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Adaptation and Tolerance of Wheat to Heat Stress
Temperature is one of the most important abiotic factors affecting yield of crop plants. Every crop species needs an optimum temperature to show its maximum potential. If the temperature is raised above a critical limit, it may cause irreversible damage to plants. When the temperature is raised beyond a certain limit for period long enough which can cause an irreversible damage to plants, it is called high temperature stress. The effect of high temperature is still more severe for cold-loving plants like wheat. This crop needs a temperature of 12–30 °C to give maximum yield. But in recent years, the increasing temperature is causing serious threat to wheat production. Wheat breeders are facing a dilemma in recent years when on one side the demand of wheat is increasing every year due to increasing population and on second side production is decreasing due to rising temperature. Heat stress causes damage at both morphological and cellular level. It may cause adverse alterations in plant growth, development, cellular and physiological processes, and yield. In wheat heat stress particularly at grain filling stage is more harmful. Due to high temperature, reactive oxygen species are generated which is harmful for plants. In their defense, plants try to cope up with heat stress by using mechanism of avoidance or tolerance. In avoidance mechanism, plant completes its life before the onset of stress and never faces the stress. Tolerance mechanism includes alteration in plant metabolism by producing compatible solutes that are able to organize heat response proteins and cellular structures which help in maintaining cell turgor. Morphologically, plant can alter its aerial and root parts which avoid overheating of plant. In wheat, heat-tolerant genotypes try to cool their canopy by increasing uptake of water from soil. In recent time, various biotechnological tools have helped in the identification of genes associated with heat tolerance in plants. Many genes controlling expression of heat response proteins (HRPs) are now tagged. In the present chapter, we have tried to discuss various adaptation mechanisms used by wheat to protect it from heat stress at morphological, cellular, physiological, and molecular level.