Unsaturated Fatty Acid Synthesis During the Development of Isolated Sunflower (Helianthus annuusL.) Seeds

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Abstract
The effect of temperature on unsaturated fatty acid synthesis in developing sunflower seed embryos (Helianthus annuus L.) has been studied using isolated seeds grown in culture. Variability between individual embryos in the response to temperature was also investigated. Oil and dry matter accumulation in cultured embryos were similar to those of embryos allowed to develop in intact plants, and the effect of increasing temperature in lowering the amount of linoleic acid in seed oil was reproduced in cultured embryos. The isolated seed culture system, therefore, constitutes a suitable model system for studies of oil synthesis in developing sunflower embryos. The decrease in linoleic acid synthesis in response to higher temperature was detectable after only 18 day-degrees incubation, and the incorporation of labelled substrates suggests that alterations in the fatty acid composition of seed oil in response to temperature are produced by an effect on the desaturation of newly synthesized oleate rather than through turnover of existing lipid. Variation in fatty acid composition between individual embryos grown at constant temperature was considerable. The detection of embryos with high linoleic acid levels following growth at high temperature indicates that potential may exist for the selection of cultivars for temperature-stable fatty acid composition in sunflower oil.

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