Calcium-dependent regulation of cyclic photosynthetic electron transfer by a CAS, ANR1, and PGRL1 complex.

Cyclic photosynthetic electron flow (CEF) is crucial to photosynthesis because it participates in the control of chloroplast energy and redox metabolism, and it is particularly induced under adverse environmental conditions. Here we report that down-regulation of the chloroplast localized Ca(2+) sensor (CAS) protein by an RNAi approach in Chlamydomonas reinhardtii results in strong inhibition of CEF under anoxia. Importantly, this inhibition is rescued by an increase in the extracellular Ca(2+) concentration, inferring that CEF is Ca(2+)-dependent.

Control of hydrogen photoproduction by the proton gradient generated by cyclic electron flow in Chlamydomonas reinhardtii.

Hydrogen photoproduction by eukaryotic microalgae results from a connection between the photosynthetic electron transport chain and a plastidial hydrogenase. Algal H₂ production is a transitory phenomenon under most natural conditions, often viewed as a safety valve protecting the photosynthetic electron transport chain from overreduction. From the colony screening of an insertion mutant library of the unicellular green alga Chlamydomonas reinhardtii based on the analysis of dark-light chlorophyll fluorescence transients, we isolated a mutant impaired in cyclic electron flow around photosystem I (CEF) due to a defect in the Proton Gradient Regulation Like1 (PGRL1) protein.

Hydrogen production by photoautotrophic sulfur-deprived Chlamydomonas reinhardtii pre-grown and incubated under high light.

We have previously demonstrated that Chlamydomonas reinhardtii can produce hydrogen under strictly photoautotrophic conditions during sulfur deprivation [Tsygankov et al. (2006); Int J Hydrogen Energy 3:1574-1584]. The maximum hydrogen photoproduction was achieved by photoautotrophic cultures pre-grown under a low light regime (25 microE m(-2) s(-1)).