EFFECT OF METHYL GLYCOSIDES AND OLIGOSACCHARIDES ON CELL-DEATH AND BROWNING OF POTATO-TUBER DISKS INDUCED BY MYCELIAL COMPONENTS OF PHYTOPHTHORA-INFESTANS

In the hypersensitive response of potato tuber tissue to an incompatible race of Phytophthora infestans the infected cells rapidly die and later turn brown. Cell-free extracts of sonicated mycelial homogenates of the fungus induce a hypersensitive-like response in tuber tissue from resistant and susceptible potato varieties. Cell death was assessed directly by the use of a vital stain, and indirectly by reflectance densitometric measurements of browned tuber tissue. A positive correlation was demonstrated between browning, measured in this way, and percentage cell death calculated from direct viability counts. A number of methyl glycosides and oligosaccharides were tested for their ability to affect sonicate-induced cell death and browning. Laminaribiose and methyl-β-d-glucopyranoside caused a significant inhibition of cell death and browning; cellobiose, gentiobiose, methyl-α-d-glucopyranoside and a number of other compounds were ineffective. The results suggest that macromolecules containing β-1,3-linked glucose residues play an active role in the interaction between mycelial components of P. infestans and the potato. Furthermore, these residues may be contained in the fungal elicitor and be specific for the active site of its receptor in the potato cell. © 1979.