PHYSIOLOGICAL RESPONSES AND TOLERANCE MECHANISMS OF LOW TEMPERATURE STRESS IN PLANTS

Among various environmental stresses, low temperature is one of the most important factors limiting the productivity and quality of economically important crops. Many food crops such as maize, sorghum, tomato, soybean and rice are adversely affected by temperature below the optimum required for their normal growth and development. Exposure to sub-optimum temperature is a major challenge to plant growth and development. The literature review shows that the exposure of chilling-sensitive plants to low temperatures causes disturbances in all physiological processes – membrane alterations, photosynthesis, respiration, water regime, mineral nutrition, and metabolism. Inactivation of metabolism, observed at low temperature is a complex function of both temperature and duration of exposure. Low temperature tolerance involves several mechanisms- alterations in fatty acid composition of membranes, enhanced efficiency of antioxidant enzyme system, accumulation of low molecular weight osmolytes, induction of molecular chaperones and expression of specific genes encoding products that confer increased cold tolerance. Understanding of various physiological responses and tolerance mechanisms of plants to low temperature stress can form the basis for management of this stress by different approaches like plant growth regulators application, development and selection of chilling-tolerant genotypes, exogenous application of growth hormones and osmoprotectants.