Impaired photosynthesis in cucumber (Cucumis sativus L.) by high root-zone temperature involves ABA-induced stomatal closure and reduction in ribulose-1,5-bisphosphate carboxylase/oxygenase activity

摘要

Effects of high root-zone temperature (RT) on ABA content, photosynthesis and its related parameters in cucumber (Cucumis sativus L., cv. Suyo) were investigated. Plants were grown in water culture at a RT of either 30 degreesC or 38 degreesC for 10 days. Other growth conditions were 30/25 degreesC air temperatures (dayight), a 14- hr photoperiod, and a light intensity of 250 mumol (.) m(-2) (.) s(-1). Plant growth was severely inhibited at 38 degreesC RT as compared with that at 30 degreesC RT. At 38 'C RT, leaves did not wilt and the leaf color was normal green, but showed a marked increase in ABA content after day 6 with a significant decrease in stomatal leaf conductance. In both RT treatments, leaf water potential declined at day 6, which was more pronounced at 38 degreesC RT than at 30 degreesC RT, but the difference was relatively small. The photochemical activity of chloroplasts was not affected by high RT. However, the CO2 exchange rate (CER) of leaves decreased linearly after day 4 in the high RT treatment. Peeling the epidermis of the abaxial leaf surface to eliminate the stomatal limitation to CER resulted in a significant but not complete recovery of CER, indicating that the high RT limited CER through a decrease in not only stomatal aperture but also photosynthetic capacity of mesophyll cells. After day 6 of high RT treatment, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) exhibited a gradual decrease in the initial level and the activation state. The results indicate that ABA-induced stomatal closure and reduction in the activation state of Rubisco are responsible for impaired photosynthesis in cucumber grown at elevated RT.