Relative Water Content Research Articles

Spermidine-induced improvements in water relations and antioxidant defense enhance drought tolerance in yarrow (Achillea millefolium L.).

Drought stress poses a serious threat to agricultural productivity worldwide. This study investigated the mitigative effects of exogenous spermidine on drought stressed yarrow (Achillea millefolium L.). Plants were subjected to three drought levels (25%, 50% and 75% field capacity) and foliar sprayed with 0, 1.5 and 3μM spermidine. Drought significantly reduced relative water content, photosynthetic pigments (chlorophyll, carotenoids), osmolyte (proline, soluble sugars) accumulation and antioxidant enzyme activities such as catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX), indicating oxidative damage. Spermidine treatment attenuated drought injury by improving the above parameters. Maximum responses were observed at 1.5μM for photosynthetic pigments and osmolytes, while 3μM performed best for secondary metabolites (phenolics, flavonoids, anthocyanins) and antioxidant enzymes. Drought also upregulated secondary metabolites like phenolics, while spermidine further augmented their levels. Moreover, spermidine maintained membrane integrity and osmotic adjustment under water deficit. Overall, spermidine enhanced yarrow's drought tolerance by modulating physiological and biochemical processes. Our findings provide insights into spermidine-induced adaptation mechanisms in plants combating water scarcity. Optimization of spermidine concentration may help develop drought-resilient crops.

Physiological and Biochemical Responses of Plants to Rooftop and Ground-level Conditions in Urban Green Spaces

An understanding of plant adaptation to rooftop environments is essential for improvising urban greening strategies; however, limited research has systematically examined the physiological and biochemical responses of plants at urban rooftops. This study addressed this gap by evaluating physiological and biochemical alterations of six herbaceous perennial species, Rosa hybrids, Murraya paniculata, Cestrum nocturnum, Pittosporum tenuifolium, Duranta, and Hibiscus rosa sinensis, cultivated in an intensive rooftop garden environment vs. optimal ground conditions. These species, acclimatized to the local climate of Pakistan, were assessed to determine the transpiration rate, photosynthetic rate, chlorophyll contents, and respiration rate using on-site measurements and standardized leaf tissue analyses. The results demonstrated significant differences in physiological and biochemical parameters between rooftop and ground-level plants. Seasonal variations and elevation profoundly influenced plant physiology and significant biochemical alterations observed in response to rooftop conditions. Photosynthetic and transpiration rates were reduced by up to 30% in winter under low light conditions, while summer conditions led to a 25% increase in transpiration rates for rooftop plants. Ground-level plants exhibited the highest respiration rates during the summer season. A leaf analysis revealed that rooftop-grown plants exhibited higher pH levels and 15% increased chlorophyll and ascorbic acid contents but 20% lower water use efficiency compared with their ground-level counterparts. Despite this, rooftop plants showed a 10% higher air pollution tolerance index. Pearson’s correlation analysis confirmed a strong positive relationship between most biochemical parameters and physiological activities with increased elevation, except for relative water content, which exhibited a negative correlation under rooftop conditions. The results indicated that those plants on rooftops exhibited reduced water use efficiency compared with that of ground-level plants undergoing distinct physiological and biochemical adaptations and showed more resilience to the pollution index in response to urban rooftop conditions. These findings provide new insights into plant adaptability in urban environments and can transform future strategies for sustainable urban greening and species selection in roof garden systems.

Curcumin, a Secondary Metabolite, Activates the Defense System by Regulating Water Status, PSII Photochemistry, and Antioxidant Capacity in Lactuca sativa Exposed to Lead and/or Arsenic Stresses

ABSTRACTLead (Pb) and arsenic (As) pollution seriously affect the physiological and biochemical processes of plants, reduce agricultural productivity, and pose a serious threat to human health. Recently, there has been an increasing interest in studies aimed at mitigating these negative effects of heavy metals. Curcumin is an important secondary metabolite belonging to the polyphenol class that provides stress tolerance to plants through its metal‐chelating activity. Therefore, in our study, curcumin (Cur1; 50 μM and Cur2; 100 μM) was applied to lettuce (Lactuca sativa L.) under lead (Pb; 100 μM) and/or arsenic (As; 100 μM) stress. It was observed that the relative growth rate of the plant decreased by 12% at Pb stress and 27% under As stress. Pb and combined stress conditions (Pb + As) reduced the relative water content by 23%. Notably, significant increases in these parameters were observed following curcumin treatment. Furthermore, exogenous curcumin application effectively mitigated the detrimental effects induced by heavy‐metal stress. On gas exchange and photosynthetic parameters, Cur1 treatment resulted in more than a twofold increase in carbon assimilation rate under Pb and Pb + As conditions. Due to Pb + As exposure, H2O2 content increased by 25% and TBARS content increased by twofold. These elevations were attenuated by curcumin with enhanced antioxidant enzyme activity. Compared to the combined stress exposure, Pb + As + Cur1 and Pb + As + Cur2 treatments resulted in 40% and 24% increased SOD activity, respectively. Curcumin treatments contributed to the maintenance of redox balance in the cell by increasing the activity of the ascorbate–glutathione (AsA‐GSH) cycle. In conclusion, curcumin applications to lettuce under Pb and/or As stress contributed to the reduction of ROS accumulation by increasing the water uptake, photosynthesis efficiency, and antioxidant enzyme capacity. These findings suggest that phenolic compounds like curcumin could be a promising strategy in agricultural practices to enhance plant resistance to heavy‐metal stress, thereby improving productivity.

Effect of Organic Fertilizer on Growth and Physiology of Brachychiton populneus (Schott& Endl) Seedlings under Drought Conditions

Drought stress negatively impacts plant growth and agricultural productivity. This study investigates whether organic fertilizer can mitigate these effects by improving the growth and physiological responses of Brachychiton populneus seedlings under drought conditions. Thus, local compost added to Brachychiton populneus (Schott & Endl) to determine whether it could aid the growth of the seedlings during drought conditions. Two drought stress levels (D1 and D2), or 60% and 30% of the soil water holding capacities (SWHC%), were applied to the seedlings compared to the control (C0). There were two additions of local compost (C1 and C2), 2000 and 4000 ppm, respectively, in comparison to the control treatments. D1C2 (soil water holding capacity of 60% and 4000 ppm compost) was the usual treatment combination. Which resulted in the longest shoot and root lengths. By registering the maximum dry matter content in the roots and shoots, the same combination also greatly increased the biomass of the seedlings. A general decline in the relative water content appears when biomass increases. The consequences of drought stress are lessened by the addition of compost, which also improves chlorophyll production and overall plant growth. Growth and physiological parameter correlations are shown by the component plot in rotated space. The highest variance is explained by component 1, and the second largest by component 2. A positive association was seen between root length, shoot height, and total dry weight, as they clustered together. Conversely, there is a negative association observed between the components of relative water content and shoot dry weight. However, component 2 and the leaf chlorophyll content (a, b, and total) showed a significant correlation. Compost provides a sustainable solution for improving drought resilience in Brachychiton populneus, making them crucial for forest nurseries and reforestation efforts in arid and semi-arid regions.

Morpho-Physiological Adaptations of Drought-Resilient and Susceptible Brassica napus Genotypes to Sulphur-Coated Urea Fertilization

This study focuses on screening drought-tolerant and sensitive genotypes of Brassica napus L. (an important oilseed crop in Pakistan) and investigates their morpho-physiological responses to sulphur-coated urea (SCU) under drought conditions. Genotypes were categorized into highly drought tolerant (HDT), moderately drought tolerant (MDT), and highly drought sensitive (HDS) through hierarchical cluster analysis. Out of 100 genotypes, 20 were HDT, 30 were MDT, and 50 were HDS. Three genotypes from each category were subjected to two drought levels (80% field capacity and 50% field capacity) and were treated with SCU, urea, or no nitrogen. Key parameters such as leaf relative water content, chlorophyll content, excised leaf water loss, and membrane stability index (MSI) were recorded. Drought-tolerant genotypes performed well in both germination and seedling stages, showing higher excised leaf water loss, relative water content, chlorophyll values, seed weight, and yield-related traits. Initially, five concentrations of PEG-6000 (5% to 25%) were tested to determine optimal levels for screening drought tolerance. Results showed that 25% PEG-6000 induced 50% drought injury index (DII), making it the most promising concentration. Various morpho-physiological traits such as germination rate, shoot/root length, fresh and dry weight, and drought tolerance indices were assessed. The study concluded that drought-tolerant genotypes responded positively to SCU application, making them suitable for cultivation in water-scarce regions of Pakistan.

Effect of Calcium Nitrate Applications on Plant Development and Some Physiological Characteristics of Sunflower Seedlings Grown Under Drought Conditions

Drought stress is one of the abiotic stresses that negatively affects plant growth, development and product yield. In recent years, nutrient solution applications to leaves have been frequently used to reduce the negative effects of drought stress. This study was conducted in 2024 at the Atatürk University, Plant Production Application and Research Center to determine the effect of calcium nitrate applications during the seedling period on the growth and some physiological characteristics of sunflower (Helianthus annuus L.) grown under drought stress. The study was based on two-factor completely randomized experimental design with three irrigation levels [full irrigation (100% (I0), 70% (I1) and 40% (I2) of field capacity), two Ca(NO3)2 concentrations (15 mM and 30 mM)]. The study was carried out as a pot trial based on this experimental design. At the end of the trial period, plant growth parameters and some physiological measurements and analyzes were performed on sunflower plants and the differences between the treatments were evaluated. According to the research findings, significant differences were observed between the different treatments and irrigation levels. The application of Ca(NO3)2 significantly influenced plant growth parameters (such as plant height, stem diameter, fresh and dry weight) and physiological parameters [such as tissue relative water content (RWC)] in sunflower grown under varying irrigation levels. At the end of the study, it was determined that dry conditions negatively affected plant growth in sunflowers and reduced the RWC value. In conclusion; calcium nitrate applications reduced this negative effect of drought compared to the control application. It can be said that especially the results obtained from the application of 15 Mm CaN at 70% (I1) irrigation level are relatively less affected by drought.

Effects of Varieties and Pot Colours on Boosting Capsicum Growth and Yield

Heat stress can significantly hinder root growth in containerized plant production, a concern that growers often overlook. One potential solution is using different container colors to minimize the effects of sunlight on the heat balance of growing media. The current varieties of capsicum (Capsicum annuum L.) often exhibit inadequate stress tolerance, limiting capacity for boosting yield in containerized systems. This research investigated the influence of pot colour and variety selection on the growth and productivity of capsicum in a containerized system within subtropical environments. Twelve treatments were tested, including three capsicum varieties ('Intruder', 'Bomby', 'Purple Beauty') and four pot colours (red, black, white, green). Results showed that 'Purple Beauty' capsicum grown in white pots demonstrated superior vegetative growth and phenological attributes compared to those grown in black pots. Soil temperatures at a depth of 5 cm were found to be 3-4°C lower in white pots and highest in black pots. Specifically, 'Purple Beauty' grown in white pots exhibited a 27.3% increase in plant height and a 22.6% larger leaf area compared to 'Intruder' grown in black pots. Twelve weeks post-transplant, the chlorophyll index (SPAD) was 12.1% higher, and shoot and root dry weights were increased by 49.6% and 55.2%, respectively, for 'Purple Beauty' in white pots compared to 'Intruder' in black pots. Additionally, 'Purple Beauty' in white pots showed a 16.1% higher leaf relative water content (LRWC) and 29.7% less electrolyte leakage. Flowering in 'Purple Beauty' grown in white pots began six days earlier, with 25.6% higher fruit sets and 34.8% fewer flower drops compared to 'Intruder' in black pots. Marketable fruit yields for 'Purple Beauty' in white pots were 35.4% higher than those for 'Intruder' in black pots. These findings suggest that 'Purple Beauty' significantly benefits from cultivation in white pots, leading to improved plant growth, reduced heat stress, and enhanced fruit yield in a containerized production system. J Bangladesh Agril Univ 22(4): 412–421, 2024

Effects of Water and Nitrogen on Eco-physiological Characteristics of Two Dominant Grassland Species on the Semiarid Loess Plateau

To investigate the eco-physiologcial traits in response to water and nitrogen supplying conditions of native species is of importance for understanding their eco-adaptation to the local environment, and also finding rational agronomy measures for using them in artificial grassland construction. In this study, using Bothriochloa ischaemum (C4 grass) and Lespedeza davurica (C3 legume) as research materials, a pot experiment was conducted to compare the leaf photosynthetic traits, leaf fluorescence parameter characteristics and leaf relative water content of the two dominant native species under three different soil moisture conditions (80%FC, 60%FC and 40%FC) and two nitrogen supplying (0 g N kg-1 and 0.025 g N kg-1) conditions when sown individually or in mixture. Results showed that as soil water content decreased from 80% FC (field capacity) to 40% FC, leaf net photosynthetic rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), and stomatal conductance (Gs) of monocultured plants showed an increasing trend, while the photosynthetic parameters of mixculture plants generally exhibited a decreasing trend. The Pn values of L. davurica were significantly higher than those of B. ishchaemum (P<0.05), and the maximum value was 12.50 mmol m-2 s-1. As soil water content decreased, the initial fluorescence values (Fo), maximum potential quantum yield of PSII (Fv/Fo), and maximum photochemical efficiency (Fv/Fm) values under no nitrogen treatment showed no significant change (P>0.05). Overall, the data indicated that when B. ischaemum and L. davurica were mixcultured, there existed a significant mutualistic effect under low soil water situation, indicating mixculture of B. ischaemum and L. davurica was beneficial for coping with drought in the semiarid region.

Responses of the five shallot cultivars to salicylic acid treatment under stress drought conditions

Salicylic acid is a growth hormone that has been widely used to induce resistance to biotic and abiotic stresses. Plant genotypes have different responses to drought stress conditions. This study aimed to analyze the response of five shallot cultivars to drought stress mediated by salicylic acid. A total of five shallot cultivars treated with salicylic acid were tested under drought stress conditions. This study used a completely randomized design with 3 factors, namely the first was the concentration of salicylic acid (0 mM, 0.5 mM, and 1 mM), the second was the shallot cultivar (Bima Brebes, Tajuk, Bauci, Super Philip and Bima Juna), and the third was drought stress (without drought stress and with drought stress). All collected data were subjected to analysis of variance (ANOVA) and the mean differences were compared using Duncan Multiple Range test (α = 95%). Observation variables included leaf length, leaf number, stomatal density, relative water content, total chlorophyll, and leaf proline content. Based on the results of the study, drought stress significantly decreased leaf length and leaf number, reduced chlorophyll content, relative water content and stomatal density, chlorophyll content, and increased proline content of the leaves. On the other hand, exogenous application of SA to drought stressed shallot plants improved morphophysiological characters of shallot. Application of 1 mM salicylic acid was the best concentration. The results of this study also obtained two cultivars that showed fairly consistent morphophysiological performance, namely Bima Juna and Tajuk cultivars. These two cultivars can be recommended as genetic materials in the assembly of drought-tolerant varieties mediated by salicylic acid.

Assessment of Physiological Traits of Fragaria vesca Genotypes Under Water Deficit Conditions

Drought is one of the key challenges of climate change. The basic global problem related to the increasing water deficit is that the vast majority of crops are species and varieties that are the result of breeding work that did not anticipate such a rapid decrease in water availability in the soil. The main objective of the conducted research was to compare the physiological and biochemical response to water deficit of plants of the species Fragaria vesca—two cultivated varieties, and one collected from the natural environment. A two-year pot experiment was conducted in a polyethylene tunnel. The substrate moisture level was monitored using tensiometer readings. Measurements of gas exchange parameters, chlorophyll “a” fluorescence, content of photosynthetic pigments in leaves, index of relative water content in leaves, total fruit yield, single fruit mass and content of K, Ca, Mg, Na, Cu, Zn, Mn, Mo and the ratio of mono- to divalent cations in leaves, roots and plant crowns were taken three times each year during the experiments. Based on one-way and two-way analysis of variance, statistically significant differences were observed between wild-growing plants and cultivated varieties under control conditions, particularly in terms of chlorophyll fluorescence values and the content of photosynthetic pigments. A significant main effect of the soil moisture level was identified for most measured parameters across the majority of assessment time points. However, a significant interaction effect between soil moisture level and genotype was less frequently observed. Significant changes in response to water deficit varied depending on the parameter and genotype, ranging from 2.5% to 106.1%. For the content of chemical elements, the changes reached up to 157.1%. The results suggest that plants obtained from natural environments exhibit better adaptation to water deficit conditions, making them suitable for use in breeding programs aimed at developing varieties resistant to soil water deficits. However, the study’s limitations, particularly the absence of molecular analyses regarding the plants’ adaptive mechanisms, should be taken into consideration.

IMPROVEMENT OF GROWTH, PHYSIOLOGICAL AND BIOCHEMICAL TRAITS OF SUNFLOWER BY IAA AND BAP UNDER SALINITY STRESS in vitro

This study was established to investigate the ability of the sunflower callus plant (Helianthus annuus L.) to tolerate salinity stress for two levels of NaCl (0 and 80 mM), three concentrations of IAA (0, 1.0, and 2.0 mg l-1), and BAP (0, 1.0, and 2.0 mg l-1) in lab conditions. Calli cultures were induced from the cotyledon of H. annuus L. cultured in an appropriate combination of growth regulators 2,4-D and kintein. The salinity results exhibited negative effects in most of the study indications, which can be revealed by a significant increase in sodium content (Na+), hydrogen peroxide (H2O2) and malondialdehde content (MDA). While, the decrease in the study indications such as fresh weight (FW), dry weights (DW), relative water content (RWC), potassium content (K+), sodium/ potassium ratio (Na+/K+), superoxide dismutase (SOD), and catalase (CAT) enzymes activity. The experiment revealed a positive effect for the exogenous growth regulators IAA and BAP in reducing the harmful effects of salinity stress on calli cultures. The nominated regulators succeeded in reducing the harmful effects of salinity stress, where the FW, DW, RFW, browning density (BI), RWC, K+, Na+/K+, SOD, and CAT enzymes activity. However, the exogenous growth regulators reduced the negative effect for each of Na+, H2O2, and MDA under the salinity stress.

Mitigating the adverse effects of drought stress on sunflower plants via foliar application of salicylic acid

Sunflower is the primary oilseed crop of Pakistan, valued for its edible oil and high yield potential under favorable conditions. However, drought stress is a major limiting factor affecting sunflower productivity, causing significant yield reductions. The present study aimed to evaluate the potential role of salicylic acid in enhancing the growth and physiological performance of sunflowers under drought stress. Drought stress was applied 20 days after sowing, with three experimental treatments conducted in five replications: (a) control (normal conditions), (b) drought stress, and (c) drought stress supplemented with 250 mg L? salicylic acid. Key findings revealed that the foliar application of 250 mg L? salicylic acid significantly improved various growth parameters, including shoot length (24.92%), root length (18.97%), fresh shoot weight (15.78%), dry shoot weight (24.15%), fresh root weight (21.32%), and dry root weight (26.72%). Moreover, chlorophyll content increased by 32.90%, stomatal conductance by 19.52%, relative water content by 20.84%, and membrane stability index by 41.79%. Moreover, salicylic acid markedly mitigated oxidative damage, reducing malondialdehyde levels by 32.81% and hydrogen peroxide levels by 17.80% compared to untreated plants. Furthermore, the treatment enhanced the activity of antioxidant enzymes, with superoxide dismutase activity increasing by 17.25%, catalase by 40.05%, and peroxidase by 10.41%. In conclusion, the foliar application of 250 mg L? salicylic acid effectively enhances the growth and physiological parameters of sunflower under drought stress, offering a sustainable and reliable strategy to mitigate the adverse effects of water scarcity on crop production.

Comparative morphological, physiological, and biochemical traits in sensitive and tolerant maize genotypes in response to salinity and pb stress

Salinity and lead are two important abiotic stresses that limit crop growth and yield. In this study, we assayed the effect of these stresses on tolerant and sensitive maize genotypes. Four-week-old maize plants were treated with 250 mM sodium chloride (NaCl) and 250 µM lead (Pb). Our results show that NaCl or Pb treatment of the sensitive genotype caused a significant reduction in the root length, plant height, total fresh and dry weights, as well as chlorophyll, and carotenoid content. Salt stress led to a significant decrease in the relative water content, shoot and root length, fresh and dry weight as well as leaf area and K+ content but increase Na+ content. Both NaCl and Pb stresses increased the antioxidant enzyme activity, proline content, malondialdehyde, and hydrogen peroxide levels. Principal component analysis (PCA) accounted for 69.8% and 16.5% of the total variation among all the variables studied. PCA also suggested a positive correlation between hydrogen peroxide, malondialdehyde, peroxidase, catalase, ascorbate peroxidase levels, and Na+ content and a negative correlation between K+ content, chlorophyll content, relative water content, leaf area, root length, plant height, and total fresh, and dry weights. Together, these results suggest that the salt-tolerant maize genotype is more suitable for adapting to Pb stress compared to the salt-sensitive genotype.

Zinc-lysine and iron-lysine mitigate chromium toxicity in pearl millet (Pennisetum glaucum) through modulating photosynthetic and antioxidant system and inhibiting chromium uptake and translocation.

Chromium (Cr) is an ever-present abiotic stress that negatively affects crop cultivation and production worldwide. High rhizospheric Cr concentrations inhibit nutrients uptake and their translocation to aboveground parts, thus can affect the growth and development of crop plants. This experiment was designed to evaluate the effects of sole and combined zinc-lysine and iron-lysine applications on photosynthetic efficacy, antioxidative defense, oxidative stress, and nutrient uptake and translocation under Cr stress. Chromium stress exhibited toxic effects on the growth, physiological, and biochemical indices of pearl millet. The combined application of zinc-lysine and iron-lysine significantly decreased malondialdehyde (MDA; 25%) and hydrogen peroxide (H2O2; 22.44%), while increased superoxide dismutase (SOD; 19.75%), catalase (CAT; 26.16%), peroxidase (POD; 19.62%), and ascorbate peroxidase (APX; 23.52%) activities under Cr toxicity compared to the control treatment. In addition, the combined application of zinc-lysine and iron-lysine effectively improved net photosynthesis (43.63%), stomatal conductance (20.05%), transpiration rate (20.14%), internal CO2 concentration (34.28%), total chlorophyll (43.12%), relative water content (23.95%), membrane stability index (32.77%), and proline content (25.53%) under stress condition and compared with control. Our results also indicated that the combined application of zinc-lysine and iron-lysine decreased Cr uptake in both shoot and root by 31.25% and 32%, and increased zinc and iron uptake by 39.28% and 36.67%, respectively, over the control, under Cr stress conditions. Moreover, under stress conditions, combined zinc-lysine and iron-lysine effectively improved growth traits particularly shoot and root dry weights, by 8% and 36.84%, respectively, over the control treatment. Overall, our results demonstrated that combined zinc-lysine and iron-lysine was more effective in mitigating Cr toxicity in pearl millet compared with the sole application of these treatments or the control.

Effects of Drought and Biochar Treatments on Some Morphological and Physiological Parameters in Turkish Hazelnut Seedlings

This study investigates the responses of 3-year-old Turkish hazelnut (Corylus colurna) seedlings to drought stress and biochar treatments, focusing on critical morphological and physiological parameters. Hazelnut, an important agricultural crop, is increasingly affected by drought due to global climate change. To mitigate these effects, biochar and the adoption of deep-rooted hazelnut systems have gained attention. The study exposed seedlings to varying levels of irrigation and biochar treatments. Results show that drought stress significantly reduced relative height growth (RHG) and relative diameter growth (RDG), while biochar had no effect on RHG and negatively impacted RDG. Decreased irrigation consistently lowered both RHG and RDG. Physiological assessments, including leaf gas exchange parameters (E, gs, Anet, WUE, iWUE, Ci/Ca) and relative water content (RWC), revealed that drought influenced these variables, whereas biochar showed no significant effect. Drought-stressed seedlings exhibited lower net photosynthesis (Anet) and stomatal conductance (gs), with no notable differences in other photosynthesis-related parameters. Chlorophyll and carotene levels also decreased under low irrigation; higher biochar doses exacerbated these reductions. Overall, the study underscores the paramount importance of water availability in hazelnut cultivation, as it had a more pronounced impact on hazelnut morphology and physiology than biochar, though the limited study duration and surface biochar treatment may have influenced these results.

Silicon Nanoparticles (SiO2 NPs) Boost Drought Tolerance in Grapevines by Enhancing Some Morphological, Physiological, and Biochemical Traits

AbstractDrought is a significant abiotic stress that adversely affects plant growth, development, and metabolic processes, posing a global threat to food security. In recent years, nanotechnology has emerged as a promising strategy to mitigate environmental challenges and has been tested on various plant species; however, its application to grapevines remains largely unexplored. This study aims to investigate the potential of silicon nanoparticles (SiO2 NPs) to modulate morphological, physiological, and biochemical parameters in grapevine saplings (5 BB/Crimson Seedless, 41 B/Crimson Seedless, and 1103 P/Crimson Seedless) under drought stress conditions. Saplings were treated with foliar applications of different concentrations of SiO2 NP solutions (0 (control), 1, 10, and 100 ppm) under well-irrigated (90–100% field capacity) and drought stress (40–50% field capacity) conditions. The results indicated that the application of SiO2 NPs at 10 ppm concentration enhanced growth parameters (such as leaf area, leaf number, shoot fresh and dry weight, root fresh and dry weight) and chlorophyll content under both well-irrigated and drought conditions. Additionally, there was an improvement in leaf relative water content (RWC) and stomatal conductance, correlating with increased protein content. Under drought conditions, oxidative stress indicators, including drought index, leaf temperature, membrane injury index, hydrogen peroxide (H2O2) content, and malondialdehyde (MDA) levels, showed a significant decrease. Concurrently, proline content, total phenolic compounds, and activities of antioxidant enzymes (SOD, CAT, and APX), which increased under drought stress, were reduced in the presence of 10 ppm SiO2 NPs, suggesting a mitigation of oxidative stress. To comprehensively evaluate the effects of SiO2 NP concentrations, irrigation regimes, and rootstock/variety combinations, correlation analysis, principal component analysis (PCA), and hierarchical clustering heatmap analysis were performed. Collectively, the findings suggest that the observed drought-induced oxidative stress tolerance in grapevine saplings in the presence of 10 ppm SiO2 NPs may result from the influence of antioxidant systems leading to a balanced redox potential. These results support the argument that SiO2 NPs play a crucial role in enhancing drought tolerance, with implications for managing drought stress in other agricultural crops as well.

Rhizobacteria and Phytohormonal interactions increase Drought Tolerance in Phaseolus vulgaris through enhanced physiological and biochemical efficiency

The cultivation of common beans (Phaseolus vulgaris L.) in semi-arid regions is affected by drought. To explore potential alleviation strategies, we investigated the impact of inoculation with Bacillus velezensis, and the application of acetylsalicylic acid (ASA) via foliage application (FA), which promote plant growth and enhance stress tolerance. A split-split-plot experiment with four replications was conducted, featuring two irrigation levels: full watering (FW, 100% of plant water requirements) and deficit watering (DW, 70% of plant water requirements) as a main plot, two ASA levels (No foliage application (NFA) 0 and 0.5 mM) as sub plot, and bacterial inoculation (BI) versus non-bacterial inoculation (NBI) as sub-sub plot. Results showed that the highest grain yield was achieved with the ASA + BI under FW (3270 kg ha−¹), a 56% increase compared to the control (2094 kg ha−¹). Under DW, the ASA + BI increased yield by approximately 30%. ASA significantly increased relative water content under deficit watering, achieving 84% with BI. Chlorophyll a content peaked at 3.11 mg g− 1 with full watering, and chlorophyll b content increased by up to 23.8% under deficit watering, indicating improved photosynthetic capacity. Malondialdehyde and hydrogen peroxide levels were reduced to 10.88 and 14.81 µmol g−¹ fresh weight, respectively, in ASA + BI treatments, demonstrating reduced oxidative stress. Antioxidant enzyme activities were significantly elevated in treated plants under DW. This study demonstrates the potential of microbial and hormonal treatments in boosting drought tolerance in common beans, providing a viable approach for sustaining crop performance under stress conditions.

Plant Growth-Promoting Rhizobacteria Paenibacillus polymyxa HL14-3 Inoculation Enhances Drought Tolerance in Cucumber by Triggering Abscisic Acid-Mediated Stomatal Closure.

Drought limits crop growth and yield. Inoculation with plant growth-promoting rhizobacteria (PGPR) emerges as a promising strategy to protect crops against drought. However, the number of drought-tolerant PGPR is limited, and the regulation mechanisms remain elusive. Here, we screened a novel drought-tolerant PGPR strain Paenibacillus polymyxa HL14-3 with high drought-tolerance potential and efficient colonization ability. P. polymyxa HL14-3 inoculation effectively alleviated drought-induced growth inhibition and oxidative stress and improved the root system architecture in cucumber. Furthermore, P. polymyxa HL14-3 improved stomatal closure and leaf relative water content, reducing water loss in cucumber under drought stress. Importantly, P. polymyxa HL14-3 inoculation enhanced drought tolerance in cucumber by inducing abscisic acid synthesis, which was counteracted by root irrigation with the ABA synthesis inhibitor fluridone. Together, our results demonstrate that P. polymyxa HL14-3 inoculation enhances drought tolerance in cucumber by triggering ABA-mediated stomatal closure, providing an effective drought-tolerant PGPR for promoting agricultural production in arid areas.

Impact of Irrigation Cessation on Physiological, Photosynthetic, and Enzymatic Activities in Wheat (Triticum aestivum L.) at Varying Plant Densities

Drought stress is one of the most critical factors reducing the performance of crop plants in arid and semi-arid regions globally, highlighting the importance of understanding underlying mechanisms to combat such stress. Therefore, this experiment aimed to investigate the effect of drought stress and planting density on the physiological characteristics, photosynthetic pigments, and enzymatic activity of wheat plants. The experiment was conducted in a factorial arrangement based on a completely randomized block design with three replications. The treatments included irrigation cessation at three levels (control, irrigation until flowering (IUF), and irrigation until the roughing (IUD)), and plant density (300, 400, 500, and 600 plants m-2). The results indicated that leaf relative water content, soluble sugars, cell membrane stability index, chlorophyll a, b, and carotenoids were significantly decreased at IUF treatment, while these parameters increased at higher plant densities. Additionally, the interaction of drought stress and plant density significantly affected leaf proline and flavonoid content, total chlorophyll, and catalase activity. The highest leaf proline content (3.88 mg g-1 FW) was observed in the treatment with IUF and a density of 600 plants m-2, representing a 192% increase compared to the control. Additionally, the highest total chlorophyll content (3.66 mg g-1 FW) was recorded at no-stress conditions with a density of 500 plants m-2. Under drought stress conditions, the activity of antioxidant enzymes also increased. Overall, our results indicate that a density of 500 plants m-2 is optimal for maintaining stable growth conditions in wheat. These findings provide valuable insights for policymakers to develop effective agronomic strategies to mitigate drought stress, particularly in arid and semi-arid regions.

Mitigating Drought by Exogenous Potassium-mediated Improvements in Water Relation, Antioxidant Defense, Morpho-physiological and Biochemical Attributes of Black Gram [Vigna mungo (L.) Hepper

Background: Globally, drought stress (DS) incidence in early development and grain-filling stages of crops like black gram has posed a serious constraint to the growth and yield of legume crops. To ensure the food and nutritional security of the rising human population, requisites developing eco-friendly, pro-farmers and cost-effective DS mitigation strategies for imparting yield sustainability to black gram. Methods: In this trial, treatments included control group entailing control (normal watering), water spray (WA, positive control), control+50 mg L-1 K2SO4, control +100 mg L-1 K2SO4, control +150 mg L-1 K2SO4, while drought treatment included drought stress (plant exposed to 15-20% by suspending water supply), water spray (WA, positive control), drought +50 mg L-1 K2SO4, drought +100 mg L-1 K2SO4 and drought +150 mg L-1 K2SO4. Result: The results exhibited that the DS seriously declined plant growth, relative water content and water potential by 24.2% and 39.3%, respectively, inducing higher levels of malondialdehyde (MDA) content and hydrogen peroxide (H2O2) concentration that reduced cell membrane stability, stomatal conductance and photosynthetic rate, than the control. However, the foliar applied K significantly improved plant growth, plant water status, gas exchange and photosynthetic performance, chlorophyll content and antioxidant enzyme activity. Exogenous application of K further reduced lipid peroxidation, cell membrane injury and hydrogen peroxide by 12.7, 17.6 and 8.70%, respectively.