Relations between haustoria of Erysiphe graminis and host cytoplasm in cells opened by microsurgery

Epidermal cells of barley (Hordeum vulgare L.), which contained haustoria of Erysiphe graminis [DC] Merat f. sp. hordei Em. Marchal, were opened with a microneedle, thereby exposing the haustorial apparatus and surviving components of the host protoplast to externally supplied osmotica. Haustoria remained alive and functional for one or more hours in the incised cell with either salt or sucrose osmotica, as indicated by growth of attached hyphae and the visible condition of the haustorium. A thin layer of host cytoplasm (the haustorial sac) remained in place around the functional haustoria. Additional host cytoplasm was seen frequently in streams, masses, or a parietal layer within 100 μm of the haustorium. The cytoplasm often migrated to the haustorium after incision and came to rest there, especially on osmotica hypertonic to the host. The amount of fungal growth after incision was positively correlated with the amount of cytoplasm near the haustorium (large amounts if cells were incised 30 μm or more from the haustorium; small amounts if cells were incised less than 10 μm from the haustorium). The times after incision that cytoplasmic organelles near the haustorium moved in streams or vibratory patterns coincided with the times after incision that hyphae grew. Most of the host cytoplasm was removed from the vicinity of the haustorium when the microneedle was swept past the haustorium repeatedly. However, the haustoria that survived in a functional condition after nearby regions of the host cell had been swept, remained enclosed by a thin layer of cytoplasm and in contact with a layer of host cytoplasm on the host wall around the haustorial neck. The results suggest that the haustorium must be in contact with small amounts of living host cytoplasm to be functional, but that the haustorium does not depend on vacuolar substances, the nucleus of the host, or cytoplasm in distant parts of the host cell.