Effect of norflurazon on lipid metabolism in soya seedlings

Norflurazon (4-chloro,5-methylamino-2-alpha-alpha-alpha,trifluoro-methyl-phenyl-3-(2H)pyridazione) (San 9789) was applied before sowing to soya seeds (Glycine max., var. Weber). At concentrations between 10(-6) M and 10(-4) M a strong effect on the morphology and the physiology of the seedlings was observed. The seedlings became depigmented due to photobleaching of the photosynthetic pigments. A 40% reduction of the total lipid content was observed at 10(-4) M. The chloroplastic contents of MGDG, DGDG and PG decreased of 41%, 63% and 22%, respectively. In contrast, the content in extra-chloroplastic lipids (mainly PC) increased. Only a few changes in total fatty composition was observed in the treated plants with a slight increase in the percentage of C-16:0 and a concomitent decrease in the C-18:3 percentage. The fatty acid composition of MGDG and DGDG were almost totally unaffected. In PG a decrease in the percentage of C-16:1 trans (from 33.6 to 21.1%) was observed, while the percentage of C-16:0 and C-18:3 increased. In the three extra-chloroplastic classes (PC, PE and pi) a large increase in the unsaturation level was observed resulting from an increase in the percentage of C-18:3. Studies of the lipid metabolism using radioactive labelling with [I-C-14]acetate as a precursor led to the conclusion that, in plants treated with norflurazon, the intra-chloroplastic pathway of desaturation was inhibited while a stimulation of the extra chloroplastic desaturation pathway was occuring, partly compensating the deficiency of the chloroplastic desaturases. (C) 1998 Elsevier Science Ltd. All rights reserved.