Regulation of Reactive Oxygen Species and Antioxidant Defense in Plants under Salinity.

The generation of oxygen radicals and their derivatives, known as reactive oxygen species, (ROS) is a part of the signaling process in higher plants at lower concentrations, but at higher concentrations, those ROS cause oxidative stress. Salinity-induced osmotic stress and ionic stress trigger the overproduction of ROS and, ultimately, result in oxidative damage to cell organelles and membrane components, and at severe levels, they cause cell and plant death. The antioxidant defense system protects the plant from salt-induced oxidative damage by detoxifying the ROS and also by maintaining the balance of ROS generation under salt stress. Different plant hormones and genes are also associated with the signaling and antioxidant defense system to protect plants when they are exposed to salt stress. Salt-induced ROS overgeneration is one of the major reasons for hampering the morpho-physiological and biochemical activities of plants which can be largely restored through enhancing the antioxidant defense system that detoxifies ROS. In this review, we discuss the salt-induced generation of ROS, oxidative stress and antioxidant defense of plants under salinity.

Exogenous Allantoin Confers Rapeseed (Brassica campestris) Tolerance to Simulated Drought by Improving Antioxidant Metabolism and Physiology.

Allantoin is an emerging plant metabolite, but its role in conferring drought-induced oxidative stress is still elusive. Therefore, an experiment was devised to explore the role of allantoin (0.5 and 1.0 mM; foliar spray) in rapeseed (Brassica campestris cv. BARI Sarisha-17) under drought. Seedlings at fifteen days of age were subjected to drought, maintaining soil moisture levels at 50% and 25% field capacities, while well-irrigated plants served as the control group. Drought-stressed plants exhibited increased levels of lipid peroxidation and hydrogen peroxide, electrolyte leakage, and impaired glyoxalase systems. Thus, the growth, biomass, and yield attributes of rapeseed were significantly impaired under drought. However, the allantoin-supplemented plants showed a notable increase in their contents of ascorbate and glutathione and decreased dehydroascorbate and glutathione disulfide contents under drought. Moreover, the activity of antioxidant enzymes such as ascorbate peroxidase, dehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and catalase were accelerated with the allantoin spray and the glyoxalase system was also enhanced under drought. Moreover, the improvement in water balance with reduction in proline and potassium ion contents was also observed when allantoin was applied to the plants. Overall, the beneficial effects of allantoin supplementation resulted in the improved plant growth, biomass, and yield of rapeseed under drought conditions. These findings suggest that allantoin acts as an efficient metabolite in mitigating the oxidative stress caused by reactive oxygen species by enhancing antioxidant defense mechanisms and the glyoxalase system.

Application of Rhizobacteria, Paraburkholderia fungorum and Delftia sp. Confer Cadmium Tolerance in Rapeseed (Brassica campestris) through Modulating Antioxidant Defense and Glyoxalase Systems.

We investigated the role of two different plant growth-promoting probiotic bacteria in conferring cadmium (Cd) tolerance in rapeseed (Brassica campestris cv. BARI Sarisha-14) through improving reactive oxygen species scavenging, antioxidant defense, and glyoxalase system. Soil, as well as seeds of rapeseed, were separately treated with probiotic bacteria, Paraburkholderia fungorum BRRh-4 and Delftia sp. BTL-M2. Fourteen-day-old seedlings were exposed to 0.25 and 0.5 mM CdCl2 for two weeks. Cadmium-treated plants resulted in a higher accumulation of hydrogen peroxide, increased lipid peroxidation, electrolyte leakage, chlorophyll damage, and impaired antioxidant defense and glyoxalase systems. Consequently, it reduced plant growth and biomass production, and yield parameters. However, probiotic bacteria-inoculated plants significantly ameliorated the Cd toxicity by enhancing the activities of antioxidant enzymes (ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and catalase) and glyoxalase enzymes (glyoxalase I and glyoxalase II) which led to the mitigation of oxidative damage indicated by reduced hydrogen peroxide, lipid peroxidation, and electrolyte leakage that ultimately improved growth, physiology, and yield of the bacterial inoculants rapeseed plants. When taken together, our results demonstrated the potential role of the plant probiotic bacteria, BRRh-4 and BTL-M2, in mitigating the Cd-induced damages in rapeseed plants.

Jute Responses and Tolerance to Abiotic Stress: Mechanisms and Approaches.

Jute (Corchorus spp.) belongs to the Malvaceae family, and there are two species of jute, C. capsularis and C. olitorious. It is the second-largest natural bast fiber in the world according to production, which has diverse uses not only as a fiber but also as multiple industrial materials. Because of climate change, plants experience various stressors such as salt, drought, heat, cold, metal/metalloid toxicity, and flooding. Although jute is particularly adapted to grow in hot and humid climates, it is grown under a wide variety of climatic conditions and is relatively tolerant to some environmental adversities. However, abiotic stress often restricts its growth, yield, and quality significantly. Abiotic stress negatively affects the metabolic activities, growth, physiology, and fiber yield of jute. One of the major consequences of abiotic stress on the jute plant is the generation of reactive oxygen species, which lead to oxidative stress that damages its cellular organelles and biomolecules. However, jute's responses to abiotic stress mainly depend on the plant's age and type and duration of stress. Therefore, understanding the abiotic stress responses and the tolerance mechanism would help plant biologists and agronomists in developing climate-smart jute varieties and suitable cultivation packages for adverse environmental conditions. In this review, we summarized the best possible recent literature on the plant abiotic stress factors and their influence on jute plants. We described the possible approaches for stress tolerance mechanisms based on the available literature.

Insight into the thiourea-induced drought tolerance in two chickpea varieties: Regulation of osmoprotection, reactive oxygen species metabolism and glyoxalase system.

The sulfhydryl bioregulator thiourea (TU) is effective in ameliorating the negative impact of different abiotic stresses in plants. To explore the significant performance of TU (5 mM TU, as foliar spray) in conferring mild (25% depletion of water from field capacity, FC), moderate (50% depletion from FC) and severe (75% depletion from FC) drought stress (applied at 25 days after sowing), physiological and biochemical responses of two chickpea (Cicer arietinum L.) cultivars (cv. BARI Chola-7 and BARI Chola-9) were investigated in the current study. Shoot fresh weight, dry weight, chlorophyll content and leaf relative water content reduced noticeably in mild, moderate and severe drought stresses over control. A sharp increase of H2O2 accumulation, thiobarbituric acid reactive substances and proline content were noticed at any level of drought stress which further declined in TU-treated drought-stressed plants. Thiourea-foliar application also increased ascorbate and glutathione contents and upregulated antioxidant enzyme activities, compared to drought-stressed plants alone. Thiourea-induced increased glyoxalase I and glyoxalase II activities are the indications of upregulated methylglyoxal detoxification system. Enhancement of antioxidant defense and glyoxalase system, osmoregulation and protection of photosynthetic pigments by TU improved growth, imparted oxidative stress tolerance, ameliorated ROS toxicity and improved physiology of chickpea plants under drought stress.

Supplemental Selenium and Boron Mitigate Salt-Induced Oxidative Damages in Glycine max L.

The present investigation was executed with an aim to evaluate the role of exogenous selenium (Se) and boron (B) in mitigating different levels of salt stress by enhancing the reactive oxygen species (ROS) scavenging, antioxidant defense and glyoxalase systems in soybean. Plants were treated with 0, 150, 300 and 450 mM NaCl at 20 days after sowing (DAS). Foliar application of Se (50 µM Na2SeO4) and B (1 mM H3BO3) was accomplished individually and in combined (Se+B) at three-day intervals, at 16, 20, 24 and 28 DAS under non-saline and saline conditions. Salt stress adversely affected the growth parameters. In salt-treated plants, proline content and oxidative stress indicators such as malondialdehyde (MDA) content and hydrogen peroxide (H2O2) content were increased with the increment of salt concentration but the relative water content decreased. Due to salt stress catalase (CAT), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glyoxalase I (Gly I) and glyoxalase II (Gly II) activity decreased. However, the activity of ascorbate peroxidase (APX), glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST) and peroxidase (POD) increased under salt stress. On the contrary, supplementation of Se, B and Se+B enhanced the activities of APX, MDHAR, DHAR, GR, CAT, GPX, GST, POD, Gly I and Gly II which consequently diminished the H2O2 content and MDA content under salt stress, and also improved the growth parameters. The results reflected that exogenous Se, B and Se+B enhanced the enzymatic activity of the antioxidant defense system as well as the glyoxalase systems under different levels of salt stress, ultimately alleviated the salt-induced oxidative stress, among them Se+B was more effective than a single treatment.