Growth and Geotropic Responses of Avena Coleoptiles to 4‐Amino‐3,5,6‐Trichloropicolinic Acid

Abstract The elongation and geotropic responses of coleoptile sections of Avena sativa L. to various concentrations of 4‐amino‐3,5,6‐trichloropicolinic acid (Tordon) proved to be qualitatively similar to those previously reported for 2,3,6‐trichlorobenzoic acid (TCBA). Tordon stimulated growth in a range of concentrations from 1 × 10−6 to 1 × 10−4M but higher concentrations were inhibitory. Geotropic curvature was extensively depressed by 1 × 10−5 and 1 × 10−4M Tordon, concentrations which accelerated elongation. A similar differential effect has been reported for TCBA and other auxins. Several other picolinic acids and related compounds were tested, but only very slight responses were noted.