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

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Abstract
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 (14)CO(2) at different stages after flowering, and the (14)C-incorporation into the grain lipids was determined at 2, 24, and 48 hours after the end of (14)CO(2)-application. By changing growth temperature from 12 C to 28 C after the application of (14)CO(2) to intact plants, a higher (14)C-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-(14)C shortly after the (14)CO(2)-application, whereas at 12 C the corresponding values were 19% and 4%, respectively. Within 2 days (14)C-activity of saturated fatty acids decreased at both temperatures, but to a lesser degree at 28 C. The higher (14)C-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 (14)C-activity of all fatty acids shortly after the (14)CO(2)-application. However, (14)C 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 (14)C-saturated fatty acids increases primarily at the expense of (14)C-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.