Changes in the S 0 and S 1 properties during dark adaptation in oxygen-evolving Photosystem-II-enriched thylakoid membranes

Abstract

Analysis of oxygen and fluorescence flash yield patterns reveal two types of period 4 behavior. Two types of oxygen-evolving center have been characterized, those with few misses which induce fluorescence oscillations (however, instead of misses a small proportion of active centers, about 10%, are lost after each flash of a series) and the others responsible for the highly damped oxygen-yield oscillations (Delrieu, M.J. and Rosengard, F. (1988) Biochim. Biophys. Acta, 936, 39–49). In this paper, further investigation of the fluorescence yield patterns shows that in the oxygen-evolving centers responsible for the period 4 fluorescence oscillations (and only in these centers), a change in the S0 and S1 properties develops during dark adaptation, affecting the S state advancement only on the first flash of a series. The miss factor (around 1–4%) was greatly increased on the first flash of a series for the S0 → S1 and S1 → S2 transitions (1) when the relatively high flash energy was decreased, (2) during the (short) dark period that followed one or three pre-flashes, (3) after partial Cl− or Ca2+ depletion. There are two possible explanations of the misses on the first flash only: (a) either after the first flash no reaction occurs in a percentage of S0 and S1 state centers and the miss factors are therefore α0 and α1, or (b) a reaction occurs after the first flash, and the reaction results in the formation of inactive S0, S1 and S2 state centers (the miss factors are then α0, α1 and α2). The centers studied represent a minor fraction of the O2-evolving centers at an ambient temperature. In these centers, a structural reorganization in the S0 and S1 states during dark adaptation could account for misses. This process is generally reversed by one flash.