A Short-Lived Effect of X-Irradiation on Rubidium Absorption by Excised Mung Bean Roots

Abstract

Investigations on the physiological effects of low doses of ionizing radiation have been hampered by the difficulty of studying immediately and directly the reaction or reactions between the primary radiation products and the vital cellular constituents within the cell which result in radiation damage. When living organisms are used, the reaction is usually measured by the effects of radiation on growth, reproduction, or viability. Since these phenomena are the end results of many complex reactions, their use to study the nature of radiation damage is obviously full of difficulties. A simple physiological process, which is sensitive to low doses of radiation and which can be easily and quickly measured after irradiation, could prove to be useful in understanding radiation effects in vivo. In a previous publication, Tanada (1) has shown that the absorption of rubidium by excised mung bean roots (Phaseolus aureus) is fairly sensitive to ultraviolet radiation. Since effects on this Rb-absorbing system can be quickly and easily measured, it appeared desirable to investigate the effects of X-irradiation on it. This system is also immediately affected by low concentrations of certain chemicals (2). Previous investigations have generally shown that ion uptake by living cells is resistant to low doses of ionizing radiation. In regards to plant cells, Higinbotham and Mika (3) have shown that absorption of ions by potato tissue is less affected by X-irradiation than the growth processes. Preliminary results with excised mung bean root tips of 1-cm length have confirmed their results. But a closer examination showed that there are two effects of X-irradiation on salt uptake by mung bean roots. At low to moderate doses there is an immediate decrease in Rb uptake. This effect is transitory and disappears in about 10 minutes. The other effect requires much higher doses and results in an increased uptake of Rb in the absence of Ca ions. In the presence of Ca, Rb absorption is decreased. This second effect appears to be irreversible. This paper reports results of investigations on the first effect.