THE PHYSIOLOGY OF HOST–PARASITE RELATIONS: XV. FINE STRUCTURE IN RUST-INFECTED WHEAT LEAVES

Abstract

Electron microscopy showed that the haustoria of P. graminis tritici on wheat were characterized by numerous mitochondria, an extensive endoplasmic reticulum, densely packed ribosomes, and a well-defined plasma membrane (plasmalemma), which was often invaginated by lomasomes. No evidence was obtained for cytoplasmic connections between the parasite and its host. Many of the haustoria formed on a resistant variety, Khapli, were necrotic but others were closely similar to those formed on a susceptible variety, Little Club. The haustorial necks were surrounded by a collar-like sheath formed by an extension of the host cell wall. The haustoria merely invaginated host protoplasts from which they were separated by granular encapsulations. The latter were apparently secreted mainly by the host and developed faster in Khapli than in Little Club. The presence of haustoria also induced the formation of an extensive, smooth-surfaced endoplasmic reticulum in the host, a contraction and fragmentation of the vacuole, an increase in the volume of the cytoplasm, and, ultimately, the complete degeneration of the host cells. The processes of breakdown of the subcellular organelles in the host were very similar to those which have been observed in uninfected cells in detached leaves senescing on water.