Temperature--jump chlorophyll fluorescence induction in plants.

In contrast to slower heating rates, a temperature jump reveals complex rise phases in the heat induced chlorophyll fluorescence emission increase in intact plants. Three rise phases have been detected which indicate the stepwise loss of different quenching mechanism of system II fluorescence. Two of the phases appear to reflect heat deactivation of the system II reaction centers, while the other may be associated with the induction of hydrogenase activity. Variations in Tmax of the jump, for the increase in different plant varieties, suggest a correlation with membrane lipid phase transitions affecting thylakoid membrane structure and the fluorescence increase.