Tissue-Specific Antioxidant Responses and PAL Gene Expression in Bread Wheat Under Drought Stress

In order to evaluate the physiological and biochemical traits regarding drought tolerance and further to determine the best criteria for screening and identification of drought tolerant chickpea genotypes, an experiment was conducted in controlled conditions in the Plant Science Research Center of Ferdowsi University of Mashhad in Iran. In this study, two tolerant genotypes (MCC392 and MCC877) and two susceptible genotypes (MCC68 and MCC448) were grown under controlled (field capacity) and drought stress (25% field capacity) conditions. In this experiment, tolerant and susceptible genotypes were compared with each other for proline, malondialdehyde and soluble protein content. We also compared these genotypes with each other for catalase, ascorbat peroxidase, peroxidase and superoxide dismutase during the stages of seedling, flowering and podding. The results showed that drought stress significantly increased proline content in the flowering and podding stages and also increased catalase activity in the three investigated stages. By contrast, the effects of drought stress on ascorbat peroxidase, peroxidase and malondialdehyde were not significant. In the flowering stage, tolerant genotype (MCC877) had higher catalase activity as well as, higher proline contents in comparison with susceptible genotypes (MCC68 and MCC448). Also, drought stress had significant effects on superoxide dismutase activity in the flowering stage. These results indicated that catalase and superoxide dismutase activity and proline content can be effective markers in the identification of drought tolerant chickpea genotypes. Also, the flowering and podding stages can be more suitable than seedling stage for comparing susceptible and tolerant genotypes under drought stress and also to classify adapted cultivars of chickpea under drought stress. Key words: Antioxidant enzymes, Chickpea (Cicer arietinum L.), drought, malondialdehyde, proline.

BackgroundDrought is one of the major constraints for plant productivity worldwide. Different mechanisms of drought-tolerance have been reported for several plant species including maize. However, the differences in global gene expression between drought-tolerant and susceptible genotypes and their relationship to physiological adaptations to drought are largely unknown. The study of the differences in global gene expression between tolerant and susceptible genotypes could provide important information to design more efficient breeding programs to produce maize varieties better adapted to water limiting conditions.Methodology/Principal FindingsChanges in physiological responses and gene expression patterns were studied under drought stress and recovery in three Mexican maize landraces which included two drought tolerant (Cajete criollo and Michoacán 21) and one susceptible (85-2) genotypes. Photosynthesis, stomatal conductance, soil and leaf water potentials were monitored throughout the experiment and microarray analysis was carried out on transcripts obtained at 10 and 17 days following application of stress and after recovery irrigation. The two tolerant genotypes show more drastic changes in global gene expression which correlate with different physiological mechanisms of adaptation to drought. Differences in the kinetics and number of up- and down-regulated genes were observed between the tolerant and susceptible maize genotypes, as well as differences between the two tolerant genotypes. Interestingly, the most dramatic differences between the tolerant and susceptible genotypes were observed during recovery irrigation, suggesting that the tolerant genotypes activate mechanisms that allow more efficient recovery after a severe drought.Conclusions/SignificanceA correlation between levels of photosynthesis and transcription under stress was observed and differences in the number, type and expression levels of transcription factor families were also identified under drought and recovery between the three maize landraces. Gene expression analysis suggests that the drought tolerant landraces have a greater capacity to rapidly modulate more genes under drought and recovery in comparison to the susceptible landrace. Modulation of a greater number of differentially expressed genes of different TF gene families is an important characteristic of the tolerant genotypes. Finally, important differences were also noted between the tolerant landraces that underlie different mechanisms of achieving tolerance.

Climate change will increase the effect of drought stress which is one of major constrains for barley production and productivity in Egypt. Identification and development new cultivars having a high drought tolerance combined with a high yield are urgently needed. In this study, a set of 60 highly homozygous and diverse barley genotypes was evaluated in well-watered (N) and dry (D) environments for two successive seasons. Five yield traits were scored; plant height, spike length, days to flowering, grain yield per spike (GYPS), and thousand kernel weight (TKW). High genetic variation was found among genotypes in all studied traits under N and D. High heritability for all traits was observed in both seasons. The drought susceptibility index (DSI) for GYPS and TKW was estimated to determine the tolerant and susceptible genotypes in both seasons. As a result, four spring barley genotypes were considered drought tolerant for TKW and GYPS in both seasons. A set of ten single sequence repeats primers, developed from wheat genome, were tested in the 60 genotypes. All SSR primers had a high polymorphism among the genotypes producing 82 marker alleles. Single marker analysis was performed for DSI, TKW, and GYPS in both seasons. Twenty QTLs were found to be associated with low DSI and high GYPS and TKW in N and D. The marker alleles associated with the 20 QTL were screened in the four tolerant genotypes. PNBYT15 included only one marker allele associated with one QTL, while, SCYT-28 included six marker alleles controlling nine QTL. The high genetic variation and heritability for the studied traits indicated that these traits could be used for selection for high yielding and drought tolerance. The four drought tolerant genotypes can be used for a further breeding program to improve drought tolerance in barley.

BackgroundDrought-tolerance ensures a crop to maintain life activities and protect cell from damages under dehydration. It refers to diverse mechanisms temporally activated when the crop adapts to drought. However, knowledge about the temporal dynamics of rice transcriptome under drought is limited.ResultsHere, we investigated temporal transcriptomic dynamics in 12 rice genotypes, which varied in drought tolerance (DT), under a naturally occurred drought in fields. The tolerant genotypes possess less differentially expressed genes (DEGs) while they have higher proportions of upregulated DEGs. Tolerant and susceptible genotypes have great differences in temporally activated biological processes (BPs) during the drought period and at the recovery stage based on their DEGs. The DT-featured BPs, which are activated specially (e.g. raffinose, fucose, and trehalose metabolic processes, etc.) or earlier in the tolerant genotypes (e.g. protein and histone deacetylation, protein peptidyl-prolyl isomerization, transcriptional attenuation, ferric iron transport, etc.) shall contribute to DT. Meanwhile, the tolerant genotypes and the susceptible genotypes also present great differences in photosynthesis and cross-talks among phytohormones under drought. A certain transcriptomic tradeoff between DT and productivity is observed. Tolerant genotypes have a better balance between DT and productivity under drought by activating drought-responsive genes appropriately. Twenty hub genes in the gene coexpression network, which are correlated with DT but without potential penalties in productivity, are recommended as good candidates for DT.ConclusionsFindings of this study provide us informative cues about rice temporal transcriptomic dynamics under drought and strengthen our system-level understandings in rice DT.

This study was undertaken to investigate oxidative stress tolerant mechanisms in chilli (Capsicum annuum L.) under drought genotypes through evaluating morphological, physiological, biochemical and stomatal parameters. Twenty genotypes were evaluated for their genetic potential to drought stress tolerant at seedling stage. Thirty days old seedlings were exposed to drought stress induced by stop watering for the following 10 days and rewatering for the following one week as recovery. Based on their survival performance, two tolerant genotypes viz. BD-10906 and BD-109012 and two susceptible genotypes viz. BD-10902 and RT-20 were selected for studying the oxidative stress tolerance mechanism. Drought reduced root and shoot length, dry weight, ratio, petiole weight and leaf area in both tolerant and susceptible genotypes, and a higher reduction was observed in susceptible genotypes. Lower reduction of leaf area and photosynthetic pigments were also found in tolerant genotypes. Moreover, tolerant genotypes showed higher recovery than susceptible genotypes after the removal of stress. A higher reduction of relative water content (RWC) may cause an imbalance between absorbed and transpirated water in susceptible genotypes. Higher accumulation of proline in tolerant genotypes might be helpful to for better osmotic maintenance than that in susceptible genotypes. Tolerant genotypes showed higher antioxidant activity as they showed DPPH radical scavenging percentage than the susceptible genotypes. Moreover, closer stomata in tolerant genotypes than susceptible ones helped to avoid dehydration in tolerant genotypes. Thus, the above morphological, physiological, biochemical and stomatal parameters helped to show better tolerance in chilli under drought stress.

BackgroundRice (Oryza sativa L.) germplasm represents an extraordinary source of genes that control traits of agronomic importance such as drought tolerance. This diversity is the basis for the development of new cultivars better adapted to water restriction conditions, in particular for upland rice, which is grown under rainfall. The analyses of subtractive cDNA libraries and differential protein expression of drought tolerant and susceptible genotypes can contribute to the understanding of the genetic control of water use efficiency in rice.ResultsTwo subtractive libraries were constructed using cDNA of drought susceptible and tolerant genotypes submitted to stress against cDNA of well-watered plants. In silico analysis revealed 463 reads, which were grouped into 282 clusters. Several genes expressed exclusively in the tolerant or susceptible genotypes were identified. Additionally, proteome analysis of roots from stressed plants was performed and 22 proteins putatively associated to drought tolerance were identified by mass spectrometry.ConclusionSeveral genes and proteins involved in drought-response, as well as genes with no described homologs were identified. Genes exclusively expressed in the tolerant genotype were, in general, related to maintenance of turgor and cell integrity. In contrast, in the susceptible genotype, expression of genes involved in protection against cell damage was not detected. Several protein families identified in the proteomic analysis were not detected in the cDNA analysis. There is an indication that the mechanisms of susceptibility to drought in upland rice are similar to those of lowland varieties.

Maize (Zea mays L.) is one of the most important cereal crops cultivated around the world. Waterlogging stress is a major production constraint of maize production in rain-fed agricultural systems. The main objective of this experiment was to investigate the effect of continuous waterlogging on morphological and biochemical traits of maize genotypes at the vegetative stage. Ten maize genotypes were treated under no waterlogging (control) and continuous waterlogging of five centimeters depth for 10 days. The treatments were applied to the plants at their 45 days of age. Visual leaf injury scores from Leaf 4 (youngest leaf is the reference point) to Leaf 7 separated tolerant and susceptible genotypes. Waterlogging stress significantly reduced the total number of live leaves and chlorophyll content in leaf tissues in susceptible genotypes. The anatomical study revealed that tolerant maize genotypes produce a large number of aerenchyma cells under waterlogging stress compared to susceptible genotypes. The enzymatic activities of ascorbate peroxidase (APX) and peroxidase (POD) exhibited a greater increase in tolerant genotypes than susceptible genotypes whereas the contents of reactive oxygen species (H2O2) greatly increased in susceptible genotypes than tolerant genotypes under waterlogging stress compared to control. Principal component 2 (PC2) indicated that increasing plant height in the genotypes BHM-14, BHM-13 and BHM-9 was associated with waterlogging tolerance. The findings of this experiment will add value to maize breeding to screen out maize genotypes for waterlogging stress tolerance.

Safflower germination and seedling growth stages are extremely sensitive to salinity. The study aimed to identify safflower genotypes' germination, seedling growth responses, and biochemical changes in tolerant and susceptible genotypes in response to salt stress. Total of 28 genotypes were subjected to salt (NaCl) treatments (0, 180, 240 mM), and germination percentage, mean germination time, seedling and root lengths, and vigor index of the genotypes were determined. The genotype, treatments, and interaction effects were significant for germination, seedling, and biochemical parameters. The genotypes' germination percentage, seedling length, root length, and vigor index decreased under salt stress. While the reduction in germination percentage of salt-tolerant genotypes was between 6-21%, it was between 46-65% in sensitive genotypes at 240 mM salt treatment. Five tolerant (Shufu, Sidwill, Finch, Yuyao, Oleic Leed) and sensitive (Huaxian, Linas, 4022, Oker, Rehbein) genotypes were chosen based on reductions in germination percentage and vigor index, and the proline, hydrogen peroxide, and malondialdehyde (MDA) contents of these genotypes were investigated. The proline content of the genotypes increased by 26 to 56 fold at 180 mM salt concentration. The hydrogen peroxide content of sensitive and tolerant genotypes increased at 180 mM salt treatment, but at 240 mM salt treatment, the hydrogen peroxide content of the sensitive genotypes continued to increase by 6-50%, hydrogen peroxide content decreased in tolerant genotypes by 10-30%. MDA contents increased in the sensitive and tolerant genotypes, but the level of increase was higher in sensitive genotypes (307-631%) than the tolerant genotypes (103-323%) at 240 mM salt treatment. The heatmap generated by means of sensitive and tolerant genotypes showed 28 coefficients and 5 of which were significant. These results show that changes in hydrogen peroxide and MDA contents are different between tolerant and sensitive genotypes. They could be useful selection criteria along with germination percentages for determining tolerant and susceptible safflower genotypes at the seedling stage.

Differential response of tossa jute (Corchorus olitorius) submitted to water deficit stress

Wheat (Triticum aestivum L.) occupies an important place among cereals and it serves as a staple food for about 35% of the world population. Crop plants experience various stresses during their life cycle under high or low temperature, drought, and salinity conditions. Among these stresses, heat stress is getting alarming as a result of global warming. Therefore, research on the mechanism of high temperature stress in plants has the importance for future generations. The present investigation was aimed at studying the effect of heat stress and revival on antioxidative system and polypeptide pattern in the leaves of wheat seedlings. Four wheat genotypes, i.e., two tolerant (HW-2045 and WH-1021) and two susceptible (HS-277 and WH-147) were selected and the enzymes of antioxidant system, levels of antioxidant metabolites and pattern of polypeptide were observed. The production of H2O2 was higher in the leaves of susceptible and tolerant genotypes under heat stress conditions. However, its level was significantly higher in susceptible as compared to tolerant genotypes. There was enhancement in the activities of antioxidative enzymes, viz. CAT, POX, GR and APX in the leaves of tolerant and susceptible genotypes under heat stress. However, higher per cent increase was observed in tolerant genotypes. Heat stress increased the SOD activity in tolerant genotypes but activity declined in susceptible genotypes. On revival, the activities of the CAT, POX and GR declined in comparison to stressed seedlings but remained higher as compared to control. Accumulation of H2O2, which is a strong oxidant, led to disruption of cellular membrane integrity as obvious from increase in MDA content and an indicator of lipid peroxidation. Higher increase of H2O2 and MDA content was observed in susceptible genotypes which indicate more oxidative stress in the heat susceptible genotypes as compared to heat tolerant genotypes. On revival, accumulation of H2O2 and MDA content was reduced in all the genotypes but their level remained higher than their respective controls. A large number of studies have revealed a positive correlation between induction of HSPs and acquisition of thermotolerance. The most studied effect of heat shock treatment was on the induction of protective heat shock proteins which disappeared on removal of heat stress. In tolerant genotype WH-1021 under stressed conditions five polypeptide bands of MW 103.7, 92.2, 83, 65 and 26 kDa appeared in comparison to unstressed seedlings, while HW-2045 showed five bands of MW 103.7, 98.5, 79, 62 and 26 kDa under heat stress. Both the susceptible genotypes showed similar polypeptide bands of MW 80, 57.9, 45.7 and 34.4 kDa in response to high temperature. The better tolerance character of HW-2045 and WH-1021 during present investigation might be due to the induction of protective heat shock proteins and much higher activities of the enzymes involved in scavenging active oxygen species.

We conducted a genome-wide transcriptomic analysis of three drought tolerant and sensitive genotypes of common bean to examine their transcriptional responses to terminal drought stress. We then conducted pairwise comparisons between the root and leaf transcriptomes from the resulting tissue based on combined transcriptomic data from the tolerant and sensitive genotypes. Our transcriptomic data revealed that 491 (6.4%) DEGs (differentially expressed genes) were upregulated in tolerant genotypes, whereas they were downregulated in sensitive genotypes; likewise, 396 (5.1%) DEGs upregulated in sensitive genotypes were downregulated in tolerant genotypes. Several transcription factors, heat shock proteins, and chaperones were identified in the study. Several DEGs in drought DB (data Base) overlapped between genotypes. The GO (gene ontology) terms for biological processes showed upregulation of DEGs in tolerant genotypes for sulfate and drug transmembrane transport when compared to sensitive genotypes. A GO term for cellular components enriched with upregulated DEGs for the apoplast in tolerant genotypes. These results substantiated the temporal pattern of root growth (elongation and initiation of root growth), and ABA-mediated drought response in tolerant genotypes. KEGG (kyoto encyclopedia of genes and genomes) analysis revealed an upregulation of MAPK (mitogen activated protein kinase) signaling pathways and plant hormone signaling pathways in tolerant genotypes. As a result of this study, it will be possible to uncover the molecular mechanisms of drought tolerance in response to terminal drought stress in the field. Further, genome-wide transcriptomic analysis of both tolerant and sensitive genotypes will assist us in identifying potential genes that may contribute to improving drought tolerance in the common bean.

In order to assess the effect of terminal heat stress on the in vitro screened heat tolerant (n=9) and susceptible (n=3) genotypes of barley, a field trial was conducted during rabi 2019-20 and 2020-21 at Punjab Agricultural University, Ludhiana, Punjab, India. Barley genotypes were sown under timely (November 26) and late sown (December 26) conditions so that late sown crop encounters heat stress during its reproductive stages of growth. The results showed that timely sown crop took significantly higher number of days to attain physiological maturity as compared to late sown crop. For anthesis and physiological maturity, timely sown crop accumulated higher growing degree days (GDD) in comparison to late sown crop. Tolerant genotypes (viz., BL 1515, BL 1729, BL 1780, BL 1784, BL 1786, BL 1792, BL 1794, BL 1797 and IBYT-E24) recorded higher number of GDD for attaining physiological maturity in comparison to susceptible genotypes (viz., BL 1723, IBON 23 and IBYT-E15) under late sown conditions. Likewise, heat use efficiency (HUE) was also lower in susceptible genotypes as compared to tolerant genotypes particularly under late sown conditions. Results also indicated that under timely sown conditions, grain yield of tolerant genotypes was statistically at par to susceptible genotypes; but under late sown conditions, tolerant genotypes out yielded susceptible genotypes. Among the tolerant genotypes, BL1786 had the highest grain yield under late sown conditions and it was statistically similar to three other tolerant genotypes namely BL1780, BL1784 and BL1792. Tolerant genotypes recorded lower tolerance index (TOL) and stress susceptibility index (SSI) values in comparison to susceptible genotypes; however, exhibited higher values of yield stability index (YSI). Correlation studies indicated that number of days taken to physiological maturity is the most crucial phenological stage determining seed yield of barley under late sown conditions.

The ever-increasing demand for rice raises the need to increase productivity by developing drought-tolerant rice varieties. Drought tolerance is a complex polygenic trait that largely depends upon plant developmental stages and showed genotype-specific variability. The experiment was conducted using drought tolerant (Binadhan-19, BRRI dhan83) and drought susceptible (BRRI dhan26, BRRI dhan48) rice genotypes at the glasshouse of Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh to characterize the seedling stage drought tolerance as well as disclose the variability of the genotypes for morphological and biochemical traits. A completely randomized design (CRD) with three replications and treatments (control and drought stress imposed by 20% PEG) was used for the experiment. Data on shoot length, root length, fresh root weight, fresh shoot weight, dry root weight, dry shoot weight, chlorophyll content (SPAD value), MDA, and H2O2 were recorded and analyzed through appropriate breeding tools. Significant variation (p<0.01) was observed for genotype, treatment, and genotype (G) × treatment (T) interactions viz., shoot length, root length, root fresh weight, shoot fresh weight, root dry weight, shoot dry weight, chlorophyll, H2O2, and MDA. Drought stress leads to a significant decrease in root and shoots growth whereas the level of H2O2 and MDA increased significantly. A greater decrease in root and shoot growth was observed in susceptible genotypes (BRRI dhan28, BRRI dhan48) compared to tolerant genotypes (BRRI dhan71, Binadhan-19). In contrast, a limited increase in H2O2 and MDA was recorded in tolerant genotypes compared to susceptible genotypes. H2O2 showed a significant positive correlation with root and shoot characteristics under control conditions, whereas H2O2 showed a significant negative correlation with chlorophyll content under drought conditions. MDA showed a significant negative correlation with most of the studied traits under well-watered conditions. Considering all of the traits at the seedling stage, the genotype Binadhan-19 is considered a drought-tolerant genotype both under well-watered and drought conditions, and this genotype was selected for further study under direct field conditions as well as for genetic improvement against drought stress.

Roselle spot caused by Corynespora cassiicola affects calyx production in Mexico. The aim of the present study was to evaluate twenty-two roselle genotypes against C. cassiicola under greenhouse conditions. The area under the disease progress curve (AUDPC) was used to detect susceptible, tolerant and resistant genotypes. Considering the incidence in leaves, susceptible genotypes were Conpoz, Sudlaz, Morcot and Sudigua (AUDPC values of 7379.2 to 5891.7); tolerant genotypes were Conayu and Chinxal (AUDPC 1341.6 and 1313.2). Based on the severity in leaves, susceptible genotypes were Sudigua, Conpoz and Morena2 (AUDPC from 788.4 to 436.3); tolerant genotypes were Almatech, Crioxal, Rojatec and Conayu (37.7 to 28.76 AUDPC). Assessment of the incidence in calyces indicated that susceptible genotypes were Morena2, Morena, Conpoz, Descop and Chinayu (AUDPC from 6572.1 to 2319.4); for the severity in calices, susceptible genotypes were Morena2, Descop, Morena, Cabxal, Chinayu and Conpoz (AUDPC from 3355.4 to 779.2). Incidence and severity on calyces evidenced resistant genotypes, which were Almatech, Criolaz2, Criocot, Criolaz, Rojatec, Criopoz, Crioxal, Chinxal and Conayu (0.0 AUDPC). In the present study, tolerant and resistant genotypes were detected to leaf and calyx spot caused by C. cassiicola in roselle.

Drought is one of the major limitations to plant productivity worldwide. Identifying suitable screening tools and quantifiable traits would facilitate the crop improvement process for drought tolerance. In the present study, we evaluated the ability of four relatively physiological parameters (variable-to-maximum chlorophyll a fluorescence ratio, F v/F m; estimated leaf chlorophyll content via SPAD index; leaf temperature, LT; and, leaf relative water content, RWC) to distinguish between drought tolerant and susceptible sugarcane genotypes subjected to a 90-d drought cycle. Eight field-grown genotypes were studied. By 45 d after the onset of treatments, the F v/F m, SPAD index and RWC of drought-stressed plants had declined significantly in all genotypes compared to values at the onset of well-watered treatments. However, the reductions were more severe in leaves of susceptible genotypes. Under drought stress, the tolerant genotypes as a group, maintained higher F v/F m (8%), SPAD index (15%), and RWC (16%) than susceptible genotypes. In general, LT of drought-stressed plants was higher (~4ºC) than that of well-watered plants but the relative increase was greater among drought susceptible genotypes. Under drought stress, LT of tolerant genotypes was on average 2.2ºC lower than that of susceptible genotypes. The results are consistent with the tolerant-susceptible classification of these genotypes and indicate that these tools can be reliable in screening for drought tolerance, with F v/F m, SPAD index and LT having the added advantage of being nondestructive and easily and quickly assessed.