Abscisic Acid in Tobacco Plants

Abstract

In tobacco plants inoculated with the wilt-inducing bacterium, Pseudomonas solanacearum, there was a correlation between decreased internode elongation, maximum multiplication of the bacterium, and an increase in the growth inhibitor content of stems 4 to 12 days after inoculation, as determined by a wheat coleoptile assay. Initial wilting of the upper leaves was also correlated with an increase in inhibitor content of these tissues.Application of either the partially purified inhibitor from tobacco or pure (+)-abscisic acid to roots, terminal buds, or petioles of tobacco plants caused a reduction of internode length which lasted from 8 to 10 days following a single treatment. Repeated treatment was necessary to obtain growth retardation over a longer period of time.The tobacco inhibitor was tentatively identified as abscisic acid, based on a comparison with authentic abscisic acid on paper, thin layer, column, and gas-liquid chromatography. On the basis of optical rotatory dispersion, circular dichroism, and ultraviolet spectra, the tobacco inhibitor was indistinguishable from abscisic acid. Increases in the inhibitor content of infected tissues are attributed primarily to abscisic acid although other substances, not separable from abscisic acid by the procedures used, could also play a role. The inhibitor was not found in P. solanacearum culture medium.