Ultrastructural and physiological properties of the host interfacial components of haustoria of Erysiphe pisi in vivo and in vitro

Abstract

The haustorium of Erysiphe pisi and its interfaces with the cytoplasm of Pisum sativum have been studied by light and electron microscopy of infected cells and haustorial complexes isolated from them. The term haustorial complex has been introduced for the haustorium, the extrahaustorial part of the host plasmalemma, and the intervening materials and structures. A method for the isolation and purification of haustorial complexes is described. It has been shown that the haustorial cytoplasm has one nucleus and is retained in isolated haustorial complexes by an amorphous plug in the septal pore between the haustorial neck and body. The body is invested by finger-like lobes arising near the neck and at the opposite end, the lobes being attached to the extrahaustorial membrane. Two annular structures, the A and B bands, in the neck wall are visible by light and electron microscopy. The A band adjoins the inner face of the host cell wall, and the extrahaustorial membrane and fungal plasmalemma are intimately associated with its surface even in the absence of both host and fungal cytoplasms. The B band is nearer the haustorial septum, comprises opaque, amorphous material and joins the extrahaustorial membrane to the neck wall; it is soluble in NaOH. The extrahaustorial membrane over the body is highly convoluted, being 20 to 25 nm thick, and osmotic experiments show that it is continuous and has high tensile strength. It is soluble in NaOH but is not destroyed by long periods in detergents, or by enzymes which degrade the host cell wall. The membrane is reduced in thickness to 15 nm and is rendered osmotically unstable by the enzymes. The extrahaustorial membrane stains with procedures specific for polysaccharides, but the remainder of the host plasmalemma does not show the special characteristics of this membrane. The extrahaustorial matrix is a fluid which reacts less intensely than the extrahaustorial membrane with the polysaccharide reagent and is removed by enzymes degrading the host cell wall. It is bounded by structures including the extrahaustorial membrane and the B neckband, none of which is permeable to its contents but some or all are permeable to water. The functional significance of these structures is discussed.