The role of mitochondrial alternative oxidase pathway during H2 photoproduction in Chlorella protothecoides under nitrogen limitation and sulfur deprivation

摘要

Mitochondrial alternative oxidase (AOX) pathway can efficiently oxidize excess NADPH generated by photosynthesis. Therefore, it has been speculated that AOX pathway can affect H2 photoproduction in followed ways: (i) consuming O2, which is favorable for the establishment of anaerobiosis; (ii) consuming NADPH and competing photosynthetic electrons with hydrogenase, which would inhibit the photoproduction of H2; (iii) protecting PSII from photoinhibition during H2 photoproduction. In our previous work, we demonstrated that H2 photoproduction was enhanced greatly in Chlorella protothecoides exposed to simultaneous nitrogen limitation and sulfur deprivation (LNS). The purpose of this study was to explore the role of AOX pathway during H2 photoproduction in C. protothecoides under nitrogen limitation (LN) and LNS conditions. In LN and LNS cultures, the photoproduction of H2 were restricted significantly when the AOX pathway was inhibited by salicylhydroxamic acid. And the inhibition of AOX pathway did not increase the amount of O2 both in LN and LNS conditions. But, the inhibition of AOX pathway decreased F_v/F_m and Φ_(PSII) significantly. All these results suggest that mitochondrial AOX pathway played an importance role in photoprotection of PSII during the H2 photoproduction process in C. protothecoides, which could supply more photosynthetic electrons to hydrogenase under LNS conditions.