Induction in the antioxidative systems and lipid peroxidation in suspension culture roots of Panax ginseng induced by oxygen in bioreactors

Abstract

Roots of mountain ginseng ( Panax ginseng) were exposed to various levels of oxygen (O 2) (30, 40 and 50%) for 15, 30 and 45 days in 5 L (working volume 4 L) airlift bioreactors. Ginsenoside accumulation and dry weight was enhanced up to 40% O 2; but thereafter declined ginsenoside and dry weight of the roots by increasing level of O 2. Gradual increase in H 2O 2 content and lipoxygenase activity (LOX), resulting in cellular damage and oxidative stress as indicated by increased malondialdehyde (MDA) content after 30 and 45 days at all O 2 levels was shown. Increased levels of O 2 (above ambient) resulted in increases in non-protein thiol (NP-SH) and cysteine content. Higher activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), catalase (CAT), guaiacol peroxidase (G-POD), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione S transferase (GST) activities indicated that antioxidant enzymes played an important role in protecting the roots from O 2 up to 45 days, except at 50% O 2 where GR, GST and GPx decreased compared to the control. However, after 45 days, SOD activity decreased significantly compared to the control in the O 2-treated roots. This reflects the sensitivity of enzymes to O 2 toxicity. In stress related experiment, roots showed increased synthesis of ginsenosides when 25 and 50 μM H 2O 2 was applied. However, higher dose and increasing treatment inhibited ginsenoside synthesis. The results indicate that plant roots could grow and protect themselves from O 2 stress by coordinated induction of various antioxidant enzymes and metabolite contents. These results suggest that O 2 supplementation is useful for ginsenoside accumulation using 5-L bioreactors.