Comparison of fatty acid composition in tissues of low linolenate mutants of soybean

Phosphatidylcholine and monogalactosyldiacylglycerol are the proposed substrates for fatty acid desaturation to form linolenic acid (18:3) in plant tissues. A comparative analysis of the compositions of PC and MGDG molecular species, together with determination of total fatty acids, was conducted in the soybean cv. Century and in C1640, a low 18:3 mutant, to evaluate the expression of this mutation in the two classes of lipids among various tissues. Seeds of C1640 and A5, another low 18:3 mutant, had decreased 18:3 levels in cotyledons and axes but not in seed coats. Vegetative tissues of C1640 and A5 had lower 18:3 levels in roots but not in leaves and stems. The amount (mo1%) of 16:0/18:3 and 18:3/18:3 PC species in cotyledons and 18:3-containing PC species in axes, decreased in C1640 compared to Century. The reduction of 16:0/18:3 and 18:3/18:3 species in both PC and MGDG also occurred in roots but little alteration existed in leaves and stems of C1640. The present results suggest the existence of a possible common mechanism for the formation of 18:3 in roots and seeds which is different from leaves and stems.