Extracellular β-1,3-Glucanases in Stem Rust-Affected and Abiotically Stressed Wheat Leaves

Abstract

Endo-beta-1,3-glucanase activity in intercellular washing fluid (IWF) from leaves of wheat (Triticum aestivum) increased 10-fold 4 days after leaves were infected with the wheat stem rust fungus (Puccinia graminis f.sp. tritici), while exo-beta-1,3-glucanase activity remained unchanged at a low level. Heat and ethylene stress had no effect, whereas mercury treatment resulted in a 2-fold increase in endo-beta-1,3-glucanase activity. With a new method of activity staining using laminarin-Remazol brilliant blue as substrate in overlay gels, 18 electrophoretic forms of endo-beta-1,3-glucanase were detected in IWF from unstressed leaves and up to 24 forms in IWF from stem rust-infected leaves. Most of the increase in beta-1,3-glucanase activity and in the number of beta-1,3-glucanases after rust infection was due to a nonspecific, stress-related effect on the plant, but two major forms of the enzyme probably originated from the fungus. beta-1,3-Glucanase was localized cytochemically with anti-barley-beta-1,3-glucanase antibodies. With preembedding labeling, the enzyme was demonstrated on the outside of host and fungal cell walls. Postembedding labeling localized the enzyme in the host plasmalemma and in the domain of host cell walls adjoining the plasmalemma, throughout walls of intercellular hyphal cells and haustoria, in the fungal cytoplasm, and in the extrahaustorial matrix. Cross-reactivity of beta-1,3-glucanases from wheat and germinated uredospores of the rust fungus with the anti-barley-beta-1,3-glucanase antibodies was confirmed in dot blot assays and on Western blots.