Physiological and biochemical responses in rice (Oryza sativa L.) to high temperature: A review

Rice is the staple food crop and is the livelihood for most of the people across the globe. Keeping the present climate change scenario in view, there is a severe threat due to rise in temperature that can affect rice yield potential. Heat stress is one of the major abiotic stresses hampering the growth of rice. Temperature at every growth stage plays a critical role in deciding the rice yields. The major effects of heat stress in rice on its morphoagronomical parameters include reduced germination, poor seedling growth, reduction in plant height and tillering, reduction in number of pollen grains, poor anther dehiscence, increased sterility, reduced grain filling and poor grain quality that ultimately lead to yield reduction. From the physiological point of view, there is an inhibition of photosynthesis and related gas exchange traits, reduction in chlorophyll content and other pigments, reduction in chlorophyll fluorescence (Fv/Fm), reduction in cell membrane thermostability as well as an imbalance between photosynthesis and respiration. Biochemically, there is an increase in accumulation of osmoprotectants (praline and glycine betaine), increase in activity of antioxidants and increase in hormone accumulation (abscisic acid and ethylene). A complete understanding of mechanisms conferring thermotolerance and identification of genotypes possessing tolerance is the pre-requisite.