In vitro formation of haustoria of the cowpea rust fungus, Uromyces vignae, in the absence of a living plant cell I. Light microscopy

Abstract

Haustoria of the cowpea rust fungus were induced to form on oil-containing collodion membranes, in the absence of any living plant material, by the application of an inactivated commercial enzyme preparation. No neckband was detected along haustorial necks and mithramycin staining showed that nuclei did not complete their migration into haustoria from the haustorial mother cells (HMCs). Haustorial walls fluoresced only slightly with calcofluor and at an intensity much less than walls of the infection structures or haustorial mother cells. Walls of germ tubes, appressoria, infection pegs, substomatal vesicles, infection hyphae, HMCs and haustoria all fluoresced uniformly but weakly when treated with (FITC)-Concanavalin A, indicating the presence of mannose, glucose or acetyl glucosamine residues of the fungal surface; fluorescence was virtually eliminated by prior treatment of the fungus with unlabelled lectin or by incubating the lectin with its hapten. With FITC-WGA, walls of germ tubes, appressoria, the thickened region of the HMC wall surrounding the infection peg and the haustorial neck wall all fluoresced more brightly than other parts of the fungus. Although fluorescence could be eliminated by mixing the FITC-WGA with chitin hydrolysate, the ability of unlabelled WGA to reduce subsequent binding of FITC-WGA to appressoria and HMCs depended on the concentration of the labelled lectin and in no instance was haustorial wall fluorescence significantly reduced. These and other data suggest that FITC-WGA binding to the haustorium may not indicate the presence of chitin.