Studies on the Mechanism of Phytohormone Damage by Ionizing Radiation. I. The Radiosensitivity of Indoleacetic Acid.

Abstract

Kinetic studies of indoleacetate destruction by X- and [gamma]-irradiation of aqueous systems indicate no unusual radio-sensitivity of the auxin. Varying the auxin concentration and purity, oxygen and H+ concentration, radiation energy, dose rate, and method of assay gave ionic yields in the order of unity. Finer variations of ionic yield are consistent with classical "indirect" action mechanisms. Acid auxin extracted from the plant and purified by chromatography does not differ significantly from synthetic IAA in sensitivity. Cosolute effects on ionic yield were determined, plant protein being a particularly effective protectant. The above observations, and the low order of auxin concentration in vivo, support the interpretation that the immediate lowering of auxin level in the plant after low-dose irradiation does not involve direct auxin photolysis.