Hypersensitive Reactivity in Potato: Transition from Inactive to Active State Induced by Infection with an Incompatible Race ofPhytophthora infestans

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Abstract
Surface cells of fresh potato tuber disks have low ability to react hypersensitively to infection with an incompatible race of P. infestans. These cells acquire hypersensitive reactivity gradually and attain almost full ability to react about 16-20 h after cutting. When the surface tissue zone (0.2-0.3 mm thick) from aged disks was removed with a razor blade, cells of the freshly cut surface also had high ability to react, indicating that the low ability of freshly cut disks to react is not caused by wounding but is due to the inherent low ability of intact cells. Treating the cut ends of petioles of unfolding young leaflets with 5 ppm blasticidin S and inoculating the intact epidermis with the incompatible race greatly reduced hypersensitive cell death. An intact potato cell, from tubers as well as from leaves, has very low initial ability to react hypersensitively to infection. The ability is induced by infection with an incompatible race of P. infestans or by wounding. Transition from state I ["active"] to state II ["active"] requires protein synthesis.