IMPACT OF UV-RADIATION ON THE PRODUCTION PATTERNS AND COMPOSITION OF DISSOLVED FREE AND COMBINED AMINO-ACIDS IN MARINE-PHYTOPLANKTON

Using the C-13 tracer technique in conjunction with gas chromatographic-mass spectrometric (GC-MS) techniques, we examined the patterns of synthesis and the composition of dissolved free and combined amino acids within phytoplankton photosynthesizing in the presence and absence of natural solar ultraviolet radiation (UVR). At levels that still permitted the uptake of carbon assimilation into the cells, WR caused a marked decline in the overall rate of cart,on incorporated into amino acids and a reduction in the pool size of total cellular amino acids (TCAA). In contrast, absolute concentrations of amino acids within the intracellular dissolved free amino acid (INDFAA) pool (measured using an amino acid analyzer) were higher in the presence of UVR. An examination of the production patterns and composition of amino acids constituting the INDFAA and TCAA pools revealed a marked diminution in the synthesis and accumulation of alanine and valine in the presence of UVR. On the other hand, the rates of synthesis and concentrations of glutamic acid (glutamic acid + glutamine) in the INDFAA and TCAA pools of phytoplankton were higher in samples exposed to UVR. These changes are discussed with reference to the known effects of UVR on nitrogen and carbon assimilation within phytoplankton.