Response of Antarctic diatom Chaetoceros neogracile under highlight stress

Abstract

Photosynthetic organisms show photoprotective response under high light stress to prevent from damage of their light harvesting systems. The photoprotective mechanism includes changes in xanthophyll pigments content catalyzed by violaxanthin epoxidase. In high irradiance, oxidized form of xanthophylls are epoxidized resulting in the increase of epoxidized xanthophylls and decrease of de-epoxidized xanthophyll. This change in xanthophyll pigments contents is called xanthophyll cycle because it is reversible depend on the light intensity. As one of diatom, Chaetoceros neogracile have diatom-specific xanthophyll pigments content: diatoxanthin and diadinoxanthin. In this study, we analyzed the relationship between xanthophyll pigment content and NPQ(non-photochemical quenching) which represent photoprotective activity. Furthermore, we analyzed transcription level of genes encoding light harvesting pigment binding protein. All of these gene products-FCPs (fucoxanthin, chlorophyll a/b binding protein) are supposed to bind with fucoxanthin, the main light harvesting pigment in diatoms. However, transcription level of some FCPs increased while some decreased. The pattern of change is corresponding to the change of diatoxanthin/diadinoxanthin level. Moreover, the changed levels came back to normal when the cells were transferred to normal light. The changes in the transcription levels of these genes imply that FCPs play different role in light harvesting and light protection. Results of this study give us advanced clue in understanding photoprotective mechanism in Antarctic diatom, yet need to be further studied about different roles of FCPs.