This project examines aspects of sphingolipid synthesis in plants. The objectives are to characterize sphingolipid synthesis and its regulation at the point of long chain base formation; to characterize the enzymatic steps involved in modifying long chain base and fatty acid components of sphingolipids and investigate the metabolic interrelationships of species involved in the formation of glucosylceramide, the predominant plant sphingolipid; and to assess degradation and turnover of glucosylceramide. Plant cell suspension cultures and rye seedlings are used as experimental systems. These two plant systems have diverse glucosylceramide molecular species compositions. The use of plant cell suspension cultures facilitates detailed in vivo studies of the regulation of sphingolipid synthesis and complements studies aimed at characterizing selected enzymatic steps in cell-free systems. Radiolabeled precursors are supplied in vitro or in vivo and the incorporation into sphingolipid products determined following separation by TLC and HPLC. Aspects of regulation are investigated under conditions in which sphingolipid metabolism is altered as a consequence of development or in response to environmental factors or biochemical regulators. It is anticipated that these studies, the first of their kind in plant cells, will provide information on the cellular regulation of sphingolipid metabolism. Current dogma holds that plant and animal cells respond to temperature stress by altering the lipid composition of their membranes. Very little experimental evidence has been generated to test this hypothesis. This project provides new information on a newly discovered class of lipids and how they change in type and amount when plants are exposed to low temperature. Fundamental new information on plant lipids will result.
