EFFECTS OF ENDOTHALL AND OTHER AQUATIC HERBICIDES ON CHLOROPHYLL FLUORESCENCE, RESPIRATION AND CELLULAR INTEGRITY

Part of the mode of action of several aquatic herbicides is cellular d isruption which can be caused by the generation of oxygen radicals or loss of adenosine triphosphate (ATP) needed to maintain cellular integ rity. In an attempt to distinguish between the varying mechanisms by w hich certain compounds cause cellular disruption, ion leakage (light a nd dark regimes), chlorophyll fluorescence, and oxygen consumption (a normal consequence of respiration) were monitored over time from leaf tissue exposed to endothall, simazine, dinoseb, diquat and gramicidin. All compounds, except simazine, caused high ion leakage in both light and dark. Diquat caused more rapid leakage in light, while endothall and gramicidin caused more rapid leakage in the dark. Diquat, dinoseb and simazine increased chlorophyll fluorescence, but endothall and gra micidin did not. Oxygen consumption was stimulated by gramicidin and d iquat but inhibited by endothall and dinoseb. Comparing the effects of compounds with known mechanisms-of-actions on ion leakage, chlorophyl l fluorescence and oxygen consumption suggest that endothall acts to i nhibit respiration.