Lack of influence of phytochrome on membrane permeability to tritiated water.

The water permeability of tissues was investigated by measuring the efflux of (3)HHO from previously loaded (in darkness) etiolated bean buds (Phaseolus vulgaris L. var. Red Kidney), pea epicotyl segments (Pisum sativum L. var. Alaska), and oat coleoptile segments (Avena sativa L. var. Garry). Red light, far red light, or darkness was applied at the time of transfer of tissue from labeled to unlabeled medium. There were no effects of light on half-time for efflux or on the maximum level of radioactivity in the medium. Based on these criteria, phytochrome exerts no apparent control over water permeability.