Ultrastructure of intercellular hyphae and haustoria of the monokaryotic stage of Puccinia lagenophorae

During the aecial infection (monokaryotic stage) of Puccinia lagenophorae, the intercellular hyphae grow densely in the mesophyll and vascular tissues of Senecio vulgaris leaves. An amorphous material is deposited between int ercellular hyphae and host cell wall and may act as adhesive material. Inte rcellular hyphae are characterized by the presence of perforate, partial an d complete septa. These hyphae contain one nucleus per compartment and glyc ogen besides the usual organelles. This stage of infection is characterized by filamentous haustoria. A penetration peg is formed as a continuation of the haustorial mother cell. The haustoria are characterized by a narrow pr oximal part, which is enclosed by a thick collar and a wide distal part enc losed by a matrix (extrahaustorial matrix), which is an extension of the ho st cell wall and bound by an invaginated host plasma membrane (extrahaustor ial membrane). The haustorium contains a single nucleus, mitochondria, ribo somes, vesicles, endoplasmic reticulum and vacuoles. The most striking feat ure of this stage is that intercellular hyphae and haustoria of the fungus heavily invade vascular tissue of the host leaf.