STUDIES ON PLANT GROWTH-REGULATING SUBSTANCES

Three synthetic growth-regulating substances, α-(2-naphthoxy)-, α-(2:4-dichloro-phenoxy)- and α-(2:4:5-trichlorophenoxy)-propionic acids, have been resolved into their (+)- and (-)-forms. The physiological activity of these isomers and of the racemic compounds has been investigated using the pea curvature and Avena cylinder test methods of assessment.
The (+)-isomers in each case displayed high activity in both tests, whereas that exhibited by the (-)-isomers was negligible. The racemic compounds showed intermediate activity.
The mode of action of aryloxyalkylcarboxylic acids is discussed in the light of the results presented. These considerations suggest the possibility that the activity of the (+)-isomers might be antagonized by the presence of the corresponding inactive enantiomorphs. Our experiments show that such antagonism does in fact operate.