Effect of elevated temperature stress on the production and metabolism of photosynthate in tomato (Lycopersicon esculentumL.) leaves

SummaryChanges in the production and metabolism of photosynthate in tomato leaves were investigated after plants were treated to an elevated daytime temperature stress of 35ºC for 40 d. Plants grown continuously at 25ºC (daytime) served as the controls. The night temperature was 15ºC. Compared to the controls, photosynthetic activity decreased in plants exposed to 35ºC. The net rate of photosynthesis (Pn) decreased, but stomatal conductance (Gs), the intercellular CO2 concentration (Ci), and the rate of transpiration (Tr) increased, while the limitation of stomatal conductance (Ls) was reduced. In parallel with the decline in Pn, the activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) increased continuously, but invertase activity decreased in heat-stressed plants. Fructose, glucose, and sucrose contents declined, but the content of starch increased in stressed plants compared to the controls. This may result from the effects of 35ºC on the rate of photosynthesis and on sucrose-metabolising enzyme activities that altered carbohydrate metabolism and changed the carbohydrate contents of leaves stressed at 35ºC.