Acclimation of Arabidopsis thaliana to the light environment: the role of photoreceptors

The regulation by light of the composition of the photosynthetic apparatus was investigated in photomorphogenic mutants of Arabidopsis thaliana (L.) H eynh. cv. Landsberg erecta. Leaf chlorophyll, photosynthesis, photosystem I I function, and ribulose-1,5-bisphosphate carboxylase-oxygenase and photosy stem II contents were determined for plants grown under high- or low-irradi ance growth regimes. Although certain mutant lines had altered chloroplast composition compared to the wild type, all photoreceptor mutants tested wer e capable of light-dependent changes in chloroplast composition and photosy nthetic function, indicating that photoreceptors do not play a central role in the regulation of acclimation at the level of the chloroplast. However, the clear acclimation defect in a det1 signal transduction mutant indicate s that photoreceptor-controlled responses either share regulatory component s with acclimation, or are important in the expression of components which in turn regulate acclimation. We suggest that the COP/DET/FUS regulatory cl uster is a focus for multiple signal transduction pathways, including some of the metabolic signals which form the basis for the acclimatory response.