Metabolism of neutral monosaccharide constituents of storage and structural carbohydrates in natural assemblages of marine phytoplankton exposed to ultraviolet radiation

We used the C-13 tracer technique in conjunction with gas chromatography-mass spectrometry to examine the impact of ultraviolet radiation (UVR) on the patterns of biosynthesis and composition of monosaccharides in natural assemblages of phytoplankton photoadapting to high light intensities. Exposure to UVR resulted in a decrease in the rates of phytoplankton photosynthesis and a marked reduction in the rates of production and pool sizes of neutral monosaccharides within the storage carbohydrate fraction (operationally: defined as carbohydrates soluble in hot water). In contrast, the biosynthesis of neutral monosaccharides associated with cell wall or structural carbohydrates (operationally defined as the fraction of carbohydrates insoluble in hot water) showed an increase in the presence of UVR, which, although marginal, was consistent from station to station. The decline in pool sizes of monosaccharides within the storage carbohydrate fraction was largely responsible for the decline in the overall carbohydrate content of the cells. The diminution in the rates of synthesis and pool sizes of glucose within this fraction represented one of the most significant differences compared to phytoplankton shielded from UVR. In the structural carbohydrate fraction, the synthesis of several component monosaccharides was consistently higher in phytoplankton exposed to WR.