The mode of action and selectivity of the hydroxybenzonitriles in selected weed species

Abstract

This paper was given at the conference organised by the Association of Applied Biologists held at Cambridge on 25-26 March 1986. The mode of action and selectivity of ioxynil-Na and bromoxynil-K is described in Matricaria inodora [M. perforata] (susceptible to ioxynil-Na and acutely susceptible to bromoxynil-K) and Viola arvensis (moderately resistant and resistant, resp.). More than 80% of the 14C-herbicide taken up remained in the treated leaf causing chlorosis and necrosis. CO2 fixation was inhibited and ultrastructural changes developed within 48 h. In V. arvensis, where CO2 fixation partially recovered, adaptative changes in chloroplast ultrastructure such as broader and higher granal stacks occurred. 14C-bromoxynil-K was more mobile than 14C-ioxynil-Na. More translocated 14C-ioxynil was recovered in the M. inodora apex than in that of V. arvensis. Bromoxynil appeared to be metabolized in V. arvensis. There were no interspecific differences in herbicide activity in thylakoids. Ioxynil was 3 to 4 times more effective as an inhibitory uncoupler in isolated chloroplasts. Ioxynil partially replaced bound 14C-bromoxynil in radioactive tracer studies whereas bromoxynil did not replace 14C-ioxynil.