Effects of salicylic acid on growth, mineral nutrition, glandular hairs distribution and essential oil composition in Salvia officinalis L. grown under copper stress

Higher uptake and translocation of copper (Cu) into plant tissues can cause serious physiological and biochemical alterations. Salicylic acid (SA) is a well-known naturally occurring signaling molecule responsible for inducing environmental stress tolerance in plants. Therefore, spraying of SA could provide protection against several types of stresses such as Cu toxicity. In this sense, a pot study was conducted to find out whether spraying of SA (0.5 and 1 mM) could ameliorate the adverse effect of Cu toxicity (40 mM) in Salvia officinalis L. plants. The results showed that the Cu stress significantly decreased the stem and root growth, and it reduced the calcium (Ca), phosphorus (P) and potasium (K) content of leaves and roots. Besides, Cu stress increased essential oil yield by 16.66% as compared to control. On the other hand, SA spraying on stressed plants significantly improved stem and root growth and increased Ca, P and K content. This improvement was more pronounced at 0.5 mM SA concentration. The essential oil content also increased under treatment with SA, specially at 0.5 mM concentration, with 116.66% enhancement as compared to stressed plants (untreated with SA). The increase in essential oil yield under all treatments was associated with significant enhancement in the density of peltate glands, with a much higher density when SA was applied at 0.5 mM concentration in presence of Cu stress. The chemical composition of oil changed according to the treatment. Cu stress led to a reduction of 19% in oxygenated monoterpenes levels, mainly due to the decrease in the major compounds, α-thujone, camphor and 1.8-cineol. However, spraying SA on stressed plants led to the recovery of normal levels of these compounds.