Synthesis, composition and location of glycerolipids in photoautotrophic soybean cell cultures

Abstract

The location, synthesis and composition of glycerolipids in photoautrophic soybean ( Glycine max L. Merr.) cell cultures were investigated to begin to elucidate the function of neutral lipids in photosynthetic tissues. The neutral lipids, diacylglycerol and triacylglycerol, were primarily located in the chloroplast which was also the primary location of diacylglycerol acyltransferase (EC 2.3.1.20), the final enzymatic step in the synthesis of triacylglycerol. The chloroplasts were also the primary location of synthesis of fatty acids from acetate and lysophosphatidic acid by glycerophosphate acyltransferase (EC 2.3.1.15). Neutral lipid made up to 20% of the total glycerolipid in dark-grown heterotrophic cells, 10% in photoautotrophic cells (both 2 weeks after subculture) and less than 1% in leaf cells. The amount of neutral lipid in photoautotrophic cells was maximal 1 week after transfer and declined to less than half that value 4 weeks after transfer. Starch content, however, increased for up to 3 weeks after transfer in parallel with dry weight accumulation. The data suggest that in these cells neutral lipids may serve for temporary storage of fatty acids and glycerol for later membrane synthesis rather than for storage of energy, a function of neutral lipids in seeds.