Abstract
Codium fragile is a green alga native to Japan, but it has flourished as an invasive species in ports around the world. In the intertidal zone where Codium grows, the irradiation varies from weak blue-green to strong white light due to changes in water depth caused by the tide. Codium can utilize green light for photosynthesis through the unique carotenoid siphonaxanthin in the light-harvesting complex. However, it does not exhibit the xanthophyll cycle, a typical photoprotective mechanism, and the mechanism of adaptation to strong light is completely unknown. In this study, we used laboratorycultivated filamentous Codium to investigate changes in pigment accumulation with the wavelength and intensity of light during culture. As a result, we found that only blue-green irradiation induced the decrease of siphonaxanthin and the complementary accumulation of an unknown carotenoid. This turned out to be 19-deoxysiphonaxanthin, a novel biosynthetic intermediate between lutein and siphonaxanthin. We also revealed that this precursor was bound to the light-harvesting complex. Further investigation is needed to link the accumulation of this pigment with photoprotective mechanisms. Changes in accumulated carotenoids due to intense blue-green light may have contributed to the evolution from dark green Codium to bright green land plants.
https://ror.org/01hvx5h04 
