Lipid synthesis and abundance of acetyl CoA carboxylase in isochrysis galbana (prymnesiophyceae) following nitrogen starvation

Fatty acid content and the rate of lipid synthesis were measured in the marine prymnesiophyte Isochrysis galbana grown under nitrogen starvation and in cultures recovering from nitrogen deprivation. Nitrogen starvation imposed a reduction in cellular soluble protein content, variation in fatty acid composition and reduction in the in vitro activity of the enzyme acetyl CoA carboxylase. An increase in total fatty acid content is attributed to a differential reduction in cell division and the rate of lipid synthesis. Recovery from nitrogen deprivation was characterized by an increase in cellular soluble protein content and in the rate of lipid synthesis. Although the in vitro activity of acetyl CoA carboxylase increased as the cultures recovered from nitrogen starvation, the total cellular fatty acid content decreased, evidently due to an acceleration in cell division. The relative cellular pool size of acetyl CoA carboxylase determined by immunoblotting decreased under nitrogen starvation conditions and increased as cells recovered from it. Cellular accumulation of acetyl CoA carboxylase during recovery from nitrogen starvation is ascribed to de novo synthesis of the enzyme that takes place in the cytoplasm. However, photosynthetic proteins such as ribulose bisphosphate carboxylase are synthesized earlier than acetyl CoA carboxylase in the recovery process.