EFFECT OF LIGHT-INDUCED-CHANGES IN THYLAKOID VOLTAGE ON CHLOROPHYLL FLUORESCENCE OF AEGOPODIUM-PODAGRARIA LEAVES

The millisecond kinetics of light-induced changes in thylakoid voltage as detected by absorbance changes at 520 nm were compared with the kinetics of the fluorescence yield on Aegopodium podagraria leaves. Frequency response measurements with red actinic light and the analysis of the response to far-red light flashes reveal that the light induced increase in thylakoid voltage is coupled to an increase in fluorescence yield. An increase in fluorescence yield of 5.4% per 10 mV increase in thylakoid voltage is found after calibration of the 520 nm absorbance changes by single-turnover flashes which are assumed to induce an increase in thylakoid voltage by 25 mV. The measured voltage sensitivity of the fluorescence yield compares well to calculations based on the assumption that the rate constant of PS II charge separation is sensitive to electric fields as proposed by Schatz et al. (Biophys. J. 54 (1988) 379-405). Based on the results of the frequency response measurements, it is estimated that about 7% of the O-I pahse of the fluorescence kinetics and 10% of the fluorescence response to single-turnover flashes are due to the voltage effect. It is discussed whether transthylakoid voltage might be of relevance for the control of PS II electron flux.