Alteration of membrane permeability of potato-tuber tissue infected by incompatible and compatible races of Phytophthora infestans during the initial phase of infection.

Abstract

Electric potential difference (EPD) between the surfaces of potato-tuber disks infected by compatible and incompatible races of Phytophthora infestans and between each of them and noninfected ones were determined during the initial period of infection. EPD began to increase almost simultaneously with host wall penetration by both the incompatible and compatible races and the increase was already larger in the former than in the latter. Electric conductivity (EC) measurements of the exudates from the infected tuber disks showed that an increase in EC was also found in both the compatible and incompatible infections. The increase in EC was larger in the incompatible combination before hypersensitive death of infected cells occurred. In both incompatible and compatible combinations the increasing rate in EC was larger when the disks were inoculated 20hr after cutting rather than just after cutting. Leakage of preabsorbed 32P from potato-tuber disks was increased by infection with both the incompatible and compatible races, and the increase was higher in the former than in the latter. All these results suggested that the permeability of cell membranes of potato tuber disks increased very soon after the infection (or at the same time as penetration occurred) when they were inoculated with either incompatible or compatible races of P. infestans. However, the rate of increase seemed to be larger in the incompatible than in the compatible combination before hypersensitive cell death of the former occurred.