Products of photosynthesis in phytoplankton off the Orinoco River and in the Caribbean Seal

Abstract

Incorporation of [14C]bicarbonate into the major end-products of photosynthesis (low molecular weight metabolites, lipid, polysaccharide, and protein) was measured at a number of stations in tropical waters. Stations with highest chlorophyll concentrations showed almost equal synthesis of low molecular weight metabolites, lipid, polysaccharide, and protein. The "oligotrophic" stations showed a greater incorporation into polysaccharide and protein and proportionally less into the other two fractions. Inshore stations also showed higher activities of the photosynthetic carboxylating enzyme, ribulose-1,5-bisphosphate carboxylase, in relation to that of the anaplerotic replenishment enzyme, phospho(enol) pyruvate carboxylase. The inshore, high chlorophyll stations were characterized by higher particulate carbon : chlorophyll ratios. However, the polysaccharide and protein contents (normalized to particulate carbon) were not higher in the offshore samples showing high incorporation of 14C into those polymers. Carbon-specific assimilation rates were greater for total C incorporation than for incorporation into the various polymers. This was most marked when assimilation was measured only over a period in the light. © 1981, by the American Society of Limnology and Oceanography, Inc.