EFFECT OF UV-B RADIATION ON THE FATTY-ACID COMPOSITION OF THE MARINE-PHYTOPLANKTON TETRASELMIS SP - RELATIONSHIP TO CELLULAR PIGMENTS

The effect of UV-B (280 to 320 nm) radiation on the fatty acid and pigment composition of Tetraselmis sp. was examined as part of a larger effort to understand the possible consequences of an enhancement in natural levels of UV-B radiation on photosynthetic processes in marine phytoplankton. At levels that still permitted the assimilation of carbon within the cell, UV-B radiation induced a rapid increase in intracellular carotenoids and a marked decline in chlorophyll a. Absolute concentrations of fatty acids within the cells were lower in presence of UV-B, attributable largely to suppression of polyunsaturated fatty acid (PUFA) synthesis. The suppression of PUFAs by UV-B radiation and the inability of the cells to produce these compounds in the dark suggests that over a diel cycle, if natural phytoplankton are exposed to UV-B radiation during the day, the tells may be incapable of restoring the cellular balance of fatty acids during the night. Amongst the PUFAs, the production of 16:4 was highly susceptible to UV-B radiation. In contrast, the production of the saturated fatty acid 16:0 continued unabated in the presence of UV-B radiation. The carbon weight ratio of 16:0 to 16:4 related well with the dose of UV-B radiation and appears to be a promising indicator of UV-B induced stress in green algae. A hypothesis explaining the selective suppression of cellular PUFA synthesis, in particular that of 16:4 by UV-B, is presented and discussed in relation to concurrent changes in intracellular pigments. The implications of enhanced UV-B radiation on the marine food chain and on biogeochemical cycling in the sea are discussed in the light of these findings.