Photosynthetic acclimation to chilling in the widespread chilling-tolerant cyanobacterium Nostoc commune

Abstract

Nostoc commune (N. commune) is a widespread chilling-tolerant cyanobacterium, whereas its photosynthetic acclimation to chilling remains largely unknown. Here, its photosynthetic responses to chilling were investigated. During 24 h exposure to chilling temperature (4 ºC), this cyanobacterium exhibited photosystem II (PSII) photoinhibition, as evident by the significant decrease in both the PSII maximum quantum yield Fv/Fm and the PSII core protein D1 abundance. However its photosystem I (PSI) maintained stable, both the maximum photo-oxidizable P700 and the PSI core protein PsaA/B abundance remained largely unchanged after chilling. Chilling activated the non-photochemical quenching to maintain energy balance of intersystem electron transport in N. commune, its quantum yield of regulated energy dissipation in PSII (Y(NPQ)) significantly rose by 41%, so that its PSII excitation pressure (1-qP) remained stable. Furthermore, the significant stimulation of cyclic electron flow (CEF) was observed upon the transfer to chilling and subsequent recovery in N. commune, and its photodamage in the presence of chloramphenicol was similar to that in the presence of methyl viologen, suggesting that CEF contributed to the PSII repair under chilling stress. The present data provide novel insight into photosynthetic acclimation to chilling, which benefit the survival of N. commune in cold habitats or during over-wintering periods and could be used as a reference for the design of robust photosynthetic cell factory.