The effect of exogenously applied putrescine (Put) on salt stress tolerance was investigated in Panax ginseng. Thirty-day-old ginseng sprouts were grown in salinized nutrient solution (150 mM NaCl) for five days, while the control sprouts were grown in nutrients solution. Putrescine (0.3, 0.6, and 0.9 mM) was sprayed on the plants once at the onset of salinity treatment, whereas control plants were sprayed with water only. Ginseng seedlings tested under salinity exhibited reduced plant growth and biomass production, which was directly interlinked with reduced chlorophyll and chlorophyll fluorescence due to higher reactive oxygen species (hydrogen peroxide; H2O2) and lipid peroxidation (malondialdehyde; MDA) production. Application of Put enhanced accumulation of proline, total soluble carbohydrate, total soluble sugar and total soluble protein. At the same time, activities of antioxidant enzymes like superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase in leaves, stems, and roots of ginseng seedlings were increased. Such modulation of physio-biochemical processes reduced the level of H2O2 and MDA, which indicates a successful adaptation of ginseng seedlings to salinity stress. Moreover, protopanaxadiol (PPD) ginsenosides enhanced by both salinity stress and exogenous Put treatment. On the other hand, protopanaxatriol (PPT) ginsenosides enhanced in roots and reduced in leaves and stems under salinity stress condition. In contrast, they enhanced by exogenous Put application in all parts of the plants for most cases, also evidenced by principal component analysis. Collectively, our findings provide an important prospect for the use of Put in modulating salinity tolerance and ginsenosides content in ginseng sprouts.
Keywords: Panax ginseng; ginseng sprouts; ginsenosides; protopanaxadiol; protopanaxatriol; putrescine; reactive oxygen species; salinity tolerance.