Carbon dynamics of logarithmetic and stationary phase phytoplankton as determined by track autoradiography

Track autoradiographic analysis of photosynthetic radiocarbon incorporation at the cellular level indicated that the carbon uptake rate and carbon pool size of exponentially growing (log phase) Scenedesmus cells was threefold that of stationary phase cells, while carbon turnover rates were similar. Carbon fixation was uncoupled from growth and cell division in the stationary phase cells, which were larger and contained less chlorophyll per unit volume than log phase cells. Changes in the temporal pattern of isotope incorporation were evident at the cell level prior to the cessation of division and transition to stationary phase, while bulk carbon fixation responded only the second day after cell division ceased. The carbon uptake patterns of a marine nanoplankter from a nutrient-enriched natural sample resembled that of log phase cells while the control population pattern resembled that of stationary cells. The physical, biochemical, and metabolic differences between log and stationary phase cells are potentially measurable by flow cytometry procedures currently in use and under development. The use of flow cytometry to sort cell types for analysis by track autoradiography and subsequent correlation of metabolic characteristics with flow cytometry signatures is a feasible means of investigating the heterogeneity of phytoplankton metabolic state in the marine environment.