DROUGHT STRESS OF APPLE-TREES ALTERS LEAF EMISSIONS OF VOLATILE COMPOUNDS

Actively growing potted apple trees (Malus domestica [L.] Borkh. cv. D elicious) unacclimated to drought stress were subjected to drought to determine changes in emissions of leaf volatile compounds, Drought str ess was imposed over a 2-week period by weighing pots every 2 or 3 day s and adding water back to an arbitrary and decreasing fraction of the original pot weight. Stem water potential was -2.7, -2.0 and -0.8 MPa for the severely stressed, moderately stressed and control trees, res pectively, 13 days after watering treatments were begun. Water use the last 4 days of the experiment was about one-half for the moderately a nd severely stressed trees compared to that of the controls. Twenty-ni ne volatile compounds were identified by using gas chromatography and mass spectroscopy, Emission rates of hexanal, (E)-2-hexenal, (E)-2-hex en-1-ol, 1-hexanol, hexyl acetate and (E)-2-hexenyl acetate were 5 to 310 rimes higher for severely stressed trees compared to those of the controls with the moderately stressed trees intermediate. The large in creases in hexanal, (E)-2-hexenal and 1-hexanol may be related to enha nced lipoxygenase activity. Volatile compounds are products of metabol ism and measurement of their changes after biotic or abiotic stresses will increase understanding of the relationship of changes in plant me tabolism by those stresses.