DIFFERENTIAL CONTROL OF XANTHOPHYLLS AND LIGHT-INDUCED STRESS PROTEINS, AS OPPOSED TO LIGHT-HARVESTING CHLOROPHYLL A B PROTEINS, DURING PHOTOSYNTHETIC ACCLIMATION OF BARLEY LEAVES TO LIGHT IRRADIANCE/

Barley (Hordeum vulgare L.) plants were grown at different photon flux densities ranging from 100 to 1800 mu mol m(-2) s(-1) in air and/or i n atmospheres with reduced levels of O-2 and CO2. Low O-2 and CO2 part ial pressures allowed plants to grow under high photosystem II (PSII) excitation pressure, estimated in vivo by chlorophyll fluorescence mea surements, at moderate photon flux densities. The xanthophyll-cycle pi gments, the early light-inducible proteins, and their mRNA accumulated with increasing PSII excitation pressure irrespective of the way high excitation pressure was obtained (high-light irradiance or decreased CO2 and O-2 availability). These findings indicate that the reduction state of electron transport chain components could be involved in ligh t sensing for the regulation of nuclear-encoded chloroplast gene expre ssion. In contrast, no correlation was found between the reduction sta te of PSII and various indicators of the PSII light-harvesting system, such as the chlorophyll a-to-b ratio, the abundance of the major pigm ent-protein complex of PSII (LHCII), the mRNA level of LHCII, the ligh t-saturation curve of O-2 evolution, and the induced chlorophyll-fluor escence rise. We conclude that the chlorophyll antenna size of PSII is not governed by the redox state of PSII in higher plants and, consequ ently, regulation of early light-inducible protein synthesis is differ ent from that of LHCII.