Function of the chloroplastic NAD(P)H dehydrogenase Nda2 for H2 photoproduction in sulphur-deprived Chlamydomonas reinhardtii

The relative contributions of the PSII-dependent and Nda2-dependent pathways for H-2 photoproduction were investigated in the green microalga Chlamydomonas reinhardtii after suphur-deprivation. For this purpose. H-2 gas production was compared for wild-type and Nda2-deficient cells with or without DCMU (a PSII-inhibitor) in the same experimental conditions. Nda2-deficiency caused a 30% decrease of the maximal H-2 photoevolution rate observed shortly after the establishment of anoxia, and an acceleration of the decline of H-2 photoevolution rate with time. DCMU addition to Nda2-deficient cells completely inhibited H-2 photoproduction, showing that the PSII-independent H-2 photoproduction relies on the presence of Nda2, which feeds the photosynthetic electron transport chain with electrons derived from oxidative catabolism. Nda2-protein abundance increased as a result of sulphur deprivation and further during the H-2 photoproduction process, resulting in high rates of non-photochemical plastoquinone reduction in control cells. Nda2-deficiency had no significant effect on photosynthetic and respiratory capacities in sulphur-deprived cells, but caused changes in the cell energetic status (ATP and NADPH/NADP(+) ratio). The rapid decline of H-2 photoevolution rate with time in Nda2-deficient cells revealed a more pronounced inhibition of H-2 photoproduction by accumulated H-2 in the absence of non-photochemical plastoquinone reduction. Nda2 is therefore important for linking H-2 photoproduction with catabolism of storage carbon compounds, and seems also involved in regulating the redox poise of the photosynthetic electron transport chain during H-2 photoproduction. (C) 2012 Elsevier B.V. All rights reserved.