Effect of N, N′-diacetyl-D-chitobiose, the potato-lectin hapten and other sugars on hypersensitive reaction of potato tuber cells infected by incompatible and compatible races of Phytophthora infestans

Cut surfaces of aged disks of potato tubers were treated with 30 kinds of sugars including 3 pentoses, 8 hexoses, 6 disaccharides, 3 methyl glucosides, 3 sugar alcohols, 6 amino sugars and laminarin, and then inoculated with incompatible or compatible races of Phytophthora infestans. Among these sugars, only N, N′-diacetyl-D-chitobiose (D-chitobiose) inhibited greatly the rapid occurrence of hypersensitive death of cells infected by an incompatible race of P. infestans, when it was pre-infectionally applied to the disks for 1 h. Post-infectional treatment with D-chitobiose done 2 h after inoculation, however, had little effect on the hypersensitive cell death. D-chitobiose had little effect on the response of the potato cells to infection by a compatible race and also on the growth of intracellular hyphae. The cells, which were pre-infectionally treated with D-chitobiose and then inoculated by the incompatible race, were plasmolyzed with 0·7 m sucrose solution, and then fixed and observed using an electron microscope. The observation showed that the percentages of the infecting hyphae, to which the host plasmalemma or vesicles torn off from the plasmalemma did not adhere or adhered only a little, was 33· 3% (for 219 hyphae observed) or 4·1% (for 171 hyphae) in the cells treated with D-chitobiose or water respectively. All these results suggested that exogenously supplied D-chitobiose inhibits the binding between host plasmalemma and infecting hyphae during the period of initial contact between them, and also inhibits rapid occurrence of the hypersensitive cell death. Since D-chitobiose has been known as a specific hapten of potato-lectin, the results suggested that potato-lectin may play a role in these phenomena.