The passive permeability to water and nonelectrolytes of epidermal cells from partially dissected coleoptiles of Hordeum vulagare was investigated in uninfected tissue and in tissue infected with a compatible race of the powdery mildew fungus, Erysiphe graminis f. sp. hordei. Permeability constants were determined plasmometrically for water and for the increasingly nonpolar electrolytes: urea, methyl urea, and ethyl urea. Measurements were taken 48 h after inoculation, usually in heavily infected tissues which exhibited concave plasmolysis. Permeability of cells to water or urea was unchanged by infection. Permeability to methyl urea was reduced significantly in the cultivar Montcalm, but not consistently in Atlas or AlgS. Permeability to ethyl urea in AlgS was reduced by half by infection. The reduced permeability occurred not only in haustoriumcontaining cells. but throughout heavily infected tissue. If tissues were left overnight on plasmolyzing solution of α-methyl glucose, uninfected tissues deplasmolyzed and regained turgor whereas infected tissue did not, suggesting that the α-methyl glucose entered healthy, but not infected cells. The results indicate that infection altered the plasmalemma of host cells, reducing passive permeability to α-methyl glucose and the more lipophilic of the nonelectrolytes tested.
Bibliographical noteFunding Information:
We thank Dr Albert H. Markhart for use of his digitizer pad for measuring protoplast length and his computer program for calculating permeability constants. This research was supported in part by United States Department of Agriculture, Competitive Research Grants Office, Grant 80-CRCR-0422.