Auxin Antagonistic Effects of Auxin Precursors of the Substituted Amide Type

Cucumber seeds were germinated in Petri-dishes for 6 days withdifferent doses of a number of N-monosubstituted amide derivativesof some chlorophenoxy-alkane-carboxylic acids. Doses of theamides studied were roughly equivalent to 0.1, 1, 10, 100, and1,000 p.p.m. in water. The gross morphological effects of theamide treatments were studied, both with and without the additionof 1 and 10 p.p.m., respectively, of the corresponding carboxylicacid. The amides studied were the N-methyl-, N-ethyl-, N-propyl-,N-iso-propyl-, N-butyl-, and N-benzyl-amides of 2,4-dichlorophenoxyaceticacid (2,4-D), -(2,4-dichlorophenoxy)-propionic acid (2,4-DP),2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and -(2,4,5-trichlorophenoxy)-propionicacid (2,4,s-TP). Thirteen of the twenty-one amide derivatives studied antagonizedthe auxintype plant-growth-regulating effects of their parentcarboxylic acid. The antagonisms observed involved not onlya decrease in the stimulatory effects of the externally appliedauxin acids (counteractions of the abnormal swellings of differentplant parts), but also reduced significantly their inhibitoryeffects, i.e. the inhibitions of growth in length of the hypocotyland of the roots. Since some auxin-type stimulatory effectswere observed with all of the amides studied, it is suggestedthat the thirteen amide derivatives play a double role as plantgrowth regulators in cucumber tissues: (1) to a certain extentthey are transformed by plant enzymes to the corresponding carboxylicacid, i.e. to auxin; and (2) the amides themselves exert anti-auxineffects.