Ultrastructural changes and localization of chitin and callose in compatible and incompatible interactions between carnation callus and Fusarium oxysporum

Calli of carnation (Dianthus caryophyllus, L.) cv. Pallas resistant and sus ceptible to Fusarium oxysporum f.sp. dianthi races 1 and 8 were exposed to fungal mycelia for 24, 48 and 72 h. The ultrastructure of the cells from ca rnation calli vas studied by transmission electron microscopy. Fungal chiti n and plant and fungal callose were detected using coloidal gold complexed to lectin wheat germ agglutinin and commercial monoclonal antibodies! (1--> 3)-beta-glucan, and standard electron microscopy and cryoultramicrotomy, Th is study provides evidence that during the incompatible reaction, proximal and uninvaded Pallas cells delayed fungal growth with newly formed callose barriers that plugged plasmodesmata, coated cells or formed a tylose-like s tructure. The plant strategy induced by race 8 in Pallas was less successfu l with the loosening of host cell walls and the earlier penetration of the pathogen. This study showed that Pallas cells did not induce alterations in hyphal cells for either interaction. The combination of fungus-infected ca rnation calli and gold cytochemistry facilitates the study of race-specific early plant defense reactions. (C) 2000 Academic Press.