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

Roots of mountain ginseng (Panax ginseng) were exposed to various levels of oxygen (O2) (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% O2; but thereafter declined ginsenoside and dry weight of the roots by increasing level of O2. Gradual increase in H2O2 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 O2 levels was shown. Increased levels of O2 (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 O2 up to 45 days, except at 50% O2 where GR, GST and GPx decreased compared to the control. However, after 45 days, SOD activity decreased significantly compared to the control in the O2-treated roots. This reflects the sensitivity of enzymes to O2 toxicity. In stress related experiment, roots showed increased synthesis of ginsenosides when 25 and 50 μM H2O2 was applied. However, higher dose and increasing treatment inhibited ginsenoside synthesis. The results indicate that plant roots could grow and protect themselves from O2 stress by coordinated induction of various antioxidant enzymes and metabolite contents. These results suggest that O2 supplementation is useful for ginsenoside accumulation using 5-L bioreactors.