Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants

Soil Chemical Analysis

Reactive oxygen species (ROS) were initially recognized as toxic by-products of aerobic metabolism. In recent years, it has become apparent that ROS plays an important signaling role in plants, controlling processes such as growth, development and especially response to biotic and abiotic environmental stimuli. The major members of the ROS family include free radicals like O2● −, OH● and non-radicals like H2O2 and 1O2. The ROS production in plants is mainly localized in the chloroplast, mitochondria and peroxisomes. There are secondary sites as well like the endoplasmic reticulum, cell membrane, cell wall and the apoplast. The role of the ROS family is that of a double edged sword; while they act as secondary messengers in various key physiological phenomena, they also induce oxidative damages under several environmental stress conditions like salinity, drought, cold, heavy metals, UV irradiation etc., when the delicate balance between ROS production and elimination, necessary for normal cellular homeostasis, is disturbed. The cellular damages are manifested in the form of degradation of biomolecules like pigments, proteins, lipids, carbohydrates and DNA, which ultimately amalgamate in plant cellular death. To ensure survival, plants have developed efficient antioxidant machinery having two arms, (i) enzymatic components like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR); (ii) non-enzymatic antioxidants like ascorbic acid (AA), reduced glutathione (GSH), α-tocopherol, carotenoids, flavonoids and the osmolyte proline. These two components work hand in hand to scavenge ROS. In this review, we emphasize on the different types of ROS, their cellular production sites, their targets, and their scavenging mechanism mediated by both the branches of the antioxidant systems, highlighting the potential role of antioxidant

Reactive oxygen species (ROS) and response of antioxidants as ROS-scavengers during environmental stress in plants

Stressful environments such as salinity, drought, and high temperature (heat) cause alterations in a wide range of physiological, biochemical, and molecular processes in plants. Photosynthesis, the most fundamental and intricate physiological process in all green plants, is also severely affected in all its phases by such stresses. Since the mechanism of photosynthesis involves various components, including photosynthetic pigments and photosystems, the electron transport system, and CO2 reduction pathways, any damage at any level caused by a stress may reduce the overall photosynthetic capacity of a green plant. Details of the stress-induced damage and adverse effects on different types of pigments, photosystems, components of electron transport system, alterations in the activities of enzymes involved in the mechanism of photosynthesis, and changes in various gas exchange characteristics, particularly of agricultural plants, are considered in this review. In addition, we discussed also progress made during the last two decades in producing transgenic lines of different C3 crops with enhanced photosynthetic performance, which was reached by either the overexpression of C3 enzymes or transcription factors or the incorporation of genes encoding C4 enzymes into C3 plants. We also discussed critically a current, worldwide effort to identify signaling components, such as transcription factors and protein kinases, particularly mitogen-activated protein kinases (MAPKs) involved in stress adaptation in agricultural plants.

Photosynthesis under stressful environments: An overview

https://www.cell.com/trends/plant-science/pdf/S1360-1385(14)00030-2.pdf

Plant salt-tolerance mechanisms

Does exogenous application of salicylic acid through the rooting medium modulate growth and photosynthetic capacity in two differently adapted spring wheat cultivars under salt stress

Exogenously applied ascorbic acid alleviates salt-induced oxidative stress in wheat

Glycinebetaine-induced modulation of antioxidant enzymes activities and ion accumulation in two wheat cultivars differing in salt tolerance

Amongst naturally occurring plant growth stimulants, moringa (Moringa oleifera Lam.) has attained enormous attention being rich in cytokinin, antioxidants and macro–micro nutrients in its leaves. In this study, potential of foliar applied moringa leaf extract (MLE; 30 times diluted), benzyl amino purine (BAP; 50 mg L−1) and hydrogen peroxide (H2O2; 120 μM) at tillering, jointing, booting and heading growth stages was evaluated to induce salt resistance in wheat. Water spray treatment was taken as control. Wheat cv. Sehar-2006 was grown under normal (4 dS m−1), medium (8 dS m−1) and high (12 dS m−1) soil saline conditions. Application of these stimulants decreased the shoot Na+ and Cl− contents, with simultaneous increase in shoot K+ contents. Maximum shoot K+ (48.62 %) contents were recorded with MLE application under high salinity. Activities of leaf antioxidants viz. superoxide dismutase, peroxidase and contents of total soluble phenolics were increased at medium salinity level; whereas ascorbate contents were also improved by MLE application at high salinity level. However, maximum increase in leaf total soluble protein (35.9 %) was observed with BAP application at medium salinity. The shoot length, shoot and root dry weights were decreased with increase in level of salt stress. Grain weight (18.5 %) and kernel yield (18.5 %) were also improved by MLE application under saline and normal conditions than other stimulators used. In conclusion, foliar applied moringa leaf extract could ameliorate salinity-induced adverse effects by activation of antioxidant defense system and decrease in accumulation of Na+ and Cl− into shoots under moderate saline conditions.

Exogenous application of moringa leaf extract modulates the antioxidant enzyme system to improve wheat performance under saline conditions

Ameliorative effect of exogenously applied glycinebetaine (GB) on photosynthetic capacity of two wheat cultivars differing in salt tolerance grown under salt stress was assessed. Plants were grown under field conditions at 2.84, 15 dS/m in split-split plot design. Different levels of GB (no spray NS, 0.1% Tween 20 solution, 50 and 100 mM GB in 0.1% Tween 20 solution) were exogenously applied as a foliar spray to salt tolerant (S-24) and moderately salt sensitive (MH-97) wheat cultivars under saline and non-saline conditions. Salt stress reduced the photosynthetic capacity of both cultivars. Reduction in photosynthetic rate was primarily due to stomatal limitations. Cultivar S-24 excelled MH-97 under salt stress with respect to photosynthetic rate and leaf turgor potential. Salt-induced reduction in photosynthetic capacity was ameliorated by exogenous application of GB. High accumulation of GB mainly contributes to OA, which is one of the factors for improving photosynthetic capacity under salt stress. Better osmotic adjustment or plant water status due to GB application increased the stomatal conductance and thus favored higher CO 2 fixation rate. The protective effect of GB on photosynthetic pigments and GB induced reduction in transpiration rate are additional factors which might have contributed to better growth of wheat cultivars under salt stress. However, cv. S-24 was higher in photosynthetic capacity and plant water status or osmotic adjustment than MH-97, which could explain the ability of the salt tolerant S-24 to show higher salt tolerance than the moderately sensitive MH-97.

Habib Ur Rehman Athar

Papers

Does exogenous application of salicylic acid through the rooting medium modulate growth and photosynthetic capacity in two differently adapted spring wheat cultivars under salt stress

Exogenously applied ascorbic acid alleviates salt-induced oxidative stress in wheat

Glycinebetaine-induced modulation of antioxidant enzymes activities and ion accumulation in two wheat cultivars differing in salt tolerance

Exogenous application of moringa leaf extract modulates the antioxidant enzyme system to improve wheat performance under saline conditions

Influence of exogenously applied glycinebetaine on the photosynthetic capacity of two differently adapted wheat cultivars under salt stress