THE ACTIVE PHOTOSYSTEM-II CENTERS CAN MAKE A SIGNIFICANT CONTRIBUTION TO THE INITIAL FLUORESCENCE RISE FROM FO TO FI

The photosystem II (PSII) centers inactive in plastoquinone reduction have been detected in leaves as well as in isolated chloroplasts. An initial variable fluorescence rise from the non-variable fluorescence level F0 to an intermediate level F(i) is believed to arise from these inactive centers, and has been widely used as a tool for studying these centers. By numerical simulation, the initial fluorescence rise originating from the active PSII centers is determined. We find that the active centers can make a significant contribution to the fluorescence rise from F0 to F(i). This is independent of light intensity. It thus appears that the use of the initial fluorescence rise to study the inactive centers might not be so straightforward as previously thought.