Green algae have evolved several photo-protective responses to cope with high-light stress. The present study examines the metabolic changes during photoacclimation to high-light in Chlamydomonas reinhardtii using nuclear magnetic resonance and mass spectrometry. Using principal component analysis, a clear metabolic response to highlight intensity was observed on global metabolite pools in Chlamydomonas, with major changes in the levels of amino acids and related nitrogen metabolites. Amino acid biosynthesis was induced during short-term photoacclimation presumably to alleviate excess excitation pressure in the plastid. An increase in mitochondrial metabolism through downstream photorespiratory and glyoxylate metabolism, pathways thought to act in a photo-protective capacity, was also observed. Long-term light stress resulted in a significant increase in antioxidant metabolites, ascorbate and dehydroascorbate. These results suggest that metabolism plays a direct role in coping with the imbalance in the excess excitation pressure generated during high-light stress; however, this metabolomics survey has generated additional questions about the roles of nitrogen assimilation associated metabolites in photoacclimatory responses to high-light in Chlamydomonas.

Plants absorb light for photosynthesis, but not all is used. Excess light energy may lead to photoinhibition of photosynthesis and irreversible photooxidative damage. Plants have evolved mechanisms for energy dissipation under high light stress. One such response may involve production of ELIP. It is of interest to know what signal(s) may be involved in ELIP expression. My hypothesis is that redox status of the chloroplast photosynthetic electron transport Chain (PETC) and/or chlororespiration may induce ELIP expression. Using the Arabidopsis thaliana immutans (im) chlororespiratory mutant, this hypothesis was tested. Etiolated seedlings of this variegated mutant were subjected to various light intensities over 0-24 hr period and ELIP mRNA levels were analyzed. These were compared with the wild type plants treated in the same manner. It was found that mature thylakoids may not be required for ELIP expression, and that both photoreceptor-dependent and independent components may be involved in ELIP expression.