Evaluation of changes in phenolic compounds and secondary metabolites of calluses and seedlings of Mellissa officinalis L. under cadmium heavy metal stress

The present study was designed and conducted to investigate the effect of different concentrations of cadmium on some physiological parameters and changes in secondary metabolites in the medicinal plant Mellissa Officinal L. under in vitro culture conditions. For this purpose, first sterile seeds of Mellissa Offcinali L. were sterilized and then cultured in MS medium. Then 28-day-old seedlings were transferred to MS medium containing different concentrations of cadmium nitrate (0,150 and 300 μM) and kept in the culture room under controlled conditions. Also, callus obtained from stem explants were transferred to hormonal medium (0.25 mg L-1 2,4-D and 5 mg L-1 BAP) containing different concentrations of cadmium (0,150 and 300 μM). Four weeks after treatment, photosynthetic pigments and levels of anthocyanin, phenols and flavonoids in seedlings were evaluated. Also, changes in secondary metabolites were investigated through GC-mass analyzes in calluses and seedlings of Mellissa Officinal L. The results showed that increasing the concentration of cadmium nitrate in the medium decreased the amount of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids and anthocyanin in seedlings. With increasing the amount of cadmium nitrate in the medium, the content of phenols and flavonoids increased significantly. The results of GC-mass showed significant changes in the amount of secondary metabolites and essential oil of Mellissa Officinal L seedlings and calli under cadmium stress. Most changes were found in γ -3-carn, transcarveole, citronlal, citronellol. Citral and β-caryophylline.