The Regulation of Photosynthetic Structure and Function During Nitrogen Deprivation in Chlamydomonas reinhardtii.

Plant physiology

PubMedID: 25489023

Juergens MT, Deshpande R, Lucker BF, Park JJ, Wang H, Gargouri M, Holguin FO, Disbrow B, Schaub T, Skepper JN, Kramer DM, Gang DR, Hicks LM, Shachar-Hill Y. The Regulation of Photosynthetic Structure and Function During Nitrogen Deprivation in Chlamydomonas reinhardtii. Plant Physiol. 2014;.
The accumulation of carbon storage compounds by many unicellular algae after nutrient deprivation occurs despite declines in their photosynthetic apparatus. To aid in understanding the regulation and roles of photosynthesis during this potentially bioenergetically valuable process, we analyzed photosynthetic structure and function after nitrogen deprivation in the model alga Chlamydomonas reinhardtii. Transcriptomic, proteomic, metabolite and lipid profiling, and microscopic time course data were combined with multiple measures of photosynthetic function. Levels of transcripts and proteins of photosystem I and II and most antenna genes fell with differing trajectories; thylakoid membrane lipid levels decreased while their proportions remained similar and thylakoid membrane organization appeared to be preserved. Cellular chlorophyll content decreased more than two-fold within 24 hrs and we conclude from transcript protein and 13C labelling rates chlorophyll synthesis was down regulated both pre- and post-translationally and that chlorophyll levels fall because of a rapid cessation in synthesis and dilution by cellular growth rather than because of degradation. Photosynthetically driven oxygen production and the efficiency of photosystem II as well as P700+ reduction and electrochromic shift kinetics all decreased over the time course without evidence of substantial energy overflow. The results also indicate that linear electron flow fell ~15% more than cyclic flow over the first 24 hrs. Comparing Calvin-Benson cycle transcript and enzyme levels with changes in photosynthetic 13CO2 incorporation rates also point to a coordinated multi-level down regulation of photosynthetic fluxes during starch synthesis before the induction of high triacylglycerol accumulation rates.