[Formation of polyunsaturated fatty acids in plants].

Higher plants synthesize large amounts of linoleic and alpha-linolenic acids by progressive desaturation of oleic acid. Plant desaturases are active only during a short period of the development of seeds or leaves. 14C-oleate desaturation has been followed experimentally in various plants (Rapeseed, Sunflower, Flax and Potato). With aged potato slices, it has been shown that oleate-desaturase is an inducible enzymatic system. With microsomes isolated from aged potato-slices, 14C-oleoyl-CoA has been desaturated in vitro. Recent results suggest that oleoyl-phosphatidylcholine is the true substrate of the desaturation system. The formation of the alpha-linolenic acid of chloroplasts has not been obtained in vitro, up to now. In vivo, the newly formed linolenic acid is found in chloroplast galactolipids. In conclusion, difference between animal and plant desaturases are underlined.