Responses of photosynthetic characteristics of oat flag leaf and spike to drought stress

Plants Distinguish Different Photoperiods to Independently Regulate Post-Flowering Vegetative Growth and Reproductive Growth

The post-flowering stage is critical for plant yield and seed quality. This can be influenced by the photoperiod; however, the underlying mechanisms are not clear. Arabidopsis thaliana was selected as the experimental material to test this phenomenon. Different photoperiod treatments were implemented during the post-flowering stage to comprehensively examine the effects of photoperiod on physiological and phenotypic characteristics. This work aims to explore the photoperiod measurement mechanisms that control post-flowering growth and development. Our results showed the following: (1) During the post-flowering stage, the photoperiod had a significant impact on both vegetative and reproductive growth. (2) Photoperiod measurement mechanisms can be categorized into absolute and photosynthetic photoperiods. These mechanisms exert distinct effects. (3) Absolute photoperiod regulated the cytokinin to auxin ratio, thereby controlling the number and length of branches and the number of siliques. Extending the absolute photoperiod had a preferential promoting effect. (4) Photosynthetic photoperiod affected duration of photosynthesis. This process regulated the formation and accumulation of photosynthetic products. Consequently, it influenced the biomass and efficiency of siliques. Extending the photosynthetic photoperiod had a positive effect. This study demonstrates that plants distinguish between photoperiodic signals and energy effects to independently control post-flowering development and growth.

A cystathionine beta-synthase domain containing protein, OsCBSCBS4, interacts with OsSnRK1A and OsPKG and functions in abiotic stress tolerance in rice

The Cystathionine-β-Synthase (CBS) domain-containing proteins (CDCPs) constitute a functionally diverse protein superfamily, sharing an evolutionary conserved CBS domain either in pair or quad. Rice genome (Oryza sativa subsp. indica) encodes 42 CDCPs; their functions remain largely unexplored. This study examines OsCBSCBS4, a quadruple CBS domain containing protein towards its role in regulating the abiotic stress tolerance in rice. Gene expression analyses revealed upregulation of OsCBSCBS4 in response to diverse abiotic stresses. Further, the cytoplasm-localised OsCBSCBS4 showed interaction with two different kinases, a cytoplasmic localised cGMP-dependant protein kinase (OsPKG) and the nucleo-cytoplasmic catalytic subunit of sucrose-nonfermentation 1-related protein kinase 1 (OsSnRK1A). The interaction with the latter assisted in trafficking of OsCBSCBS4 to the nucleus as well. Overexpression of OsCBSCBS4 in rice resulted in enhanced tolerance to drought and salinity stress, via maintaining better physiological parameters and antioxidant activity. Additionally, OsCBSCBS4-overexpressing rice plants exhibited reduced yield penalty under stress conditions. The in silico docking and in vitro binding analyses of OsCBSCBS4 with ATP suggest its involvement in cellular energy balance. Overall, this study provides novel insight into the unexplored functions of OsCBSCBS4 and demonstrates it as a new promising target for augmenting crop resilience.

StTCTP Positively Regulates StSN2 to Enhance Drought Stress Tolerance in Potato by Scavenging Reactive Oxygen Species

Drought is a negative agronomic effect that can lead to an increase in reactive oxygen species (ROS) levels. Excessive drought can severely alter cell membrane fluidity and permeability, significantly reducing cell viability. The Gibberellic acid-stimulated Arabidopsis (Snakin/GASA) gene family has an important role as antioxidants in inhibiting the accumulation of ROS and improving crop drought resistance. However, the regulatory mechanism of potato StSnakin-2 (StSN2) in response to drought, along with how StSN2 expression is regulated, is not well understood. In this study, we found that StSN2 was induced by drought. Overexpression of StSN2 significantly increased drought tolerance, whereas silencing StSN2 increased sensitivity to drought. Overexpression of StSN2 resulted in higher antioxidant enzyme (superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD)) activity, and lowered hydrogen peroxide (H2O2) and malondialdehyde (MDA) accumulation during drought stress. Also, overexpression of StSN2 increased the relative water content (RWC) of leaves and reduced the water loss in leaves. We screened the upstream regulatory protein translation-controlled tumor protein (StTCTP) of StSN2 through DNA pull-down combined with mass spectrometry. Yeast one-hybrid (YIH), electrophoretic mobility shift assay (EMSA), and luciferase reporting assay (LUC) indicated that StTCTP binds the StSN2 promoter. Like StSN2, StTCTP was highly expressed in response to drought. Overexpression of StTCTP increased the photosynthetic rate and CAT enzyme activity, and lowered H2O2 and MDA accumulation during drought. Meanwhile, overexpression of StTCTP increased leaf RWC and reduced water loss. Our research strongly suggested that StSN2 effectively cleared ROS and significantly boosted the drought resistance of potatoes. Furthermore, as a transcriptional activator of StSN2, StTCTP, much like StSN2, also enhanced the potato's drought tolerance. The results provided a foundation for the further study of StSN2 regulatory mechanisms under drought stress.

Photosynthetic performance and carbon metabolism in the ear organs of oats under drought stress

Sufficiently exploiting the potential of crop photosynthesis is one of the critical ways for improving cultivation production to face global climate change. In this study, oat plants were potted with three watering treatments. The glumes, lemmas, and flag leaves were sampled on days 0, 7, and 14 after the first floret blossomed under the control (denoted as CK-0, CK-7, and CK-14), drought stress (denoted as DS-7, and DS-14) and rewatering treatments (RW-14). Paraffin cross-section structures were observed, and the absolute water content, photosynthetic enzyme activities, carbohydrate content, dry matter weight, and total C and total N accumulation were determined in the glumes, lemmas and flag leaves. The results showed that stomatal tissues were present in both the inner and outer epidermis in the glumes and lemmas, and chloroplasts existed in the cells of both ear organs. Compared to CK-14, the absolute water content was significantly decreased in the flag leaves, stems, and seeds under DS-14, while drought stress did not significantly affect the water status of the glumes, lemmas, and peduncles. Drought stress significantly decreased the PEPC activities in the glumes, lemmas, and flag leaves, and the glumes had significantly higher PEPC activity than the flag leaves in the late stages of grain filling. Compared to CK-7, fructose and sucrose content was significantly decreased in the flag leaves under DS-7, while drought stress significantly increased the fructose, sucrose, and starch content in the glumes and lemmas. In addition, soluble sugar content was significantly increased in all glumes, lemmas, and flag leaves under drought stress. Rewatering significantly increased the carbohydrate content in the flag leaves, while it had no significant effect on the glumes and lemmas. As growth continued, the C and N contents and the dry matter mass in the seeds gradually increased, which was transferred from the glumes, lemmas, leaves, and stems. The results suggest that oats can tolerate a certain degree of drought without affecting the ears' physiological function and yield, and ear organs can maintain water status and photosynthetic performance, which plays a major role in the maintenance of seed yield under drought stress conditions.

Applying microbial biostimulants and drought-tolerant genotypes to enhance barley growth and yield under drought stress

With climate change, the frequency of regions experiencing water scarcity is increasing annually, posing a significant challenge to crop yield. Barley, a staple crop consumed and cultivated globally, is particularly susceptible to the detrimental effects of drought stress, leading to reduced yield production. Water scarcity adversely affects multiple aspects of barley growth, including seed germination, biomass production, shoot and root characteristics, water and osmotic status, photosynthesis, and induces oxidative stress, resulting in considerable losses in grain yield and its components. In this context, the present review aims to underscore the importance of selecting drought-tolerant barley genotypes and utilizing bio-inoculants constructed from beneficial microorganisms as an agroecological approach to enhance barley growth and production resilience under varying environmental conditions. Selecting barley genotypes with robust physiological and agronomic tolerance can mitigate losses under diverse environmental conditions. Plant Growth Promoting Rhizobacteria (PGPR) play a crucial role in promoting plant growth through nutrient solubilization, nitrogen fixation, phytohormone production, exopolysaccharide secretion, enzyme activity enhancement, and many other mechanisms. Applying drought-tolerant genotypes with bio-inoculants containing PGPR, improves barley's drought tolerance thereby minimizing losses caused by water scarcity.

Effect of nitrogen reduction combined with biochar application on soda saline soil and soybean growth in black soil areas

The combination of biochar and nitrogen (N) fertilization in agricultural salt-affected soils is an effective strategy for amending the soil and promoting production. To investigate the effect of nitrogen reduction combined with biochar application on a soda saline soil and soybean growth in black soil areas, a pot experiment was set up with two biochar application levels, 0 (B0) and 4.5 t/hm2 (B1); two biochar application depths, 0-20 cm (H1) and 0-40 cm (H2); and two nitrogen application levels, conventional nitrogen application (N0) and nitrogen reduction of 15% (N1). The results showed that the application of biochar improved the saline soil status and significantly increased soybean yield under lower nitrogen application. Moreover, increasing the depth of biochar application enhanced the effectiveness of biochar in reducing saline soil barriers to crop growth, which promoted soybean growth. Increasing the depth of biochar application increased the K+ and Ca2+ contents, soil nitrogen content, N fertilizer agronomic efficiency, leaf total nitrogen, N use efficiency, AN, Tr, gs, SPAD, leaf water potential, water content and soybean yield and its components. However, the Na+ content, SAR, ESP, Na+/K+, Ci and water use efficiency decreased with increasing biochar depth. Among the treatments with low nitrogen input and biochar, B1H1N1 resulted in the greatest soil improvement in the 0-20 cm soil layer compared with B0N0; for example, K+ content increased by 61.87%, Na+ content decreased by 44.80%, SAR decreased by 46.68%, and nitrate nitrogen increased by 26.61%. However, in the 20-40 cm soil layer, B1H2N1 had the greatest effect on improving the soil physicochemical properties, K+ content increased by 62.54%, Na+ content decreased by 29.76%, SAR decreased by 32.85%, and nitrate nitrogen content increased by 30.77%. In addition, compared with B0N0, total leaf nitrogen increased in B1H2N1 by 25.07%, N use efficiency increased by 6.7%, N fertilizer agronomic efficiency increased by 32.79%, partial factor productivity of nitrogen increased by 28.37%, gs increased by 22.10%, leaf water potential increased by 27.33% and water content increased by 6.44%. In conclusion, B1H2N1 had the greatest effect on improving the condition of saline soil; it not only effectively regulated the distribution of salt in soda saline soil and provided a low-salt environment for crop growth but also activated deep soil resources. Therefore, among all treatments investigated in this study, B1H2N1 was considered most suitable for improving the condition of soda saline soil in black soil areas and enhancing the growth of soybean plants.

Integrative transcriptome and metabolome analysis reveals the mechanism of fulvic acid alleviating drought stress in oat

Drought stress inhibits oat growth and yield. The application of fulvic acid (FA) can improve the drought resistance of oats, but the corresponding molecular mechanism of FA-mediated drought resistance remains unclear. Here, we studied the effects of FA on the drought tolerance of oat leaves through physiological, transcriptomic, and metabolomics analyses, and identified FA-induced genes and metabolites related to drought tolerance. Physiological analysis showed that under drought stress, FA increased the relative water and chlorophyll contents of oat leaves, enhanced the activity of antioxidant enzymes (SOD, POD, PAL, CAT and 4CL), inhibited the accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2) and dehydroascorbic acid (DHA), reduced the degree of oxidative damage in oat leaves, improved the drought resistance of oats, and promoted the growth of oat plants. Transcriptome and metabolite analyses revealed 652 differentially expressed genes (DEGs) and 571 differentially expressed metabolites (DEMs) in FA-treated oat leaves under drought stress. These DEGs and DEMs are involved in a variety of biological processes, such as phenylspropanoid biosynthesis and glutathione metabolism pathways. Additionally, FA may be involved in regulating the role of DEGs and DEMs in phenylpropanoid biosynthesis and glutathione metabolism under drought stress. In conclusion, our results suggest that FA promotes oat growth under drought stress by attenuating membrane lipid peroxidation and regulating the antioxidant system, phenylpropanoid biosynthesis, and glutathione metabolism pathways in oat leaves. This study provides new insights into the complex mechanisms by which FA improves drought tolerance in crops.

Photosynthetic performance of glumes of oat spikelets is more stable for grain-filling stage under drought stress

Drought stress affects plant photosynthesis, leading to a reduction in the quality and yield of crop production. Non-foliar organs play a complementary role in photosynthesis during plant growth and development and are important sources of energy. However, there are limited studies on the performance of non-foliar organs under drought stress. The photosynthetic-responsive differences of oat spikelet organs (glumes, lemmas and paleas) and flag leaves to drought stress during the grain-filling stage were examined. Under drought stress, photosynthetic performance of glume is more stable. Intercellular CO2 concentration (Ci), chlorophyll b, maximum photochemical efficiency of photosystem II. (Fv/Fm), and electron transport rate (ETR) were significantly higher in the glume compared to the flag leaf. The transcriptome data revealed that stable expression of the RCCR gene under drought stress was the main reason for maintaining higher chlorophyll content in the glume. Additionally, no differential expression genes (DEGs) related to Photosystem Ⅰ (PSI) reaction centers were found, and drought stress primarily affects the Photosystem II (PSII) reaction center. In spikelets, the CP43 and CP47 subunits of PSII and the AtpB subunit of ATP synthase were increased on the thylakoid membrane, contributing to photosynthetic stabilisation of spikelets as a means of supplementing the limited photosynthesis of the leaves under drought stress. The results enhanced understanding of the photosynthetic performance of oat spikelet during the grain-filling stage, and also provided an important basis on improving the photosynthetic capacity of non-foliar organs for the selection and breeding new oat varieties with high yield and better drought resistance.

Germination and stress tolerance of oats treated with pulsed electric field at different phases of seedling growth

This study explores the impact of pulsed electric field (PEF) application on oat seedling growth and stress tolerance. PEF treatment (99 monopolar, rectangular pulses lasting 10 µs each, with a frequency of 13 Hz and a nominal electric field strength of 2250 V/cm) was applied at two growth stages: (i) when the seedlings had 0.2 cm roots emerging from the kernel, and (ii) when they had a 0.4 cm shoot emerging from the kernel. Post-treatment, the seedlings were hydroponically grown for 8 days. To induce stress, the hydroponic medium was augmented with PEG (15 %) to induce drought stress and NaCl (150 mM) to induce salinity stress. Results demonstrate that applying PEF improved the growth of the root and shoot of oat seedlings. This effect was more pronounced when applied to more developed seedlings. When PEF was applied during the later stage of germination, seedlings exposed to salinity stress showed enhanced shoot growth compared to the control. Under the studied conditions, the application of PEF had no impact on the growth of seedlings under drought stress.

Drought priming at seedling stage improves photosynthetic performance and yield of potato exposed to a short-term drought stress

Potato (Solanum tuberosum L.) is an important food and vegetable crop worldwide. In recent years, the arid environment resulting from climate change has caused a sharp decline in potato yield. To clarify the effect of drought priming at the seedling stage on the tolerance of potato plants to drought stress during tuber expansion, we conducted a pot experiment to investigate the physiological response of the plants generated from seed potatoes of the variety 'Favorita' to varied water supply conditions: normal water supply at the seedling stage (control), normal water supply at the seedling stage and drought stress at the mid-tuber-expansion stage (non-primed), and drought priming at the seedling stage plus drought stress at the mid-tuber-expansion stage (primed). Drought priming resulted in an increase in the number of small vascular bundles in potato plants compared to non-primed plants. It also altered the shape and density of stomata, enhancing water use efficiency and reducing whole-plant transpiration. The primed plants maintained the basal stem cambium for a longer time under drought stress, which gained an extended differentiation ability to generate a greater number of small vascular bundles compared to non-primed plants. Drought priming increased the amount and rate of dry matter translocation, and so reduced the adverse effects on tubers of potato under drought stress. Therefore, drought priming at the seedling stage improved the photosynthetic performance and yield, and probably enhanced the drought tolerance of potato.

Co-Expression of JcNAC1- and JcZFP8-Improved Agronomic Traits of Tobacco and Enhanced Drought Resistance through NbbHLH1 and NbbHLH2

Previous studies have identified numerous transcription factors involved in drought response, each of which play different roles in plants. The objective of the present study was to evaluate the effectiveness of two transcription factors on drought response in Jatropha curcas L., JcNAC1 and JcZFP8. The overexpression of these transcription factors in tobacco (Nicotiana benthamiana L.) improved drought resistance, but JcZFP8 delayed germination and JcNAC1 reduced biomass and yield. By constitutively co-expressing these two genes in tobacco, drought resistance was improved, and the negative effects of each of them were overcome. The transgenic plants with double-gene co-expression showed stronger drought tolerance with 1.76-fold greater accumulation of proline and lower H2O2 and malondialdehyde (MDA) content to 43 and 65% of wildtype (WT) levels, respectively. The expression levels of NbbHLH1 and NbbHLH2 genes upregulated linearly with the increased drought tolerance of double genes co-expression plants. In drought conditions, the leaf water contents of bhlh1, bhlh2, and bhlh1bhlh2 deletion mutants obtained by CRISPR-CAS9 knockout technique were maintained at 99%, 97%, and 97% of WT. The bhlh1bhlh2 was found with lower germination rate but with higher reactive oxygen levels (1.64-fold H2O2 and 1.41-fold MDA levels). Thus, the co-expression of two transcription factors with different functions overcame the adverse traits brought by a single gene and enhanced the shared drought-tolerant traits, which can provide guidance on theory and selection of gene combinations for the application of multi-gene co-expression in agriculture in the future.

Different Responses to Water Deficit of Two Common Winter Wheat Varieties: Physiological and Biochemical Characteristics

Since water scarcity is one of the main risks for the future of agriculture, studying the ability of different wheat genotypes to tolerate a water deficit is fundamental. This study examined the responses of two hybrid wheat varieties (Gizda and Fermer) with different drought resistance to moderate (3 days) and severe (7 days) drought stress, as well as their post-stress recovery to understand their underlying defense strategies and adaptive mechanisms in more detail. To this end, the dehydration-induced alterations in the electrolyte leakage, photosynthetic pigment content, membrane fluidity, energy interaction between pigment-protein complexes, primary photosynthetic reactions, photosynthetic and stress-induced proteins, and antioxidant responses were analyzed in order to unravel the different physiological and biochemical strategies of both wheat varieties. The results demonstrated that Gizda plants are more tolerant to severe dehydration compared to Fermer, as evidenced by the lower decrease in leaf water and pigment content, lower inhibition of photosystem II (PSII) photochemistry and dissipation of thermal energy, as well as lower dehydrins' content. Some of defense mechanisms by which Gizda variety can tolerate drought stress involve the maintenance of decreased chlorophyll content in leaves, increased fluidity of the thylakoid membranes causing structural alterations in the photosynthetic apparatus, as well as dehydration-induced accumulation of early light-induced proteins (ELIPs), an increased capacity for PSI cyclic electron transport and enhanced antioxidant enzyme activity (SOD and APX), thus alleviating oxidative damage. Furthermore, the leaf content of total phenols, flavonoids, and lipid-soluble antioxidant metabolites was higher in Gizda than in Fermer.

Sensitivity of the Photosynthetic Apparatus in Maize and Sorghum under Different Drought Levels

Drought is one of the main environmental stress factors affecting plant growth and yield. The impact of different PEG concentrations on the photosynthetic performance of maize (Zea mays L. Mayflower) and sorghum (Sorghum bicolor L. Foehn) was investigated. The activity of the photosynthetic apparatus was assessed using chlorophyll fluorescence (PAM and JIP test) and photooxidation of P₇₀₀. The data revealed that water deficiency decreased the photochemical quenching (qP), the ratio of photochemical to nonphotochemical processes (Fv/Fo), the effective quantum yield of the photochemical energy conversion in PSII (Φ_PSII), the rate of the electron transport (ETR), and the performance indexes PI_total and PI_ABS, as the impact was stronger in sorghum than in maize and depended on drought level. The PSI photochemistry (P₇₀₀ photooxidation) in sorghum was inhibited after the application of all studied drought levels, while in maize, it was registered only after treatment with higher PEG concentrations (30% and 40%). Enhanced regulated energy losses (Φ_NPQ) and activation of the state transition under drought were also observed in maize, while in sorghum, an increase mainly in nonregulated energy losses (Φ_NO). A decrease in pigment content and relative water content and an increase in membrane damage were also registered after PEG treatment. The experimental results showed better drought tolerance of maize than sorghum. This study provides new information about the role of regulated energy losses and state transition for the protection of the photosynthetic apparatus under drought and might be a practical approach to the determination of the drought tolerance of plants.