenine increased ROS levels in roots and the addition of the autophagy inducer rapamycin reduced root ROS levels. In conclusion, hypoxia stress induced ROS accumulation in wheat roots where ROS acted as an autophagy signal. Furthermore, higher levels of autophagy and antioxidant enzyme expression in the stele facilitated the elimination of oxidative damage caused by excessive ROS and thereby increased cell survival; in the cortex, a large number of cells died and formed aerenchyma.Copyright © 2020 Elsevier Masson SAS. All rights reserved.

The main objectives of this study were to find the possible structural association between the activity of enzymatic antioxidants and the grain yield of triticale plants as well as identifying the genotypic variability which might be effective on this association. Accordingly, expression levels of superoxide dismutase (SOD) isozymes (Mn-SOD, Cu/Zn-SOD, and Fe-SOD) were appraised to distinguish any possible relationship between SOD expression and drought resistance of triticale. A novel analytical method for distinguishing elite genotypes based on measured features was proposed. Additionally, a new programing based on SAS-language (IML) was introduced to estimate the genetic parameters rooted from combined ANOVA model (linear mixed model), which is capable of being used in any field study other than the current one.Thirty genotypes of triticale were studied under normal and drought stress conditions during 6 years (three different locations). Accordingly, based on the results of genetic variability, heatmap analysis, biplot graph, and clustering technique, two genotypes with the highest genetic distance were selected to appraise the differential expression profiling of three SOD isozyme in shoot and root organs.Field experiments and bioinformatics results showed that superoxide dismutase (SOD) was the most influential antioxidant in resistance of triticale to drought stress; therefore, it could be used as an indirect selection index in early stages to distinguish resistant genotypes to drought stress. Additionally, Mn-SOD and Fe-SOD showed roughly similar expression levels for both genotypes under drought stress. However, Cu/Zn-SOD expression level was higher in root and shoot of the tolerant genotype than the susceptible genotype.Heatmap analysis that is applied for the first time to screen suitable genotypes, showed to be highly capable of distinguishing elite genotypes and pointing out the proper features for selection criteria. Bioinformatics results indicated that SOD is more important than other enzymatic antioxidant for being considered as selection criteria or candidate gene for transgenic purposes. Based on expressional results, Mn-SOD announced as a general isozyme that is probably highly expressed in most of the species, while, Cu/Zn-SOD was introduced as a genotype specific isozyme that is likely more expressed in tolerant genotypes.

Water deficit is one of the major factors limiting crop productivity worldwide. Plant roots play a key role in uptaking water, perceiving and transducing of water deficit signals to shoot. Although the mechanisms of drought-tolerance have been reported recently, the transcriptional regulatory network of wheat root response to water stress has not been fully understood. In this study, drought-tolerant cultivar JM-262 and susceptible cultivar LM-2 are planted to characterize the root transcriptional changes and physiological responses to water deficit. A total of 8197 drought tolerance-associated differentially expressed genes (DEGs) are identified, these genes are mainly mapped to carbon metabolism, flavonoid biosynthesis, and phytohormone signal transduction. The number and expression level of DEGs involved in antioxidative and antiosmotic stresses are more enhanced in JM-262 under water stress. Furthermore, we find the DEGs related to root development are much more induced in JM-262 in phytohormone signal transduction and carbon metabolism pathway. In conclusion, JM-262 may alleviate the damage of drought by producing more osmoprotectants, ROS scavengers, biomass and energy. Interestingly, hormone signaling and cross-talk probably play an important role in promoting JM-262 greater root systems to take up more water, higher capabilities to induce more drought-related DEGs and higher resisitance to oxidative stresse.Copyright © 2018 Elsevier B.V. All rights reserved.

Globally, salinity threatens the agricultural crops productivity by inhibiting plant growth and development through osmotic stress and ionic cytotoxicity. The polygenic nature of salinity offers several pragmatic shotgun approaches to improve salinity tolerance. The present study investigated the potential of glutathione (GSH; 1 mM) as an antioxidant and moringa leaf extract (MLE; 3%) as an organic biostimulant applied in sequence as seed priming and foliar spray on wheat growth, physiology and metabolic adaptation under saline conditions (9.16 dS m). Plants without any treatment and water spray (HO) were considered controls. Salinity induced osmotic stress reduced the plant tissue water status and photosynthetic performance, and perturbed ionic (K/Na, Ca/Na, K+Ca/Na) and hormonal (IAA, GA, zeatin, ABA) homeostasis, consequently affected growth and yield in wheat. Sequenced applied MLE and/or GSH improved osmotic stress tolerance by stabilizing membrane integrity and decreasing electrolyte leakage. These positive results were owed to enhanced endogenous GSH and ascorbate levels. Improved tissue water status was attributed to increased osmotic adjustment, better ionic and hormonal homeostasis contributed to improving photosynthetic efficiency and growth under salinity. Exogenously applied MLE and GSH sequences improved grain yield, which was attributed to the maintenance of green leaf area and delayed senescence associated with an increase in photosynthetic pigments and chlorophyll fluorescence traits. In crux, exogenous applied MLE and/or GSH can be the best physiological strategy to reduce the deleterious effects of salinity and improve physiological and metabolic adaptation in wheat under saline field conditions.Copyright © 2020 Elsevier Masson SAS. All rights reserved.

Lead (Pb), like other heavy metals, is not essentially required for optimal plant growth; however, plants uptake it from the soil, which poses an adverse effect on growth and yield. Asparagine (Asp) and thiourea (Thi) are known to assuage the negative impacts of heavy metal pollution on plant growth; however, combined application of Asp and Thi has rarely been tested to discern if it could improve wheat yield under Pb stress. Thus, this experimentation tested the role of individual and combined applications of Asp (40 mM) and Thi (400 mg/L) in improving wheat growth under lead (Pb as PbCl, 0.1 mM) stress. Lead stress significantly reduced plant growth, chlorophyll contents and photosystem system II (PSII) efficiency, whereas it increased Pb accumulation in the leaves and roots, leaf proline contents, phytochelatins, and oxidative stress related attributes. The sole or combined application of Asp and Thi increased the vital antioxidant biomolecules/enzymes, including reduced glutathione (GSH), ascorbic acid (AsA), ascorbate peroxsidase (APX), catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Furthermore, the sole or the combined application of Asp and Thi modulated nitrogen metabolism by stimulating the activities of nitrate and nitrite reductase, glutamate synthase (GOGAT) and glutamine synthetase (GS). Asp and Thi together led to improve plant growth and vital physiological processes, but lowered down Pb accumulation compared to those by their sole application. The results suggest that Asp and Thi synergistically can improve wheat growth under Pb-toxicity.Copyright © 2022. Published by Elsevier Masson SAS.