Effects of heat stress on carbon transport from tomato leaves

Export of radioactive carbon from two cultivars of tomato, (Lycopersicon esculentum Mill.) leaves was inhibited in response to heat stress. Increasing temperatures resulted in a marked decrease in leaf starch levels. The depletion of starch concentration in the leaves was primarily due to hydrolysis and an inhibition of starch formation. At high temperatures, starch hydrolysis was inhibited in Roma VF, a heat sensitive cultivar, while Saladette, a heat tolerant cultivar was not similarly affected. Callose formation was found on phloem sieve tube plates of leaf petioles exposed to 72 h of high temperatures. More sieve tube plates were covered with a thicker callose layer in Roma VF than in Saladette.