Kinetics of the fluorescence yield of chlorophyll a2 in spinach chloroplasts at liquid nitrogen temperature du ring and following a 16 μs flash

Abstract

If, at liquid nitrogen temperature, the initial fluorescence yield of chlorophyll a 2 is high ( e.g. after preillumination), a 16 μs flash produces in a few microseconds a decrease in fluorescence yield, followed by an increase, which occurs after roughly 10–20 μs, when the intensity of the flash has become negligible. It is concluded that during a flash, a quencher or quenching state T is formed, which disappears in a dark reaction in a time of the order of 10 μs. The kinetics are the same and can be interpreted in the same way as the kinetics at room temperature earlier reported by Duysens et al. (Abstr. VI. Int. Congr. on Photobiol. Bochum 1972, No. 277). If the flash is given when the initial fluorescence yield is low, then the fluorescence yield increases only markedly at the end of the flash, when the intensity has become low. Even for a strong flash, the increase is only about 20% of the maximum increase attained after a large number of flashes. This indicates that at low temperature, in contradistinction to room temperature, the reduction of the primary oxidant Q is less efficient than the formation of the quencher T. For the interpretation of the experiments it was not necessary to introduce other light-induced quenchers than T, such as the oxidized primary reductant, P +.