Reproductive Stage Drought Tolerance in Wheat: Importance of Stomatal Conductance and Plant Growth Regulators

Drought stress requires plants to adjust their water balance to maintain tissue water levels. Isohydric plants (‘water-savers’) typically achieve this through stomatal closure, while anisohydric plants (‘water-wasters’) use osmotic adjustment and maintain stomatal conductance. Isohydry or anisohydry allows plant species to adapt to different environments. In this paper we show that both mechanisms occur in bread wheat (Triticum aestivum L.). Wheat lines with reproductive drought-tolerance delay stomatal closure and are temporarily anisohydric, before closing stomata and become isohydric at higher threshold levels of drought stress. Drought-sensitive wheat is isohydric from the start of the drought treatment. The capacity of the drought-tolerant line to maintain stomatal conductance correlates with repression of ABA synthesis in spikes and flag leaves. Gene expression profiling revealed major differences in the drought response in spikes and flag leaves of both wheat lines. While the isohydric drought-sensitive line enters a passive growth mode (arrest of photosynthesis, protein translation), the tolerant line mounts a stronger stress defence response (ROS protection, LEA proteins, cuticle synthesis). The drought response of the tolerant line is characterised by a strong response in the spike, displaying enrichment of genes involved in auxin, cytokinin and ethylene metabolism/signalling. While isohydry may offer advantages for longer term drought stress, anisohydry may be more beneficial when drought stress occurs during the critical stages of wheat spike development, ultimately improving grain yield.

Evaluation of the Morpho-Physiological, Biochemical and Molecular Responses of Contrasting Medicago truncatula Lines under Water Deficit Stress

Medicago truncatula is a forage crop of choice for farmers, and it is a model species for molecular research. The growth and development and subsequent yields are limited by water availability mainly in arid and semi-arid regions. Our study aims to evaluate the morpho-physiological, biochemical and molecular responses to water deficit stress in four lines (TN6.18, JA17, TN1.11 and A10) of M. truncatula. The results showed that the treatment factor explained the majority of the variation for the measured traits. It appeared that the line A10 was the most sensitive and therefore adversely affected by water deficit stress, which reduced its growth and yield parameters, whereas the tolerant line TN6.18 exhibited the highest root biomass production, a significantly higher increase in its total protein and soluble sugar contents, and lower levels of lipid peroxidation with greater cell membrane integrity. The expression analysis of the DREB1B gene using RT-qPCR revealed a tissue-differential expression in the four lines under osmotic stress, with a higher induction rate in roots of TN6.18 and JA17 than in A10 roots, suggesting a key role for DREB1B in water deficit tolerance in M. truncatula.

Screening of Mungbean Accessions Under Salinity Stress

Experiments were conducted to identify suitable agro-morphological indicators of salinity tolerance and to classify fifty mungbean accessions into different salt tolerant groups by screening under different NaCl solution in pot culture in green house condition for two growing seasons. Results reveled that the early growth phase of mungbean is highly affected due to salinity and the interrelationship between salinity and accessions was also statistically significant for yield parameters under different levels of salinity stress. Salt tolerant accessions were less affected at high salinity and could be produced better total dry matter as compared to others. On the basis of relative total dry matter (RTDM%), accessions were categorized as highly tolerant, moderately susceptible and highly susceptible. G4 was found to be the best tolerant line after considering both the seasons and all the tested parameters. Correlation study suggested that germination was least affected while seedling length, pod and seed yield severely fractured due to salinity. These desirable parameters may take part in future breeding programme as salinity indicators and also by getting introduced into the susceptible lines, whereas, the tolerant accessions can be introduced as tolerant checks. Bangladesh J. Bot. 50(3): 475-482, 2021 (September)

Identification of proteins in sensitive and tolerant lines of sunflower (Helianthus annus L.) under water deficit

<p>The importance of examining environmental stresses and their role in predicting and evaluating the growth and yield of crops is very evident. Environmental stresses are the most important factor in reducing agricultural yields worldwide. In order to evaluate the environmental impact of water loss on the amount of proteins affected in sunflower, an experiment was conducted in randomized complete block design with three replications at Karaj Oil Seeds Research Institute. In order to study the response of susceptible line (BGK221) and tolerant line (RGK46) under drought stress conditions, extraction of protein by acetone deposition method was performed in 8 leaves and of 3 seedlings in each replication. The amount of extracted protein was determined by Bradford method using two-dimensional electrophoresis and existence of significant difference between the bands in sensitive and tolerant lines was investigated. A total of 467 repeatable bands were found in the tolerant line and 417 repeatable bands appeared in the sensitive line. Among these proteins, 6 bands in tolerant line (No 503, 1901, 904, 3301, 7011, 9005) and 6 bands in sensitive line (No 704, 811, 3205, 4108, 7307, and 9207) were significantly affected by drought stress. In both sensitive and tolerate lines the main consequence is increase in amount of protein. The results showed that the most important factor of tolerant line adaptive for environmental stress conditions is maintaining normal cell metabolism, keeping moisture in the cell, strengthening cellular structure and antioxidant defense. The study also showed that drought stress had the greatest effect on cytoplasmic and nucleus proteins, metabolism and energy of proteins</p>

Transcriptome Analysis of Tolerant and Susceptible Maize Genotypes Reveals Novel Insights about the Molecular Mechanisms Underlying Drought Responses in Leaves

Maize (Zea mays L.) is the most essential food crop in the world. However, maize is highly susceptible to drought stress, especially at the seedling stage, and the molecular mechanisms underlying drought tolerance remain elusive. In this study, we conducted comparative transcriptome and physiological analyses of drought-tolerant (CML69) and susceptible (LX9801) inbred lines subjected to drought treatment at the seedling stage for three and five days. The tolerant line had significantly higher relative water content in the leaves, as well as lower electrolyte leakage and malondialdehyde levels, than the susceptible line. Using an RNA-seq-based approach, we identified 10,084 differentially expressed genes (DEGs) with 6906 and 3178 DEGs been annotated and unannotated, respectively. Two critical sets of drought-responsive DEGs, including 4687 genotype-specific and 2219 common drought-responsive genes, were mined out of the annotated DEGs. The tolerant-line DEGs were predominantly associated with the cytoskeleton, cell wall modification, glycolysis/gluconeogenesis, transport, osmotic regulation, drought avoidance, ROS scavengers, defense, and transcriptional factors. For the susceptible line, the DEGs were highly enriched in the photosynthesis, histone, and carbon fixation pathways. The unannotated DEGs were implicated in lncRNAs, including 428 previously reported and 22% putative TE-lncRNAs. There was consensus on both the physiological response and RNA-seq outcomes. Collectively, our findings will provide a comprehensive basis of the molecular networks mediating drought stress tolerance of maize at the seedling stage.

Comparative transcriptome analyses of maize seedling root responses to salt stress

Salt stress affects crop yield by limiting growth and delaying development. In this study, we constructed 16 transcriptome libraries from maize seedling roots using two maize lines, with contrasting salt tolerance, that were exposed to salt stress for 0, 6, 18 and 36 h. In total, 6,584 differential expression genes (DEGs; 3,669 upregulated, 2,915 downregulated) were induced in the salt-sensitive line and 6,419 DEGs (3,876 upregulated, 2,543 downregulated) were induced in the salt-tolerant line. Several DEGs common to both lines were enriched in the ABA signaling pathway, which was presumed to coordinate the process of maize salt response. A total of 459 DEGs were specifically induced in the salt-tolerant line and represented candidate genes responsible for high salt-tolerance. Expression pattern analysis for these DEGs indicated that the period between 0 and 6 h was a crucial period for the rapid response of the tolerant genes under salt stress. Among these DEGs, several genes, Aux/IAA, SAUR, and CBL-interacting kinase have been reported to regulate salt tolerance. In addition, the transcription factors WRKY, bZIP and MYB acted as regulators in the salt-responsive regulatory network of maize roots. Our findings will contribute to understanding of the mechanism on salt response and provide references for functional gene revelation in plants.

Identification of QTLs Controlling Salt Tolerance in Cucumber (Cucumis sativus L.) Seedlings

Cucumber is very sensitive to salt stress, and excessive salt content in soils seriously affects normal growth and development, posing a serious threat to commercial production. In this study, the recombinant inbred line (RIL) population (from a cross between the salt tolerant line CG104 and salt sensitive line CG37) was used to study the genetic mechanism of salt tolerance in cucumber seedlings. At the same time, the candidate genes within the mapping region were cloned and analyzed. The results showed that salt tolerance in cucumber seedlings is a quantitative trait controlled by multiple genes. In experiments carried out in April and July 2019, qST6.2 on chromosome six was repeatedly detected. It was delimited into a 1397.1 kb region, and nine genes related to salt tolerance were identified. Among these genes, Csa6G487740 and Csa6G489940 showed variations in amino acid sequence between lines CG104 and CG37. Subsequent qRT-PCR showed that the relative expression levels of both genes during salt treatment were significantly different between the two parents. These results provide a basis for the fine mapping of salt tolerant genes and further study of the molecular mechanism of salt tolerance in cucumber seedlings.

INFLUENCE OF SEED SIZE ON MAIZE SEEDLINGS WHEN SOWN UNDER WATER DEFICIT CONDITIONS

Seed size may affect the initial development of seedlings, especially under adverse conditions such as water deficit. The objective of this study was to characterize the influence of seed size on traits presented by maize seedlings under contrasting conditions of water availability. The experiment was conducted with a tolerant line (L91), a non-tolerant line (L57), and with the F2 resulting from the cross between those lines. The seeds were classified with the use of round-hole sieves and those retained on sieves of sizes 22, 20 and 18/64” were used. The seeds were sown in trays containing sand and, in order to simulate water deficit, the water retention capacity was adjusted to 10% (stress) and 70% (control). Four replications were used, with 25 seeds per treatment, which were stored in a growth chamber at 25 ºC for 7 days. Then the number of seminal roots, length of root and shoot, and their weights (fresh, dry and total) were evaluated. The seed size directly influences the development of maize seedlings, when subjected to water restriction, regardless of whether they are lines or F2. In this case, the larger-size sieves (22 and 20) were superior when compared with the size 18. In the early stages, the L57 was more tolerant to water restriction when compared with L91.

Western tolerance: the rule of democracy or the offensive of dehumanization?

In the West, there is a total substitution of concepts, expressed in the idea of tolerance, according to which humanism manifests itself in respect for any system of values. The criteria for good and evil are neutralized, and the Weld of what is permitted is expanded. Values and life practices that were traditionally considered unacceptable and marginal in the culture receive the status of normal and even necessary. When the boundaries of tolerance are not defined, the idea itself becomes dehumanizing. But the dehumanizing meaning of the ongoing cultural transformations is hidden behind emotionally attractive names like human rights and democracy. Socially harmful ideology and the life practices it absolutizes are given a lot of emotionally euphonious names, which are simulacra that hide the true essence of the phenomena being signified. Ne protection of minority rights under the banner of democracy and human rights is usually an attack on the rights of the majority, and human rights are wrongly identified with the rights of the minority. The absolutization of the rights of social minorities (and the most radical ones in relation to traditional culture) is at the same time an infringement of the rights of the majority. The social majority becomes oppressed. Ne idea of tolerance implanted anti-democratic, without taking into account the views of the public. In the West, it is necessary to show tolerance both to different practices and points of view, and to the very fact of planting this tolerant line. That is, a mandatory tolerance for tolerance is instilled. The common idea of postmodern relativization of values is not entirely correct. The sick, the evil, and the unreasonable are given more right to exist than the healthy, the good, and the reasonable. But instead of equating the worthy and the unworthy, a “sociocultural inflection” is carried out towards the unworthy. Criticism of homosexuality is presented as reprehensible intolerant homophobia, and parents who are negative about gay propaganda risk becoming clients for juvenile services. Even schools began to reorient themselves under the apologia of sexual perversion, which is a reversal to the de-intellectualization and dehumanization of children’s minds. Trends that are referred to as ways to protect human rights, freedom, and democracy actually lead to social dehumanization.

Chromatin-Level Differences Elucidate Potential Determinants of Contrasting Levels of Cold Sensitivity in Maize Lines

Maize is a subtropical, cold-sensitive species. However, some varieties of this species have the potential to withstand long-term low temperatures, even at the seedling stage. The molecular basis of this phenomenon has not been determined. In a chromatin-level study, we compared the cold-stress reaction of seedlings of two maize inbred lines showing contrasting levels of cold sensitivity. The cold-tolerant line was selected based on field data and previous physiological and transcriptomic level studies. The first condition of gene expression—chromatin accessibility—was assessed by formaldehyde-aided isolation of regulatory elements method and DNA sequencing. Potentially expressed genes and cis-regulatory sequences open for interaction with transcription factors have been defined. The results of this study suggest that during cold stress, the tolerant maize line shifted resources from growth to defense. This shift was shown by potential hormone-level events—degradation of growth-promoting gibberellins and synthesis of jasmonic and abscisic acids. This finding is congruent with the xeromorphic morphology of seedlings of the cold-tolerant line and their ability to regrow when stress ceases. It is a common reaction of cold-tolerant maize lines. Moreover, in the cold-tolerant line, several genes from the low-temperature signaling pathways were potentially expressed. Additionally, numerous stress-response AP2/EREBP-binding cis-motifs were accessible in the cold-tolerant line. Differently in the cold-sensitive B73 line, MADS-binding cis-motifs were the most abundant. Development of the photosynthetic apparatus is crucial for the survival of maize seedlings at low temperature. Our results suggest efficient photosynthesis in seedlings of the cold-tolerant line, as was described earlier in physiological-level analyses.