Studies of onion root respiration: II. The effect of temperature on the apparent diffusion coefficient in different segments of the root tip

Abstract

The Gerard-Fenn equation for diffusion into a cylinder was used to calculate the apparent diffusion coefficient oxygen in each of three segments of onion root tip at each of the four temperatures described in the first paper of this series. These coefficients were then used to determine the activation energy of diffusion (log D vs 1/T graphs) with the result that those for the two most apical zones of root agreed closely with the theoretical value. Certain coefficients were also used to calculate the distance to which oxygen penetrates the root when the external pressure of oxygen is limiting. From these values it was shown that the rate of oxygen consumption across the radius of the root is not perfectly linear (as the Gerard-Fenn equation demands) but the departure from linearity is not sufficient to completely invalidate the results.