Preliminary evidence for the involvement of suberization in infection of Casuarina

Abstract

Histochemistry of infected cells in mature nodule lobes of Casuarina showed that walls of infected host cells had a ligninlike component (ultraviolet-stimulated autofluorescence and staining with auramine O, phloroglucinol staining, and resistance to degradation by hydrolytic enzymes). Cytoplasm of infected cells had a pronounced affinity for lipid stains (Sudan black B, Rose Bengal fluorescence), though walls of infected cells were less clearly stained. When nodules were digested several days in cold 50% chromic acid, the walls of infected cells and suberized host tissue (epidermis, endodermis) were not degraded. Endophyte cell wall components were also found to be resistant to chromic acid digestion. The digested tissue retained the capacity to adsorb lipid dyes. These observations suggested that walls of infected host cells had become impregnated with a suberinlike compound. The hydrophobic quality of this wall was evident when its ultrastructure was examined after en bloc staining with the polar stain KMnO4. This stain did not penetrate the walls of mature infected cells, perhaps because of the presence of aliphatic compounds similar to those found in suberin. As is known for suberizing tissue, peroxidase activity (via diaminobenzidine oxidation) was high in nodule cortical tissue cell walls. The peroxidase stain was also localized on endophyte hyphae. This report is the first instance associating a suberizationlike host reaction with infection of an actinorhizal plant.