Different responses of shoot and root cultures of Glehnia littoralis to yeast extract

Iron availability alters ascorbate-induced stress metabolism in Glehnia littoralis root cultures

Our previous study indicated that formation of furanocoumarin phytoalexins could be induced in Glehnia littoralis root cultures by treatment with 10-40 mM ascorbic acid (AsA). This furanocoumarin production is much less evident when G. littoralis roots are treated with AsA under iron-deficient conditions. Instead, two large unknown peaks appeared in the HPLC chromatogram, whose chemical structures were elucidated by spectroscopic methods as being 6, β-dihydroxyphenethyl ferulate (DF) and 6-hydroxyphenethyl ferulate (HF), respectively. Their maximal level of induction was observed at 20 mM AsA, and the production of DF always exceeded that of HF. This is the first report of these compounds in G. littoralis and of the modulation of the phytoalexin biosynthetic pathway in G. littoralis by iron deficiency.

Constitutive expression of bergaptol O-methyltransferase in Glehnia littoralis cell cultures

We investigated whether exogenously supplied precursors of bergapten, namely umbelliferone, psoralen and bergaptol, could be utilized to produce bergapten without elicitation in Glehnia littoralis cell suspension cultures. The levels of added psoralen and bergaptol in the medium soon decreased, and this was followed by the detection of bergapten in both culture fluid and cells. Umbelliferone was also incorporated but in this case no bergapten was produced; instead, skimmin, umbelliferone monoglucoside, was detected. To determine whether conversion of psoralen to bergapten was due to enzyme induction by precursor feeding, the transcript accumulations and enzyme activities of bergaptol O-methyltransferase (BMT, EC 2.1.1.69), which catalyzes the last step of bergapten synthesis, and of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5), which catalyzes the initial step of the phenylpropanoid biosynthetic pathway and is known as a marker enzyme of elicitation, were examined. The results showed that both the expression and the activity of BMT were always detected in all cells, including control cells. Since PAL was slightly induced in the cells supplied with/without precursors, phenylethyl alcohol (PEA, a competitive inhibitor of PAL) was applied to suspension cells prior to the addition of psoralen. PAL activity was effectively inhibited by PEA at 1-5 mM concentrations. Under these conditions, PEA did not affect bergapten production by cell cultures fed with psoralen at all. These results demonstrate that BMT is constitutively expressed in G. littoralis cell cultures.