Ultrastructural demonstration of different peroxidase activities during the bean rust infection process

During penetration and infection of the bean leaf by the rust fungus, at 22 h after artificial inoculation, the following sites of peroxidase activity were observed which might influence the interaction of the host and parasite: (I) The guard cell walls of the stoma are covered with a layer that shows peroxidase activity. This activity might influence the infection peg of the fungus. (2) Within the leaf, the infection hypha of the bean rust fungus contacts a layer of peroxidase activity at the outer surface of the host cells. In the compatible combination employcd, no differences in the peroxidase activity at this site were detected between cells which came in contact with hyphae and those which did not. (3) The penetration peg ofthe haustorial mother cell enters the host cell and differentiates to form the haustorial neck. Here, a very strong peroxidase activity was observed, which might be a defence reaction of the host against the pathogen. (4) During the development of the haustorial body, peroxidase activity was seen on the rough endoplasmic reticulum and in the Golgi bodies. It is suggested that peroxidase is synthesized on the endoplasmic reticulum and secreted towards the partly invaginated sheath by the Golgi bodies. (5) Peroxidase activity was observed on the nuclear envelope of some nuclei in infected cells.