Effect of rifampin application time on crown-gall tumor induction by Agrobacterium tumefaciens

Abstract

Rifampin was applied to Kalanchöe leaves, primary pinto-bean leaves, and carrot root discs at various times after inoculation with Agrobacterium tumefaciens. Inhibition of tumor induction was substantial and maximal when rifampin (200 μg/ml) was applied to the wound sites immediately after bacterial inoculation. The time period after inoculation during which rifampin remained inhibitory varied with the plant host used. Inoculated Kalanchöe leaves remained sensitive to rifampin for 36 h while pinto-bean leaves and carrot discs remained sensitive for 20 and 4 h, respectively. Rifampin failed to inhibit tumor induction when applied to plant wounds inoculated with rifampin-resistant mutants of A. tumefaciens. Tumor weight was typically enhanced by rifampin in the Kalanchöe and carrot assays when applied after the period in which it was inhibitory. The viability of A. tumefaciens in vitro and while on the plant was substantially reduced by rifampin. Nevertheless, the lethal effect of the drug on A. tumefaciens was insufficient to fully account for its inhibitory effect on tumor induction.