Chloroacetamide Mode of Action, II: Inhibition of Very Long Chain Fatty Acid Synthesis in Higher Plants

Abstract

H erbicide, C hloroacetam ide, V L C FA , C ucum is sativus, H ordeum vulgare, Zea m ays In short-term -ex p erim en ts [14C ]-labelled m alonic acid, stearic acid and acetate have been incorporated into leaf fatty acids of seedlings of C ucum is sativus, H ordeum vulgare and Zea mays. The p attern of labelled fatty acids changed m arkedly by tre a tm e n t with the chloroacet am ide herbicides m etazachlor, m etolachlor or butachlor. D uring a 2-h incubation time, 1 [!M chloroacetam ide specifically in hibited up to 100% the form ation of the satu rate d very long chain fatty acids (V L C FA s) with a carb o n n u m b er o f 20, 22 and 24. In cucum ber and barley a 50% inhibition of V LC FA form ation is achieved w ith 10 to 100 nM m etazachlor rep resen t ing the m ost sensitive effect of inhibitors on fatty acid elongation re p o rte d as yet. Sensitivity of fatty acid elongation dep en d s on the am ide stru ctu re p resen t in the com pound and on its stereochem istry. Inhibition of oleic acid inco rp o ratio n correlates with grow th inhibition by chloroacetam ides of the intact cell (com p. Pestic. Sei. 52, 3 8 1 -3 8 7 , 1998). The presen t study extends this correlation to inhibition of V L C FA synthesis in higher plants. O bviously the prim ary m ode of action of chlo ro acetam id es and related herbicidal substances is involved in the enzymic four-step fatty acid elongation system.

Very-Long-Chain Fatty Acid Biosynthesis is Inhibited by Cafenstrole, N,N-Diethyl-3-mesitylsulfonyl-1H-1,2,4-triazole-1-carboxamide and Its Analogs

“…Although the approximate I50 value for oleic acid elongation in Scenedesmus for com pounds 4, 5 and 6 were about 10_ 6m , the I50 value Table II Matthes et al (1998). * 2 for the assay with Scenedesmus cells see Couderchet et al (1998).…”

“…Its phytotoxic symptoms, namely impaired seedling emergence and stunting have been reported as very similar to those of chloroacetamide herbicides, such as alachlor or butachlor (Fukazawa et al, 1995). Re cently, a strong inhibition of very-long-chain fatty acid (VLCFA) biosynthesis by cafenstrole has been found in unicellular Scenedesmus cells (Couderchet et al, 1998), in cucumber cotyledons (Matthes et al, 1998), and with a cell-free micro somal preparation from leek seedlings (Allium porrum-, Böger et al, 2000). Incorporation of exog enously applied [14C]-oleic acid into an insoluble non-lipid fraction of Scenedesmus acutus cells was drastically decreased by the herbicide.…”

“…The in-vitro biosynthesis of VLCFAs and local ization of enzymes related to elongation, as well as their purification, have been examined for seed elongases of various plants and particularly for the extraplastidic elongase of leek cells (Cassagne et al, 1994;Matthes et al, 1998;Böger et al, 2000). This information on VLCFA biosynthesis in leek prompted us to use this plant as a model to study inhibitors affecting the biosynthesis pathway.…”

Effect of fentrazamide on the growth, morphology and anatomy of Echinochloa crus-galli and Echinochloa oryzicola

“…Fentrazamide inhibited the biosynthesis of very long chain fatty acids as well as chloroacetamides, oxyacetamides, including mefenacet, cafenstrole and thenylchlor. [4][5][6][7][8] Fedtke and Hess et al reported that the morphological effect of mefenacet on green algal cells was similar to that observed for thiocarbamates and chloroacetamides. 9) The macroscopic symptoms of mefenacet on E. oryzicola were dark green coloration, stunting of leaves, and strong growth inhibition of plants.…”

Action of fentrazamide on protein metabolism and cell division in plants

“…Cycloheximide (an inhibitor of protein biosynthesis) at 10 mM showed a marked inhibitory effect on the incorporation of 24. 7) Recently, complete inhibition of VLCFA elongases from Arabidopsis thaliana by 100 mM fentrazamide treatment was reported. 8) Although fentrazamide has been used in paddy fields in Japan since its introduction in the late 1990s, the mode of action at the molecular level has not yet been elucidated.…”