Influence of potassium nitrate on antioxidant level and secondary metabolite genes under cold stress in Panax ginseng

The overall survival mechanism and secondary metabolite synthesis under cold stress conditions (4A degrees C) at exogenous supply with KNO3 were studied in mountain ginseng adventitious root cultures. Expressed sequence tags encoding antioxidant enzymes, such as catalase (CAT), ascorbate peroxidase (APX), glutathione peroxidase (GPX), and also ginsenoside-related secondary metabolites were obtained, and expression studies were carried out using quantitative real-time PCR. Chilled adventitious root cultures grown in vitro with or without an exogenous supply with K+ were differentially regulated. Expressions of PgCAT, PgAPX, and PgGPX-1 were increased, whereas PgGPX-2 and all ginsenoside-related secondary metabolite genes showed slight down-regulation upon chilling stress. Interestingly, the most genes were up-regulated at the increased potassium supply except the cytochrome P450 gene, which shows clearly the specific effect of potassium on the antioxidant level and secondary metabolite gene expression involved in the survival mechanism. In addition, we studied the activities of catalase, ascorbate peroxidase, guaiacol peroxidase, and phenylalanine ammonia-lyase, which showed similar pattern of changes. Adventitious root dry weight and relative water content were found to increase at 0.05 mM KNO3. The high level of potassium is needed for Panax ginseng under chilling conditions to increase its cold tolerance through activating the anti-oxidant system as well as to increase ginsenoside-related secondary metabolite transcripts.