High Temperature Stress Causes Transient Change in the Photosynthetic Machinery and Sucrose Metabolism of Sugarcane (Saccharum spp.)

Temperature extremes are among the major abiotic stresses affecting sugarcane yield and quality. High temperature stress in selected sugarcane clones reduced the total chlorophyll content, SPAD chlorophyll index and photosynthetic efficiency based on fluorescence parameters (F_v/F_m) by 18, 20 and 10% respectively, compared to ambient temperature grown plants. Such transient changes to the photosynthetic machinery caused 30, 15 and 20% reduction in photosynthetic rate, stomatal conductance and intercellular CO concentration respectively, over control. Significant reduction in SPS and SS enzyme activity was noticed due to long term exposure to elevated temperature treatment particularly in sensitive varieties (Co 8021 and Co 0315). Overall, the variation among traits for photosynthetic efficiency based on fluorescence parameters, SPAD chlorophyll index and transpiration rate was significant only under elevated temperature which indicates the effectiveness of using these traits to screen for thermotolerance.