بیوتکنولوژی و بیوشیمی غلات (Mar 2023)
A review of physiological and biochemical aspects of heat stress in rice
Abstract
Global warming has increased the earth's average temperature, and the tensions resulting from extreme heat have increased in different regions. Heat stress occurs in the form of an increase in temperature beyond the critical threshold for a certain period of time in different stages of the growth of crop plants. Therefore, the quantitative and qualitative changes in crop plants, including rice, as a result of heat stress caused by the global increase in temperature is one of the most critical concerns in many rice-growing regions of the world, including our country. Plants were adapted to heat stress by changing physiological, biochemical, and molecular metabolism. A stable photosynthetic system can reduce heat damage and increase grain yield under heat-stress conditions. The damage caused by high temperatures can be different in different rice growth stages, from germination to seedling stage, flowering, and seed ripening. The flowering and seed-filling stages are heat-sensitive stages in rice plants. Thermal damage in these stages can cause significant economic losses to rice production. In this article, an attempt has been made to review the physiological changes of rice under the influence of heat stress. The studied changes include the biochemical reaction of the plant during heat stress (electrolyte leakage, lipid peroxidation level and antioxidant enzyme activity), photosynthesis, membrane changes, plant changes to tolerate or escape from heat stress, changes in metabolism at the physiological, biochemical and molecular levels, adaptation to heat, regulating the activity of transcription factors related to heat stress response and changes in the expression pattern of genes under the influence of heat stress. Also, the relationship between heat stress and the biochemical characteristics that determine the quality of rice and the factors affecting the efficiency of rice grain quality, including the metabolic activities of sugar and starch and the gene expression of quality traits of rice under the influence of heat stress, were studied. Finally, the ability of rice breeding to deal with heat stress was reviewed. In the discussion of breeding for heat tolerance in rice, heritability and genetic diversity of traits related to heat stress tolerance, the results of studies conducted in the field of identifying QTLs for heat tolerance, the use of classical crossing to introduce varieties resistant to heat stress, induced mutation in breeding rice was evaluated for increased heat stress tolerance. The results have shown that rice can tolerate non-lethal heat stress by avoiding, escaping, or physical changes at the cellular level, such as changing the physical state of the membrane, synthesis of specialized heat shock proteins, and enhancing anti-oxidative defense. Changes in the physical state of the membrane and its compounds, the production of heat shock proteins, transcription factors, osmolytes, and increasing the level of antioxidant defense are the key processes to maintain the cellular oxidation-reduction balance in heat stress. Investigating the quality changes of rice under heat stress showed that the decrease in the level of enzymes in the synthesis of sucrose and starch causes significant damage to the yield and quality of the grain in hot weather. Also, the identification of several QTLs for heat tolerance, induction mutation, classical breeding using the crossing of a high-quality variety and a heat stress-resistant variety had favorable results in the identification and introduction of heat stress-resistant cultivars. Based on the reviewed results, it can be concluded that heat stress is an inevitable condition in rice cultivation; therefore, identifying and reviewing its physiological changes can be very important and provide appropriate breeding goals.
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