Effect of infection by Phytophthora infestans and treatment with its zoosporial components on uptake of 3H-leucine and protein synthesis in potato tuber tissue

Both sides of aged disks of potato tuber (Rishiri, R1-gene) were inoculated by incompatible race 0 or compatible race 1 of Phytophthora infestans. Five min pulse label experiments with L-leucine-4, 5-3H of the infected disks showed that uptake of radioactivity from 3H-leucine into the disks was greatly reduced by infection with the incompatible race as previously reported, but the ratio of incorporated radioactivity in acid insoluble fraction of the disks to total radioactivity in the 20, 000×g supernatant was increased with infection by the incompatible race 0. In the case of compatible race 1, the infection had less effect on the incorporation ratio of the radioactivity into acid insoluble fraction than with the incompatible race 0. These results suggested that reduction in 3H-leucine uptake may be due to alteration of physiological activity of host plasma membrane, but not to reduction of metabolic activity. Treatment of tuber disks with insoluble fraction of the zoosporial homogenate of race 0 or race 1 greatly reduced the uptake of 3H-leucine by the disks. The supernatant fraction of the zoosporial homogenates also reduced the uptake, but the effect was lost by dialysis. Little difference was observed in the effect of insoluble and soluble fractions of the zoosporial homogenates of both race 0 and race 1. The insoluble fraction of the zoosporial homogenates of both race 0 and race 1 had little effect on the ratio of the radioactivity in acid insoluble fraction of the tuber disks to total uptake of the radioacitivy in 20, 000×g supernatant. These results suggest that some substances in insoluble components of zoosporial homogenate of P. infestans may be at least one cause of the reduction in uptake of 3H-leucine which begins to occur in a very early period of inoculation with race 0 or race 1 while penetration hasn't yet occurred.