Salinity modulates growth, oxidative metabolism, and essential oil profile in Curcuma longa L. (Zingiberaceae) rhizomes

Turmeric (Curcuma longa L.) is of great importance due to its medicinal properties and industrial uses. However, as in most plants, physiological and biochemical changes occur in turmeric plants subjected to saline conditions. This study aimed to evaluate the growth and antioxidant response of turmeric plants, and the yield and composition of turmeric essential oil under saline stress. The study was greenhouse-based, and 180 days old turmeric plants were treated with 50, 100, and 150 mM NaCl solutions for 130 days. Plants grown under high NaCl concentrations showed significantly reduced shoot length and shoot and rhizome biomass accumulation. Large amounts of proline accumulated in the leaves at 150 mM NaCl. Lipid peroxidation and malondialdehyde content increased with salinity in both leaves and rhizomes. Antioxidant enzymes showed greater activity in the leaves of plants exposed to high NaCl concentrations. Salinity altered the yield and chemical composition of the essential oil in the rhizomes. A total of 114 compounds were identified in the essential oil, with the main compounds from the sesquiterpenes class. Sesquiterpenes can constitute a secondary antioxidant system which can assist the primary antioxidant defense system to maintain the levels of hydrogen peroxide in cells at concentrations sub-lethal to turmeric plants. In addition, the presence of rhizomes has a mitigating effect on salt stress in this species due to the antioxidant activity of the essential oil present in the rhizomes.