RESUMEN
Se is an essential element required for various metabolic pathways and act as an antioxidant in the various redox-reactions of primary and secondary plant production of – biomolecules. Geranium is an important essential monoterpene oil(s) bearing plant. Culturing the plant at different doses of Se from 0-1.0 mg Se ml-1 revealed that Se plays an important role as an in antioxidant promoter, apart from its micronutrient essentiality. 0.25 mg Se ml-1 is the critical concentrations for maximum content of (0.21%) total essential monoterpene oil(s). At concentration below and above 0.25 mg Se ml-1, the CO2 assimilation rate, photosynthetic pigments content and ultimately the accumulation of essential monoterpene oil(s) are affected. The maximum peroxidase and SOD activities were obtained at 0.25 mg Se ml-1, with the production of biomolecule geraniol. Results revealed an oxidoreducable reaction of Se in the formation of monoterpene essential oil(s) and possibly for the major constituents Geraniol.