SECRETION AND ENDOCYTOSIS AT THE INTERFACE OF PLANTS AND FUNGI

Secretion products and the uptake of material from the outside of the protoplasts of plants and microbes may influence the mutual interactio n in host-parasite systems. Organelles involved in secretion by rust f ungi have been characterized using immune-electron microscopy. Protein s with the C-terminal histidine - aspartic acid - glutamic acid - leuc ine tetrapeptide (HDEL) signal sequence accumulated in tubular vesicul ar complexes of the ER in the parasitic phase of the fungi. The tubula r complexes were differentiated from smooth cisternae that probably co rrespond to the Golgi equivalent. In the plant, material was secreted into the papilla and at the same time, endocytosis of 1,3-beta-glucans by clathrin-coated vesicles occurred at the penetration site of the m onokaryotic appressorium. During further development of monokaryotic h austoria, different wall layers were produced around these haustoria. Components of those layers were plant cell wall constituents most of w hich were also detected in the Golgi apparatus. One layer was rich in callose, which is supposed to be synthesized at the plasma membrane. O bviously, endo- and exo-cytosis occur permanently by host and parasite during fungal development within the plant.