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Regulation of phenylpropanoid metabolism by exogenous precursors in axenic cultures of Sphagnum fallax
Author(s) -
Rasmussen Susanne,
Peters Gotje,
Rudolph Hansjörg
Publication year - 1995
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1995.tb00812.x
Subject(s) - sphagnum , cinnamic acid , biochemistry , metabolism , chemistry , p coumaric acid , incubation , phenylpropanoid , coumaric acid , endogeny , phenylalanine , botany , food science , biology , biosynthesis , enzyme , amino acid , ferulic acid , ecology , peat
Sphagnum plantlets, cultivated in continuous‐feed bioreactors, are characterised by high levels of free endogenous phenolics and a pronounced excretion of some phenolics into the effluent culture medium. The transfer of Sphagnum fallax , precultivated in continuous‐feed bioreactors, to batch cultures resulted in an increased flux through phenylpropanoid metabolism and an accumulation of p ‐coumaric acid to 0.1 μ M and of trans ‐sphagnum acid up to 0.5 μ M in the external medium [ 3 H]‐labelled L‐phenylalanine (7.7 GBq mol −1 ) was rapidly taken up, resulting in an enhanced synthesis and excretion of p ‐coumaric and trans ‐sphagnum acid. Specific activities were 6.9 and 5.4 GBq mol −1 , respectively, for these cinnamic acids excreted into the external medium. Endogenous pools of trans ‐cinnamic and p ‐coumaric acid did not increase and no labelling could be detected in these compounds. Cell wall‐bound activity amounted to ca 14% of the applied activity after 48 h of incubation, 59% of which was recovered in dioxane/2 M HCl extracts of the cell wall. Exogenously applied trans ‐cinnamic acid (0.1 m M ) was taken up to 46% and resulted in a transient endogenous accumulation of trans ‐cinnamic acid, the level of free endogenous p ‐coumaric and trans ‐sphagnum acid was found to have decreased. The concentrations of p ‐coumaric and trans ‐sphagnum acid in the culture medium rose to 17 and 2.4 μ M , respectively, after 48 h of incubation in 0.1 m M trans ‐cinnamic acid. Exogenously applied p ‐coumaric acid (0.1 m M ) was taken up to 79% from the incubation solution but not stored endogenously, as metabolic products trans ‐sphagnum acid and an unknown p ‐coumaric acid‐conjugate accumulated in the external medium and endogenously. These results give evidence for the biosynthetical route from phenylalanine to sphagnum acid and a channelling of pathway intermediates by the enzymes L‐phenylalanine ammonia‐lyase (EC 4.3.1.5) and cinnamic acid 4‐hydroxylase (EC 1.14.13.11).