Adverse Effects Of Water Deficit Research Articles

Effect of different timing of water deficit combined with foliar application of ascorbic acid on physiological variables of sour passion fruit

The objective of this study was to evaluate the effects of deficit irrigation treatments during different phenological stages and foliar application of ascorbic acid on gas exchange, photosynthetic pigments, chlorophyll fluorescence, electrolyte leakage, relative water content and yield of ‘BRS GA1’ sour passion fruit. Treatments were distributed in randomized blocks, in a split-plot scheme, with plots consisting of six deficit irrigation treatments, based on crop evapotranspiration – ETc (irrigation with 100% ETc - FULL; irrigation with 50% ETc in the vegetative stage - VEG; flowering stage - FLO; fruiting stage - FRU; successively in the vegetative/flowering stages - VEG + FLO and vegetative/fruiting stages - VEG + FRU) and subplots represented by three concentrations of ascorbic acid - AsA (0, 0.5 and 1.0 mM). Water deficit induces changes in photosynthetic activity across all developmental stages of sour passion fruit, resulting in reduced yield in the period of 160 and 200 days after transplanting. Notably, flowering exhibits the greatest physiological acclimatization to water deficit conditions, albeit with more pronounced losses in the yield. When water deficit occurs during the vegetative and fruiting stages and is coupled with foliar application of ascorbic acid at 0.5 mM, there is an enhancement in the synthesis of photosynthetic pigments in ‘BRS GA1’ sour passion fruit. Overall, foliar application of ascorbic acid at concentrations of 0.5 and 1.0 mM emerges as a viable strategy to mitigate the adverse effects of water deficit on the physiology and yield of sour passion fruit at 200 days after transplanting.

Seed priming with mepiquat chloride and foliar applications of salicylic acid and proline improve the adverse effects of water deficit in cotton (Gossypium hirsutum L.)

Seed priming with mepiquat chloride and foliar applications of salicylic acid and proline improve the adverse effects of water deficit in cotton (Gossypium hirsutum L.)

Water Deficit Severity during the Preceding Year Determines Plant Tolerance to Subsequent Year Drought Stress Challenges: A Case Study in Damask Rose

Damask rose is an important essential oil crop. In the present study, plants were subjected to three different water deficit levels (70, 40, and 10% available water content) for two periods (June–October). Plant phenology, growth, essential oil yield, gas exchange features, membrane stability and major antioxidant defense elements were monitored across two years. Soil water deficit was related to quicker completion of the growth cycle (up to 7.4 d), and smaller plants (up to 49.7%). Under these conditions, biomass accumulation was jointly constrained by decreased leaf area, chlorophyll content, CO2 intake, and photosynthetic efficiency (up to 82.8, 56.9, 27.3 and 68.2%, respectively). The decrease in CO2 intake was driven by a reduction in stomatal conductance (up to 41.2%), while the decrease in leaf area was mediated by reductions in both number of leaves, and individual leaf area (up to 54.3, and 64.0%, respectively). Although the reactive oxygen species scavenging system was activated (i.e., proline accumulation, and enhanced activity of three antioxidant enzymes) by water deficit, oxidative stress symptoms were still apparent. These effects were amplified, as soil water deficit became more intense. Notably, the adverse effects of water deficit were generally less pronounced when plants had been exposed to water severity during the preceding year. Therefore, exposure to water deficit elicited plant tolerance to future exposure. This phenotypic response was further dependent on the water deficit level. At more intense soil water deficit across the preceding year, plants were less vulnerable to water deficit during the subsequent one. Therefore, our results reveal a direct link between water deficit severity and plant tolerance to future water stress challenges, providing for the first time evidence for stress memory in damask rose.

Beneficial Microorganisms Affect Soil Microbiological Activity and Corn Yield under Deficit Irrigation

Water scarcity is one of the main factors that decrease the growth and productivity of corn, since it negatively affects gas exchange and the general metabolism of the crop. The use of beneficial microorganisms (BM) has been considered a potential attenuator of water stress. This study aimed to evaluate the effect of BM and water deficit on growth, gas exchange, grain yield, and soil microbial activity. A field experiment was carried out, in which the treatments were composed of a 2 × 4 factorial scheme, corresponding to two irrigation levels (100% of ETc and 50% of ETc) and to four treatments (T) referring to the soil inoculation with BM (C: control; T1: Bacillus amyloliquefaciens + Azospirillum brasiliense; T2: B. subtilis; and T3: A. brasiliense). The evaluations were carried out in the flowering phase (plant growth, gas exchange, and foliar nitrogen content) and at the end of the plant cycle (grains yield, mineral nitrogen, and microbiological activity). The 50% reduction in irrigation depth severely restricted corn growth and gas exchange and decreased the grain yield by 38%. The water deficit increased the protein content in the grains and the concentration of mineral nitrogen in the soil when the plants were inoculated with BM. Under water stress, inoculation with BM increased corn productivity by 35% and increased soil microbial activity. The inoculation of plants with BM, either in combination (Bacillus amyloliquefaciens + A. brasiliense) or alone (B. subtilis), attenuated the adverse effects of water deficit in maize.

Spermine mitigates the adverse effects of water deficit by strengthening antioxidant enzymes and anthocyanin pathway-related gene expressions

Water deficit is regarded as one of the worst causes of low agricultural productivity. It disrupts morphophysiological and biochemical processes in plants. In the current research, spermine effectively induced defense responses to abiotic stresses. The foliar spray with spermine ameliorated the adverse impacts of water deficit on zinnia plants (Zinnia elegans L.). The aim of this study was to investigate the effects of foliar spraying of spermine on growth characteristics, enzyme antioxidants activity, gas exchange and genes expression related to the anthocyanin biosynthesis pathway (ABP) of zinnia plants grown under water-deficit treatments. The evaluations involved measuring growth characteristics (i.e. height, flower biomass, total plant biomass, fresh and dry plant weight, flower diameter, and vase life), photosynthesis and gas exchange (stomata conductivity, intracellular CO2, transpiration), water use efficiency (WUE), lipid peroxidation (MDA), enzymatic activity (POD and APX) and genes expression related to ABP (CHS, CHI, F3H, F3'H, ANS, 3GT, DFR and AT2). Spermine mitigated the adverse impacts of severe water-deficit on the growth characteristics, flower longevity, and WUE. Our results showed that spermine boosted antioxidant enzymes activity and reduced lipid peroxidation of zinnia under severe and moderate water-deficit. Real-time PCR analysis of genes related to ABP revealed that the early (CHI, CHS and F3H) and late (ANS and 3GT) biosynthetic genes were promptly induced by both water deficit and spermine treatments. We showed that DFR and AT2 genes were induced by different levels of drought stress, while the F3'H gene was expressed only by the exogenous application of spermine. Spermine decreased the MDA content and enhanced the water-deficit tolerance of zinnia plants by maintaining morphological integrity, gaseous exchange, chlorophyll index, WUE, APX, and POD enzyme activities, as well as gene expressions related to ABP. Spermine (3 mM) can be applied as a foliar treatment to alleviate the adverse impacts of water-deficit in zinnia plants.

Mycorrhizal Colonization Modulates the Essential Oil Profile and Enzymatic and Non-Enzymatic Antioxidants to Mitigate the Adverse Effects of Water Deficit in Salvia subg. Perovskia.

Among traditional Iranian herbs, Perovskia species (a subgenus of Salvia), while being valued ornamentals, are also studied for numerous potential pharmacological and therapeutic aspects. The current study was conducted to assess the effectiveness of two species of arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae and Rhizophagus intraradices, separately and in combination, in terms of the essential oil content and compositions along with the enzymatic and non-enzymatic antioxidants in Salvia abrotanoides and S. yangii in response to three levels of irrigation, including 100% FC as well-watered, 75% FC (moderate irrigation deficit), and 50% FC (severe irrigation deficit). In both species, essential oil content, enzyme antioxidant activities, total phenolics, and flavonoids were increased significantly with the severity of stress; this increase was more pronounced in mycorrhizal inoculated herbs. Furthermore, leaf phosphorus concentration, relative water content, chlorophylls a and b, and total carotenoids decreased in parallel with reducing soil moisture; albeit, AMF inoculation improved the stress symptoms under increasing severity of water restriction compared with their control conditions. In addition, the percentage of root colonization was positively correlated with the relative water content (RWC) and leaf phosphorus concentration. Taking into account the essential oil groups, AMF colonization elevated some essential oil components, such as oxygenated monoterpenes, 1,8-cineol, camphor, and borneol, whereas the main sesquiterpenes, including E-β-caryophyllene and α-humulene, remarkably decreased. Taken together, these findings highlighted the role of symbiosis with AMFs in increasing the tolerance of water deficit stress in S. abrotanoides and S. yangii and improving their essential oil composition.

Plant growth promoting microorganisms (PGPM) as an eco-friendly option to mitigate water deficit in soybean (Glycine max L.): Growth, physio-biochemical properties and oil content

Drought, as an important challenge in Iran, affects all growth indicators for plants. Application of plant growth promoting microorganisms (PGPM) can reduce the detrimental effects of water deficit on plants. Two separate field experiments were conducted at the Tehran and Hashtrood sites, Iran in 2019 to study the influences of Azotobacter chroococcum (Az) and Piriformospora indica (Pi) or Az + Pi on growth, physio-biochemical properties and oil content of soybean (Glycine max L.) under water deficit conditions. Although water deficit dramatically reduced the plant height, percent vegetation cover and relative water content (RWC), plots treated with Az and Pi exhibited higher performance mentioned traits at both sites. Besides, co-inoculation of Az and Pi increased proline in Tehran (48.85 and 29.24% in leaf and root, respectively) and Hashtrood (46.91 and 48.91% in leaf and root, respectively) under severe water deficit. Accumulation of glycine betaine, soluble sugars and proteins increased for plots which received Az and Pi. Under severe water deficit conditions, the co-inoculation with Az and Pi enhanced the oil content of soybean by 12.87 and 9.37% at Tehran and Hashtrood sites respectively. Application of Az and Pi resulted in reducing the adverse effects of water deficit on oil quality of soybean by increasing the linoleic and linolenic acid in oil. Moreover, inoculation of soybean with Az and Pi can provide drought tolerance by improving ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD) and peroxidase (POX) activity. However, co-inoculation with Az and Pi was generally more effective in the alleviation of water deficit detrimental effects than sole inoculation with Az and Pi. Consequently, it can be a good approach for improving tolerance, growth and oil production of soybean under water deficit conditions.

USING FUEL LYSIMETERS

This paper presents data on the effects of cotton maintenance on cotton yield under lysimeter conditions in reducing the adverse effects of water deficit. New, promising and zoned cotton varieties were analyzed by taking soil samples at the end of the vegetation period after applying mineral fertilizers, irrigation, and inter-row tillage. That is, the amount of humus in the soil compared to the beginning of the period of operation, at the end of the period of operation in the lysimeter with new varieties in the lysimeter with the regionalized Bukhara-8 and Sultan varieties, is explained.

Potency of Titanium Dioxide Nanoparticles, Sodium Hydrogen Sulfide and Salicylic Acid in Ameliorating the Depressive Effects of Water Deficit on Periwinkle Ornamental Quality

In this study, the optimal concentration of sodium hydrosulfide (NaSH), salicylic acid (SA), and titanium dioxide nanoparticles (TiO2NPs), and their relative effectiveness on alleviating the adverse effects of water deficit on ornamental quality, were investigated in periwinkle. Plants were cultivated under three water deficit levels (80, 50, and 20% available water content) and received two foliar applications of TiO2NPs (0, 0.5 and 1 mM), NaSH (0.5 and 1 mM), or SA (1 and 2 mM). Water deficit deteriorated ornamental quality, amplified the risk of buckling (lower stem strength) and suppressed longevity. It decreased both light interception (leaf area) and carbon assimilation. Besides impaired hydration status, water-stressed plants underwent oxidative damage as indicated by reduced chlorophyll content, elevated membrane degradation, and lipid peroxidation. Spray treatments improved all traits, besides stem strength and proline content. Additionally, they enhanced carotenoid content and the activities of catalase and peroxidase. Their relative effectiveness (TiO2NPs > NaSH > SA) and optimal concentration (i.e., 0.5 mM (TiO2NPs, NaSH), and 1 mM (SA)) was independent of water deficit level. In conclusion, this study provides practices for improved ornamental quality and longevity independently of water availability, with their positive effect being stronger under irregular or limited water supply.

Biofilm forming rhizobacteria affect the physiological and biochemical responses of wheat to drought

Plant growth promoting rhizobacteria (PGPR) can attenuate the adverse effects of water deficit on plant growth. Since drought stress tolerance of bacteria has earlier been associated to biofilm formation, we aimed to investigate the role of bacterial biofilm formation in their PGPR activity upon drought stress. To this end, a biofilm-forming bacterial collection was isolated from the rhizospheres of native arid grassland plants, and characterized by their drought tolerance and evaluated on their plant growth promoting properties. Most bacterial strains formed biofilm in vitro. Most isolates were drought tolerant, produced auxins, showed 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity and solubilized mineral phosphate and potassium, but at considerably different levels. Greenhouse experiments with the most promising isolates, B1, B2 and B3, under three levels of water deficit and two wheat varieties led to an increased relative water content and increased harvest index at both moderate and severe water deficit. However, the bacteria did not affect these plant parameters upon regular watering. In addition, decreased hydrogen peroxide levels and increased glutathione S-transferase activity occurred under water deficit. Based on these results, we conclude that by improving root traits and antioxidant defensive system of wheat, arid grassland rhizospheric biofilm forming bacilli may promote plant growth under water scarcity.

Impact of melatonin and tryptophan on water stress tolerance in white lupine (Lupinus termis L.).

Melatonin has been identified as a signal molecule that regulates plant responses to different abiotic and biotic stresses. Melatonin (MT) and its precursor tryptophan (Try) have a major role in improving plant stress tolerance to different environmental stresses such as water deficiency. The rapid increase in the Egyptian population caused insufficient protein sources, especially those of animal origin, in their diet. The possible solution is to augment the diet with legumes such as white lupine which are relatively rich in protein. Thus, the current experimental work was carried out to find changes in growth, biochemical aspects and yield quantity and quality of white lupine plant with sprayingof both MT and Try at different concentrations on plant shoot under water deficit stress conditions. Results showed that water deficit (75 or 50% of water irrigation requirements; WIR) caused significant reduction in growth, photosynthetic pigments, indole acetic acid and yield compared with those received 100% WIR. Seed yield significantly decreased (p < 0.05) by 26.98 and 41.64% by decreasing WIR to 75 and 50%. The decrease was accompanied by significant increase in phenolic contents, hydrogen peroxide, lipid peroxidation and some antioxidant enzymes, while nitrate reductase enzyme was decreased. However, external application of either MT or Try significantly alleviated the adverse effects of water deficit (growth suppression), since MT or Try-treated plants recovered more quickly than untreated plants. Moreover, MT or Try-treated plants had higher photosynthetic pigments, indole acetic acid, phenolic, as well as yield quantity and quality under the three WIR as compared with untreated plants. Melatonin treatment at 100µM and Tryptophan at 200µM increased weight of seeds/plant by 78.29 and 52.19%, 71.49 and 43.78% and 41.21 and 13.07% in plants irrigated with 100, 75 and 50% WIR, respectively. Exogenous MT and Try significantly reduced hydrogen peroxide and malondialdehyde content, while markedly increased the activities of antioxidant enzymes and nitrate reductase under different WIR. Finally, the current study concluded that MT and Try treatments alleviated the detrimental effects of water deficiency and accelerated the recovery mainly via improving white lupine plants tolerance in forms of enhancing photosynthetic pigments, indole acetic acid, phenolic and antioxidant capacity.

Investigation of improving the drought tolerance in persian petunia (Petunia sp.) by exogenous application of salicylic acid and gibberellic acid

Plants respond to water deficit through several mechanisms. Among which, plant hormones play an important role in induction to abiotic stress tolerance. To bring this issue closer, an experiment was conducted to examine whether salicylic acid (SA) and gibberellic acid (GA3) exogenous applications through foliar spray could alleviate detrimental effects of water deficit on Persian petunia. Treatments consisted of water stress in three levels: 100% field capacity (F.C.) as control, 50, and 25% F.C linked with different concentrations of GA3 and SA sprayed at four levels (0, 100, 200 and 300 mg L–1). Results showed that the dry and fresh biomass, leaf area, photosynthetic pigments levels, relative water content (RWC) and the total number of flowers were significantly (P≤0.01) reduced in response to water deficit. However, free proline concentration and root-to-shoot ratio significantly increased in stressed plants. Plants subjected to severe water stress (25% F.C.), exhibit about 66% stomatal conductance rate lower than the plants grown at 100% F.C. The results showed that SA-treated plants exhibited reduced negative effect of water stress on most of the qualitative and quantitative attributes compared to control, while GA3 application had little impact on studied traits. Importantly, stomatal conductance and RWC were improved in water-stressed plants treated with SA. Moreover, SA-treated plants produced more flowers at all water deficit levels compared to GA3 sprayed plants. It can be concluded that Persian petunia plants respond to water deficit through adaptive changes at biochemical and morphological levels and that adverse effects of water deficit could be alleviated by exogenous application of SA.

Phosphorus deficiency enhances water deficit impact on some morphological and physiological traits in four faba bean (&lt;em&gt;Vicia faba L.&lt;/em&gt;) varieties

Moroccan soils, generally present low available phosphorus (P) levels which occur in almost all arid and semi-arid regions. Faba bean is one of the most significant crops in Morocco and is influenced by these constraints that affect its nutrient uptake and nitrogen fixation capacity and hence plants development. Therefore, we evaluated the response of four Vicia faba varieties - Aguadulce (Ag), Alfia (Al), Luz de Otono (LO) and Reina Mora (RM) -, grown under biological nitrogen fixation to water deficit and two phosphorus levels. The trial was conducted under greenhouse conditions and water stress was induced by keeping pots at 40% substrate field capacity (FC) versus 80% FC for the controls while phosphorus deficiency treatment consisted in the application of 25 μmol P plant−1 week−1 versus 125 μmol P plant−1 week−1 for sufficient P treatment. The results revealed a significant effect of water deficit and phosphorus deficiency either alone or combined on plants dry weights, leaf water parameters and nutrient concentrations. However sufficient phosphorus supply mitigated the adverse effects of water deficit on faba bean. We noticed significant differences between the studied varieties. Ag showed high performance concerning dry weights (1.25 g and 1.88 g plant–1 respectively for shoot and root) and high concentration of nitrogen N (4.7%) and P (0.27 mg g–1 DW) and was then qualified as the most tolerant variety to water deficit combined with P limitation. While RM was the least tolerant variety, as it showed the lowest dry weights (0.51 g and 1.4 g plant–1 respectively for shoot and root) and concentration (2.74% and 0.19 mg g–1 DW respectively for N and P). The tolerance was related to the ability to ensure efficient osmoregulation by glycine betaine accumulation, to keep leaf water balance and cell membrane stability that contribute together with adequate symbiotic nitrogen fixation to plant growth performance under combined stresses.&#x0D; Highlights - Varieties tolerant to low phosphorus and water deficiency are needed in arid and semi-arid regions with low P. - Phosphorus nutrition is advantageous for mitigating the effect of water deficit on faba bean (Vicia faba) plants and conversely, deficient P supply reduces resilience to water deficit. - The faba bean variety Aguadulce showed high tolerance to the combined effect of water deficit and phosphorus deficiency in terms of growth, leaf water potential, stomatal conductance, membrane permeability and glycine betaine accumulation. - Reina Mora was the least tolerant variety to water deficit combined with P limitation. - Combined limitation of water and phosphorus induced accumulation of glycine betaine in leaves.

Integrated application of biochar and bio-fertilizer improves yield and yield components of Cowpea under water-deficient stress

A low amount of organic matter and insufficient irrigation are two main challenges facing successful crop production in arid and semiarid regions. Application of biochar as an organic amendment to soil not only can help increase organic matter in soil, but also may alleviate adverse effects of water deficit on plant growth and yield production. To test this hypothesis, a two-year field experiment was conducted to assess the effect of sugarcane biochar on yield and yield components of cowpea in water-deficient soil. Treatments consisted of two levels of seed treatment with nitroxin, three levels of biochar application (0, 4, and 8 ton/ha), and a threelevel irrigation regime (60, 90, and 120 mm from evaporation pan class A), laid out in a split-factorial design. Results showed that the seed number per plant was significantly higher in cowpea when grown with biochar, possibly due to the relief of water-deficient stress and higher phosphorus and potassium content. Biomass production of cowpea declined under a severe waterdeficit condition (ir3) compared to normal irrigation (ir1) in 2018 and 2019, decreasing by 39% and 42%, respectively. The maximum biomass obtained from application of 8 ton/ha biochar reached 617.43 and 664.92 g/m2 in 2018 and 2019, respectively. Seeds treated with nitroxin exhibited 10% and 8% greater biomass production in 2018 and 2019 as compared with control treatments. Seed yield increased with the addition of biochar to soil under all irrigation regimes; however, the maximum seed yield of 266.46 and 275.36 g/m2 was observed when there was no water-deficient stress condition and application of 8 ton/ha biochar in 2018 and 2019, respectively.

ANTITRANSPIRANTS APPLICATION FOR IMPROVING THE BIOCHEMICAL CHANGES OF BARLEY UNDER WATER STRESS

Field experiment carried out at Nubaria Agricultural Research station, National Research Centre, Egypt to study the role of antitranspirants application{Salicylic Acid (SA), K2SO4 and MgCO3} in alleviating drought-induced changes of some sensitive barley varieties. Foliar application of the antitranspirants compounds registered a positive effect on plant pigment, relative water content, nutrient contents and proline accumulation under water stress condition especially after spraying SA. The barley varieties Tamellalet and Giza 125 highly responded to antitranspirants application especially after foliar application of SA and MgCO3 over remaining varieties. Application of MgCO3 produced the most balanced nutrients for Tamellalet variety under normal irrigation system whereas, under stress condition. The data together provide some indication that Ksar-Megrine and Tombari cultivars has more efficient H2O2 scavenging machinery at least in peroxisomes under drought stress. Application of antitranspirants treatments led to significant increase of CAT, POD and GR activity which could alleviate the adverse effect of water stress on barley leaves. Results concluded that antitranspirants application could be effective for barley production in arid and semi-arid areas to reduce the adverse effects of water deficit.

Effect of Wheat Straw as a Cover Crop on the Chlorophyll, Seed, and Oilseed Yield of Trigonella foeunm graecum L under Water Deficiency and Weed Competition.

The effects of water stress on fenugreek crops are well documented. However, little is known about how these plants respond to water deficits under a soil-mulching system when the surface is protected. Therefore, the current research aims to demonstrate the possibility of reducing the impact of water stress and weed competition on the fenugreek crop through the use of wheat residues as a cover crop on the soil surface. A field experiment was carried out during the winter season (2016–2017) using a split-plot design arrangement with three replicates. The experiments included four levels of water deficit, which consisted of a 40% depletion treatment as a control plot, and 50%, 60%, and 70% depletion from the field capacity (DFC) for the other studied fields. The subplot division consisted of mulching the soil with wheat residues. The results demonstrated that soil-mulching systems and a water deficit are able to impact the fenugreek yield of seed and oil. Additionally, soil mulching led to a decrease in weed density and biomass, chlorophyll content, and biological yield. Although high water deficit (70% DFC) led to yield and growth reduction, the use of wheat residue as a cover crop moderated the effect of a strong water deficit on plants and showed clear reduction of weed growth. Therefore, the results suggest that soil mulching can mitigate the adverse effects of water deficit by conserving soil moisture and decreasing weeds, which can be considered an acclimation mechanism under water-deficit conditions to avoid yield loss. Moreover, the allelopathic effects of wheat residue were observed on fenugreek crops subjected to irrigation after depleting 40% soil water moisture, but these effects disappeared within 90 days of sowing. We conclude that these results can help future agricultural planning and systems in order to increase productivity, reduce irrigation costs, and conserve soil quality.

Physiological responses of spring wheat to 5-aminolevulinic acid under water stress applied at seedling stage

5-Aminolevulinic acid relieves the effects of environmental stresses in plants. Therefore, the aim of our study was to evaluate the effects of 5-aminolevulinic acid (5-ALA) on the activity of the photosynthetic apparatus in spring wheat. Other analyzed parameters involved plant height, relative turgidity, membrane status, and chlorophyll level. The plant material consisted of three genotypes of spring wheat (J × Z, R × K, K × M), subjected to mild and severe drought in the early phase of vegetative development. 5-ALA showed a positive effect on the activity of the photosynthetic apparatus under water stress. The relieving action of 5-ALA on PSII was the most evident in J × Z genotype during severe soil drought. 5-ALA positively influenced the maximum photochemical efficiency of PSII (Fv/Fm), the overall performance index of PSII photochemistry (PI) and the effective quantum field of PSII (φEo). In the same genotype, the investigated acid stimulated light energy absorption (ABS/CSm), and enhanced the amount of excitation energy trapped in PSII reaction centers (TRo/CSm) and the amount of energy used for electron transport (ETo/CSm). Moreover, 5-aminolevulinic acid showed its potential to overcome the adverse effects of water deficit on Triticum aestivum L. by increasing plant growth, relative turgidity, and chlorophyll content and reducing the degree of damage to cell membranes at the early phase of vegetative development.

Salicylic acid induced changes in physiological traits and essential oil constituents in different ecotypes of Thymus kotschyanus and Thymus vulgaris under well-watered and water stress conditions

Drought stress is one of the most important environmental stresses limiting the growth and effectiveness of plants, however, exogenous application of salicylic acid (SA) as a signaling molecule may counteract the adverse effects of stress on plant productivity. The present study was designed to determine the effects of different concentrations of SA (0, 100, and 150 ppm) on morpho-physiological traits and essential oil constituents in different ecotypes of two thymus species (Thymus vulgaris and T. kotschyanus) under well-watered and water stress conditions. The results demonstrated that foliar application of SA results in better efficacy of thyme in water stress conditions by reducing the content of cellular injury indices such as hydrogen peroxide (H2O2), malondialdehyde (MDA), and improving growth and metabolite attributes including root and shoot dry weight, total chlorophyll, leaf carotenoids, proline, and total soluble carbohydrate contents. Treatment with SA under both water availability conditions led to the improvement of essential oil content in some ecotypes, especially in Zanjan ecotype of T. kotschyanus. Furthermore, gas chromatography–mass spectrometry analysis of essential oils exhibited that the thymol, carvacrol, linalool, p-cymene, and γ-terpinene were identified as the main components of essential oils under employed treatments. SA application at 100 ppm was increased both essential oils content and compositions as well as thymol content by 93.39% in T. kotschyanus (Zanjan ecotype) under both well-watered and water stress conditions. Appropriate concentration of SA significantly reduced the adverse effects of water deficit on thyme species through improved morphological and physiological parameters, and increased the quantity and quality of essential oils.

Dynamics of endogenous hormone regulation in plants by phytohormone secreting rhizobacteria under water-stress

Although the physiological benefits of plant growth promoting rhizobacteria (PGPR) to plants are well known, the precise mechanisms that make these PGPR such wonderful friends of plants under adverse environmental conditions are still under investigation. We have previously reported that one such PGPR, Pseudomonas putida GAP-P45 ameliorates the adverse effects of water deficit in Arabidopsis thaliana by upregulating proline turnover and polyamine biosynthesis (Ghosh et al. Ann Microbiol 67:655–668, 2017; Sen et al. Plant Physiol Biochem 129:180–188, 2018). In this study, we investigated the impact of this phytohormone secreting strain on the regulation of endogenous phytohormone (abscisic acid, auxin, cytokinin and gibberellic acid) modulation in A. thaliana under normal and water stress conditions. We analyzed the content of all four phytohormones secreted by the bacteria in the nutrient medium as well as in the roots and shoots (separately) of the inoculated plants at three different days, post treatments. We observed that, while water stress increased the accumulation of abscisic acid and decreased the content of auxin and cytokinin in shoots and roots; the level of gibberellic acid decreased in shoots but increased in roots due to stress. Inoculation with GAP-P45 under water stress effectively reversed the trends of phytohormone accumulation, making their levels similar to the non-stressed, non-inoculated control plants. This happened despite there being no change in the water-potential of the medium due to GAP-P45 inoculation. We also observed that the pattern of phytohormones secreted by the PGPR varied depending on composition of nutrient media and culture conditions. We conclude that P. putida GAP-P45 alleviates water stress in A. thaliana by altering the endogenous hormone accumulation and re-distribution in both roots and shoots without causing any change to the water-potential of the medium.

Efficacy of ascorbic acid as a cofactor for alleviating water deficit impacts and enhancing sunflower yield and irrigation water–use efficiency

Ascorbic acid (AsA) is considered as one of the most important and profusely known occurring water soluble antioxidants in plants, however, it is not well known to what extent this antioxidant might contribute in alleviating the adverse effects of water deficit on plant growth, yield and irrigation water use efficiency (IWUE). In attempt to clarify whether exogenous application of AsA could alleviate the adverse effects of water deficit on sunflower plants, two seasons (2014 and 2015) of field experimentation were conducted using six combinations of two AsA levels (AsA(–) and AsA(+), i.e. zero and 450 ppm AsA, respectively) and three irrigation water amounts (I100, I85, and I70, i.e. 100, 85 and 70% of crop evapotranspiration, respectively). Under water shortage, leaf chlorophyll content increased but proline content lowered in AsA–treated plants compared to the untreated ones. Lower values of LAI, head weight, seed yield ha–1, and oil yield ha–1 were recorded with decreasing water supply, while the highest values were gained when supplying plants with sufficient water (I100) plus application of AsA (i.e. AsA(+)), i.e., I100AsA(+). Plants under the latter treatment grew well and possessed higher yields compared to that of suffering from deficit water without AsA application, i.e. I85AsA(–) or I70AsA(–). Head weight and seed as well as oil yields ha–1 produced in 2014 season under sufficient water supply without AsA application (I100AsA(–)) could be achieved under moderately water–stressed condition in conjunction with applying AsA (I85AsA(+)). Implication of AsA tends to minimize the reduction in seed yield due to insufficient water supply, where I85AsA(+) and I85AsA(–), each saved same percentage of water (15.0%) but the reduction in seed yield associated the former treatment was less than that under the latter one. On the other hand, IWUE reached the maximal values in both seasons under I100AsA(+) treatment but, however, without marked differences in comparing to those recorded I85AsA(+) in 2014 season. Moreover, the differences in IWUE values exhibited by I100AsA(–) and I85AsA(+) did not reach the P < 0.05 level of significance in 2015 season, which could reveal the positive role of AsA in alleviating water stress.