Mentha piperita L. demonstrates a potential tolerance at molecular and biochemical level to Pb stress: New perspectives

• Severe Pb condition significantly increase in menthol content. • Essential oil content improve Mentha piperita L tolerance to heavy metal stress. • Advance breeding programs are vital to develop species wiht high secondary metabolite content. Mentha piperita L., belonging to Lamiaceae , is widely cultivated to extract one of the most invaluable compounds, such as menthol used in the pharmaceutical and food industries. However, abiotic stress adversely affects high yields, compelling researchers to utilize biotechnological approaches to improve tolerance in this plant. Therefore, this study aimed to investigate stress responses at biochemical, molecular, and metabolic levels under four Pb concentrations:0, 100, 300, and 600 ppm. The results indicated that the relative abundance of menthofuran synthase ( MFS ) was downregulated, whereas menthol reductase ( MR ) and pulegone reductase ( PR ) were upregulated. Accordingly, GC–MS data have demonstrated an increasing tendency of menthol content with intensifying Pb stress. Moderate stress decreased the total chlorophyll, chlorophyll a/b, and carotenoid content and increased the oxygen peroxide content compared to the control. Although the total protein level was unaffected, the plant antioxidant system, especially the enzymatic system, showed high activity at Pb levels of 600 and 300 ppm, respectively. In conclusion, the correlation between menthol content and the relative expression level of genes involved in biosynthetic pathways under Pb stress demonstrates the contribution of this metabolite in withstanding such abiotic environmental factors. These findings pave the way for further metabolomic studies of medicinal plants of interest to cultivate them under severe conditions.