Biological evidence for a 1:1 Ca2+:glyphosate association in deposit residuals on the leaf surface of barley

It has long been known that calcium ion antagonizes glyphosate, but it was not clear whether the stoichiometry of their interaction is 1:1 or 1:2. Two independent methods were used to determine which stoichiometry was the most probable. First, dose-response curves of barley (Hordeum vulgare L.) plants treated with glyphosate were determined in the presence of 0, 1.25, 2.5, 5 and 10 mM CaCl 2 . The doses of 'free' glyphosate (=not inactivated by calcium ion) were computed using the assumptions of 1:1 and 1:2 stoechiometries. The response curves were redrawn as a function of 'free' glyphosate. Analysis showed that the 1:2 hypothesis could be rejected, whereas the 1:1 hypothesis was highly pro…