Alterations in Carbohydrate Metabolism and Modulation of Thermo-Tolerance in Tomato under Heat Stress

Heat stress affects the source and sink activities, growth and development, economic yield and harvest index of plants negatively. Heat stress has got severe effects on the biochemical reactions of photosynthesis which included irreversible damages of RuBisCO, oxygen evolving complexes, PSII reaction centres and disruptions of chloroplast ultrastructure and thylakoid membrane. Sugars are products of photosynthesis in plants which serve as substrates for energy metabolism and are required for synthesis of cellulose and starch polysaccharides. Glucose, fructose, sucrose, mannose, trehalose, maltose etc. are the sugars present in plants. Abiotic stresses like temperature, drought, flood and salinity causes crucial differences in the carbohydrate metabolism. Sugars acts as primary signaling molecules and regulate signals that control the expression of many genes and enzymes involved in carbohydrate metabolism. Decrease in crop productivity under heat stress is chiefly associated with alterations in carbohydrate accumulation and resulting defects in assimilation partitioning from source to sink. It is essential to understand the responses and acclimatization processes to extreme temperatures in plants, such that the mechanisms underlying can be used for developing heat-tolerant varieties. Sugars such as glucose, sucrose, fructan, raffinose and trehalose not only acts structural component and metabolic resources also regulate genes associated with heat stress tolerance and reduce the chances of crop loss. The external application of compounds like osmoregulators, phytohormones, signaling molecules, etc., have exhibited positive responses in stress tolerance due to its growth promoting and antioxidant activities.