EFFECT OF HIGH-TEMPERATURE ON PLANT-GROWTH AND CARBOHYDRATE-METABOLISM IN POTATO

This study was undertaken to determine the role of sucrose-metabolizin g enzymes in altered carbohydrate partitioning caused by heat stress. Potato (Solanum tuberosum L.) genotypes characterized as susceptible a nd tolerant to heat stress were grown at 19/17 degrees C, and a subset was transferred to 31/29 degrees C. Data were obtained for plant grow th and photosynthesis. Enzyme activity was determined for sucrose-6-ph osphate synthase (SPS) in mature leaves and for sucrose synthase, ADP- glucose pyrophosphorylase, and UDP-glucose pyrophosphorylase in develo ping tubers of plants. High temperatures reduced growth of tubers more than of shoots. Photosynthetic rates were unaffected or increased sli ghtly at the higher temperature. Heat stress increased accumulation of foliar sucrose and decreased starch accumulation in mature leaves but did not affect glucose. SPS activity increased significantly in matur e leaves of plants subjected to high temperature. Changes in SPS activ ity were probably not due to altered enzyme kinetics. The activity of sucrose synthase and ADP-glucose pyrophosphorylase was reduced in tube rs, albeit less quickly than leaf SPS activity. There was no interacti on of temperature and genotype with regard to the enzymes examined; th erefore, observed differences do not account for differences between g enotypes in heat susceptibility.