Response of polyamine pools in marine phytoplankton to nutrient limitation and variation in temperature and salinity

Previous field observations suggest that the composition of intracellular polyamine pools in phytoplankton determines the profile of polyamines released to the surrounding environment; thus, knowing how these pools vary among species and in response to factors affecting phytoplankton growth provides a basis for understanding fluctuations in dissolved polyamines. Our analyses of the polyamine content of axenic marine phytoplankton cultures show that intracellular polyamine pools are large (100s to 1000s mu mol l(-1) of biovolume) and that putrescine and spermidine are the major compounds present; however, composition varied with species. Norspermidine and norspermine were the dominant compounds found in the diatom Thalassiosira pseudonana and the dinoflagellate Amphidinium carterae, respectively. We explored the effects of temperature, salinity and nutrient limitation on polyamine pools in T. pseudonana, and found that either increasing temperature or decreasing salinity increased polyamine concentrations in cells and in the growth medium. Nutrient (N, P or Si) limitation caused reductions of intracellular polyamine concentrations, but release was enhanced under N or Si limitation. Polyamine ratios in the media were not the same as in intracellular pools, suggesting selective release or uptake of polyamines by phytoplankton. Thus, the composition of the dissolved polyamine pool in seawater can vary significantly and on short time scales, depending on phytoplankton community composition and environmental factors affecting phytoplankton physiology. Our work provides experimental verification that biological mechanisms support inferences derived from environmental correlations about the factors controlling polyamine distributions in the sea.