Subcellular Phosphorus Kinetics for Lake Ontario Plankton

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Abstract
The subcellular distribution of recently incorporated 32PO4 was used to demonstrate that plankton in the surface waters of Lake Ontario were phosphorus deficient to some extent throughout the entire study period from April to October 1982. Most (~80%) of the initial uptake of carrier-free radioactive PO4 was in the low molecular weight (LMW) fraction. Ribonucleic acid (RNA) was the other major fraction. Although uptake was often complete within 1 h, changes in the subcellular distribution continued for 6–20 h with about half the LMW32P being transferred to RNA. Both a phospholipid fraction and a fraction extracted with hot trichloroacetic acid (HTCA) containing DNA and high molecular weight polyphosphate increased to 4–15% of the total isotope incorporated. In contrast with these experiments where net P uptake was zero, with added PO4 the net influx continued for periods in excess of 30 h but the subcellular distribution was constant within 2–4 h. About 80% of the initial uptake was as LMW32P and a rapid net synthesis of LMW polyphosphate was observed. These patterns were common for both small and large plankton size classes.