Cytological and physiological comparisons between autofluorescence and haloes which appeared at penetration sites of appressoria of Erysiphe graminis and Erysiphe pisi on barley coleoptiles were made using dye stains and fluorescence microscopy. Haloes induced by these fungi on barley coleoptiles were successfully detected by various dyes when the inoculated coleoptiles were treated with 70% ethanol at 80 °C for 30 min before staining. Responses of haloes on coleoptiles to basic and acid dyes were very similar to those on barley leaves which have been reported earlier. In time-course studies, haloes were not detected until at least 15 min after initiation of cytoplasmic aggregation. The occurrence of haloes was suppressed by supplemental Ca2+, but unaffected by K+, Na+, and Li+. Similar results were obtained in haloes induced by both fungi. Autofluorescent regions remained in situ after the inoculated coleoptile cells were plasmolyzed, suggesting that this phenomenon might be closely associated with host cell walls. As reported earlier, autofluorescence preceded the appearance of cytoplasmic aggregates by 1–10 min and, moreover, its appearance was enhanced by divalent cations such as Ca2+, Mg2+, and Mn2+, but not by monovalent cations such as K+, Na+, and Li+. Based on these results and earlier studies, it was concluded that the autofluorescence and haloes represented different responses in host cell walls to the penetration activities of both pathogenic and nonpathogenic fungi.
Primary germ tubes and host cell penetrations from appressoria of Erysiphe graminis hordei.
