Lipid biosynthesis from [14C]-glucose in the coral Montipora digitata

ABSTRACT:     Glucose has been implicated in functioning as a form of carbon translocated from symbiont zooxanthellae to the host coral cell. The present paper describes the lipid biosynthesis from ¹⁴C]-glucose in the coral tissue. To study the incorporation of ¹⁴C]-glucose into lipids, the branch tips of the coral Montipora digitata were incubated with ¹⁴C]-glucose or another radiolabeled substrates. The lipid biosynthesis from ¹⁴C]-glucose was dependent on light, and was decreased by dark conditions or by photosystem II inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Of the lipid classes, the light dependency was more pronounced with the biosynthesis of triacylglycerols (TG) and wax compared with phospholipids. Examination of ¹⁴C]-label distribution in the glycerolipids suggested that ¹⁴C]-glucose supplied mainly the fatty acid moiety of newly synthesized TG, while ¹⁴C]-glucose provided evenly the fatty acid moiety and the glycerol skeleton of phospholipids. The comparison of ¹⁴C]-labeling of lipid from host coral tissue and symbiont zooxanthellae suggested that ¹⁴C]-glucose entered the coral cell and was processed in parallel in the zooxanthellae and host cells. Furthermore, the coral cells used various ¹⁴C]-labeled sugars for lipid synthesis with similar lipid labeling profile as was the case for glucose. The current study thus supports the view that the low-molecular-weight compound, sugars and amino acids, once translocated from zooxanthellae to host cell were metabolized toward lipogenesis as well as glycerol.