Reactive oxygen species (ROS) are produced in plants as byproducts during many metabolic reactions, such as photosynthesis and respiration. Oxidative stress occurs when there is a serious imbalance between the production of ROS and antioxidant defense. Generation of ROS causes rapid cell damage by triggering a chain reaction. Cells have evolved an elaborate system of enzymatic and nonenzymatic antioxidants which help to scavenge these indigenously generated ROS. Various enzymes involved in ROS-scavenging have been manipulated, over expressed or downregulated to add to the present knowledge and understanding the role of the antioxidant systems. The present article reviews the manipulation of enzymatic and nonenzymatic antioxidants in plants to enhance the environmental stress tolerance and also throws light on ROS and redox signaling, calcium signaling, and ABA signaling.

This work was designed to evaluate whether external application of nitric oxide (NO) in the form of its donor S-nitroso-N-acetylpenicillamine (SNAP) could mitigate the deleterious effects of NaCl stress on chickpea (Cicer arietinum L.) plants. SNAP (50 μM) was applied to chickpea plants grown under non-saline and saline conditions (50 and 100 mM NaCl). Salt stress inhibited growth and biomass yield, leaf relative water content (LRWC) and chlorophyll content of chickpea plants. High salinity increased electrolyte leakage, carotenoid content and the levels of osmolytes (proline, glycine betaine, soluble proteins and soluble sugars), hydrogen peroxide (H2O2) and malondialdehyde (MDA), as well as the activities of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase in chickpea plants. Expression of the representative SOD, CAT and APX genes examined was also up-regulated in chickpea plants by salt stress. On the other hand, exogenous application of NO to salinized plants enhanced the growth parameters, LRWC, photosynthetic pigment production and levels of osmolytes, as well as the activities of examined antioxidant enzymes which is correlated with up-regulation of the examined SOD, CAT and APX genes, in comparison with plants treated with NaCl only. Furthermore, electrolyte leakage, H2O2 and MDA contents showed decline in salt-stressed plants supplemented with NO as compared with those in NaCl-treated plants alone. Thus, the exogenous application of NO protected chickpea plants against salt stress-induced oxidative damage by enhancing the biosyntheses of antioxidant enzymes, thereby improving plant growth under saline stress. Taken together, our results demonstrate that NO has capability to mitigate the adverse effects of high salinity on chickpea plants by improving LRWC, photosynthetic pigment biosyntheses, osmolyte accumulation and antioxidative defense system.

Salinity stress affected crop production of more than 20% of irrigated land globally. In the present study the effect of different concentrations of NaCl (0, 100, and 200 mM) on growth, physio-biochemical attributes, antioxidant enzymes, oil content, etc. in Brassica juncea and the protective role of Trichoderma harzianum (TH) was investigated. Salinity stress deteriorates growth, physio-biochemical attributes, that ultimately leads to decreased biomass yield in mustard seedlings. Higher concentration of NaCl (200 mM) decreased the plant height by 33.7%, root length by 29.7% and plant dry weight (DW) by 34.5%. On the other hand, supplementation of TH to NaCl treated mustard seedlings showed elevation by 13.8, 11.8, and 16.7% in shoot, root length and plant DW respectively as compared to plants treated with NaCl (200 mM) alone. Oil content was drastically affected by NaCl treatment; however, TH added plants showed enhanced oil percentage from 19.4 to 23.4% in the present study. NaCl also degenerate the pigment content and the maximum drop of 52.0% was recorded in Chl. ‘a’. Enhanced pigment content was observed by the application of TH to NaCl treated plants. Proline content showed increase by NaCl stress and maximum accumulation of 59.12% was recorded at 200 mM NaCl. Further enhancement to 70.37% in proline content was recorded by supplementation of TH. NaCl stress (200 mM) affirms the increase in H2O2 by 69.5% and MDA by 36.5%, but reduction in the accumulation is recorded by addition of TH to mustard seedlings. 200 mM NaCl elevated SOD, POD, APX, GR, GST, GPX, GSH, and GSSG in the present study. Further enhancement was observed by the application of TH to the NaCl fed seedlings. NaCl stress suppresses the uptake of important elements in both roots and shoots, however, addition of TH restored the elemental uptake in the present study. Mustard seedlings treated with NaCl and TH showed restricted Na uptake as compared to seedlings treated with NaCl alone. In conclusion, TH proved to be very beneficial in imparting resistance to the mustard plants against NaCl stress through improved uptake of essential elements, modulation of osmolytes and antioxidants.

Several reactive oxygen species (ROS) are continuously produced in plants as byproducts of many metabolic reactions, such as photosynthesis, photorespiration and respiration. Depending on the nature of the ROS species, some are highly toxic and rapidly detoxified by various cellular enzymatic and nonenzymatic mechanisms. Oxidative stress occurs when there is a serious imbalance between the production of ROS and antioxidative defence. ROS participate in signal transduction, but also modify cellular components and cause damage. ROS is highly reactive molecules and can oxidize all types of cellular components. Various enzymes involved in ROS-scavenging have been manipulated and over expressed or down regulated. An overview of the literature is presented in terms of primary antioxidant free radical scavenging and redox signaling in plant cells. Special attention is given to ROS and ROS-anioxidant interaction as a metabolic interface for different types of signals derived from metabolisms and from the changing environment.

Calcium (Ca) plays important role in plant development and response to various environmental stresses. However, its involvement in mitigation of heavy metal stress in plants remains elusive. In this study, we examined the effect of Ca (50 mM) in controlling cadmium (Cd) uptake in mustard (Brassica juncea L.) plants exposed to toxic levels of Cd (200 mg L−1 and 300 mg L−1). The Cd treatment showed substantial decrease in plant height, root length, dry weight, pigments and protein content. Application of Ca improved the growth and biomass yield of the Cd-stressed mustard seedlings. More importantly, the oil content of mustard seeds of Cd-stressed plants was also enhanced with Ca treatment. Proline was significantly increased in mustard plants under Cd stress, and exogenously sprayed Ca was found to have a positive impact on proline content in Cd-stressed plants. Different concentrations of Cd increased lipid peroxidation but the application of Ca minimized it to appreciable level in Cd-treated plants. Excessive Cd treatment enhanced the activities of antioxidant enzymes superoxide dismutase, ascorbate peroxidase and glutathione reductase, which were further enhanced by the addition of Ca. Additionally, Cd stress caused reduced uptake of essential elements and increased Cd accumulation in roots and shoots. However, application of Ca enhanced the concentration of essential elements and decreased Cd accumulation in Cd-stressed plants. Our results indicated that application of Ca enables mustard plant to withstand the deleterious effect of Cd, resulting in improved growth and seed quality of mustard plants.