Selective herbicide activity of 2,5-di(benzylamine)-p-benzoquinone against the monocot weed Echinochloa crusgalli. An in vivo analysis of photosynthesis and growth.

Six 2,5-diamino-p-benzoquinone derivatives previously characterized as photosystem I electron acceptors were tested for their postemergence herbicide activity. By induction kinetics of chlorophyll a fluorescence performed in vivo it was determined that 2,5-di(benzylamine)-p-benzoquinone diverted electrons at the reducing side of the chloroplast photosystem I. This derivative decreased the efficiency of photosystem II as evidenced by the decrease in the F(v)/F(m) change in Echinochloa crusgalli leaf disks. In addition, 2,5-di(benzylamine)-p-benzoquinone was a CO(2) assimilation inhibitor to Rubisco: the A/C(i) curve analysis indicates that 2,5-di(benzylamine)-p-benzoquinone affected both the carboxylation reaction itself and the regeneration of RuBP. 2,5-di(benzylamine)-p-benzoquinone did not exhibit any effect on the dicot plants Phaseolus vulgaris and Physalis ixocarpa or the monocot Zea mays. These species may have metabolized the herbicide to an inactive compound. Thus, 2,5-di(benzylamine)-p-benzoquinone was found to be a selective herbicide against the monocot weed E. crusgalli.