Cerium-Promoted Ginsenosides Accumulation by Regulating Endogenous Methyl Jasmonate Biosynthesis in Hairy Roots of Panax ginseng.

Ru Zhang,Pengcheng Hu,Bianling Zhang,Shiquan Tan,Ling Li

doi:10.3390/molecules26185623

Abstract

Among rare earth elements, cerium has the unique ability of regulating the growth of plant cells and the biosynthesis of metabolites at different stages of plant development. The signal pathways of Ce3+-mediated ginsenosides biosynthesis in ginseng hairy roots were investigated. At a low concentration, Ce3+ improved the elongation and biomass of hairy roots. The Ce3+-induced accumulation of ginsenosides showed a high correlation with the reactive oxygen species (ROS), as well as the biosynthesis of endogenous methyl jasmonate (MeJA) and ginsenoside key enzyme genes (PgSS, PgSE and PgDDS). At a Ce3+ concentration of 20 mg L−1, the total ginsenoside content was 1.7-fold, and the total ginsenosides yield was 2.7-fold that of the control. Malondialdehyde (MDA) content and the ROS production rate were significantly higher than those of the control. The activity of superoxide dismutase (SOD) was significantly activated within the Ce3+ concentration range of 10 to 30 mg L−1. The activity of catalase (CAT) and peroxidase (POD) strengthened with the increasing concentration of Ce3+ in the range of 20–40 mg L−1. The Ce3+ exposure induced transient production of superoxide anion (O2•−) and hydrogen peroxide (H2O2). Together with the increase in the intracellular MeJA level and enzyme activity for lipoxygenase (LOX), there was an increase in the gene expression level of MeJA biosynthesis including PgLOX, PgAOS and PgJMT. Our results also revealed that Ce3+ did not directly influence PgSS, PgSE and PgDDS activity. We speculated that Ce3+-induced ROS production could enhance the accumulation of ginsenosides in ginseng hairy roots via the direct stimulation of enzyme genes for MeJA biosynthesis. This study demonstrates a potential approach for understanding and improving ginsenoside biosynthesis that is regulated by Ce3+-mediated signal transduction.

Highlights

For thousands of years, Panax ginseng has been one of the most valued herbal medicines in oriental countries [1]
The production of O2− induced by Ce3+ resulted in an increase in the methyl jasmonate (MeJA) level, and such a phenomenon was effectively inhibited by DPI because the reduction of O2− limited the production of H2O2. These results suggest that NADPH oxidase is responsible for the Ce3+-induced production of reactive oxygen species (ROS), and MeJA biosynthesis is dependent on the oxidative burst
The culture of hairy roots is a promising alternative to improve the production of target secondary metabolites through various elicitors or precursors supplemented in the media

Summary

Introduction

Panax ginseng has been one of the most valued herbal medicines in oriental countries [1]. Because the cultivation period of ginseng is long and the active ingredients mainly accumulate in aged roots, it is sensible to efficiently culture ginseng cells or tissues in high yield [6,7]. It has been reported that REEs have important regulatory effects on plant physiology [8,9]. An appropriate amount of REEs promotes the photosynthesis rate, root development and increase in biomass, and improves plant resistance against stress by altering the activities of some antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) [10,11]. All the results show that at optimized conditions, Ce3+ can promote plant growth and physiological properties in tissue or callus culture

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Conclusion