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

Both sides of aged disks of potato tubers were inoculated with incompatible race 0 or compatible race 1 of P. infestans. The uptake of radioactivity from 3H-leucine into the disks was greatly reduced by the infection with the incompatible race, but the ratio of incorporated radioactivity in the acid soluble fraction of the disks to total radioactivity in the 20,000 x g supernatant was increased by the infection with the incompatible race 0. In case of the compatible race 1, the infection had less effect on the incorporation ratio of the radioactivity into the acid insoluble fraction than the case of the race 0. The results suggested that the reduction in 3H-leucine uptake may be due to alteration of the physiological activity of host plasma membrane, instead of the reduction of metabolic activity. The treatment of tuber disks with the 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 homogenate also reduced the uptake, but the effect was lost by dialysis. The results suggest that some substances in the insoluble components of the zoosporial homogenate of P. infestans may be at least one cause of the reduction in the uptake of 3H-leucine which begins to occur at very early period of the inoculation with race 0 or race 1 while penetration has not yet occurred. (Kobatake, H.)