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Ascorbate accumulation during sulphur deprivation and its effects on photosystem II activity and H 2 production of the green alga Chlamydomonas reinhardtii
Author(s) -
Nagy Valéria,
VidalMeireles André,
Tengölics Roland,
Rákhely Gábor,
Garab Győző,
Kovács László,
Tóth Szilvia Z.
Publication year - 2016
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/pce.12701
Subject(s) - chlamydomonas reinhardtii , photosynthesis , hydrogenase , photosystem i , photosystem ii , biophysics , photoinhibition , electron transport chain , chemistry , chloroplast , biochemistry , biology , botany , enzyme , mutant , gene
In nature, H 2 production in Chlamydomonas reinhardtii serves as a safety valve during the induction of photosynthesis in anoxia, and it prevents the over‐reduction of the photosynthetic electron transport chain. Sulphur deprivation of C. reinhardtii also triggers a complex metabolic response resulting in the induction of various stress‐related genes, down‐regulation of photosynthesis, the establishment of anaerobiosis and expression of active hydrogenase. Photosystem II (PSII) plays dual role in H 2 production because it supplies electrons but the evolved O 2 inhibits the hydrogenase. Here, we show that upon sulphur deprivation, the ascorbate content in C. reinhardtii increases about 50‐fold, reaching the mM range; at this concentration, ascorbate inactivates the Mn‐cluster of PSII, and afterwards, it can donate electrons to tyrozin Z + at a slow rate. This stage is followed by donor‐side‐induced photoinhibition, leading to the loss of charge separation activity in PSII and reaction centre degradation. The time point at which maximum ascorbate concentration is reached in the cell is critical for the establishment of anaerobiosis and initiation of H 2 production. We also show that ascorbate influenced H 2 evolution via altering the photosynthetic electron transport rather than hydrogenase activity and starch degradation.