The effects of Z(3-phenyl-1,2,4,4-thiadiazol-5-yl)thio] acetic acid, a synthetic growth regulator, on auxin uptake by tobacco stem segments and crown gall suspension culture cells

Abstract

Z(3-phenyl-1,2,4-thiadiazol-5-yl)thio] Acetic acid (PTAA) is a novel synthetic plant growth regulator causing disturbance of trophic responses and increased branching in one-year-old apple trees and a variety of other species. Its effects are similar to those of 2,3,5-triiodobenzoic acid (TIBA), an inhibitor of popular auxin transport. Auxin uptake by both tobacco stem segments and Parthenocissus tricuspidata crown gall tissue culture cells is stimulated 2–3 fold by both PTAA and TIBA, probably as a result of inhibition of a component of auxin efflux from the cells. The optimum concentration of PTAA is 0.5–10 μ mol/l at pH 4.5 and 10–100 μ mol/l at pH 6.5 for the crown gall cells and about 10 μ mol/l at Ph 6.0 for tobacco stem tissue. It is suggested that PTAA may be an inhibitor of polar auxin transport. Such inhibition may partly account for its growth-modifying properties.