Comparative herbicide binding by photosynthetic membranes from resistant mutants

Abstract

Resistance patterns against herbicides inhibiting photosynthetic electron transport have been obtained from several mutants of higher plants and algae. While most of the herbicides assayed show varying resistance patterns with different mutants, resistance against metribuzin is generally very high and always present. On the other hand, no resistance is measured using the phenol-type herbicide ioxynil. With both herbicides replacement experiments vs 14C-labeled atrazine yield a mixed-type competition, i.e., loss of binding sites (receptors) and increasing binding constant. Contrary to ioxynil, the phenol-type herbicide bromonitrothymol gives normal binding and (competitive) replacement data. A mutant of Bumilleriopsis filiformis was isolated which is resistant against bromonitrothymol. Resistance generally does not lead to total loss of binding of a certain inhibitor. A model with two independent receptors at a binding protein is presented, which may explain the nonspecific binding at high herbicide concentrations.