Observations on Rhythmical-potential Difference Fluctuations in Onion-roots and the Radiosensitivity of This Reaction

Summary

A sine periodical voltage change between the root tip and any reference point of the root has been studied in Allium cepa. The amplitude is some millivolts, and the period of the order of 15 min.

The voltage–time-curves are registered automatically. Unpolarizable electrodes are used and connected to the root via tap water in special electrode vessels. Gassing the water of the apical electrode with oxygen or nitrogen, there appear small, characteristic disturbances of the curves but no changes of their general shape. Extremely small quantities of carbon monoxide, however, instantaneously bring the swinging system to a standstill for hours. This suggests that the oscillating system is connected with cellular respiration, and that some enzymatic step herein may be a key reaction.

The oscillations studied are disturbed by ionizing radiation. Under hyperoxia some few rads gamma- or x-rays at the root tip can bring the system to a standstill for some minutes; about 10 rads gamma-radiation given for 30 sec can result in a complete deletion of a full period (figure 3). These low dose reactions are reversible and follow mostly in a few seconds after the irradiation. Irradiations under anoxia produce no or very small changes at these doses.