Plant Relative Water Content Research Articles

Salt stress alleviation in Calendula officinalis L. by potassium nanoparticles application and Streptomyces bacteria inoculation

The current study was conducted to mitigate salt stress on Calendula officinalis L. plants using Streptomyces (Sm) bacteria alone or in combination with potassium nanoparticles (K NPs). Based on the results, morphometric characters, leaf SPAD and relative water content in plants treated with Sm bacteria and K NPs increased compared to the nontreated control under salinity stress. However, leaf ionic leakage, malondialdehyde (MDA) and hydrogen peroxide (H2O2) content decreased considerably in these treated plants. Also, under salt stress, the activity of antioxidant enzymes was higher in Sm bacteria + K NPs -treated plants than in controls. In all plants, endogenous indole acetic acid (IAA) content increased compared to plants grown in non-saline conditions. Inoculated plants reflected a relative increase in IAA by about 28% over the uninoculated plants. The highest amount of abscisic acid (ABA) and putrescine (Put) was related to those plants treated with Sm bacteria + K NPs, which the amounts were 43% and 47% higher than in control plants, respectively. Application of Sm bacteria + K NPs had a helpful outcome on both macronutrients (N-NO- 3, P, K and Mg) and micronutrients (Fe, Zn, and Mn) of vines leaves. In general, the inoculation of Sm bacteria + K NPs application by improving the uptake of nutrients, regulating phytohormones and increasing the antioxidant enzymes activity resulted in salinity tolerance improvement in calendula plants.

The biochemical properties of Satureja species affected by micronutrients, genotype, and locations in drought stress conditions

Medicinal plants, as important sources of secondary metabolites, are used for treating different diseases. It is accordingly pertinent to find methods, which may improve their growth and quality in different conditions including variable stresses. It was hypothesized micronutrients use and suitable genotypes may improve Satureja growth and quality in drought stress conditions. The objective of this study was to investigate the effects of drought stress (irrigating plants each 3 (A1), 6 (A2) and 9 days (A3)), micronutrients (Mn and Cu at 0 (M1), 20 (M2) and 40 mgL−1 (M3)), and field location (Isfahan (F1) and Golpayegan (cooler) (F2), Isfahan province, Iran) on the biochemical properties of different Satureja species including S. bakhtiarica, S. khuzestanica and S. mutica. The experimental treatments significantly affected the measured parameters including nodule number, essential oil, antioxidant activity, proline, Mn and Cu contents, and relative water content. Although Cu and Mn, enhanced plant biochemical properties, especially in M2, in some cases, the two micronutrients, unfavorably affected plant properties in M3. The responses of genotypes were different in the two research fields and S. bakhtiarica performed better in F2. The highest essential oil was resulted by A2. The two micronutrients improved plant responses in drought stress by increasing nodule number (148 %), and essential oil yield (143 %) and decreasing plant relative water content and conserving plant water. The use of Mn and Cu is recommendable for planting Satureja species in drought stress conditions, as the two nutrients may enhance plant tolerance by increasing proline production and antioxidant activities.

Improvement of morphophysiological and anatomical attributes of plants under abiotic stress conditions using plant growth-promoting bacteria and safety treatments.

Drought and salinity are the major abiotic stress factors negatively affecting the morphophysiological, biochemical, and anatomical characteristics of numerous plant species worldwide. The detrimental effects of these environmental factors can be seen in leaf and stem anatomical structures including the decrease in thickness of cell walls, palisade and spongy tissue, phloem and xylem tissue. Also, the disintegration of grana staking, and an increase in the size of mitochondria were observed under salinity and drought conditions. Drought and salt stresses can significantly decrease plant height, number of leaves and branches, leaf area, fresh and dry weight, or plant relative water content (RWC%) and concentration of photosynthetic pigments. On the other hand, stress-induced lipid peroxidation and malondialdehyde (MDA) production, electrolyte leakage (EL%), and production of reactive oxygen species (ROS) can increase under salinity and drought conditions. Antioxidant defense systems such as catalase, peroxidase, glutathione reductase, ascorbic acid, and gamma-aminobutyric acid are essential components under drought and salt stresses to protect the plant organelles from oxidative damage caused by ROS. The application of safe and eco-friendly treatments is a very important strategy to overcome the adverse effects of drought and salinity on the growth characteristics and yield of plants. It is shown that treatments with plant growth-promoting bacteria (PGPB) can improve morphoanatomical characteristics under salinity and drought stress. It is also shown that yeast extract, mannitol, proline, melatonin, silicon, chitosan, α-Tocopherols (vitamin E), and biochar alleviate the negative effects of drought and salinity stresses through the ROS scavenging resulting in the improvement of plant attributes and yield of the stressed plants. This review discusses the role of safety and eco-friendly treatments in alleviating the harmful effects of salinity and drought associated with the improvement of the anatomical, morphophysiological, and biochemical features in plants.

Humic Acid Mitigates Drought Stress in Tomato

Drought stress, one of the most important abiotic stresses, severely limits global crop production. To increase tolerance to this stress, environmentally friendly practices are emphasised. Humic acid, one of the most important natural biostimulants, has positive effects on plant growth and yield. Recently, it has also been reported to play an important role in resistance to various abiotic stresses. However, many physiological and molecular mechanisms by which humic acid confers drought resistance have not been fully elucidated. Therefore, the effects of humic acid application on different morphological and physiological stress indicators and some antioxidative enzyme gene expressions of tomato seedlings under drought stress conditions were investigated in this study. It was found that drought stress decreased shoot fresh/dry weight, root fresh/dry weight, shoot and root length, chlorophyll and relative water content of plants by 67%, 56%, 31%, 38%, 22%, 20%, 15% and 25%, respectively. Humic acid application significantly increased these parameters, while reducing ion leakage, MDA and proline levels. The antioxidant enzyme gene expression of tomato seedlings under drought conditions showed no significant difference in SOD and APX gene expression, whereas CAT gene expression increased and GR gene expression decreased with humic acid application. Our results showed that humic acid application interacted with stress-related antioxidant enzyme gene expression and may be effective in reducing drought stress.

Effectiveness of manganese foliar spraying to mitigate salt stress in ornamental cabbage: Insights into morphological, physiological biochemical adaptations and mTERF gene responses

Salinity has been the subject of research for many years. However, salt stress studies on ornamental plants have increased recently. It is very important to determine the responses of bedding flowers, which are widely used in landscaping, to salt stress, and to strengthen the defense against stress. Ornamental cabbage (Brassica oleareacea L.) is widely used bedding flower in winter. The aim of this study was determining the effects of foliar application of manganese (Mn) on morphological, physiological, biochemical, and molecular parameters in ornamental cabbage ('Pigeon Purple F1′) under salt stress. Plants were irrigated with 4 different irrigation solutions which containing 0 [control], 75, 150 and 300 mM NaCl concentrations and Mn (4000 ppm) was sprayed to the leaves on 0, 7th and 14th days of the salt stress application. The application of manganese did alleviate the negative effects of salinity on shoot fresh weight and shoot dry weight in 75 mM NaCl plants. Ion leakage for 0 and 75 mM NaCl decreased with foliar spraying of Mn, but relative water content of plants did not change with Mn application. Lipid peroxidation (7.6 %) and H2O2 (hydrogen peroxide) (21.3 %) contents increased with Mn foliar spraying. Superoxide dismutase (SOD) and peroxidase activity did not change with Mn application under salinity. The highest catalase activity obtained from 150 mM (13.81 Unit g−1 leaf) and 300 mM NaCl (16.00 Unit g−1 leaf) which treated with Mn. Root Na content was lower with Mn-treated plants when compared control plants under salt stress. Foliar spraying of Mn significantly increased the K content of the plants. Furthermore, Na/K and Na/Ca ratios which are important indicators for salt stress also decreased by Mn application under saline conditions. In addition, m TERF genes were measured by using the q-RT PCR. In most cases, mTERF expression was slightly induced by salinity, while manganese application generally led to downregulation of mTERFs.

Host- and virus-induced gene silencing of HOG1-MAPK cascade genes in Rhizophagus irregularis inhibit arbuscule development and reduce resistance of plants to drought stress.

Arbuscular mycorrhizal (AM) fungi can form beneficial associations with the most terrestrial vascular plant species. AM fungi not only facilitate plant nutrient acquisition but also enhance plant tolerance to various environmental stresses such as drought stress. However, the molecular mechanisms by which AM fungal mitogen-activated protein kinase (MAPK) cascades mediate the host adaptation to drought stimulus remains to be investigated. Recently, many studies have shown that virus-induced gene silencing (VIGS) and host-induced gene silencing (HIGS) strategies are used for functional studies of AM fungi. Here, we identify the three HOG1 (High Osmolarity Glycerol 1)-MAPK cascade genes RiSte11, RiPbs2 and RiHog1 from Rhizophagus irregularis. The expression levels of the three HOG1-MAPK genes are significantly increased in mycorrhizal roots of the plant Astragalus sinicus under severe drought stress. RiHog1 protein was predominantly localized in the nucleus of yeast in response to 1M sorbitol treatment, and RiPbs2 interacts with RiSte11 or RiHog1 directly by pull-down assay. Importantly, VIGS or HIGS of RiSte11, RiPbs2 or RiHog1 hampers arbuscule development and decreases relative water content in plants during AM symbiosis. Moreover, silencing of HOG1-MAPK cascade genes led to the decreased expression of drought-resistant genes (RiAQPs, RiTPSs, RiNTH1 and Ri14-3-3) in the AM fungal symbiont in response to drought stress. Taken together, this study demonstrates that VIGS or HIGS of AM fungal HOG1-MAPK cascade inhibits arbuscule development and expression of AM fungal drought-resistant genes under drought stress.

Influence of Salicylic and Succinic Acids on the Indicators of Growth and Photosynthesis and the Content of Chlorophyll in Wheat Plants Grown under Water Deficiency

In the conditions of climate warming, the frequency and intensity of droughts have increased, therefore, the development of methods that increase the resistance of crops to water scarcity is of great importance. The aim of the work is to study the effect of salicylic and succinic acids on growth indicators, photosynthetic activity indicators and on the content of pigments in the leaves of plants grown under conditions of irrigation and water scarcity. Wheat plants were grown under laboratory conditions. The seeds were pre-soaked in distilled water (control), in a solution of 0.05 mM salicylic acid or in a solution of 0.05 mM succinic acid. After the appearance of the first roots on the 3rd day, the germinated seeds were transferred to 200 ml vegetative vessels filled with soil and grown at 22-24C in natural light and daily watering. On day 5, the plants were divided into groups watering and water shortage. The water shortage group was stopped watering until the end of the experiment. On day 11, the indicators of the maximum and effective quantum yield of photosystem II, photochemical and non-photochemical quenching and electron flux density were determined using a FRAME-fluorimeter. On the 16th day of growing plants, the quantitative content of chlorophyll a and b and carotenoids was determined, the relative water content in shoots and roots was calculated. The relative water content in plants hardly changed when treated with acids under irrigation conditions, but in case of water deficiency, treatment with succinic acid reduced the water content in the root by 6%. In conditions of lack of moisture, acid treatment increased the effective quantum yield of photosystem II, the photochemical quenching coefficient of chlorophyll and the electron flux density by an average of 17-20%. Under irrigation conditions, treatment with salicylic and succinic acids caused a decrease in the content of chlorophyll a (by 11 and 32%, respectively), carotenoids (by 57 and 32%) and an increase in the content of chlorophyll b (by 49 and 23%). When treated with succinic acid, the total content of chlorophyll a + b decreased by 14%. In conditions of water deficiency, treatment with salicylic acid increased the relative content of chlorophylls and carotenoids by an average of 2.6 and 3.3 times, when treated with amber - by 3.5 and 2.0 times, respectively, compared with the control in terms of raw weight. The use of the studied acids can be recommended for potential use in agriculture.

Interactions between hydrogen sulphide and rhizobia modulate the physiological and metabolism process during water deficiency-induced oxidative defense in soybean.

Hydrogen sulphide (H2 S), a new gas signal molecule, participates in the regulation of various abiotic stresses in plants. However, how the tandem working of H2 S and rhizobia affects the adaptation of soybean to water deficiency is still unclear. In this study, we investigated the adaptation mechanism of H2 S and rhizobia in soybean to water deficiency. Our results revealed that H2 S and rhizobia jointly enhanced the leaf chlorophyll content and relative water content in plants, and caused an increase in the biomass of soybean seedlings under water deficiency. Besides, in the absence of water, H2 S enhanced the biomass by affecting the number of nodules and nitrogenase activity during vegetative growth. The expression of nodulation marker genes including early nodulin 40 (GmENOD40), ERF required for nodulation (GmERN) and nodulation inception genes (GmNIN1a, GmNIN2aand GmNIN2b) were upregulated by H2 S and rhizobia in the nodules. Moreover, the combined effect of H2 S and rhizobia was proved to affect the enzyme activities and gene expression level of antioxidants, as well as osmotic protective substance content and related gene expression levels under water deficiency in soybean seedlings. In addition, the metabolomic results suggested that the combined effect of H2 S and rhizobia remarkably promoted the contents of lipids and lipid-like molecules. Our results indicated that H2 S and rhizobia synergistically reduced the oxidative damage caused by water deficiency through increasing the accumulation of metabolites and strengthening the plant antioxidant capacity.

New Normalized Difference Reflectance Indices for Estimation of Soil Drought Influence on Pea and Wheat

Soil drought is an important problem in plant cultivation. Remote sensing using reflectance indices (RIs) can detect early changes in plants caused by soil drought. The development of new RIs which are sensitive to these changes is an important applied task. Previously, we revealed 46 normalized difference RIs based on a spectral region of visible light which were sensitive to the action of a short-term water shortage on pea plants under controlled conditions (Remote Sens. 2021, 13, 962). In the current work, we tested the efficiency of these RIs for revealing changes in pea and wheat plants induced by the soil drought under the conditions of both a vegetation room and open ground. RI (613, 605) and RI (670, 432) based on 613 and 605 nm wavelengths and on 670 and 432 nm wavelengths, respectively, were effective for revealing the action of the soil drought on investigated objects. Particularly, RI (613, 605) and RI (670, 432) which were measured in plant canopy, were significantly increased by the strong soil drought. The correlations between these indices and relative water content in plants were strong. Revealed effects were observed in both pea and wheat plants, at the plant cultivation under controlled and open-ground conditions, and using different angles of measurement. Thus, RI (613, 605) and RI (670, 432) seem to be effective tools for the remote sensing of plant changes under soil drought.

The soybean Phytoglobin1 (GmPgb1) is involved in water deficit responses through changes in ABA metabolism

Soybean (Glycine max), a major grain crop worldwide, is susceptible to severe yield loss due to drought. Soybean plants over-expressing and downregulating the soybean Phytoblobin1 (GmPgb1) were evaluated for their ability to cope with polyethylene glycol (PEG)-induced water deficit. Sense transformation of GmPgb1, which was more expressed in shoot tissue relative to roots, increased overall plant performance and tolerance to water stress by attenuating the PEG depression of photosynthetic gas exchange parameters and chlorophyll content, as well as reducing leaf injury and promoting root growth. The higher plant relative water content, as a result of GmPgb1 over-expression, was associated with higher transcript levels of three aquaporins: GmTIP1;5 and GmTIP2;5 GmPIP2;9, known to confer water stress tolerance. Opposite results were observed in plants suppressing GmPgb1, which were highly susceptible to PEG-induced stress. Transcriptional and metabolic analyses revealed higher ABA synthesis in dehydrating leaves of plants over-expressing GmPgb1 relative to those suppressing the same gene. The latter plants exhibited a transcriptional induction of ABA catabolic enzymes and higher accumulation of the ABA catabolite dehydrophaseic acid (DPA). Administration of 8′-acetylene ABA, an ABA agonist resistant to the ABA catabolic activity, was sufficient to restore tolerance in the GmPgb1 down-regulating plants suggesting that regulation of ABA catabolism is as important as ABA synthesis in conferring PEG-induced water stress tolerance. Screening of natural soybean germplasm also revealed a rapid and transient increase in foliar GmPgb1 in tolerant plants relative to their susceptible counterparts, thus confirming the key role exercised by this gene during water stress.

Forage accumulation and radiation use of alfalfa under deficit irrigation

AbstractThe supply of high‐quality forage is fundamental to the development of ruminant animal production in drought areas where irrigation provides strong support to the forage production. The objective was to explore the response of alfalfa (Medicago sativa L.) growth and radiation use to deficit irrigation in a 2‐yr field study. Two deficit‐irrigation treatments and a full‐irrigation control (CK) were established under flood irrigation. Growth‐related indicators and radiation use were measured regularly. Results showed that deficit irrigation reduced forage accumulation, leaf area index (LAI), plant relative water content (RWC), and radiation use efficiency (RUE) of alfalfa. Compared with CK, slight deficit irrigation (SD) and moderate deficit irrigation (MD) decreased forage accumulation rate by 20 and 30%, respectively. Logistic model as a function of growing degree days (GDD) fitted well LAI change (R2 > .9). Deficit irrigation reduced the average rate of quick growth of LAI from 5 to 36%. Water deficit did not significantly change the GDD corresponding to the rapid growth phase but reduced the growth rate. Under deficit irrigation, decreased LAI did not always lead to significant cumulative intercepted photosynthetically active radiation (CIPAR) decrease, but resulted in significantly lowered RUE. In conclusion, the decrease of forage accumulation of alfalfa under deficit irrigation would be caused mainly by weakened photosynthetic ability (representing RUE).

Evaluation of some Medicinal Plants for Green Belt Development in Rock Quarrying Locations at Lokpaukwu, Abia State, Nigeria

This study evaluated air pollution tolerance plants as well as anticipated performance indices of some medicinal plants growing in the Lokpaukwu rock quarrying area in order ascertain their suitability for green belt development. Two quarry locations A which is older and has a higher level of activity, and B were used for the study with a control location at Abia State University, Uturu. Out of the sixteen dominant plant species identified, five species; Alchornea cordifolia, Baphia pubescens, Napoleona imperialis, Nauclea latifolia and Vitex doniana. were randomly selected for the study. Leaf samples were randomly collected in triplicate from the lowest branch of each selected plants with similar characteristics. Relative water content of plants was significantly higher (p<0.05) at the study area suggesting stomatal occlusion by dust while chlorophyll content was significantly lower at the quarry sites, a clear indication of pollution stress. Chlorophyll content was also lower in all plants at site B, being significant in N. imperialis and V. doniana. N. imperialis had the highest APTI of 19.15 at the quarry site suggesting suitability for green belt development at the quarry site. Based on API, V. doniana is the most suitable for green belt development among the five plant species.

Exogenous proline enhances salt tolerance in acclimated Aloe vera by modulating photosystem II efficiency and antioxidant defense

This study investigated the ameliorating effect of exogenous proline on some physiological responses of salt acclimated and non-acclimated Aloe vera plants against subsequent salt stress (EC 21 dS/m). Compared to control, salinity decreased leaf growth and relative water content (RWC), leaf contents of chlorophyll a, carotenoids, K/Na ratio, photosystem performance index (PIabs), while promoted leaf contents of hydrogen peroxide (H2O2), maloendialdehyde (MDA) and Na, which subsequently induced oxidative stress. However, foliar applied proline was effective in alleviating the deleterious effects of salinity. Maximum amelioration of salt stress by exogenous proline was found only in salt-acclimated plants, which was attributed to the reduced leaf Na accumulation together with enhanced K content. Proline pretreatment improved plant relative water content, which was correlated with enhancement in leaf proline concentration. We showed that application of proline on salt-acclimated stressed plants alleviated the damage to PSII functioning induced by salinity, contributing to the improvement of the oxygen-evolving complex efficiency of PSII (Fv/Fo) and the quantum yield of electron transport (ΦEo). This improvement of PSII activity was achieved by higher carotenoids and phenolic accumulation. Additionally, proline treatment reduced the accumulation of H2O2 and MDA, indicating that proline pretreatment was more effective in lowering oxidative damage in salt-exposed acclimated plants, which was associated with the activation of SOD, CAT and APX enzymes. Thus, proline pretreatment could protect salt acclimated Alo vera plants against subsequent salt stress through improving K/Na ratio and water relations attributes as well as enhancing antioxidant systems, resulting in better photosynthesis under salt stress.

Climatic and physiological regulation of the bimodal xylem formation pattern in Pinus pinaster saplings.

Seasonality in tree cambial activity and xylem formation encompass large variation in environmental conditions. Abiotic stressors such as warming or drought also modulate plant behavior at species and individual level. Despite xylem formation susceptibility to carbon (C) and water availability, it is still unknown which are the key physiological variables that regulate xylogenesis, and to what extent plant performance contributes to further explain the number of cells in the different phases of xylem development. Xylogenesis and physiological behavior was monitored in saplings of Pinus pinaster Aiton, a bimodal growth pattern species, distributed in different irrigation regimes. Xylogenesis and plant physiological behavior were compared between treatments and the relationship between climate, physiology and the number of cells in the cambium, enlargement and cell-wall thickening phases was evaluated. Xylogenesis regulation shifted from physiological to climatic control as cell differentiation advanced to mature tracheids. The number of cells in the cambium increased with assimilation rates and decreased with the water potential gradient through the plant. Enlargement was the most susceptible phase to plant relative water content, whereas no physiological variable contributed to explain the number of cells in the wall thickening phase, which declined as temperatures increased. All treatments showed a bimodal growth pattern with a second growth period starting when primary growth was completed and after plants had experienced the highest summer hydraulic losses. Our study demonstrates the importance of including physiological responses and not only climate to fully understand xylogenesis, with special attention to the enlargement phase. This is critical when studying species with a bimodal growth pattern because the second growth peak responds to internal shifts of C allocation and may strongly depend on plant hydraulic responses and not on a fine tuning of cambial activity with soil water availability.

Natural volcanic tuff as a soil mulching: effect on plant growth and soil chemistry under water stress

Efficient water management in agricultural sector necessitates the manipulation of all possible options for water supply and demand management methods. The purpose of this study was to determine the usefulness of using natural volcanic tuff as a soil mulching on plant and soil properties under different water levels. The experiments were performed using 1-year-old olive transplants planted in barrels filled with silty clay soil. Half of the barrels were covered with a coarse volcanic tuff, while the other samples were remained without covering and considered as control. The two sets of barrels were irrigated with four levels of water which correspond to 75%, 65%, 55%, and 45% of the field capacity. The treatments were arranged in a randomized complete block design with three replications. Results revealed that plant height, number of branches, trunk diameter, shoots length, shoot diameter, number of leaves, and plant weight for soil covered with volcanic tuff were significantly greater than control plants after the fifth growing season. The leaf water potential and relative water content of plants grown in mulched soil were significantly greater than those of control. An increase in nutrient contents of soil and plant tissues was found as a result of soil amendment with volcanic tuff. In summary, a positive influence of volcanic tuff additions on olive growth, leaves water status, and soil nutrient levels was determined.

Plant growth promoting rhizobacteria from heavy metal contaminated soil promote growth attributes of Pisum sativum L.

Abstract In natural soil environment, microbial communities demonstrate a cooperative relationship with crops yield through the plant growth promoting rhizobacteria (PGPR). In present report, we have explored the PGPRs for the plant growth promoting activities. In our recent report, the isolated strains were isolated from the industrial soil. Out of four rhizobacterial species, two strains (Bacillus thuringiensis PS-1 and Azotobacter chroococcum PS-2) have shown higher PGPR activity. Both stains were selected for their growth promoting activity in garden pea (Pisum sativum) variety P88 which had significantly higher germination percentage. Four different treatments, P. sativum without bacterial inoculum, P. sativum + B. thuringiensis PS-1, P. sativum + A. chroococcum PS-2 and P. sativum + bacterial consortium (control) were considered to make the comparative analysis of parameters like seed germination, plant height, plant relative water content, chlorophyll content, number of pods, number of leaves and root length in P. sativum. Among these treatments, seeds treated with bacterial consortium were significantly better in terms of plant height (87.78 ± 4.15 cm; p

How Kentucky bluegrass tolerate stress caused by sodium chloride used for road de-icing?

Salts used in road de-icing during winter season inhibit the growth and development of lawn grass species. The mechanism of plant tolerance/sensitivity to such treatments is still not clear. Moreover, there is a lack of fast and non-invasive tool to detect the effect of these salts on plants growth. This study was designed to understand the tolerance mechanism of Kentucky bluegrass plants on salinity, based on some biometric and physiological parameters. In this experiment, we simulated the urban conditions where salts are used intensively for roads de-icing. Germination capacity was evaluated at five salt solutions of NaCl (0, 50, 100, 150 and 200 mM), and physiological parameters were measured during the tillering phase at salinity levels of 0, 150 and 300 mM of NaCl. Seeds of Kentucky bluegrass did not germinate under salinity. During tillering phase, salinity affected length, area and dry mass of roots as well as the relative water content of plants, negatively. Moreover, it influenced the maximum chlorophyll fluorescence yield, quantum yield of photosystem II and electron transport rate at early period of stress. This allows us to recommend these parameters for early detection of soil salinity effects on Kentucky bluegrass plants. It seems to be that the tolerance of this plant towards salinity is based on retaining water content in leaves that allow more efficient functioning of photosynthetic apparatus.

Beneficial Effects of Silicon Application in Alleviating Salinity Stress in Halophytic Puccinellia Distans Plants

Little is known on the impact of silicon (Si) nutrition in halophytes. Accordingly, response of Si accumulating halophyte Puccinellia distans to Si nutrition was investigated. The experiment was carried out as factorial in a completely randomized design. Plants were hydroponically raised for six weeks under two salinity (0 and 200 mmol L− 1 NaCl) and Si (0 and 1.5 mmol L− 1 Na2SiO3) levels. Si improved plant dry weight and water relations under salinity. Salinity decreased the plant relative water content (RWC) but Si increased this parameter. Transpiration rate and stomatal density however, declined by salinity and Si even intensified these salt effect. Si affected salt tolerance mechanisms in P. distans. Thus, +Si plants had greater soluble sugars and amino acids and lower Na+ but increased cellulose and lignin and Na+ secretion from leaves. These possibly indicate more efficient osmotic adjustment and better operation of either salt exclusion and / or excretion mechanisms. In congruence, Si greatly enhanced the activity of H+-ATPase in both roots and shoots. +Si plants had reduced stress symptoms evidenced by lower proline and reduced electrolyte leakage indicating better membrane functioning. Altogether, Si application led to better performance of P. distans plants under saline conditions.

Bacillus methylotrophicus CSY-F1 alleviates drought stress in cucumber (Cucumis sativus) grown in soil with high ferulic acid levels

Drought and ferulic acid (FA) inhibit plant growth. Here, we investigated whether Bacillus methylotrophicus CSY-F1 alleviates drought stress in cucumber (Cucumis sativus) plants grown in high-FA soil. Cucumber seedlings grown in high-FA soil were inoculated with CSY-F1 for 20 d, and then subjected to drought for 3 d. In rhizospheric soil of drought-stressed seedlings, CSY-F1 decreased FA levels and increased soil water contents, polysaccharide levels, and catalase, phosphatase, urease, and sucrase activities at low or high FA concentrations. In drought-stressed seedlings grown in FA-containing soil, CSY-F1 improved plant growth, and reduced leaf wilting; CSY-F1 decreased superoxide radical, hydrogen peroxide, and malonaldehyde levels. CSY-F1 increased superoxide dismutase (SOD), catalase, guaiacol peroxidase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase activities in these seedlings. In addition, CSY-F1 elevated plant relative water content and osmotic potential, and enhanced ascorbate and glutathione contents, proline and soluble sugar levels, and catalase, copper/zinc SOD, manganese SOD, CsPYL1, and CsPYL2 transcript levels. CSY-F1 increases the polysaccharide levels and enzyme activities in soil, and enhances antioxidant enzyme activities, proline and soluble sugar levels, and transcript levels of CsPYL1 and CsPYL2 in leaves, thus alleviating drought stress in cucumber under FA conditions.

Effects of 24-epibrassinolide and the synthetic brassinosteroid mimic on chili pepper under drought

Drought is major stress that severely reduces plant growth and productivity. To improve drought tolerance, an exogenous brassinosteroids (BRs) has been used effectively in the field condition. However, the application of BRs is expensive due to the scarcity of natural BRs and the multistep synthesis of BRs. In an attempt to reduce the cost, 7,8-dihydro-8α-20-hydroxyecdysone (DHECD) has been proposed to function as an imitation of 24-epibrassinolide (EBR). In this study, chili pepper plants (Capsicum annuum L. var. frutescens (L.) Kuntze) were sprayed with DHECD, EBR at 1 µM or distilled water (control). Plants were subjected to severe water stress (25% pot water capacity) for 5 days and their physiological effects and yield were investigated. The result showed that the applications of DHECD and EBR before the beginning of water stress could improve leaf water status determined by relative water content in plants grown under drought condition. The electrolyte leakage, lipid peroxidation level, and H2O2 production were significantly declined, while the accumulations of proline and total soluble sugar were increased in the treated plants. Moreover, the net photosynthesis (PN) was elevated due to the increases of stomatal conductance (gs) and intercellular CO2 concentration (Ci) after BR pretreatments under drought. In addition, applications of DHECD and EBR maintained all chlorophyll fluorescence parameters; Fv/Fm, Fv′/Fm′, ΦPSII, qP, and ETR, to remain the photosynthesis. As a result, shoot biomass, fruit yield and capsaicin level were considerably enhanced in the treated plants. DHECD showed better performance to maintain membrane integrity; however, EBR had more effect on the osmotic maintenance. The result also showed that pretreatment with BRs had little or no effect on well-watered plants. The study concluded that DHECD and EBR alleviated the impact of drought on physiological responses and consequently minimized yield loss.