Histological responses of infection structures and intercellular mycelium of Uromyces phaseoli var. typica and U. phaseoli var. vignae to the HNO 2-MBTH-FeCl 3 and the IKI-H 2SO 4 tests

Abstract

The IKI-H 2 SO 4 and the HNO 2 -MBTH-FeCl 3 staining reactions for chitosan, chitin and hexosamine were examined in the rust fungi Uromyces phaseoli var. typica and U. phaseoli var. vignae . Identical reactions were seen for both organisms. No staining was observed in any fungal structure when treated directly with IKI-H 2 SO 4 . However, after autoclaving in alkali to convert chitin to chitosan, this lest resulted in a pink-violet colouration of the walls of germ tubes, infection structures and intercellular mycelium. In ccnlrast, the walls of urediospores, germ tubes, appressoria and intercellular mycelium, but not those of the substomatal vesicles, infection hyphae, or young secondary hyphae, turned blue with HNO 2 -MBTH-FeCl 3 in the absence of alkali treatment A comparison of the 2 staining reactions applied to particles of partially purified chitin which had been deacetylated to different degrees, suggested that the fungal material reactive with HNO 2 -MBTH-FeCl 3 was hexosamine which was not in the form of chitosan. The results suggest that while the walls of germ tubes, infection structures, and intercellular mycelium all contain chitin, there is a change in other wall components as the fungus enters the plant, and again as the intercellular mycelium becomes established.