Leptosphaeria maculans and cryptogein induce similar vascular responses in tissues undergoing the hypersensitive reaction in Brassica napus

Cotyledons of Brassica napus cultivars displayed an hypersensitive reaction (HR) after either inoculation with an avirulent isolate of Leptosphaeria maculans (L. maculans), the fungus responsible for blackleg of crucifers, or infiltration with an elicitin, cryptogein. In the first case, ultrastructural observations revealed that the lumen of vessels located in the areas displaying a hypersensitive response was occluded by a fibrillar-like material. This material was labeled with anti-pectin antibodies, but not with antibodies specific for cellulose, callose, hemicellulose, or hydroxyproline-rich glycoprotein. Xylem and phloem parenchyma cells displayed ultrastructural features including morphological changes of nuclei and coagulation of the cytoplasm, reminiscent of cell death. None of these reactions were observed in plants infected with a virulent isolate of L. maculans or in controls. The host responses following infiltration with cryptogein appear similar to these following inoculation with an avirulent isolate of L. maculans. The data show that responses of vascular parenchyma cells are associated with the HR induced by an avirulent isolate of L. maculans and that cryptogein can mimic effects of an avirulent isolate of L. maculans at the vascular level. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.