Silver nanoparticle pollutants activate oxidative stress responses and rosmarinic acid accumulation in sage

In this study, physiological and molecular responses of sage (Salvia officinalis) to silver nanoparticles (SNPs) were studied. It is supposed that sage oxidative responses can be activated to overcome the negative effects of SNPs. Results showed the penetration of SNPs via leaf epidermis into the parenchyma cells after foliar application. A significant decrease of photosynthetic pigments and increase of cell injury indicators, the activity of enzymatic antioxidants and also the content of non-enzymatic antioxidants were observed after exposure of sage plants to 50 and 1000 mg l^-1 SNPs compared to control plants. Phenolic compounds generally increased, but not in linear response to the dose level. The most abundant phenolic acid, rosmarinic acid (RA), increased more than eightfold at 100 mg l^-1 SNPs. Furthermore, the content of RA, salvianolic acid A and B was positively correlated with the activity of phenylalanine ammonia-lyase and RA synthase, but not with tyrosine aminotransferase. It could be concluded that the content of phenolic compounds increased in response to lower SNPs concentrations (50 and 100 mg l^-1 ). However, the oxidative stress responses continued above these concentrations.