Changes of Excitation Spectra of in vivo Chlorophyll Fluorescence during Induction of Photosynthesis

Excitation spectra of chlorophyll fluorescence from intact rye leaves were registered at dif­ ferent steps of the induction of photosynthesis after dark adaptation. Analysis of these spectra indicates that at least two processes related to spectroscopic features are responsible for a flu­ orescence quenching. The first one, active during the first 100 s of illumination, was interpret­ ed to consists in an overall decrease of the fluorescence quantum yield of antenna pigments and chlorophylls, in particular close to the reaction centers. The second type of a fluorescence decrease (between 100 s and 300 s o f illumination) was found to be in large extent related to decrease of the rate of an excitation energy transfer between accessory xanthophyll pigments and chlorophylls emitting fluorescence. This latter molecular mechanism is discussed as being related to violaxanthin availability to de-epoxidation in the xanthophyll cycle.