Oxygen-Induced Free Radical in Wheat Roots

Abstract

ESR experiments have shown that free radicals are formed in wheat plant roots as a result of exposure to O₂. Although the radical(s) has not been positively identified, the nature of the spectra allows simple oxygen-derived radicals, such as O⁻₂, HO₂ and OH, to be excluded as possibilites. Adsorption of Cu(II), but not Zn(II) or Cd(II) by the root results in a rapid decay of the radical signal to reach a level of 10% of its original intensity after a few minutes.

Introduction

In previous work on the uptake of copper(II) and oxovanadium(IV) ions by wheat roots^1-3, electron spin resonance (ESR) spectra demonstrated the presence of free radicals whose concentrations varied during the course of the experiments. This free radical is the subject of the present investigation which has been performed with the objective of identifying the origin of its signal. As the plant roots used in the earlier papers were exposed to high levels of transition metals and, in addition, were confined in a moist atmosphere in a narrow bore (3mm internal diameter) quartz tube, the present experiments are concerned with identifying the possible effects of metal ion exposure and oxygen depletion and enrichment on the free radical concentration. A spin trap has also been used in an attempt to identify radical species that may have been formed, but which had half-lives too short for them to be seen in the direct ESR experiments.

Key Words:

• ESR
• O₂-induced free radical
• wheat roots