Abstract
Aged tuber slices of potato cultivars Rishiri (R1-gene) and Irish cobbler (r-gene) were inoculated with race 0 (incompatible with Rishiri and compatible with Irish cobbler) and race 1 (compatible with both cultivars) of Phytophthora infestans. After inoculation, they were treated, at intervals, with 3H-leucine, H332PO4 and 86RbCl solution for 50min, and then washed and homogenized. Uptake of 3H-leucine, and 32P into the 2×104×g supernatant fraction of the homogenates of the slices (Rishiri and Irish cobbler) infected by both races were already lower than those of noninfected ones 1.4hr after inoculation, when most of encysted zoospores had germinated but not yet penetrated the host-cell wall. From about 2.4hr after inoculation, when about 20% of the appressoria had begun to penetrate, the rates of uptake of 3H-leucine and 32P begun to decrease more rapidly in the incompatible host-parasite combination than in those of compatible combinations: At this stage, no death of the infected cells has occurred yet even in the incompatible combination. In the case of 86Rb ion, on the contrary, the rate of uptake was higher in slices infected by the incompatible race than in non-infected slices or slices infected by the compatible race at 18C. At 10C, however there was little difference among the rates of uptake in the non-infected slices and slices infected by incompatible and compatible races.
The most plausible explanation of these results is that the physiological activity of host-plasmalemma and/or the metabolic activity is altered by infection with the incompatible race in an early period of infection when no host cell death has occurred. From these results it was presumed that the alteration of physiological activity of plasmalemma and/or metabolism of host caused by recognition of infection by an incompatible race of P. infestans might occur almost simultaneously with penetration.
