Accumulation of H_2O_2 in plasma membrane modifications of susceptible Japanese pear leaves treated with AK-toxin I produced by Alternaria alternata Japanese pear pathotype

摘要

Alternaria alternata Japanese pear pathotype is the causal fungus of black spot disease in susceptible cultivars of Japanese pear plants and produces three host-specific toxins (AK-toxin I, II and III). It has been widely accepted that AK-toxin I specifically acts on plasma membranes of susceptible pear leaves and causes partial dysfunction of the membranes, suggesting that the successful colonization of fungi in host tissues is achieved by the dysfunction. The toxin caused plasma membrane modifications associated with leakage of Na~+ and Mg~(++) ions only in susceptible leaves within 1 h after the treatment. The toxin had two different potential abilities: it caused both plasma membrane modification as membrane damages and the callose secretion of the modification sites. Although the pathological significance of the callose accumulation has remained unclear yet, the damaged plasma membranes, due to the toxin attack was expected to be accompanied with the occurrence of oxidative burst. Therefore, we made an attempt to detect H_2O_2 in th toxin-treated susceptible leaves by using cytochemical CeCl_3 method.