Thylakoid Membrane Fluidity Changes the Response of Isolated Pea Chloroplasts to High Temperature

Abstract

The exposure of isolated chloroplasts or leaves of higher plants to thermal stress leads to considerable changes in the structural organization of thylakoid membranes and their photosynthetic activities. The changes in chloroplast architecture (1) were accompanied by heat-induced physical dissociation of the “peripheral” light-harvesting chlorophyll a/b complex II (LHC II) from the PSII core complex (2,3). CO₂ fixation, O₂ evolution and photophosphorylation capability is markedly inhibited after incubation of isolated chloroplasts at temperature above 35°C (4). PSII-mediated electron transport is reported to be particularly susceptible to heat stress (5). In contrast, PSI-mediated electron transport rate is stimulated at temperature above 35°C (5, 6). The heat-induced increase of P700⁺, the enhancement of spillover and an increase of absorption cross-section of PSI after short heat treatment were also observed (7).