Surface carbohydrates and cell wall structure of in vitro-induced uredospore infection structures ofUromyces viciae-fabae before and after treatment with enzymes and alkali

Abstract

Uredospores ofUromyces viciae-fabae differentiate to form germ tubes, appressoria, infection hyphae and haustorial mother cells on oil-containing collodion membranes. The cell walls of these infection structures were studied with the electron microscope and with FITC-labeled lectins before and after treatment with enzymes and inorganic solvents. Binding of the FITC-labeled lectins was measured with a microscope photometer. The enzymes pronase E, laminarinase, chitinase and lipase had different effects on each infection structure. Pronase treatment uncovered the chitin of germ tubes, appressoria and haustorial mother cells, but not of substomatal vesicles and infection hyphae. A mixture of α- and β-1,3-glucanase which also contained chitinase activity dissolved germ tubes and appressoria completely, but not infection pegs, substomatal vesicles, infection hyphae and haustorial mother cells. After treatment with laminarinase or lipase, an additional layer, which is especially obvious over the substomatal vesicle, infection hypha and haustorial mother cell, bound to LCA-FITC. In the wall of the haustorial mother cell, a ring, which surrounds the presumed infection peg, had strong affinity for WGA after protease and sodium hydroxide treatment. The infection structures have a fibrillar skeleton. The main constituent seems to be chitin. This skeleton is more dense or has a higher chitin content in the walls of appressoria and haustorial mother cells. The fibrils of the skeleton extend throughout the cell wall of the germ tube and appressorium. They are embedded within amorphous material of complex chemical composition (α-1,3-glucan, β-1,3-glucan, glycoprotein). The chitin of the infection peg, substomatal vesicle, infection hypha and haustorial mother cell is covered completely with this amorphous material. These results show, that each infection structure has distinct surface and wall characteristics. They may reflect the different tasks of the infection structures during host recognition and leaf penetration.