Effect of infection by Phytophthora infestans on the membrane potential of potato cells

Abstract

The membrane potential (Ψm) of potato cells (cultivar Rishiri) infected by incompatible and compatible races of Phytophthora infestans was measured, while the infection process of the measured cells was observed under a microscope. The passive (Ψd) and respiration dependent electrogenic (Ψp) components of Ψm were also analysed using the anoxia method. Cytoplasm often gathered around the inserted microelectrode and sometimes disturbed the measurement. However, it was shown that the experimental system was suitable for the long-term measurement of fm during the infection process. At the moment of penetration of the host cell wall by both the incompatible and compatible races, no signal such as an action potential was observed in the Tm. Infection by the incompatible race caused little change of Tm for a while after penetration, but |Ψd| then began to decrease. |ΨP| did not decrease, but rather increased and apparently compensated for the decrease in |Ψd|, resulting in little or slow reduction of |Ψm|. Later |Ψp| also decreased and Ψm began to depolarize gradually and at about one to several hours after penetration, rapid depolarization took place to reach a steady level of −45 to −55 mV before the cell content became granulated. In some instances, slow and steady depolarization was followed by cell death. Ψd and Ψp of the uninfected cell did not change for more than 10 h after the beginning of the measurement. The compatible race had no effect on either Ψp or Ψd at least within 24 h infection.