COMPUTER-SIMULATION MODEL FOR THE BIOSYNTHESIS OF GALACTOSYLDIACYLGLYCEROLS AND FATTY-ACID DESATURATION IN PLANTS - DETERMINATION OF RATES OF DESATURASE ACTIVITY IN MONOGALACTOSYLDIACYLGLYCEROL

The level of unsaturation of the constituent fatty acids of many glycerolipids in plant membranes is modified by environmental factors. The measurement of the rate of the desaturation of these fatty acids is essential to an understanding of how plants adapt to changing environments. This is difficult because of the complexity of the system and the problems involved in measuring rates of these enzyme reactions in cell-free preparations. A computer program has been developed that simulates the synthesis of galactosyldiacylglycerols and desaturation of their fatty acids in chloroplasts. The program uses the rate of incorporation and distribution of C-14 in fatty acids after (CO2)-C-14 feeding to estimate rates of desaturation in the fatty acids of glycerolipids. Data are presented to demonstrate the use of the program in comparing rates of desaturation in the five enzyme reactions associated with mono-galactosyldiacylglycerol in the chloroplastic pathway of leaves from Brassica napus. The method represents a quick, reliable, and accurate measure of desaturase activity in vivo and is the only method available to estimate desaturase activity of all five enzymes at the same time.