Chlorsulfuron blocks 2,4-D-induced cell enlargement and NADH oxidase in excised sections of soybean hypocotyls.

Elongation of soybean hypocotyl sections induced by the auxin herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), was blocked by micromolar concentrations of the sulfonylurea herbicide chlorsulfuron (2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-trizin-2- yl)amino]carbonyl]benzenesulfonamide). The inhibition at equimolar concentrations of 2,4-D and chlorsulfuron was overcome by a 10- or 100-fold excess of 2,4-D. Stimulation by 2,4-D of an 2,4-D-responsive NADH-oxidase activity of the soybean plasma membrane also was blocked by the presence of concentrations of chlorsulfuron equimolar to the 2,4-D. Chlorsulfuron alone was largely without effect on either cell elongation or the auxin-stimulated NADH-oxidase activity over a range of chlorsulfuron concentrations. The results show a clear correlation between inhibition of auxin-stimulated cell elongation and the inhibition of an auxin-stimulated component of a plasma membrane NADH-oxidase activity.