Essential oil and volatile emissions of basil (Ocimum basilicum) leaves exposed to NaCl or Na2SO4 salinity

The volatile compounds emitted by living leaves of basil (Ocimum basilicum L. cv. Genovese) plants under saline conditions were investigated by means of headspace–solid phase microextraction (HS-SPME) and gas chromatography coupled with mass spectrometry (GC–MS). Furthermore, the composition of the essential oil obtained by hydrodistillation of the leaves was studied. Plants were grown for 15 d without salt or with an equimolar concentration of Na+ in the form of Na2SO4 (25 mM) and NaCl (50 mM), after which the growth, the essential oil, and the volatile constituents of the leaves were determined. Fifty-four components were identified belonging to different chemical classes. Under control conditions, the essential oil was rich in linalool (45.9%), 1,8-cineole (16.7%), eugenol (10.3%), trans-α-bergamotene, and epi-α-cadinol (4.9%). The main volatiles detected in the headspace of leaves of untreated basil plants were linalool (29.8%), followed by 1,8-cineole (19.2%), trans-α-bergamotene (10.0%), and eugenol (7.0%). Under saline conditions, leaf growth was more depressed by 25 mM Na2SO4 than 50 mM NaCl, and essential oil concentration increased by 22% in the NaCl, but decreased by 18% in the Na2SO4 treatment, respectively. Both salts caused some changes in the essential oil and composition of volatile compounds. Most prominent was a strong negative correlation between eugenol and methyleugenol proportions, which may indicate an enhancement of the O-methyltransferase activity. In comparison to the essential oil, the composition of volatiles showed some variations in their emission profile under both salts, the most important was an increase of eugenol. It is therefore concluded that the decrease of eugenol occurring in basil essential oil caused by both salts could be due to the enhancement of the eugenol O-methyltransferase activity, an enzyme that accepts eugenol as substrate, generating methyl eugenol, and also to the increase of the eugenol emission as shown by the SPME profil