Abstract
The aim of this study was to investigate the effect of CO
2 at various concentrations (1, 2.5 and 5%) on antioxidant enzymes and ginsenoside accumulation in
Panax ginseng roots in 5
l airlift bioreactors (working volume 4
l). One and 2.5% CO
2 was beneficial for root biomass accumulation, but 5% CO
2 decreased the biomass. Ginsenoside concentration decreased with increasing concentration of CO
2. No significant difference was observed in the malondialdehyde (MDA) content and lipoxygenase (LOX) activity between respective controls and CO
2 treated roots. Antioxidant enzymes such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), glutathione reductase (GR), catalase (CAT), guaiacol peroxidase (G-POD) including reduced ascorbate and total glutathione were induced in CO
2 exposed roots which emphasized the protective role of antioxidants against CO
2 induced stress. Superoxide dismutase activity (SOD) which was induced after 15 days was significantly inhibited after 45 days. Glutathione-
S-transferase (GST) and glutathione peroxidase (GPX) activities also increased when the roots were subjected to 1 and 2.5% CO
2 compared to the respective controls but not at 5%. A higher reduced ascorbate to oxidized (ASC/DHA) ratio in CO
2 treated root indicates the plant's ability to tolerate CO
2 stress. These observations suggest that an increase in antioxidant enzymes may affect a defense response to the cellular damage induced by CO
2. Probably, this increase could not stop the deleterious effects of CO
2 concentration on ginsenoside concentration, but reduced stress severity and thereby allowing root growth to occur.