Acclimation of hydrogen peroxide enhances salt tolerance by activating defense-related proteins in Panax ginseng C.A. Meyer.

The effect of exogenously applied hydrogen peroxide on salt stress tolerance was investigated in Panax ginseng. Pretreatment of ginseng seedlings with 100 µM H2O2 increased the physiological salt tolerance of the ginseng plant and was used as the optimum concentration to induce salt tolerance capacity. Treatment with exogenous H2O2 for 2 days significantly enhanced salt stress tolerance in ginseng seedlings by increasing the activities of ascorbate peroxidase, catalase and guaiacol peroxidase and by decreasing the concentrations of malondialdehyde (MDA) and endogenous H2O2 as well as the production rate of superoxide radical (O2(-)). There was a positive physiological effect on the growth and development of salt-stressed seedlings by exogenous H2O2 as measured by ginseng dry weight and both chlorophyll and carotenoid contents. Exogenous H2O2 induced changes in MDA, O2(-), antioxidant enzymes and antioxidant compounds, which are responsible for increases in salt stress tolerance. Salt treatment caused drastic declines in ginseng growth and antioxidants levels; whereas, acclimation treatment with H2O2 allowed the ginseng seedlings to recover from salt stress by up-regulation of defense-related proteins such as antioxidant enzymes and antioxidant compounds.

Transcript pattern of cytochrome P450, antioxidant and ginsenoside biosynthetic pathway genes under heavy metal stress in Panax ginseng Meyer.

The differential transcript patterns of five antioxidant genes, four genes related to the ginsenoside pathway and five P450 genes related to defense mechanism were investigated in in vitro adventitious roots of Panax ginseng after exposure to two different concentrations of heavy metals for 7 days. PgSOD-1 and PgCAT transcription increased in a dose-dependent manner during the exposure to CuCl(2), NiCl(2), and CdCl(2), while all other tested scavenging enzymes didn't show significant increase during heavy metal exposure. Conversely, the mRNA transcripts of PgSQE, PgDDS were highly responsive to CuCl(2) compared to NiCl(2) exposure. However, the transcript profile of Pgß-AS was highly induced upon NiCl(2) treatment compared to CuCl(2) and CdCl(2) exposure. The expressions of PgCYP716A42, PgCYP71A50U, and PgCYP82C22 were regulated in similar manners, and all showed the highest transcript profile at 100 µM of CuCl(2), CdCl(2), and NiCl(2) except PgCYP71D184, which showed the highest transcript level when subjected to 10 µM CuCl(2) and NiCl(2). Thus it may suggest that in P. ginseng heavy metal interaction on cell membrane induced expression of various defense related genes via jasmonic acid pathway and also possesses cross talk networks with other defense related pathways.

Expression of the ginseng PgPR10-1 in Arabidopsis confers resistance against fungal and bacterial infection.

Korean ginseng (Panax ginseng C. A. Meyer) consists of nine cultivars from three Jakyung, Chungkyung, and Hwangsook lines. Among three previously identified PR-10 homologs from ginseng (PgPR10-1, PgPR10-2, and PgPR10-3), we found that the exact same sequence of PgPR10-2 exist in all tested nine cultivars. But a deletion and SNP was found in American ginseng (Panax quinquefolius). PR-10 proteins are known to be small and cytosolic, and showed similar three-dimensional structure. Here we show that the heterologous overexpression of PgPR10-1 in Arabidopsis showed enhanced resistance against Pseudomonas syringe, Fusarium oxysporum, and Botrytis cinerea and in-frame tagging with fluorescent protein showed its cytoplasm and nucleus localization. Protein-protein interaction of PgPR10-2 with PgPR10-1, PgPR10-2 and PgPR10-3 suggests that the PgPR10 proteins might form multimeric complexes in different cellular compartments to function in development and in defense-related mechanism. Differential response of PgPR10-1 and PgPR10-2 against different sets of biotic stresses in ginseng plant supports this notion.

Expression and stress tolerance of PR10 genes from Panax ginseng C. A. Meyer.

Pathogenesis-related 10 protein families (PgPR10 proteins) from ginseng are reported to have ribonuclease activity, conferring defense-related resistance against various stresses. Homology-based PCR using PgPR10-2 specific primers allowed for the isolation of two additional PgPR10 genes. PgPR10-1 is identical to the previously reported ribonuclease 1, while PgPR10-3 is a newly-discovered protein, suggesting that the PgPR10s are a multi-gene family. Differential organ-specific transcripts of PgPR10-1 and PgPR10-2 in the flower bud and root, respectively, indicate that there are tissue-specific functional roles for this gene family. Overexpression of PgPR10-2 in Arabidopsis conferred longer root length and a tolerant growth phenotype on NaCl-supplemented media. Further changes in transcriptional levels against sets of abiotic stressors suggest similar functional roles of PgPR10-1 in the root and predominantly in the flower organ based on its higher expression levels. Overall, this suggests that the manipulation of PgPR10 genes in plants can be used as valuable tool to enhance its physiological status.