Time-resolved fluorescence spectroscopy of photosynthetic systems using synchrotron radiation. Part 1.—Fluorescence kinetics of lettuce chloroplasts

Abstract

Fluorescence-decay profiles of lettuce chloroplasts in the wavelength range 680–720 nm have been measured by the single-photon counting technique using synchrotron radiation for excitation. The decay profiles all require a sum of three exponential components to give acceptable agreement between calculation and experiment. Chloroplasts alone exhibit lifetimes for the three components of 92–104 ps, 523–600 ps and 1679–1915 ps, with the middle component making the largest contribution to the overall decay. Addition of potassium ferricyanide to the chloroplasts has little effect, but DCMU produces a redistribution of fluorescence intensity such that the decay profile is now dominated by the slowest of the three components. The effect of DCMU is mitigated to some extent by the subsequent addition of potassium ferricyanide. These results are discussed in terms of the most recent assignments of the various fluorescent components in chloroplasts.