AN INVESTIGATION OF HERBICIDE INTERACTION WITH THE H-ATPASE ACTIVITY OF PLANT PLASMA-MEMBRANES()

This study has investigated the activity of several herbicide classes at the plant plasma membrane. Two-phase partitioning was used to prepa re highly purified plasma membrane vesicles from the monocotyledon wee d black-grass (Alopecurus myosuroides Huds.) and the dicotyledon crop sugar beet (Beta vulgaris L. cv. Celt). The purity of the plasma membr ane H+-ATPase activity was characterised with respect to inhibitors, p H and substrate specificity. In both species, contamination of the pla sma membrane by tonoplast fragments was largely eliminated and chlorop hyll was absent. In addition, the plasma membrane H+-ATPase from black -grass and sugar beet exhibited high vanadate sensitivity and a sharp pH profile around 6.5. Subsequently, H+-ATPase activity was assayed in the presence (100 mu M) and absence of four graminicide classes and a uxin-type herbicides. Graminicides, including the aryloxyphenoxypropio nate diclofop-methyl and the thiocarbamate triallate, inhibited H+-ATP ase activity by 50-80% in both species. However, other graminicides, i ncluding the cyclohexanediones and the chloroacetamide alachlor, had n o affect. Similarly, auxin-type herbicides such as 2,4-D and MCPA did not inhibit H+-ATPase activity. Results are discussed in relation to t he proposed mode of action of these herbicides. (C) 1998 SCI.