Metabolic inhibition of size-fractionated marine plankton radiolabeled with amino acids,glucose, bicarbonate,and phosphate in the light and dark

The effects of various metabolic inhibitors (dichlorophenyl dimethylurea, chloramphenicol, cycloheximide, carbonyl cyanide m-chlorophenyl hydrazone) on the accumulation of radiolabeled substrates (amino acids, glucose, bicarbonate, phosphate) by size-fractionated marine microbial plankton from the Sargasso Sea and the eastern Canadian arctic were studied in time-course fashion during experimental incubations either exposed to or shielded from ambient solar radiation. Picoplankton accounted for 65% of the organic substrates and phosphate accumulated by the assemblages. The rate of organic substrate accumulation was stimulated by solar radiation in some cases but inhibited in other cases. Presumably, stimulation and inhibition co-occur and the measured response is the net result arising from these counteracting tendencies. Approximately 40% of H¹⁴ CO₃^– accumulation in the Sargasso Sea was associated with the picoplankton. The insensitivity of picoplankton¹⁴C-labeling to cycloheximide suggested active prokaryotic photosynthesis rather than heterotrophic assimilation of¹⁴C-labeled algal photosynthates as the route of labeling. The usefulness of some inhibitors was restricted in this study because of inconsistent correlations between the intended primary metabolic effect and the measured ecological response within the duration of the experiment.