Changes of plasmolysis form in epidermal cells of Hordeum vulgare infected by Erysiphe graminis: evidence for increased membrane–wall adhesion

Abstract

When coleoptile epidermal tissues of Hordeum vulgare were plasmolyzed with α-methylglucose or mannitol, 24–72 h after inoculation with Erysiphe graminis f. sp. hordei, host protoplasts tended to pull away from one or more sites on longitudinal host cell walls producing a concave pocket at each site. This contrasted with the usual convex form of plasmolysis in uninfected tissue in which protoplasts pulled from the short transversal end walls of host cells forming protoplasts with convex ends. The tendency for concave plasmolysis encompassed entire inoculated areas at 5 colonies/mm2 and above. The concave response occurred in coleoptiles inoculated 7–12 days after planting, but not in ones inoculated at 5 days. It occurred in four of five barley lines tested at 48 h postinoculation. Treatment before plasmolysis with 10 mM Ca2+ promoted the disease-induced concavities; treatment with 15 mM K+ partially inhibited them. The concave form in plasmolyzed infected tissue was changed to the convex form by addition of 250 μM octylguanidine to the plasmolyticum or by replacement of α-methylglucose with isosmolar urea or methyl urea solutions. The results suggest that Erysiphe graminis infection increased adhesion of the host plasmalemma to the cell wall, probably as a consequence of change in membrane structure and bridging by Ca2+ ions.