Ultrastructural observations on Puccinia menthae infections.

Abstract

Haustoria and associated regions of the hostpathogen interfaces of the autoecious rust Puccinia menthae, during mono- and dikariotic phases of development on its host Mentha spicata, differed in ultrastructural and cytochemical features. By application of the PA-TCH-SP procedure, polysaccharides were shown not only to be major constituents of the walls of intercellular hyphae, haustorial mother cells (HMC) and haustoria of both the monokaryon and dikaryon (m- and dhaustoria, respectively) of P. menthae, but were also present within the extra-haustorial matrix (EM) of both types of haustoria. In the neck region of d-haustoria, which is structurally more differentiated than in m-haustoria, there was evidence for the presence of lipopolysaccharides and glycoprotein. However, the characteristic neck-band, which stains densely in conventional staining of the d-haustorium, did not react with PA-TCH-SP. The outermost layer of the dikaryotic HMC wall was completely digested by protease, whereas treatment with protease and cellulase did not affect either mono- or dikariotic intercellular hyphae or walls of m-haustoria, although these treatments indicated the presence of protein and cellulose in the EM. In dikaryotic infections, protein was found to be a major constituent of the EM. Cellulase treatment resulted in almost complete digestion of the host wall, except for a thin outer layer, whereas hyphal and haustorial walls were unaffected. The morphology and structural differences observed between the mono- and dikaryotic infection structures of P. menthae, and their interactions with host cells were clarified, and confirmed the possibility of their functional differences. Such information should facilitate further comparative studies on host-parasite interfaces at different stages of the rust life cycle and other biotrophic fungi.