Morphological and molecular changes in the unicellular green alga Dunaliella salina grown under supplemental UV-B radiation: cell characteristics and photosystem-II damage and repair properties

The effect of supplemental UV-B radiation during growth in the green alga Dunaliella salina was investigated. At the cellular level, supplemental UV-B radiation induced a doubling of the cell volume, a phenomenon attributed to a slow-down in the rate of cell division. At the thylakoid mebrane level, supplemetal UV-B radiation induced photodamage to the 32 kDa (D1) and 34 kDa (D2) reaction center proteins of Photosystem II. The molecular target of photodamage to D1 and D2, and the temporal sequence of events leading to repair of Photosystem II from this UV-B photodamage, appeared to be different from those that operate under photosynthetically active radiation (PAR). Thus, mechanistically, photodamage and repair under supplemental UV-B may be a distinctly different phenomenon from the damage and repair cycle induced by visible light.