MICROBIOASSAYS TO DETERMINE THE ACTIVITY OF MEMBRANE DISRUPTER HERBICIDES

Two methods to determine the activity of membrane disrupter herbicides on leakage from cucumber (Cucumis sativa L., ''Medalist'') cotyledon discs are described. In these bioassays, leakage could be measured fro m a single disc (4 mm diameter) in 300 mu l of incubation solution. Th e 96-well microtiter plates were convenient assay containers because a large number of replications and herbicide concentrations could be re sted side-by-side without an excessive space requirement. In the first assay, nitrite leakage was measured from discs incubated in nitrate s olution. Nitrite was sequestered in cells as long as the membranes rem ained intact. A loss in membrane integrity, caused by membrane disrupt er herbicides (acifluorfen, oxyfluorfen, paraquat, oxadiazon, sulfentr azone), resulted in the leakage of nitrite into the incubation solutio ns. Membrane disruption was also measured directly with N-methyl benzo thionoline hydrazone hydrochloride which forms a stable chromatophore with saturated and unsaturated aldehydes, ketones, keto acids, and man y other related compounds. Leakage of ammonia and malonyl dialdehyde w ere also measured. These assays may have advantages in industrial or a cademic laboratories where comparison of the activities of herbicides under several experimental conditions is necessary. (C) 1995 Academic Press, Inc.