INHIBITION OF FATTY-ACID DESATURATION IN SYCAMORE CELLS DEPRIVED OF IRON

The growth of isolated sycamore cells in a medium devoid of iron induc ed a marked reduction of the unsaturation level of fatty acids: the pr oportion of linolenic acid (C18:3) in polar lipids (phospholipids and galactolipids) decreased whereas a parallel increase in the proportion s of oleic (C18:1) and linoleic (C18:2) acid was observed. In our expe rimental conditions, no direct effect of iron deprivation on fatty aci d and glycerolipid biosynthesis could be observed. When sycamore cells were incubated in the presence of [C-14]acetate, the level of unsatur ation in fatty acids was very strongly reduced: no polyunsaturated fat ty acids were synthesized in iron-deprived cells: only [C-14]palmitic and [C-14]oleic acids accumulated in glycerolipids. In contrast, sycam ore cells grown in an iron-containing medium in the presence of[C-14]a cetate were able to synthesize glycerolipids containing C-14-labelled C18:2 and C18:3. We concluded that, in sycamore cells, iron is essenti al for C18:1-->C18:2-->C18:3 desaturations. In contrast, C18:0-->C18:1 desaturation is much less sensitive to iron deprivation under our exp erimental conditions.