Rapid light-induced changes of energy distribution between photosystems I and II

Abstract

Chlorophyll fluorescence induction phenomena (Kautsky effect) have been very useful in the study of photosynthesis (for a review see [ 11. It has long been assumed that the fluorescence induction kinetics are independent of measuring wavelength. Recently it was discovered in Butler’s laboratory that the F690/F730 ratio undergoes changes during the slower part of the induction period (R. J. Strasser, personal communication), where other investigators [2-41 had already observed fluorescence changes, independent of photosystem II acceptor Q*. These slowfluorescence changes are believed to reflect ion-induced changes in energy distribution between the two photosystems (for reviews see [ 1,5,6] ). Any increase in the energy fraction distributed to System I should lead to an increase of System I fluorescence centered around 735 nm relative to System II fluorescence at 685 nm. In earlier work we concluded that not only slow fluorescence changes but also certain rapid transients are due to changes of energy ‘spill-over’ from pigment system II to pigment system I [7,8]. If this conclusion is correct, rapid changes in the ratio of System I and System II fluorescence are also expected. With a system developed to monitor fluorescence ratios automatically and having a time resolution under 1 ms, we did discover very fast changes. Our new data support earlier conclusions of rapid energy distribution changes and suggest a ‘switch’ mechanism, which operates far faster than ion-induced conformational changes of the thylakoid membrane could occur.