CYTOCHEMICAL EVIDENCE OF A FUNGAL CELL-WALL ALTERATION DURING INFECTION OF EUCALYPTUS ROOTS BY THE ECTOMYCORRHIZAL FUNGUS CENOCOCCUM-GEOPHILUM

When the ectomycorrhizal fungus Cenococcum geophilum changes from a sa prophytic to a symbiotic stage, its cell wall structure becomes simpli fied. The external hyphal wall layer which, in the saprophytic stage, is highly reactive to the Gomori-Swift test becomes poorly reactive an d can no longer be distinguished from the internal wall layer in the H artig net hyphae. The intensely stained external wall layer was also a bsent from pure cultures of Cenococcum geophilum grown on a medium wit h a low sugar content. This cell wall alteration could be due to a dec rease in the amount of melanin or of melanin plus cystine-containing p roteins. This change may be necessary for increased nutrient exchange between symbionts through hyphal walls.