Radial Exchange of Labeled Water in Intact Maize Roots

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Abstract
Equilibration of maize (Zea mays) roots with tritiated water was compared with theoretical curves for the single cell, sheet, cylinder, and sphere and was found to follow the cylinder curve. This was interpreted to indicate that the epidermis does not constitute a barrier to the entrance of water. The stele was removed from roots after treatment with tritiated water, and the equilibration of the stele was compared with that of the cortex. This equilibration was not greatly different from the theoretical equilibration to be expected of uniform tissue. It was concluded that the endodermis did not constitute a barrier to the diffusion of water. The apparent diffusion coefficient of tritiated water in a maize root at 25[degree] was 5 X 10-6 cm2 sec-1. The apparent diffusion coefficient was decreased by metabolic inhibitors, or low-temperature treatment. The apparent diffusion coefficient remained unchanged with treatment by dimethyl sulfoxide or 2,4-dichlorophenoxyacetic acid. The apparent diffusion coefficient increased about 3-fold when the roots were killed with hot water. The data indicated that at least 70% of the water movement in a normal root involved the protoplasm.

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