EFFECT OF NORFLURAZON ON LIPID-METABOLISM IN SOYA SEEDLINGS

Norflurazon a-alpha,trifluoro-methyl-phenyl-3-(2H)pyridazione) (San 97 89) 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 t he morphology and the physiology of the seedlings was observed. The se edlings 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-chl oroplastic lipids (mainly PC) increased. Only a few changes in total f atty composition was observed in the treated plants with a slight incr ease in the percentage of C-16:0 and a concomitent decrease in the C-1 8:3 percentage. The fatty acid composition of MGDG and DGDG were almos t totally unaffected. In PG a decrease in the percentage of C-16:1 tra ns (from 33.6 to 21.1%) was observed, while the percentage of C-16:0 a nd C-18:3 increased. In the three extra-chloroplastic classes (PC, PE and pi) a large increase in the unsaturation level was observed result ing 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 prec ursor 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 occuri ng, partly compensating the deficiency of the chloroplastic desaturase s. (C) 1998 Elsevier Science Ltd. All rights reserved.