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Abstract
To investigate the enzyme variations responsible for the synthesis of phenolics, 40 day-old adventitious roots of Panax ginseng were treated with 200 microM methyl jasmonate (MJ) or salicylic acid (SA) in a 5 L bioreactor suspension culture (working volume 4 L). Both treatments caused an increase in the carbonyl and hydrogen peroxide (H2O2) contents, although the levels were lower in SA treated roots. Total phenolic, flavonoid, ascorbic acid, non-protein thiol (NPSH) and cysteine contents and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical reducing activity were increased by MJ and SA. Fresh weight (FW) and dry weight (DW) decreased significantly after 9 days of exposure to SA and MJ. The highest total phenolics (62%), DPPH activity (40%), flavonoids (88%), ascorbic acid (55%), NPSH (33%), and cysteine (62%) contents compared to control were obtained after 9 days in SA treated roots. The activities of glucose 6-phosphate dehydrogenase, phenylalanine ammonia lyase, substrate specific peroxidases (caffeic acid peroxidase, quercetin peroxidase and ferulic acid peroxidase) were higher in MJ treated roots than the SA treated ones. Increased shikimate dehydrogenase, chlorogenic acid peroxidase and beta-glucosidase activities and proline content were observed in SA treated roots than in MJ ones. Cinnamyl alcohol dehydrogenase activity remained unaffected by both MJ and SA. These results strongly indicate that MJ and SA induce the accumulation of phenolic compounds in ginseng root by altering the phenolic synthesis enzymes.
Highlights
Phenolic compounds are naturally occurring substances in plants, many of which are thought to play physiological roles such as antibacterial, antiviral, anticancer agents and scavengers of most types of oxidizing molecules [1]
Molecules 2007, 12 dehydrogenase activity remained unaffected by both methyl jasmonate (MJ) and salicylic acid (SA). These results strongly indicate that MJ and SA induce the accumulation of phenolic compounds in ginseng root by altering the phenolic synthesis enzymes
The root growth was measured as fresh weight (FW) and dry weight (DW) at 0, 3, 5, 7 and 9 days after treatment
Summary
Phenolic compounds are naturally occurring substances in plants, many of which are thought to play physiological roles such as antibacterial, antiviral, anticancer agents and scavengers of most types of oxidizing molecules [1]. In relation to this, increased activity of phenylalanine ammonia lyase (PAL) and other related enzymes such as peroxidase has been reported in plants subjected to various stresses [3]. They are synthesized primarily through the pentose phosphate pathway (PPP) and shikimate pathways [4]. The phenylpropanoid pathway is the main metabolic route for the synthesis of natural secondary metabolites such as phenolics, flavonoids, lignin etc. Oxidation of peroxidases makes the cell wall more mechanically rigid by cross-linking matrix polysaccharide and glycoprotein molecules, modifying the mechanical properties of the cell wall. Cross linking of matrix polysaccharides in cell walls are likely to inhibit cell wall degrading enzymes of the pathogen
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