Temperature-Dependent Modulation of the Photoinhibition-Sensitivity of Photosystem II in Solanum tuberosum Leaves

High temperature (38°C) dramatically exacerbated the photoinhibitionof photosystem II in 23°C-grown potato leaves. This workshows the existence of an adaptive mechanism that cancels thesynergism between heat and strong light and markedly enhancesthe resistance of photosystem II to photodamage. Photoinhibition-resistanceof photosystem II was triggered by exposing leaves in weak lightto moderately elevated, non-injurious temperatures in the range32–38°C and was established within about 20 min, thusproviding a rapid process of photosynthetic adaptation to simultaneousincrease in temperature and light intensity. The reversal at23°C occurred on a much longer time scale of several hours.Temperature-induced increase in PSII photoresistance did notrequire de novo protein synthesis, as judged from its insensitivityto cycloheximide and chloramphenicol, and was not accompaniedwith any apparent change in the antenna size of photosystemII. From the presented chlorophyll fluorescence data, one canpostulate that temperature-dependent regulation of the photoinhibition-sensitivityof photosystem II could primarily involve a change in the PSIIreaction center, the nature of which remains to be established. (Received January 27, 1994; Accepted April 18, 1994)