Variations in Distribution of14C in Cell Extracts of Phytoplankton Living Under Natural Conditions

A modification of the14C technique was used to study variations in the distribution of14C in cell extracts of phytoplankton living under natural conditions. In the upper photic zone (0.5 m), cell volume declined steadily from April to June, but total14C uptake increased gradually with increasingly large fractions of14C incorporated into an ethanolsoluble cell extract (probably low molecular weight carbohydrates and organic acids) rather than into an insoluble fraction (probably protein and polysaccharides). In the middle photic zone (3 m), cell volume also declined and total14C uptake increased gradually, but increasingly large fractions of14C were in the insoluble fraction. Cell volume and total14C uptake in the lower photic zone (6 m) increased proportionally. Increasingly large fractions of14C were in the insoluble fraction from March to June. Variations in14C distribution appear to be related to active cell turnover during a Synedra sp. bloom on one occasion and to chromatic adaptation by the dominant phytoplankter Oscillatoria rubescens at another time.