Biochemical responses in Salvia limbata CA Mey. towards mercury and lead induced in vitro oxidative stress

In recent years, the increase in industrial and agricultural activities has heightened concerns about heavy metal pollution. In vitro conditions are an important tool for determining the optimum and toxic amounts of heavy metals and for evaluating plant species, especially those that are difficult to germinate, against unfavorable soil conditions. Therefore, this study evaluated heavy metal toxicity by applying different Hg (0.5-1.0 ppm) and Pb (1.0-2.0 ppm) concentrations to medicinal aromatic Salvia limbata plants in vitro. To assess heavy metal toxicity, we measured photosynthetic pigments, sugar and proline contents, MDA and H₂O₂ levels, antioxidant enzyme activities, and mineral element composition. Photosynthetic pigments and total soluble sugar content decreased with increased heavy metal concentrations. On the contrary, MDA, proline, and H₂O₂ contents increased 2- to 3-fold compared to control, especially at a Pb concentration of 2 ppm. Enzymatic antioxidants (SOD, CAT, APX and GR) were affected differently according to concentration under Hg stress while displaying higher activity under Pb stress compared to the control group. GR, APX, CAT, and SOD activities increased by 437.1%, 201.1%, 95.8%, and 29.9%, respectively, at 2 ppm Pb. Additionally, plants exposed to Hg and Pb stress factors generally had lower mineral element contents. Partial increases were recorded Mo and Co contents in 1 ppm Pb treatment and Mg, K, P, and Zn contents in 0.5 ppm Hg treatment. Our results confirm that Pb and Hg induce oxidative stress and damage S. limbata. Furthermore, the research results will provide important data for a deeper understanding of the harmful effects of lead and mercury on plants and their tolerance mechanisms.