Resting spore formation and xanthophyll pigments of the marine planktonic diatom Chaetoceros pseudocurvisetus
1998
Oku, O. (Tokyo Univ. of Fisheries (Japan)) | Kamatani, A.
To clarify the survival mechanism of resting spores exposed to light, comparative studies of photosynthetic pigments between vegetative cells and resting spores were conducted. Diatoms, Chaetoceros pseudocurvisetus Mangin, collected from Sagami Bay were sued in batch culture experiments. Nutrient conditions of each culture are nutrient rich. Light intensity and temperature were adjusted to 160 muE m(-2)s(-1) (14L: 10D) and 20 +- 1 degrees C, respectively. Vegetative cells with various specific growth rates and resting spores were collected from the cultures, and photosynthetic pigments of these cells were measured by reverse-phase HPLC. Chl. a and fucoxanthin levels decreased in resting spores more than in vegetative cells, but the molar ratio of the xanthophyll cycle pool to Chl. a increased. The molar ratio of epoxy-free xanthophyll cycle pigment to Chl. a was highest in resting spores. Furthermore, de-epoxidation of xanthophyll cycle pigments by light exposure was much higher in resting spores (76%) than in vegetative cells (22-37%). Epoxidation and de-epoxidation of xanthophyll cycle pigment in resting spores was synchronized to environmental light-dark cycles, these results suggest that the diadinoxanthin-diatoxanthin xanthophyll cycle of resting spores is more active than that of vegetative cells. Previous studies have shown that the xanthophyll cycle and the increase of the molar ratio of xanthophyll pigment to Chl. a play various important voles for photoprotective mechanisms, such as dissipation of excessive energy and quenching of active oxygen. Thus, it is thought that these changes in pigment composition and content in resting spores increase survival under light-excess environment conditions
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