THE ROLE OF ABSCISIC AND PHASEIC ACIDS IN APPLE LEAF WATER RELATIONS

Apple leaf abscisic acid (ABA) levels and water potentials were independent within a -0.5 to -3.0 megapascal (MPa) range. Water-stress-induced increases in ABA were more closely correlated with changes in leaf turgor potential; however, the correlation coefficient was not sufficiently high to suggest a causal relationship. Metabolites having the same retention time as phaseic acid (PA) were observed in less than 10% of the leaf extracts. These compounds, however, were probably the result of solvent or diazomethane contamination, since the presence of PA could not be confirmed by mass spectrum analysis. Apple leaves appear to adapt to water stress by other than ABA- or PA-induced stomatal closure.