Influence of ionic interactions on essential oil and phenolic diterpene composition of Dalmatian sage (Salvia officinalis L.)

The potential of four essential cations (K+, Ca2+, Mg2+ and Fe2+) to alleviate salt toxicity was studied in sage (Salvia officinalis L.) plants grown in pots. Two concentrations of the following chloride salts: KCl, CaCl2, MgCl2 and FeCl3, were used together with 100 mM NaCl to study the effects of these nutrients on plant growth, leaf essential oils (EOs) and phenolic diterpenes composition. The sage plants accumulated Na+ in their leaves (includers); this has affected secondary metabolites’ biosynthesis. Treatment with 100 mM NaCl slightly decreased borneol and viridiflorol, while increased manool concentrations. Addition of KCl, CaCl2 and MgCl2 increased considerably in a dose-dependent manner the oxygen-containing monoterpenes (1.8-cineole, camphor, β-thujone and borneol) in 100 mM NaCl-treated sage. Whereas, the contents of viridiflorol decreased further with the addition of KCl in 100 mM NaCl-treated sage. Our results suggest that the changes in EOs composition were more related to K+ and Ca2+ availability than to Na+ toxicity. Furthermore, treatment with NaCl decreased by 50% carnosic acid (CA), a potent antioxidant, content in the leaves. K+ and Ca2+ promoted the accumulation of CA and its methoxylated form (MCA) in the leaves. The concentration of CA was positively correlated with leaf K+ (r = 0.56, P = 0.01) and Ca2+ (r = 0.44, P = 0.05) contents. It appears that different salt applications in combination with NaCl treatments had a profound effect on EOs and phenolic diterpene composition in sage. Therefore, ionic interactions may be carefully considered in the cultivation of this species to get the desired concentrations of these secondary metabolites in leaf extracts.

Research highlights
► In this study, we evaluated how increased cation supply can alleviate the toxic effects of NaCl. We measured plant growth and EOs and phenolic diterpene composition of the leaves of Dalmatian sage. We found that sage plants accumulated Na+ in their leaves (includers); this has affected secondary metabolites’ biosynthesis. Addition of KCl, CaCl2 and MgCl2 increased considerably in a dose-dependent manner the oxygen-containing monoterpenes in 100 mM NaCl-treated sage. Our results suggest that the changes in EOs composition were more related to K+ and Ca2+ availability than to Na+ toxicity. A higher supply of these two cations led to the accumulation of carnosic acid (CA) and its methoxylated form in the leaves. It appears that ionic interactions may be carefully considered in the cultivation of this species to get the desired concentrations of EOs and phenolic diterpenes in the leaf extracts.