Copper-induced changes in the growth, oxidative metabolism, and saponin production in suspension culture roots of Panax ginseng in bioreactors

Roots of Panax ginseng exposed to various concentrations of Cu (0.0, 5, 10.0, 25.0, and 50.0 mu M) accumulated high amounts of Cu in a concentration-dependent and duration-dependent manner. Roots treated with 50 mu M Cu resulted in 52% and 89% growth inhibition after 20 and 40 days, respectively. Saponin synthesis was stimulated at a Cu concentration between 5 and 25 mu M but decreased at 50 mu M Cu. Malondialdehyde content (MDA), lipoxygenase activity (LOX), superoxide ion (O-2(center dot-)) accumulation, and H2O2 content at 5 and 10 mu M Cu-treated roots were not increased but strongly increased at 50 mu M Cu resulting in the oxidation of ascorbate (ASC) and glutathione (GSH) to dehydroascorbate (DHA) and glutathione disulfide (GSSG), respectively indicating a clear oxidative stress. Seven well-resolved bands of superoxide dismutase (SOD) were detected in the gel and an increase in SOD activity seemed to be mainly due to the induction of Fe-SOD 3. Five to 10 mu M Cu slightly induced activity of ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR), guaiacol peroxidase (G-POD) but inhibited monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) enzyme activities. No changes in catalase (CAT) activity and in activity gel were found up to 25 mu M Cu, but both G-POD and CAT activities were inhibited at 50 mu M Cu. Glutathione metabolism enzymes such as gamma-glutamylcysteine synthetase (gamma-GCS), glutathione-S-transferase (GST), and glutathione peroxidase activities (GPx) were activated at 5 and 10 mu M Cu but were strongly inhibited at 50 mu M Cu due to the Cu accumulation in root tissues. The strong depletion of GSH at 50 mu M Cu was associated to the strong induction of gamma-glutamyltranspeptidase (gamma-GGT) activity. These results indicate that plant could grow under Cu stress (5-25 mu M) by modulating the antioxidant defense mechanism for combating Cu induced oxidative stress.