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 a s variations in bulk leaf endogenous BBB and IAA concentrations were s tudied in PEG-treated plants of Fatsia japonica Decne and Plank. Under stress induced by PEG vesicles containing fibrous material and electr on-dense bodies associated with plasma membranes were observed. Cytoch emical examination indicated that electron-dense bodies corresponded t o lipids and the fibrous material of the vesicles were polysaccharides . Chloroplasts, mitochondria, nuclei and Golgi apparatus also showed m odifications. A strong relationship was found between increasing PEG-i nduced water stress, increasing endogenous ABA and ultrastructural cha nges. In relation with leaf ontogeny and ABA concentration a higher AB A 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 a bscisic acid concentration could be related with the ultrastructural c hanges.