Plasmalemma-bound ATPase of potato tubers and its inhibition by Phytophthora infestans-derived elicitors of the hypersensitive reaction

Plasmalemma (PM) vesicles were isolated from tuber disks of potato cv. Kennebec and ATPase activity was characterized. The activity was synergistically stimulated by K + and Na + in the presence of Mg 2+ at a pH optimum of 6.5 and increased by the canalogenic antibiotic, alamethicin, suggesting that the enzyme is located inside the right side-out vesicles. It was, on the other hand, inhibited by diethylstilbestrol, ouabain and orthovanadate. Arachidonic acid (AA), present in potato late blight fungus, Phytophthora infestans and considered as a pure elicitor of the hypersensitive resistance response of potato, markedly decreased the (K + + Na +)-stimulated activity of the ATPase when added to PM preparation. The mycelial homogenate, which has been termed a crude elicitor and which also contains AA, had a negligible effect on the enzyme. Both crude elicitor and AA inhibited the ATPase activity when applied to tuber disks. The inhibition was expressed within 3 h after treatments as a result of one of the earliest actions of elicitors. The effect on the ATPase might be the cause of other metabolic changes that finally manifest themselves in the hypersensitive reaction.