Abstract
AM-toxin, a host-specific toxin produced by an apple pathotype of A. alternata, causes leaf necrosis only to susceptible apple cultivars. When leaves of the susceptible apple (cv. Hokuto) were treated with AM-toxin I, levels of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and galactolipids drastically decreased concomitant with the appearance of necrosis, whereas free sterol, sterol glycoside and cerebroside were unaffected. On the contrary, AM-toxin I caused a large increase in phosphatidic acid, and fatty acid composition of this accumulated lipid resembled that of PC and PE in untreated leaves. When AM-toxin I was applied to leaves from a resistant apple mutant that was produced from shoots of the same cultivar by X-ray irradiation, neither lipid changes nor necrosis was observed. Therefore, AM-toxin-induced changes in selective lipids in the susceptible plants may be responsible for the disintegration of cellular membrane structure and function, followed by the appearance of necrosis.
