Host-Pathogen Interactions XXXIV. A Heat-Labile Activity Secreted by a Fungal Phytopathogen Releases Fragments of Plant Cell Walls that Kill Plant Cells. Steven H. Doares. Complex Carbohydrate Research Center and Department of Biochemistry, The University of Georgia, Athens 30602 U.S.A. Peter Bucheli, Peter Albersheim, and Alan G. Darvill. Complex Carbohydrate Research Center and Department of Biochemistry, The University of Georgia, Athens 30602 U.S.A. . MPMI 2:346-353. Accepted 24 July 1989. Copyright 1989 The American Phytopathological Society.

Magnaporthe grisea (anamorphs: Pyricularia oryzae Cav., P. grisea), the ascomycetous causal agent of rice blast, was grown in liquid shake culture either on a minimal salts medium with a selected carbon source or on a complete (yeast extract-casein hydrolysate-sucrose) medium. When grown on pectin or isolated plant cell walls as the carbon source, the fungus secreted, into the culture medium, a heat-labile activity capable of killing plant cells. Plant cell death was monitored by the ability of suspension-cultured maize cells to incorporate [¹⁴C]leucine into acid-precipitable material. The heat-labile killing activity was neither secreted when the fungus was grown on sucrose or xylan nor produced when the fungus was grown on a complete medium. Heat-stable wall fragments, capable of killing plant cells, were released from isolated maize suspension-cultured cell walls treated with the heat-labile killing activity.