Effect of salicylic acid foliar application on growth, glandular hairs and essential oil yield in Salvia officinalis L. grown under zinc stress

Abstract

Abstract Background Generally, zinc (Zn) is an essential element and acts as a plant nutrient, but at higher concentrations, it is toxic. Higher uptake and translocation of Zn into plant tissues can cause serious physiological and biochemical alterations. However, salicylic acid (SA) is an endogenous regulator of growth and signaling molecule responsible for inducing environmental stress tolerance in plants. Therefore, spray application of SA could provide protection against several types of stresses such as Zn toxicity. In this context, the ameliorative effect of SA (0.5 and 1 mM) on Salvia officinalis L. under Zn stress (40 mM) was studied. Results Zn stress decreased growth, chlorophyll content, essential oil yield and peltate glandular trichome density. This toxicity can be linked to a strong accumulation of Zn in the various parts of the plant. In addition, Zn stress disturbed nutrients assimilation (K, P and Ca). However, spray of SA, particularly at 0.5 mM improved all parameters studied under both Zn and normal conditions. The positive effects of SA under Zn stress condition may be due to the decrease of Zn accumulation in different parts of the plant. This decrease was accompanied by an increase in K, P and Ca content. In addition, the histological study of S. officinalis leaves showed the presence of two types of glandular hairs, the peltate and capitate glands. In the leaves of stressed plants, we noticed the presence of glands with deformations in the form of pockets in the number of one or more as well as the glands with an oval form. On the other hand, all these abnormalities glands were not detected in stressed plants that were sprayed with SA. Therefore, the absence of these anomalies under the effect of SA showed the remedial effect of this growth regulator. Conclusion The findings of the present work suggest that spraying SA maybe useful for improving the plant growth in Zn-contaminated areas.