Dynamic photoprotective mechanisms in Chaetoceros neogracile

Abstract

The Antarctic environment including low temperature and extremely fluctuating irradiation are especially harmful to photosynthetic organisms. To cope with this harmful environment, Antarctic diatom Chaetoceros neogracile has photoprotective mechanism. In this study, we confirmed that xanthophyll cycle is one of the most important photoprotective mechanism in C. neogracile. Interconversion between diadinoxanthin(DD) and diatoxanthin(DT) had great effect on non-photochemical quenching(NPQ).We also found that C. neogracile contains various fucoxanthin chlorophyll a/c binding protein(FCP) genes which are divided into two groups based on the expression pattern under different light intensity. The changes in DD/DT composition and FCP transcription levels are coincided with changing light intensity.However, when DTT, an inhibitor of violaxanthin de-epoxidase was treated, DD/DT composition did not change, while expression of FCPs is changed in response to light regime. Therefore, we conclude that the xanthophyll cycle is an important photoprotective mechanism by increasing NPQ in C. neogracile. Although we did not observe correlation between the level of FCP transcripts and NPQ, it is suggested that high light induced FCP may play a photo-protective role in psychrophilic C. neogracile.