Abstract
Young leaves of cultivar Nijisseiki and Chojuro of Japanese pear were treated with 100ppm citrinin which exerts a pathological effect similar to that of AK-toxin and the ultrastructural changes in the treated leaves were observed. Within 3h of treatment, citrinin caused a rapid electrolyte-loss in Nijisseiki leaves without any visible symptoms. The invagination of plasma membrane at the both ends of plasmodesmata in the vascular bundle sheath cells was the first obvious change in the ultrastructure. By 8h after treatment, the veinal necrosis appeared and invaginations of plasma membrane became more extensive in both vascular bundle sheath and mesophyll cells. The spaces between cell wall and invaginated plasma membrane contained many lomasome-like vesicles, the central cores extended from plasmodesmata and electron-lucent materials. Cellular membranes were disrupted in necrotic cells of Nijisseiki leaves treated with citrinin for 12h. Citrinin did not affect the cells of resistant Chojuro leaves even after 12h of treatment. These results suggest that citrinin acts upon plasma membrane of Nijisseiki cells and that permeability changes are correlated with the plasma membrane modifications.
