Influence of Temperature and Seed Ripening on the in vivo Incorporation of 14CO2 into the Lipids of Oat Grains (Avena sativa L.)

To elucidate the influence of growth temperature and of stage of maturity on lipid synthesis in seeds, oat plants (Avena sativa nuda L., variety NOS) were fed with 14CO2 at different stages after flowering, and the 14C-incorporation into the grain lipids was determined at 2, 24, and 48 hours after the end of 14CO2-application. By changing growth temperature from 12 C to 28 C after the application of 14CO2 to intact plants, a higher 14C-labeling of saturated fatty acids was found at the higher temperature. At 28 C, palmitic and stearic acids contained 23% and 9% respectively of total fatty acid-14C shortly after the 14CO2-application, whereas at 12 C the corresponding values were 19% and 4%, respectively. Within 2 days 14C-activity of saturated fatty acids decreased at both temperatures, but to a lesser degree at 28 C. The higher 14C-labeling of saturated fatty acids and its lower decrease within 2 days at 28 C clearly show a direct influence of temperature on fatty acid biosynthesis in oat grains. At all stages of grain growth, oleic acid had the highest 14C-activity of all fatty acids shortly after the 14CO2-application. However, 14C activity of oleic acid rapidly decreases in favor of linoleic acid. With increasing maturity, the intensity of lipid synthesis in the grains decreases; simultaneously, the relative amount of 14C-saturated fatty acids increases primarily at the expense of 14C-oleic acid. These tendencies, which were observed in oat plants grown at day temperatures of 12 C during seed development, seem to be paralleled by lipid synthesis in younger grains grown at day temperatures of 28 C. This indicates an indirect influence of growth temperature on lipid synthesis in oat grains during maturation.