Salicylic Acid-induced Nitric Oxide and ROS Generation Stimulate Ginsenoside Accumulation in Panax ginseng Roots

We evaluated the involvement of nitric oxide (NO) in salicylic acid (SA)-induced accumulation of ginsenoside in adventitious roots of Panax ginseng and its mediation by reactive oxygen species (ROS). Related effects of SA on components of the antioxidant system were also sought. Adventitious roots of P. ginseng were grown in suspension culture for 3 weeks in MS medium and treated over 5 days with SA (100 mu M) alone, SA in combination with the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), or PTIO alone. Nitric oxide, the superoxide anion (O-2(center dot-)), H2O2, nitrite, nonprotein thiol, and ascorbate were monitored together with ginsenoside, NADPH oxidase activity, and several antioxidant enzymes. Salicylic acid did not inhibit root growth but induced accumulation of ginsenoside, lipid peroxidation, and generation of NO and O-2(center dot-). It also enhanced activities of NADPH oxidase, superoxide dismutase, catalase, and peroxidase, including ascorbate peroxidase. These effects were suppressed by PTIO. Salicylic acid also decreased glutathione reductase activity. Inclusion of PTIO with SA decreased the activity of glutathione reductase further. Treatment with SA plus PTIO also decreased nonprotein thiol and ascorbate contents but caused nitrite to overaccumulate. Salicylic acid applied to adventitious roots in culture induced accumulation of ginsenoside in an NO-dependent manner that was mediated by the associated increases in O-2(center dot-), which gave other antioxidant responses that were dependent on NO.