Increases in Free Amino Acid Levels in Tomato Plants Accompanying Herbicide-Induced Disease Resistance

Abstract

Tomato seedlings grown in the presence of low levels of various dinitroaniline herbicides to induce resistance toFusarium oxysporumSchlecht f. sp.lycopersicihad strongly elevated levels of free amino acids. The greatest change occurred with the two most prominent amino acids in tomato seedling tissues, glutamine and asparagine. The dose-related changes in response to herbicide treatment were largest in roots but levels in hypocotyls and cotyledons were also increased significantly. Plants treated similarly with the unrelated herbicide acetochlor, which does not induce resistance, had near normal levels of free amino acids. Tests following removal of the seedlings from contact with the dinitroaniline herbicide trifluralin indicated that disease protection was short-lived and the loss of resistance was accompanied by a decline in the level of the free amino acids. The possible impact of increased levels of free amino acids on resistance to disease is discussed. Although free amino acids are probably not directly related to the observed protection, it is proposed that the levels in the roots of tomato seedlings treated with dinitroaniline herbicides and possibly other inducers can be used as an indicator of the extent of resistance induction.