Drought stress of apple trees alters leaf emissions of volatile compounds

Actively growing potted apple trees ( Malus domestica [L.] Borkh. ev. Delicious) unacclimated to drought stress were subjected to drought to determine changes in emissions of leaf volatile compounds. Drought stress was imposed over a 2‐week period by weighing pots every 2 or 3 days and adding water hack to an arbitrary and decreasing traction 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, respectively. 13 days alter watering treatments were begun. Water use the last 4 days of the experiment was about one‐half for the moderately and severely stressed trees compared to that of the controls Twenty‐nine volatile compounds were identified by using gas chromatography and mass spectroscopy. Emission rates of hexanal, (E)‐2‐hexenal, (E)‐2‐hexen‐1‐ol, 1‐hexenol, hexyl acetate and (E)‐2‐hexenyl acetate were 5 to 310 times higher for severely stressed trees compared to those of the controls with the moderately stressed trees intermediate. The large increases in hexanal. (E)‐2‐hexenal and l‐hexanol may be related. In enhanced lipoxygenase activity. Volatile compounds are products of metabolism and measurement of their changes after biotic or abiotic stresses will increase understanding of the relationship of changes in plant metabolism by those stresses.