Algae. 2001; 16(3): 295-302.

Photoadaptation of Photosynthesis in Red-Tide Causative Algae

Seung-Kook Kwak, Ok-Hee Lee, Kyung-Je Cho

Department of Biology, School of Environmental Science and Engineering, Inje University

Photosynthesis rate and photoadaptation of red-tide causative algae blooming off the southern coast of Korea were evaluated over 25-800 μmol m-2 s-1 irradiances. Saturation in carbon assimilation of algae occurred at irradiances approximately 100 μmol m-2 s-1 or less and saturation points of dinoflagellates were higher than diatom or raphidophyceaen algae. Photoadaptation in low irradiance and photoprotection in high irradiance were observed in these algal group. Three types of photoadapation strategies have been observed based on P-I curves of chlorophyll a and cell normalized photosynthetic rate (Pchl and Pcell, respectively). Photoadaptation of dinoflagellates was accomplished by increase in cellular pigment and Pcell to suggest the increase of photosynthetic unit (PSU) numbers per cell. In Pseudo-nitzschia pungens, photoadaptation by decrease of Pchl with increasing the size of light-harvesting component of PSU. However, in Heterosigma akashiwo, Pchl and Pcell under low irradiance were higher than those under the high irradiance. It suggested that the species may have another photoapatation type. In the high irradiance(800 μmol?m-2?s-1), light-dependant and biochemical conversion of xanthophyll pigments were observed. In Chlamydomonas sp. and heterosigma akashiwo, zeaxanthin increased rapidly from vioxanthin in excessive irradiance (zeaxanthin cycle). However, dinoflagellates had diatoxanthin cycle to form diatoxanthin from diadinoxanthin.

Keywords : photoadaptation, photosynthesis, red-tide causative algae, xanthophyll cycle