Plants are confronted with a variety of environmenmtal stresses resulting in enhanced production of ROS. Plants require a threshold level of ROS for vital functions and any change in their concentration alters the entire physiology of plant. Delicate balance of ROS is maintained by an efficient functioning of intriguing indigenous defence system called antioxidant system comprising enzymatic and non enzymatic components. Down regulation of antioxidant system leads to ROS induced oxidative stress causing damage to important cellular structures and hence anomalies in metabolism. Proper mineral nutrition, in addition to other agricultural practices, forms an important part for growth and hence the yield. Potassium (K) is a key macro-element regulating growth and development through alterations in physiological and biochemical attributes. K has been reported to result into accumulation of osmolytes and augmentation of antioxidant components in the plants exposed to water and salt stress. In the present review an effort has been made to revisit the old findings and the current advances in research regarding the role of optimal, suboptimal and deficient K soil status on growth under normal and stressful conditions. Effect of K deficiency and sufficiency is discussed and the information about the K mediated antioxidant regulation and plant response is highlighted.
Present communication reports laboratory and pot experiments conducted to study the influence of water and osmotic stress on nitrogen uptake and metabolism in two wheat (Triticum aestivum L) cultivars with and without potassium supplementation. Polyethylene glycol 6000-induced osmotic stress/restricted irrigation caused a considerable decline in the activity of nitrate reductase, glutamate synthase, alanine and aspartate aminotransferases, and glutamate dehydrogenase. Potassium considerably improved nitrogen metabolism under normal water supply conditions and also resulted in amelioration of the negative impact of water and osmotic stresses indicating that potassium supplementation can be used as a potential tool for enhancing the nitrogen use efficiency in wheat for exploiting its genetic potential.
This report discusses water stress-induced changes and their amelioration by added potassium in Sorghum bicolor L. Chlorophylls, carotenoids, and the activity of nitrogen metabolizing enzymes viz., nitrate reductase, alanine aminotransferase and aspartate aminotransferase were adversely affected under water stress and restricted irrigation. Osmotic as well as water stress trigger ROS production while potassium ameliorated these changes to some extent and increased the activity of SOD, CAT, APX, and GR and the contents of GSH and AsA. Water stress-induced changes ultimately reflecting on growth and yield parameters like plant height, biomass yield, grain yield, days to flowering, and days to maturity. Added potassium affected these parameters positively, both under normal and stress conditions, indicating the use of potassium as a tool for mitigating the water stress induced deleterious changes in sorghum to some extent by enhancing the nitrogen use efficiency and strengthening the enzymatic and non-enzymatic antioxidant components. The results obtained here exhibited similar trends in seedlings and plants raised in sand cultures and field conditions, making them more meaningful and comprehensible. | INTRODUCTIONInadequate water supply is one of the important factors that limit crop productivity and grain quality. The severity of water stress depends not only on the magnitude and duration of the stress, but also on the developmental stage of the plant at which the stress is imposed.Water stress not only modifies the morphology of a plant but also severely affects its metabolism (Khan et al., 1993;Ober et al., 1991;Saeed et al., 1997). Altered cellular metabolism in response to water stress results in reduced growth and crop yield because of excess production of ROS and damage to cell membranes, proteins, nucleic acids, and other components of the cell (Gill & Tuteja, 2010;Tambussi et al., 2000). Limited water supply affects physiological and biochemical processes in plants such as photosynthesis, enzyme activities, plant water relations, integrity of membranes, all in all resulting in metabolic dysfunctions (Abid et al., 2018;Gill & Tuteja, 2010). Water deficit induces the oxidative stress in plants by the excess production of reactive oxygen species (ROS), which have the potential to cause membrane dysfunction and the leakage of important cellular components like mineral ions, e.g. K + (Blokhina et al., 2003;Kapoor et al., 2020). Potassium (K) nutrition to plants stimulates root growth, which helps with the efficient absorption of soil water (Saxena, 1985). Potassium treatments improved dry matter and total nitrogen content in faba bean plants subjected to restricted water supply during the post flowering period, probably by promoting growth and not by enhancing the nitrogen fixation efficiency (Kurdali et al., 2002). K availability to plants was reported to be related to soil water content, which highly influenced the mass flow and diffusion rates of K in soils (Doussan et al., 2003).
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