EFFECTS OF WATER-STRESS ON CELLULAR ULTRASTRUCTURE AND ON CONCENTRATIONS OF ENDOGENOUS ABSCISIC-ACID AND INDOLE-3-ACETIC-ACID IN FATSIA-JAPONICA LEAVES

Ultrastructural alterations in mesophyll cells as well as variations i n bulk leaf endogenous ABA and IAA concentrations were studied in wate r-stressed field-grown plants of Fatsia japonica. Under water deficit cellular membranes were modified and an increase in vesicles was obser ved. The main damage to the chloroplasts included thylakoid swelling a nd disruption of the chloroplast envelope. Concomitant variations in a bscisic acid and indole-3-acetic acid were observed. Despite the expec ted increased in endogenous ABA concentration in relation to water str ess, after the highest concentration of ABA, observed at predawn in se verely stressed plants (psi(predawn) = -0.681 MPa), there was a sharp decline from 2768 pmol g fw(-1) to 145 pmol g fw(-1); thus in severely stressed plants ABA levels were not related to changes in bulk leaf A BA contents. Water stress did not influence the concentrations of indo le-3-acetic acid, although the increase in the endogenous abscisic aci d concentration could be related with the ultrastructural changes.