ENDOCYTOSIS OF 1,3-BETA-GLUCANS BY BROAD BEAN CELLS AT THE PENETRATION SITE OF THE COWPEA RUST FUNGUS (HAPLOID STAGE)

The penetration hypha of basidiospore-derived infection structures of the cowpea rust fungus (Uromyces vignae Barclay) in epidermal cells of the nonhost, broad bean (Vicia faba L.), was studied with the electro n microscope after high-pressure freezing and freeze substitution. Aft er fungal invasion of the epidermis, a plug in the penetration hypha s eparated the infection structures on the cuticle from the intraepiderm al vesicle of the fungus. The plug and the fungal cell wall reacted wi th a polyclonal 1,3-beta-glucan antibody. The plug in the haploid stag e seems to have a task similar to the septum formed in the diploid sta ge of the fungus. Around the penetration hypha, the plant wall stained darkly and a papilla was deposited by the plant. In the papilla, 1,3- beta-glucans were labelled by a monoclonal and a polyclonal antibody. In the infected epidermal cell, clathrin-coated pits, coated vesicles, partially coated reticula and multivesicular bodies were found. The c ontents of the coated pits, coated vesicles, partially coated reticula and multivesicular bodies bound to monoclonal and polyclonal 1,3-beta -glucan antibodies. Accumulation and uptake of this paramural material into the plant cell by endocytosis is concentrated at the fungal pene tration site. It may influence the host-parasite interaction.