CELL-WALL SYNTHESIS IN COTTON ROOTS AFTER INFECTION WITH FUSARIUM-OXYSPORUM

Fusarium oxysporum f. sp. vasinfectum penetration hyphae infect living cells in the meristematic zone of cotton (Gossypium barbadense L.) ro ots. We characterized wall modifications induced by the fungus during infection of the protodermis using antibodies against callose, arabino galactan-proteins, xyloglucan, pectin, polygalacturonic acid and rhamn ogalacturonan I in high-pressure frozen, freeze-substituted root tissu e. Using quantitative immunogold labelling we compared the cell walls before and after hyphal contact, cell plates with plasmodesmata during cytokinesis, and wall appositions induced by fungal contact. In the a lready-existing wall, fungal contact induced only minor modifications such as an increase of xyloglucan epitopes. Wall appositions mostly ex hibited epitopes similar to the cell plate except that wall apposition s had a much higher callose content. This study shows that wall apposi tions induced by Fusarium oxysporum hyphae are the result of normal ce ll wall synthesis and the addition of large amounts of callose. The ap positions do not stop fungal growth.