Light-quality and irradiance adaptation of the composition and function of pea-thylakoid membranes

Abstract

The effect of light quality and light quantity during growth on the composition and function of pea thylakoids was investigated. Pea plants were grown at seven irradiance levels in four light-quality regimes with different red to far-red ratios (control, far-red-enriched, far-red-deficient and red). Both the chlorophyll a chlorophyll b ( Chl a Chl b ) ratios and the coupling-factor activities increased with increasing levels of irradiance in a curvilinear response in each light regime. This results in a linear relationship between Chl a Chl b ratios, and hence modulations of chlorophyll-proteins and coupling-factor activities in each case, regardless of the red/far-red ratio of the four light-quality sources. Under conditions of long-term irradiance in peas, the modulations of the amounts of core Photosystem II (PS II) complex, core Photosystem I complex, cytochrome b f complex and ATP synthetase on the one hand vs. the antenna chlorophyll a b- proteins of PS II and PS I on the other do not appear to be influenced by the phytochrome photoequilibrium. We suggest that the levels of NADPH and ATP formed during photosynthesis are the crucial factor in promoting gene expression and regulating the composition, structure and function of thylakoid membranes.