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
2003
Nada, K. (Mie Univ., Tsu (Japan). Faculty of Bioresources) | He, L.X. | Tachibana, S.
Summary 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 deg C or 38 deg C for 10 days. Other growth conditions were 30/25 deg C air temperatures (day/night), a 14- hr photoperiod, and a light intensity of 250 micro mol · m sup(-2) . s sup(-1) Plant growth was severely inhibited at 38 deg C RT as compared with that at 30 deg C RT. At 38 deg 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 deg C RT than at 30 deg C RT, but the difference was relatively small. The photochemical activity of chloroplasts was not affected by high RT. However, the C02 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.
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