CYTOLOGICAL EVENTS INDUCED BY ARACHIDONIC-ACID IN POTATO-TUBERS

Necrosis of potato tuber cells is enhanced, after 24 h incubation, by arachidonic acid (AA), an elicitor of the hypersensitive response in S olanum tuberosum L. and also by Fenton's reagents (a hydroxyl radical- generating system) either alone or in association with AA. The phenome non is independent of tuber age. In aged tubers, phenylthiourea (PTU) causes a significant reduction of AA-induced cell necrosis. Necrosis o bserved in the presence of PTU alone is lower than in other treatments , and neither different from the controls nor affected by tuber age. C ell size is not affected by treatments or ageing. Nuclear hypertrophy occurs independently of tuber age, with the highest values after treat ment with AA and Fenton's reagents. Nucleolar extrusion is observed in all treatments but earliest in the presence of AA. AA also enhances t he number of lignified parenchymal cells and, to a lesser extent, the number of tracheary elements.