The polyphasic rise of chlorophyll fluorescence upon onset of strong continuous illumination: II. partial control by the photosystem II donor side and possible ways of interpretation

Abstract

The fluorescence rise kinetics in saturating light display two well separated com ponents with largely different properties. The rapid rise from Fo to a first interm ediate level, I1, is photochem ically controlled, while the following phases leading to a secondary interm ediate level, I2, and to a peak level, P, are limited by thermal reactions. Treatments which primarily affect components at the photosystem II donor side are shownto increase quenching at I1 and/or to suppress the secondary fluorescence rise to I2. Preillumination by single turnover saturating flashes causes I,- quenching oscillating with period-4 in dependence of flash number. It is suggested that this quenching correlates with (S2 + S3) states of the watersplitting enzyme system. Suppression of the secondary, I1-I2 rise component is invariably found with treatments which lower electron donation rate by the watersplitting system and are known to favor the low potential form of cyt b 559. Three different mechanisms are discussed on the basis of which donor-side dependent quenching could be interpreted: 1) Non-photochemical quenching by accumulation of the P 680+ radical cation. 2) Dissipative photochemical quenching at aspecial population of PS II centers (ß- or non- B centers) displaying low donor capacity and high rates of chargerecom bination. 3) Dissipative photochem ical quenching via cyclic electron flow around PS II, involving alternate donors to P 680+ (like cyt b 559 or carotenoid in their low potential forms), which can com pete when donation rate from the w ater splitting system is slowed down. The possibility of donor-side limitation also being involved in “energy dependent™ quenching is discussed. © 1987, Walter de Gruyter. All rights reserved.