Bleaching herbicide effects on plastids of dark-grown plants: lipid composition of etioplasts in amitrole and norflurazon-treated barley leaves

The effects of the bleaching herbicides amitrole (125 muM) and norflurazon (100 muM) on etioplast lipids were studied in barley plants (Hordeum vulgare L. cv. Express) grown for 7 d either at 20degreesC or 30degreesC in darkness. Total lipid, glycolipid and phospholipid contents of control etioplasts were increased at 30degreesC in comparison with those at 20degreesC. The two herbicides caused a decrease in the total lipid, glycolipid and phospholipid amounts compared to the untreated etioplasts and lowered the lipid to protein ratio. In the controls, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) accounted for about 66 mol% of the etioplast polar lipids, while the remainder was represented by sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), in approximately equal proportions. Both amitrole and norflurazon increased MGDG at both temperatures, but decreased DGDG except with norflurazon at 30degreesC. As a consequence, the MGDG to DGDG molar ratio was higher in the herbicide-treated etioplasts compared to the controls at both the growth temperatures. The amount of the negatively charged polar lipids SQDG and PG were decreased by treatments with amitrole at 20degreesC and norflurazon at 30degreesC. The two herbicides determined different responses in the fatty acid unsaturation of the individual polar lipids. Changes in the lipid composition of etioplasts and the interaction between the pigment-protein complex, protochlorophyllide-NADPH-protochlorophyllide oxidoreductase, and polar lipids are discussed.