Some exploratory experiments on the permeability of papillae induced in barley coleoptiles by Erysiphe graminis f.sp. hordei

Abstract

Impermeability to ions and small molecules has been cited as a possible basis of the resistance of papillae to fungal penetration: nonporous papillae could prevent nutrient transfer or disrupt recognition between pathogen and suscept. We have tested the ability of lanthanum ions and a few, selected, small molecules to permeate both normal papillae and oversize papillae induced in barley coleoptiles by Erysiphe graminis f.sp. hordei. The probes were applied to living, usually untreated, coleoptiles and were detected by light or electron microscopy. Hydrophilic probes up to 389 Da were able to permeate both kinds of papillae freely. Although the results with the lipophilic probes were more difficult to interpret, the 479-Da probe did not freely permeate unaltered papillae of either kind. We conclude that unaltered papillae are permeable to some cations and small, hydrophilic molecules and infer that impermeability to similar chemicals cannot explain why oversize papillae, but not normal papillae, are highly resistant to penetration by the fungus.