The effect of haloxyfop-ethoxyethyl on lipid metabolism in oat and wheat shoots

The grass herbicide haloxyfop-ethoxyethyl was applied in 52 % ethanol solution to the first leaf of oat and wheat plants at the one and a halfleaf stage. At various times after the application to the shoots were cut at the upper end of the coleoptile sheath and the growth from the cut area was determined. An inhibition of the growth of oat was obvious in plants cut 3-6 h after application and was total in plants cut 14 h after treatment. In wheat the reaction was somewhat slower. At the same time as inhibition of growth was noted, a reduction in the total amount of lipids per g fresh weight and a mol percentage increase in linolenic acid were observed in the treated plants. The effects were most distinct in the basal parts of the shoot and no effect was seen in the coleoptile sheath. The largest changes both quantitatively and in the relation between the fatty acids were found in phosphatidylcholine. Incorporation of exogenous 14C-acetate was studied in various parts of treated and non-treated wheat plants, and it was similar in the treated plants and in the control plants. The distribution of 14C-label between the fatty acids markedly differed from the endogenous fatty acids profile in both treated and non-treated plants. The main part of the radioactivity was incorporated into fatty acids shorter than 16 C-atoms, in palmitic acid and oleic acid, with only 11-21% found in polyunsaturated fatty acids. The simultaneous decrease in lipid content and relative increase in linolenic acid in the haloxyfop-treated plants indicate that the enzymes desaturating the oleic and linoleic acid in complex lipids are unaffected, or less inhibited than the net-lipid synthesis by haloxyfop treatment. Also, de novo fatty acids synthesis from exogenous 14C-acetate was unaffected by herbidide treatment