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Electron-dense crystals formed in plant roots exposed to uranyl acetate have been used to identify binding sites and to follow the pinocytotic uptake of uranyl in the oat rootcap. Before uranyl enters the protoplast, the plasmalemma is greatly dilated. After uranyl is sequestered in vacuoles, the tonoplast is similarly dilated.

Wheeler, Harry, and Homer S. Black. (Louisiana State U., Baton Rouge.) Effects of Helminthosporium victoriae and victorin upon permeability. Amer. Jour. Bot. 50(7): 686–693. Illus. 1963.—Helminthosporium victoriae, the causal agent of Victoria blight of oats, produces a potent toxin called victorin. All of the symptoms of Victoria blight, both visible and biochemical, can be induced in susceptible plants either by infection with H. victoriae or by treatment with victorin. Among the effects produced both by the fungus and the toxin are marked changes in respiration and cell permeability. These are of special interest because they are characteristic of many plant diseases. This paper is concerned with the nature of changes in permeability and the possible relation of these to changes in respiration observed in tissues infected with H. victoriae or treated with victorin. Suseeptible oat tissues treated with victorin lost electrolyes when suspended and shaken in distilled water more rapidly than control tissues, and the magnitude of the effect varied with the concentration of victorin applied. Similar results were obtained with naturally infected susceptible plants but not with inoculated or victorin‐treated resistant plants. The rate of electrolyte loss from victorin‐treated tissue had a low temperature coefficient typical of a physical process and was not dependent upon oxygen tension. The concentration of victorin needed to produce an increase in the rate of electrolyte loss was approximately 50‐fold less than that required to induce a significant increase in the respiratory rate. Changes in permeability were detected within 5 min after victorin was applied, whereas respiratory changes were not clearlyevident until after 30 min. These results indicate that if a causal relationship between these 2 phenomena exists, changes in permeability are responsible for changes in respiratory activity rather than vice versa.

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