Kinetics of Action of Different Photosystem II Herbicides on Thylakoids

The kinetics o f inhibition o f photosystem II electron transfer by different diuron-like herbi­ cides (ureas, triazines, triazinones. biscarbam ates, uraciles) were studied, mainly by chloro­ phyll fluorescence measurem ents. Uracil derivatives and cyanazine, a particu lar triazine, were the slowest acting com pounds. The half-times o f action were strongly tem perature-dependent and were o f the order o f tens o f seconds at 5 C for urea or triazine inhibitors. The role o f different lim iting steps in the binding process is discussed.