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.

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.

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The plant height was studied in Corchorus capsularis (cultivars D-154 and CVL-1) and Corchorus olitorius (cultivars O-4 and R-26) grown under various water regimes. The cultivars were grown under constant drought, constant saturation, alternate saturation and drought and different levels of standing water (5 cm, 10 cm, 20 cm and 30 cm) conditions. The cultivar 0-4 had been found to be tolerant to drought but susceptible to waterlogging condition, particularly at the young stage. On the tolerance of submersion, the test cultivars could be placed as D-154 > CVL-1 > R-26 > O-4. The plants of CVL-1 became shorter than that of the O-4 in constant drought. On the contrary, the plants of O-4 and R-26 became shorter than that of the CVL-1 and D-154 in standing water conditions. The plants of O-4 and R-26 died earlier when they were exposed to standing water condition in young stage compared to those of the CVL-1 and D-154. It appears that the plant height is highly affected by constant drought in case of Corchorus capsularis and by standing water in case of Corchorus olitorius. The stressed plants of all the cultivars are shorter than their corresponding control plants.

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Abiotic stress has become an alarming issue for plant survival due to the constant changes in the environment. Abiotic stresses such as drought, salt, waterlogging, and heavy metals largely influence plant growth and development that finally reduce crop productivity. The present study was carried out to investigate the responses of jute (Corchorus olitorius cv. O-9897) plant under different abiotic stresses. At 15th days after sowing plants were exposed to different abiotic stresses for various duration. Two doses of NaCl (200 and 400 mM) were applied to impose salt stress, while two doses of CdCl2 (2 and 4 mM) were applied for cadmium (Cd) stress. Waterlogging stress was applied for 5 and 15 days. Whereas drought stress was imposed on plants for 10 and 15 days. Leaf relative water content, SPAD value, plant height, above ground fresh and dry weight, leaf area, and stem diameter decreased upon exposure to salt, water deficit, Cd, and waterlogging stresses. These abiotic stresses resulted in oxidative damage which was evident by the increased levels of lipid peroxidation, H2O2, and electrolyte leakage (EL) together with altered antioxidant enzymes activities and glyoxalase system which are crucial for plants to fight against oxidative damage. Both duration of waterlogging and drought stress drastically affected plant morphophysiology, whereas C. olitorius could tolerate moderate level of salt (200 mM NaCl) and Cd (2 mM CdCl2). So the present study reveals that abiotic stresses cause substantial damages to the morphophysiology and oxidative stress tolerance of C. olitorius where the higher doses of NaCl and CdCl2 as well as the increased duration of waterlogging and drought resulted in more deleterious effect.

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.

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