CHANGES IN CELL ULTRASTRUCTURE AND ENDOGENOUS ABSCISIC-ACID AND INDOLE-3-ACETIC-ACID CONCENTRATIONS IN FATSIA-JAPONICA LEAVES UNDER POLYETHYLENE GLYCOL-INDUCED WATER-STRESS

Ultrastructural alterations in epidermal and mesophyll cells as well as variations in bulk leaf endogenous BBB and IAA concentrations were studied in PEG-treated plants of Fatsia japonica Decne and Plank. Under stress induced by PEG vesicles containing fibrous material and electron-dense bodies associated with plasma membranes were observed. Cytochemical examination indicated that electron-dense bodies corresponded to lipids and the fibrous material of the vesicles were polysaccharides. Chloroplasts, mitochondria, nuclei and Golgi apparatus also showed modifications. A strong relationship was found between increasing PEG-induced water stress, increasing endogenous ABA and ultrastructural changes. In relation with leaf ontogeny and ABA concentration a higher ABA level was observed in younger than in older leaves. The differences in the endogenous concentrations of indole-3-acetic acid are unclear, except after 7 days of PEG-treatment. The increase in the endogenous abscisic acid concentration could be related with the ultrastructural changes.