Increase In Relative Water Content Research Articles

Optimizing Cucumis sativus seedling vigor: the role of pistachio wood vinegar and date palm compost in nutrient mobilization.

The goal of this research is to enhance the quality of cucumber seedlings grown in greenhouses by experimenting with various soilless culture mediums (CMs) and the application of pistachio wood vinegar (WV). The experimental setup was designed as a factorial experiment within a randomized complete block design (RCBD), in greenhouse conditions featuring three replications to assess the effects of different culture media (CMs) and concentrations of pistachio wood vinegar (WV) on cucumber seedling growth. Cucumber seeds were planted in three CMs: coco peat-peat moss, coco peat-vermicompost, and date palm compost-vermicompost mixed in a 75:25 volume-to-volume ratio. These were then treated with pistachio WV at concentrations of 0, 0.5, and 1%, applied four times during irrigation following the emergence of the third leaf. The study revealed that treating seedlings with 0.5% WV in the date palm compost-vermicompost CM significantly enhanced various growth parameters. Specifically, it resulted in a 90% increase in shoot fresh mass, a 59% increase in shoot dry mass, an 11% increase in root fresh mass, a 36% increase in root dry mass, a 65% increase in shoot length, a 62% increase in leaf area, a 25% increase in stem diameter, a 41% increase in relative water content (RWC), and a 6% improvement in membrane stability index (MSI), all in comparison to untreated seedlings grown in coco peat-peat moss CM. Furthermore, chlorophyll a, b, total chlorophyll, and carotenoid levels were 2.3, 2.7, 2.6, and 2.7 times higher, respectively, in seedlings treated with 0.5% WV and grown in the date palm compost-vermicompost CM, compared to those treated with the same concentration of WV but grown in coco peat-peat moss CM. Additionally, the Fv/Fm ratio saw a 52% increase. When plant nutrition was enhanced with the date palm compost-vermicompost CM and 1% WV, auxin content rose by 130% compared to seedlings grown in coco peat-peat moss CM and treated with 0.5% WV. The study demonstrates that using 0.5% WV in conjunction with date palm compost-vermicompost CM significantly betters the quality of cucumber seedlings, outperforming other treatment combinations.

Foliar Application of Biostimulant Mitigates Water Stress Effects on Soybean

Climate change has emerged as a challenge for soybean cultivation around the world, stimulating the development of technological alternatives that aim to mitigate the damage caused by water deficit. From this perspective, algae extract-based biostimulants have been tested to reduce water stress in several crops, but little is known about their effects on soybean. Thus, we hypothesize that a commercial biostimulant based on Ascophyllum nodosum can improve the physiological performance and water relations of Glycine max plants subjected to water deficit. To test this hypothesis, we set up an experiment in controlled conditions in a greenhouse, considering five treatments (control; application of biostimulant; water deficit (WD); WD + application of biostimulant; and WD + split application of biostimulant). The experiment was designed in completely randomized blocks with four replications per treatment and conducted in polyethylene pots containing 10 L of soil and three plants per pot. The irrigation was carried out daily; the water deficit was 50% soil moisture at field capacity, starting at the R1 stage (beginning of flowering, where there is at least one flower open at any node on the plant) and maintained for ten days. The biostimulant was applied concurrently with the onset of water deficit. We confirmed the hypothesis that foliar application of 1.0 L ha−1 of the biostimulant reduces the deleterious effects of the common water deficit at the beginning of the reproductive stage of soybean through the reduction of damage from oxidative stress (reduction of malondialdehyde synthesis by 31.2% in relation to the WD plants), maintenance of water potential and cellular homeostasis (10.2% increase in relative water content when compared with WD plants), and conservation of the contents of chlorophyll in leaves and stimulation of photosynthesis and carboxylation (68% increase in net photosynthetic rate and 49.3% increase in carboxylation efficiency in relation to WD plants). However, when applied in installments, the biostimulant was not efficient in reducing soybean water stress. Therefore, we conclude that the application of a biostimulant based on A. nodosum can help reduce the harmful effects of water deficit on soybean plants, opening up perspectives for the mass use of this extract in agricultural crops produced on a large scale.

Potassium silicate enhances drought tolerance of Bellis perennis by improving antioxidant activity and osmotic regulators

Ornamental plants can usually encounter various types of environmental stress, which reduce plant productivity. A proper application of fertilizers can improve plantsʼ tolerance to drought stress. Nutrients such as potassium and silicon are known to have beneficial effects. This study aimed to evaluate the growth of Bellis perennis under drought stress (80, 70, and 60% FC) and with the application of potassium silicate (0, 2, and 4 mM). The results showed that potassium silicate (2 and 4 mM) increased K and Si accumulation in plants under drought stress. Plants treated with potassium silicate under drought stress exhibited a lower degree of electrolyte leakage and less MDA accumulation in the following order: 2 and 4 mM potassium silicate. An increase in relative water content and chlorophyll was observed with application of potassium silicate under drought stress. Regardless of potassium silicate, the plant enzymatic defense system was significantly improved compared to non-stressed plants. Potassium silicate enhanced the amount of osmotic regulators (carbohydrate and proline) and secondary metabolites (flavonoids and phenols) compared to control plants regardless of drought stress. The anthocyanin content in the flowers significantly decreased by 32.2% when the plants were treated with 4 mM potassium silicate at 60% FC, compared to 80% FC. In conclusion, potassium silicate mitigated the effects of drought stress, enhanced plant tolerance to drought stress, increased the activity of antioxidant enzymes, and improved the amounts of osmotic regulators and secondary metabolites.

Co-application of melatonin and zeolite boost bamboo tolerance under cadmium by enhancing antioxidant capacity, osmolyte accumulation, plant nutrient availability, and decreasing cadmium absorption

Bamboo, a fast-growing and high biomass plant, is one of the income resources of local people in the south and southeast of Asia, known as a food resource with high calories and fiber. However, increased heavy metal contamination cases in bamboo shoots have recently caused concerns. Recently, the role of zeolite and melatonin in the emendation of plant soil and increasing plant growth has been discovered, yet, there is no data on the combined effect of the two on bamboo species. The concurrent interaction in higher plants, particularly, remains elusive. Here, we investigated the role of a combination of zeolite and melatonin in bamboo under cadmium (Cd) stress. In one-year-old bamboo plants (Sasa kongosanensis f. aureo– striatusor), the treatments included a single 150 µM foliar spray of melatonin (Me) and 15 g Zeolite (Ze) kg−1 soil under four concentrations of Cd toxicity (0, 100, 150, and 200 mg L−1). The Cd-induced oxidative stress with overproduction of reactive oxygen species (ROS), lipoperoxidation, and membrane permeability imbalance in bamboo plants reduced biomass and growth. However, melatonin and zeolite alone and together significantly increased plant nutrients in the soil by enhancement of 23% in phosphorous, 23% in nitrogen, 20% in magnesium, 15% in calcium, 10% in potassium as well as 17% increase in relative water content (RWC), 7% in water content (WC), 16% in soluble carbohydrate, 34% in proline, 29% in antioxidant activity, and 26% in non-antioxidants, 13% in ascorbic acid, 24% in anthocyanin, 28% in chlorophylls, 14% in shoot, and 16% in root dry biomass and 15% in shoot length. We concluded that combining 150 µM melatonin and 15 g zeolite with essential mechanisms such as improving antioxidants, increasing plant nutrient availability, reducing Cd absorption, and raising osmolyte accumulation promotes bamboo durability against Cd toxicity and can help further reduce metal toxicity in bamboo species. Such an approach might subsequently have benefits for food safety.

Transcriptome, Biochemical and Phenotypic Analysis of the Effects of a Precision Engineered Biostimulant for Inducing Salinity Stress Tolerance in Tomato.

Salinity stress is a major problem affecting plant growth and crop productivity. While plant biostimulants have been reported to be an effective solution to tackle salinity stress in different crops, the key genes and metabolic pathways involved in these tolerance processes remain unclear. This study focused on integrating phenotypic, physiological, biochemical and transcriptome data obtained from different tissues of Solanum lycopersicum L. plants (cv. Micro-Tom) subjected to a saline irrigation water program for 61 days (EC: 5.8 dS/m) and treated with a combination of protein hydrolysate and Ascophyllum nodosum-derived biostimulant, namely PSI-475. The biostimulant application was associated with the maintenance of higher K+/Na+ ratios in both young leaf and root tissue and the overexpression of transporter genes related to ion homeostasis (e.g., NHX4, HKT1;2). A more efficient osmotic adjustment was characterized by a significant increase in relative water content (RWC), which most likely was associated with osmolyte accumulation and upregulation of genes related to aquaporins (e.g., PIP2.1, TIP2.1). A higher content of photosynthetic pigments (+19.8% to +27.5%), increased expression of genes involved in photosynthetic efficiency and chlorophyll biosynthesis (e.g., LHC, PORC) and enhanced primary carbon and nitrogen metabolic mechanisms were observed, leading to a higher fruit yield and fruit number (47.5% and 32.5%, respectively). Overall, it can be concluded that the precision engineered PSI-475 biostimulant can provide long-term protective effects on salinity stressed tomato plants through a well-defined mode of action in different plant tissues.

Exogenous application of carbon nanoparticles alleviates drought stress by regulating water status, chlorophyll fluorescence, osmoprotectants, and antioxidant enzyme activity in Capsicum annumn L.

Drought is one of the most important abiotic stresses that has a huge negative effect on crop yield. Carbon nanoparticles (CNPs) have received greater attention for their impact on the plants under abiotic stress conditions. However, it is urgently required to apply CNPs to the chili pepper (Capsicum annuum L. cv. Kaskada), which has not yet been studied. The goal of this study was to find out how CNPs affect the growth of chili pepper plants, chlorophyll pigments, proline content, and the activity of antioxidant enzymes when the plants are stressed by drought. Therefore, we synthesized and functionalized CNPs of oil fly ash by one-pot ball milling fabrication. X-ray photoelectron spectroscopy (XPS) was used to identify oxidative moieties on the CNPs surface after exposure to nitric and acetic acids. In the present study, functionalized CNPs were sprayed onto the leaves of 20-day-old plants at various concentrations (6 and 12mg L-1) to determine their effects. We demonstrate that drought stress considerably reduces the plant height, fresh weight (FW), and dry weight (DW). Nevertheless, the exogenous application of functionalized CNPs caused an increase in relative water content (RWC), chlorophyll stability index (CSI), and chlorophyll fluorescence (Fv/Fm) under drought stress. Exogenous functionalized CNPs dramatically increased proline content under drought by reducing abscisic acid (ABA) content in the leaves. When subjected to drought stress, functionalized CNPs boosted antioxidant activities such as superoxide dismutase (SOD) and catalase (CAT) activity. Overall, the positive effects of CNPs on chili pepper seedlings open up new possibilities for developing innovative agricultural techniques, especially when plants are grown in drought conditions.

Effects of different water conditions on the cadmium hyperaccumulation efficiency of Rorippa sylvestris (L.) Besser and Rorippa amphibia Besser.

Increasing the translocation and accumulation of cadmium (Cd) in Cd hyperaccumulator is an important technology to improve the phytoremediation efficiency of Cd-contaminated soil. In order to investigate the effects of different water conditions on the growth and Cd accumulation ability of Cd hyperaccumulators Rorippa sylvestris (L.) Besser and Rorippa amphibia Besser in Cd-polluted soil, clone seedlings of them were transplanted into pots filled with 50mgkg-1 Cd-contaminated soil and cultured with water conditions of soil relative water content (RWC) 35%, 55%, 75%, 95%, and flooding respectively. The results showed the following: with the increase of RWC, the height of R. sylvestris and R. amphibia increased gradually, the dry biomass of shoot and whole plant increased and reached the maximum in 95% and then decreased in flooding; the Cd concentrations in shoots of R. sylvestris and R. amphibia were more than 100mgkg-1 except for 35% and flooding; Cd bioconcentration factors (BCFs) of R. amphibia reached the maximum of 3.8870 in 75% and R. sylvestris reached the maximum of 3.2330 in 95%; sufficient water resulted in the decrease of photosynthetic rate due to more Cd accumulation. However, under flooding condition, because of the decrease of Cd bioavailability in soil, the accumulation of Cd in shoots declined and the net photosynthetic rate (Pn) enhanced slightly.

Changes in physiological responses of OsCaM1-1 overexpression in the transgenic rice under dehydration stress.

Calmodulin, a primary calcium sensor in eukaryotes, binds calcium and regulates the activity of effector proteins in response to calcium signals that evoked in response to abiotic and biotic stress. To identify physiological responses associated with improved tolerance under dehydration stress that may be regulated by calmodulin in rice, the transgenic rice overexpressing OsCaM1-1, the control, and the wild-type KDML105 differing in their dehydration tolerance were compared 24 h after exposure to dehydration stress. The results demonstrated a greater increase in relative water content, relative growth rate, abscisic acid, photosynthetic pigment and proline contents, and antioxidant activities in the transgenic rice plants, whereas Na/K and Na/Ca ratio, lipid peroxidation, and electrolytic leakage decreased. The OsCaM1-1 gene overexpression in the transgenic rice showed greater tolerance to dehydration stress than non-transgenic rice, suggesting that OsCaM1-1 might play an important role in mitigating dehydration stress.

Melatonin alleviates the adverse effects of water stress in adult olive cultivars (Olea europea cv. Sevillana & Roughani) in field condition

Olive trees are considered among the most resilient crops in Mediterranean basin. However, prolonged water stress may adversely affect plant productivity and quality of fruits and oil. Therefore, it is essential to design new agronomic strategies to improve plant water stress tolerance and secure yield and product stability of this important agricultural crop. Under water deficit, plants cope with serious threats, and melatonin (MEL), as a versatile signaling biomolecule, can play a crucial role in morphological and physiological modifications of plants able to enhance drought stress tolerance. In this view, the current research aimed at elucidating the potential beneficial role of exogenous foliar application of MEL (0 and 100 µM) to Sevillana and Roughani olive cultivars under different water stress levels (100%, 75%, and 50% ET). In particular, the morphological, physiological and biochemical changes occurring in leaves treated with or without MEL and the quality of fruits and oil were discussed. A decrease of electrolyte leakage (EL) and malondialdehyde (MDA) content as well as an increase of relative water content (RWC) in MEL-sprayed leaves of drought stress trees were observed. The application of MEL was also associated with higher K+ to Na+ ratio, Ca2+ content, phenolic and soluble carbohydrates contents and a lower decline chlorophyll (Chl) levels. MEL-treated leaves also showed higher catalase (CAT) and peroxidase (POD) activities, responsible for scavenging reactive oxygen species (ROS) generated during drought stress in a severity-dependent manner. MEL-foliar application enhanced the oil content and yield in the olive fruits in both cultivars compared to the untreated ones. Since MEL was also able to exert a beneficial effect on both Sevillana and Roughani cultivar trees by improving their crop water productivity (WPc) under water deficit, it can be considered an effective eco-friendly candidate to minimize the detrimental consequences of water stress.

Plant growth-promoting rhizobacteria Shewanella putrefaciens and Cronobacter dublinensis enhance drought tolerance of pearl millet by modulating hormones and stress-responsive genes.

Drought is a major abiotic stress that affects crop productivity. Endophytic bacteria have been found to alleviate the adverse effects of drought on plants. In the present study, we evaluated the effects of two endophytic bacteria Shewanella putrefaciens strain MCL-1 and Cronobacter dublinensis strain MKS-1 on pearl millet (Pennisetum glaucum (L.) R. Br.) under drought stress conditions. Pearl millet plants were grown under three water levels: field capacity (FC), mild drought stress (MD), and severe drought stress (SD). The effects of inoculation on plant growth, physiological attributes, phytohormone content, and drought stress-responsive genes were assessed. The inoculation of pearl millet seeds with endophytes significantly improved shoot and root dry weight and root architecture of plants grown under FC and drought stress conditions. There was a significant increase in relative water content and proline accumulation in the inoculated plants. Among the phytohormones analyzed, the content of ABA and IAA was significantly higher in endophyte-treated plants under all moisture regimes than in uninoculated plants. C. dublinensis-inoculated plants had higher GA content than uninoculated plants under all moisture regimes. The expression level of genes involved in phytohormone biosynthesis (SbNCED, SbGA20oX, and SbYUC) and coding drought-responsive transcription factors (SbAP2, SbSNAC1 and PgDREB2A) was significantly higher under SD in endophyte-inoculated plants than in uninoculated plants. Thus, these endophytic bacteria presumably enhanced the tolerance of pearl millet to drought stress by modulating root growth, plant hormones, physiology and the expression of genes involved in drought tolerance.

Depth profiling of epidermal hydration inducing improvement of skin roughness and elasticity: in vivo study by confocal Raman spectroscopy

Skin hydration in the stratum corneum plays an important role in skin condition, and skin efficacy properties are influenced by its hydration level. However, few studies have identified the correlation between changes in skin hydration content and skin characteristics by skin depth level. This study aims to determine how changes in skin hydration at specific depth levels affect skin condition by long-term tracking changes in hydration of stratum corneum and viable epidermis after usage of moisturizer. Ten volunteers were recruited and subjected to in vivo confocal Raman spectroscopy to perform water content profiling at skin depths of up to 52μm. Mechanical properties of skin were measured using Cutometer and Antera 3D. Skin-elasticity and roughness values observed before and after 15days of moisturizing emulsion use were compared to demonstrate the correlation between observed changes in skin efficacy parameters and skin water content at specific depths. Significant increase in relative water content at specific depths was observed in this study. Among mechanical properties of skin, only R4, R6, and R8 parameters demonstrated significant changes. Additionally, rates of change in values of the R6 and R8 parameters revealed a high correlation with water content changes at viable epidermis depths below the stratum corneum. On the other hand, skin roughness parameter showed a correlation with water content changes at the outermost layer of stratum corneum. Results of this study indicate that skin elasticity is influenced by its hydration level at viable epidermis depths and skin roughness at stratum corneum each. This suggests that monitoring depth profiles of water content using in vivo confocal Raman spectroscopy provides a breakthrough in tracking the skin efficacy effect of topically applied substances.

海岸黑松和紫穗槐对间歇强净风和风沙流吹袭的生理响应机制

以海岸防风固沙优势树种紫穗槐（Amorpha fruticosa Linn）和黑松（Pinus thunbergii Parl）为研究对象，利用野外便携式沙风洞用间歇风吹模拟自然阵风，通过分析间歇强净风（18m/s）和强风沙流（172.93g cm^-1 min^-1）吹袭过程中和风后恢复中，两树种叶片膜脂过氧化产物含量、抗氧化酶活力、渗透调节物含量的变化，以探讨其对自然阵风吹袭响应机制及自愈修复生理机制。结果表明，自然状况下，紫穗槐和黑松叶片相对含水量（RWC）相近，但抗氧化酶活力及种类和渗透调节物含量及种类上存在差异。紫穗槐叶片丙二醛含量（MDA）、脯氨酸含量及过氧化氢酶（CAT）和过氧化物酶（POD）活力分别较黑松高93.3%、78.6%、118.8%、6.5倍。而黑松可溶糖含量和超氧化物歧化酶（SOD）活力较紫穗槐高111.5%和28.2%。在间歇净风和风沙流处理中，随着风吹袭次数增多，黑松叶片RWC趋于小幅降低，可溶性糖含量及POD、SOD、CAT活力呈小幅波动式变化；紫穗槐叶片RWC大幅下降，伴随着脯氨酸含量，POD、CAT、SOD活力大幅增高和MDA含量下降。在风吹袭中，叶片抗氧化酶活力和渗透调节含量的变化与叶片含水量变化密切相关。在风吹袭处理后的恢复期，黑松叶片MDA、可溶性糖、脯氨酸含量和CAT活力下降，但叶片一直维持较高可溶性糖含量和SOD活力；而紫穗槐伴随叶片RWC回升，而MDA、可溶性糖、脯氨酸含量下降和POD、CAT、SOD活力的增高。研究表明，风吹袭引发叶片水分亏缺成为启动植物对缺水补偿机制的诱导因子（自愈修复）。在风吹袭中增高的渗透调节物通过提高细胞吸水力为自愈修复提供物质基础，而抗氧化酶通过抑制膜脂过氧化、维护膜的完整性和弹性为自愈修复提供生理保护。因此，渗透调节和抗氧化酶通过维护水分平衡和氧自由基代谢平衡而在抗风生长和自愈修复中起重要生理保护作用。;In this study, the coastal area wind and sand blowing resistant Amorpha fruticosa Linn and Pinus thunbergii Parl were used as materials to learn how they responded physiologically to intervals of strong wind and wind-drift blowing, and what mechanisms of physiological adaptation and self-repairing were involved in their resistance to wind-drift blowing and self-repairing after wind blowing. The plants were subjected to 18 m/s wind speed and wind-drift blowing (172.93g cm^-1 min^-1) for 20 min and allowed to repair for 24h after the blowing treatment (repair period); these treatments were repeated three times using an outdoor portable wind tunnel. Relative water content (RWC), malondialdehyde (MDA), proline, soluble sugar, and the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were measured in the leaves of the plants. The results showed that in the natural environment, there were no difference in RWC in the two species, but there were differences in the kinds of antioxidant enzyme and osmotic regulators between A. fruticosa and P. thunbergii, with the MDA content, proline content, and the activities of CAT and POD in leaves of A. fruticosa higher by 93.3%, 78.6%, 118.8%, and 650% than those in leaves of P. thunbergii. The soluble sugar content and SOD activity in leaves of P. thunbergii were higher by 111.5% and 28.2% than those in leaves of A. fruticosa. With increasing repetitions of blowing, RWC tended to decrease to a lower level, while the soluble sugar content and the activities of POD, SOD, CAT exhibited slight fluctuations in the leaves of P. thunbergii, but in A. fruticosa leaves, RWC dramatically dropped, and proline content and the activities of POD, CAT, and SOD significantly increased. Furthermore, during the repairing period, the contents of MDA, soluble sugar, and proline and CAT activity decreased in the leaves of P. thunbergii but the contents of MDA, soluble sugar, and proline decreased, and the activities of POD, CAT, and SOD increased, accompanied by an increase of RWC, in the leaves of A. fruticosa. These results indicate that water shortage induced by wind blowing was a direct factor causing physiological regulation and activating the compensation mechanism for water shortage (self-healing repair) in both trees. Although the two tree species belonged to different families and used different kinds of osmotic regulator and antioxidant enzymes in the physiological regulation of wind resistance, they both had the same strong ability to regulate physiological mechanisms during strong wind blows and post-wind repairing periods. It suggests that water shortage might activate the self-healing physiological mechanism. Under wind blowing, the increased content of soluble sugar and proline might provide materials for self-healing by improving cell water absorption, while antioxidases played an important physiological protective role in inhibition of membrane lipid peroxidation, thus maintaining membrane integrity and elasticity for self-healing. Therefore, self-healing is the key physiological adaptative mechanism for the two trees to adjust to the intervals of strong sea wind blowing on the coast.

Implications of ectomycorrhizal inoculation for drought stress tolerance of Atlas cedar (Cedrus atlantica (Endl.) Carrière) seedlings

Background: Ectomycorrhizal inoculation is a promising strategy to minimise the initial transplant shock and increase plant survival and growth during the first years of out-planting in the field. The aim of this research was to investigate the effect of sporal inoculum of three ectomycorrhizal fungi: Cortinarius cedretorum, Amanita vaginata and Inocybe geophylla on tolerance levels of Atlas cedar (Cedrus atlantica (Endl.) Carrière) seedlings subjected to applied drought stress in nursery conditions. Methods: Carpophores, seeds and organic forest soil were collected under pure stands of Atlas cedar. After fifteen months of growth, seedlings were subjected to drought stress by withholding water for thirty days; we assessed morphological and physiological variables of all seedling batches (inoculated and uninoculated, controlled and stressed seedlings) Results: All roots of inoculated stressed seedlings were mycorrhizal. The mycorrhization rates were 67%, 64.6% and 53.6% for stressed seedlings inoculated with Cortinarius cedretorum, Amanita vaginata, Inocybe geophylla, respectively. This root mycorrhization was accompanied by a significant improvement in seedling growth, especially height and length of the main root (10.2 cm, 52 cm) reached in stressed seedlings inoculated with Cortinarius cedretorum. There was a significant increase in relative water content, total chlorophyll, carotenoids, soluble sugars and starch, superoxide dismutase and ascorbate peroxydase enzyme activities in inoculated stressed seedlings compared with uninoculated seedlings. Conclusions: Inoculation of Atlas cedar seedlings with spores of ectomycorrhizal fungi remains a very effective alternative for improving growth and the morphological and physiological status of seedlings under drought conditions. Cortinarius cedretorum appears to be consistently advantageous followed by Amanita vaginata and Inocybe geophylla.

Additions of optimum water, spent mushroom compost and wood biochar to improve the growth performance of Althaea rosea in drought-prone coal-mined spoils

Ecosystem degradation as a result of coal mining is a common phenomenon in various regions of the world, especially in arid and semi-arid zones. The implementation of appropriate revegetation techniques can be considered crucial to restore these degraded areas. In this regard, the additions of spent mushroom compost (SMC) and wood biochar (WB) to infertile and degraded soils have been reported to enhance soil fertility and plant growth under water (W) deficit conditions. However, the combined application of W, SMC and WB to coal mine degraded soils, to promote Althaea rosea growth and facilitate subsequent restoration, has not been explored yet. Hence, in the current study a pot experiment was carried out by growing A. rosea on coal mine spoils to assess the influence of different doses of W, SMC and WB on its morpho-physiological and biochemical growth responses. The results indicated that several plant growth traits like plant height, root length and dry biomass significantly improved with moderate W-SMC-WB doses. In addition, the simultaneous application of W-SMC-WB caused a significant decrease in hydrogen peroxide (H2O2) (by 7–56%), superoxide anion (O2●‒) (by 14–51%), malondialdehyde (MDA) (by 23–46%) and proline (Pro) contents (by 23–66%), as well as an increase in relative water content (by 10–27%), membrane stability index (by 2–24%), net photosynthesis rate (by 40–99%), total chlorophylls (by 43–113%) and carotenoids (by 31–115%), as compared to the control treatment. The addition of SMC and WB under low-W regime enhanced leaf water use efficiency, and soluble sugar content, also boosting the activity of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase in leaf tissues, thus reducing the oxidative stress, as proved by low levels of H2O2, O2●‒, MDA and Pro contents. Finest growth performance under optimum doses of W (60% field capacity), SMC (1.4%) and WB (0.8%) suggest that revegetation of A. rosea with the recommended W-SMC-WB doses would be a suitable and eco-friendly approach for ecological restoration in arid degraded areas.

Ectopic expression of GmNHX3 and GmNHX1, encoding two Glycine max Na<sup>+</sup>/H<sup>+</sup> vacuolar antiporters, improves water deficit tolerance in Arabidopsis thaliana

The importance of Na+/H+ antiporters in salt tolerance in plants has been demonstrated in many studies, but much less is known about their protective role during drought stress. To study their possible contribution to water deficit tolerance, two closely related soybean Na+/H+ antiporters belonging to the intracellular NHX exchanger protein family, GmNHX3 and GmNHX1, were evaluated in transgenic Arabidopsis thaliana. A. thaliana plants ectopically expressing GmNHX3 or GmNHX1 displayed a more drought-tolerant phenotype compared to wild-type plants, which was accompanied by an increase in relative water content and chlorophyll content during stress conditions. Both GmHNX1 and GmHNX3 transgenic lines accumulated higher amounts of Na+ and K+ cations, showed increased antioxidant enzyme activities and less membrane damage due to lipid peroxidation under water deficit, as compared to non-transformed plants. Furthermore, plants expressing GmNHX3 showed an increased sensitivity to abscisic acid as deduced from stomatal closure and seed germination inhibition studies. Finally, a significant up-regulation of abiotic stress-related genes was observed in both transgenic lines compared to wild-type plants in response to abscisic acid and mannitol treatments. These results demonstrate that GmNHX3 and GmNHX1 antiporters confer protection during drought stress in A. thaliana and hence are potential genetic targets to improve drought tolerance in soybean and other crops.

Overexpression of the white clover TrSAMDC1 gene enhanced salt and drought resistance in Arabidopsis thaliana

S-adenosylmethionine decarboxylase (SAMDC) mediates the biosynthesis of polyamines (PAs) and plays a positive role in plants’ response to adversity stress tolerance. In this study, we isolated a SAMDC gene from white clover, which is located in mitochondria. It was strongly induced when white clover exposed to drought (15% PEG6000), salinity (200 mM NaCl), 20 μM spermidine, 100 μM abscisic acid, and 10 mM H2O2, especially in leaves. The INVSc1 yeast introduced with TrSAMDC1 had tolerance to drought, salt, and oxidative stress. Overexpression of TrSAMDC1 in Arabidopsis showed higher fresh weight and dry weight under drought and salt treatment and without growth inhibition under normal conditions. Leaf senescence induced by drought and saline was further delayed in transgenic plants, regardless of cultivation in 1/2 MS medium and soil. During drought and salt stress, transgenic plants exhibited a significant increase in relative water content, maximum photosynthesis efficiency (Fv/Fm), performance index on the absorption basis (PIABS), activities of antioxidant protective enzymes such as SOD, POD, CAT, and APX, and a significant decrease in accumulation of MDA and H2O2 as compared to the WT. The concentrations of total PAs, putrescine, spermidine, and spermidine in transgenic lines were higher in transgenic plants than in WT under normal and drought conditions. These results suggested that TrSAMDC1 could effectively mitigate abiotic stresses without the expense of production and be a potential candidate gene for improving the drought and salt resistance of crops.

Identification of New Biocontrol Agent against Charcoal Rot Disease Caused by Macrophomina phaseolina in Soybean (Glycine max L.)

Controlling agricultural pests using suitable biocontrol agents has been considered the best strategy for sustainable agriculture. Charcoal rot caused by a necrotrophic fungus Macrophomina phaseolina is responsible for a 30–50% annual reduction in soybean yield worldwide. Little is known about the role of Bacillus clausii in reducing charcoal rot disease severity in the soybean crop. In this study, we investigated plant growth promoting and antagonistic potential of Pseudomonas putida (MT604992) and Bacillus clausii (MT604989) against charcoal rot disease incidence in soybean. Among twenty bacteria isolated from soil and water samples of two different hot springs of Gilgit-Baltistan, Pakistan, 80% were siderophore positive; 65% were hydrogen cyanide (HCN) positive; 55%, 30%, and 75% were phosphate, potassium, and zinc solubilizers, respectively. Based on higher antagonistic activities and plant growth promoting traits five strains were selected for in vitro screening. Out of all tested strains, Pseudomonas putida and Bacillus clausii showed a significant increase in germination, growth, and disease suppression in soybean. These strains produced a pronounced increase in relative water content, photosynthetic pigments, membrane stability, proline, antioxidant enzymes status, phytohormones content (Salicylic acid, and Jasmonic acid), and disease suppression in comparison to control plants. Bacillus clausii mitigated the disease by 97% with a marked increase in the proline content (73% and 89%), superoxide dismutase (356% and 208%), peroxidase (439% and 138.6%), catalase (255.8% and 80.8%), and ascorbate peroxidase (228% and 90%) activities in shoots and roots, respectively. Infected plants showed an increase in salicylic acid and jasmonic acid content which was further increased with the application of the selected strains to increase resistance against pathogens. To our knowledge, this is the first study showing a rise in salicylic acid and jasmonic acid in Macrophomina phaseolina infected plants. These two strains are suggested as a cost-effective, eco-friendly, and sustainable alternative to chemical fungicides. However, there is a need to explore the field testing and molecular mechanisms leading to disease suppression by these strains.

Chlorophyll Fluorescence Parameters and Antioxidant Defense System Can Display Salt Tolerance of Salt Acclimated Sweet Pepper Plants Treated with Chitosan and Plant Growth Promoting Rhizobacteria

Salinity stress deleteriously affects the growth and yield of many plants. Plant growth promoting rhizobacteria (PGPR) and chitosan both play an important role in combating salinity stress and improving plant growth under adverse environmental conditions. The present study aimed to evaluate the impacts of PGPR and chitosan on the growth of sweet pepper plant grown under different salinity regimes. For this purpose, two pot experiments were conducted in 2019 and 2020 to evaluate the role of PGPR (Bacillus thuringiensis MH161336 106–8 CFU/cm3) applied as seed treatment and foliar application of chitosan (30 mg dm−3) on sweet pepper plants (cv. Yolo Wonder) under two salinity concentrations (34 and 68 mM). Our findings revealed that, the chlorophyll fluorescence parameter (Fv/Fm ratio), chlorophyll a and b concentrations, relative water content (RWC), and fruit yield characters were negatively affected and significantly reduced under salinity conditions. The higher concentration was more harmful. Nevertheless, electrolyte leakage, lipid peroxidation, hydrogen peroxide (H2O2), and superoxide (O2−) significantly increased in stressed plants. However, the application of B. thuringiensis and chitosan led to improved plant growth and resulted in a significant increase in RWC, chlorophyll content, chlorophyll fluorescence parameter (Fv/Fm ratio), and fruit yield. Conversely, lipid peroxidation, electrolyte leakage, O2−, and H2O2 were significantly reduced in stressed plants. Also, B. thuringiensis and chitosan application regulated the proline accumulation and enzyme activity, as well as increased the number of fruit plant−1, fruit fresh weight plant−1, and total fruit yield of sweet pepper grown under saline conditions.

Effect of Salt-Tolerant Bacterial Inoculations on Rice Seedlings Differing in Salt-Tolerance under Saline Soil Conditions

Salt-tolerant plant growth-promoting rhizobacteria (PGPR) could be an alternative to alleviate salinity problems in rice plants grown in the coastal areas. This study was conducted to isolate and characterize salt-tolerant PGPR and observe their effects on the physiological and biochemical properties of rice plants grown under non-saline and saline glasshouse conditions. Three strains were selected based on their salt-tolerance and plant growth-promoting properties under in vitro saline conditions. These strains were identified as Bacillus tequilensis (UPMRB9), Bacillus aryabhattai (UPMRE6), and Providencia stuartii (UPMRG1) using a 16S rRNA technique. The selected strains were inoculated to three different rice varieties, namely BRRI dhan67 (salt-tolerant), Putra-1 (moderate salt-tolerant), and MR297 (salt-susceptible) under glasshouse conditions. Results showed that the MR297 rice variety inoculated with UPMRB9 produced the highest total chlorophyll content, with an increment of 28%, and lowest electrolyte leakage of 92%. The Putra-1 rice variety also showed a 156% total dry matter increase with the inoculation of this bacterial strain. The highest increase of relative water content and reduction of Na/K ratio were found upon inoculation of UPMRE6 and UPMRB9, respectively. The biggest significant effects of these bacterial inoculations were on relative water content, electrolyte leakage, and the Na/K ratio of the BRRI dhan67 rice variety under saline conditions, suggesting a synergistic effect on the mechanisms of plant salt-tolerance. This study has shown that the application of locally-isolated salt-tolerant PGPR strains could be an effective long-term and sustainable solution for rice cultivation in the coastal areas, which are affected by global climate change.

Improving salt tolerance and yield by Mn supplementation in Vigna radiata

The present study was carried out in the year 2016-17 to understand the effects of salinity stress on relative water content (RWC), superoxide dismutase (SOD) activity, proline content, reducing sugar content and yield attributes in Vigna radiata and role of foliar application of manganese in improving salinity tolerance. Plants were subjected to varying levels of NaCl induced salinity (0, 100, 200 and 300 mM). The plant samples were analyzed from 25 days to 65 days of plant growth at every 10-day interval. Yield attributes were recorded at 85 days. Results revealed that there was a slight increase in RWC, SOD activity and yield attributes at 100 mM NaCl concentration as compared to control plants, whereas, an abrupt decrease was recorded at higher salt regimes (i.e. 200 and 300 mM NaCl). However, increase in salinity resulted in increased proline and total reducing sugar contents. The foliar application with Mn (0.15%) ameliorated the negative effects of high salinity and increased the yield. Hence, it was concluded that foliar application of Mn may alleviate the adverse effects of excess salinity on Vigna radiata plants.