Comparison of the effects of glyphosate and related compounds on indole-3-acetic acid metabolism and ethylene production in tobacco callus

Pretreatment of tobacco callus (Nicotiana tabacum L.) with glyphosate and related compounds promoted to a different degree the metabolism of radiolabeled indole-3-acetic acid ([2-¹⁴C]IAA) by increasing both conjugation and oxidation, and consequently lowered the level of free [2-¹⁴C]IAA. At identical concentrations, glufosinate ammonium was more active than glyphosate whereas glyphosine and aminomethylphosphonic acid were less active. These compounds also selectively reduced ethylene production and inhibited fresh-weight growth of tobacco callus. The activities of the tested compounds on IAA metabolism were correlated with those on inhibition of growth, suggesting that, under the experimental condition, the effect on IAA metabolism was a major contribution to their toxic action. This information may be useful for the design and testing of new herbicides and plant growth regulators of this type.