The occurrence of cytoplasmic aggregates induced by Erysiphe pisi in barley coleoptile cells before the host cell walls are penetrated

Abstract

The timing of formation of cytoplasmic aggregates induced by Erysiphe pisi appressoria in barley coleoptiles, and wall penetration by the appressoria, was investigated by light microscopy and scanning electron microscope (SEM) micromanipulation. Observations of E. pisi appressoria on living barley coleoptiles by light microscopy revealed the unique responses of host cells to this fungus: first, a small cytoplasmic aggregate formed below the appressorium, lasted for 20·9 ± 15·4 min, then vanished. After a further interval of 42·7 ± 21·0 min, a second cytoplasmic aggregate developed below the same appressorial lobe. At 21·4 ± 7·5 min after the initiation of the second cytoplasmic aggregate, a penetration-pore-like structure became visible in the lobe. Scanning electron microscope micromanipulation indicated that the penetration-pore-like structure observed by light microscopy represented the penetration pore or peg produced by the fungal appressorium. Observations of appressoria by differential interference contrast microscopy and micromanipulation at the SEM level lead us to conclude that the first and second cytoplasmic aggregates were initiated before the host wall was penetrated.