Uromyces phaseoli and Phaseolus vulgaris

To study the function of bean rust haustoria either the host, Phaseolus vulgaris, or the parasite, Uromyces phaseoli, were labeled with 3H-lysine. 24h and 48 h after inoculation samples of the infected leaves were taken and processed for electronmicroscopic autoradiography. When the host was labeled, silver grain densities over the structures of host and parasite were compared. Very low grain densities were found over developing haustoria of the bean rust and higher grain densities over mature and old haustoria. Compared with mature haustoria, reduced grain densities were observed over intercellular hyphae. It is assumed that a flow of labeled metabolites from the host cell to the haustorium and then to the intercellular hypha took place. When sporelings originating from labeled uredospores infected the leaf, no detectable amount of 3H-lysine or its metabolites were found to be transferred from the intercellular hyphae or haustoria to cells of the leaf parenchyma.