Abstract
This is the first report on identification of all B-type proanthocyanidins from monomers to decamers (monomers—flavan-3-ols, dimers, trimers, tetramers, pentamers, hexamers, heptamers, octamers, nonamers, and decamers) and some of their gallates in leaves of Japanese knotweed (Fallopia japonica Houtt.), giant knotweed (Fallopia sachalinensis F. Schmidt) and Bohemian knotweed (Fallopia × bohemica (Chrtek & Chrtkova) J.P. Bailey). Flavan-3-ols and proanthocyanidins were investigated using high performance thin-layer chromatography (HPTLC) coupled to densitometry, image analysis, and mass spectrometry (HPTLC–MS/MS). All species contained (−)-epicatechin and procyanidin B2, while (+)-catechin was only detected in Bohemian and giant knotweed. (−)-Epicatechin gallate, procyanidin B1 and procyanidin C1 was only confirmed in giant knotweed. Leaves of all three knotweeds have the same chemical profiles of proanthocyanidins with respect to the degree of polymerization but differ with respect to gallates. Therefore, chromatographic fingerprint profiles of proanthocyanidins enabled differentiation among leaves of studied knotweeds, and between Japanese knotweed leaves and rhizomes. Leaves of all three species proved to be a rich source of proanthocyanidins (based on the total peak areas), with the highest content in giant and the lowest in Japanese knotweed. The contents of monomers in Japanese, Bohemian and giant knotweed were 0.84 kg/t of dry weight (DW), 1.39 kg/t DW, 2.36 kg/t, respectively, while the contents of dimers were 0.99 kg/t DW, 1.40 kg/t, 2.06 kg/t, respectively. Giant knotweed leaves showed the highest variety of gallates (dimer gallates, dimer digallates, trimer gallates, tetramer gallates, pentamer gallates, and hexamer gallates), while only monomer gallates and dimer gallates were confirmed in Japanese knotweed and monomer gallates, dimer gallates, and dimer digallates were detected in leaves of Bohemian knotweed. The profile of the Bohemian knotweed clearly showed the traits inherited from Japanese and giant knotweed from which it originated.
Highlights
Japanese knotweed (Fallopia japonica Houtt.; synonyms: Reynoutria japonica Houtt., Polygonum cuspidatum Sieb. & Zucc., Polygonum reynoutria Makino), giant knotweed
The same combination of the stationary phase and developing solvent used for high performance thin-layer chromatography (HPTLC)-MS/MS analyses of Japanese knotweed rhizomes, which were performed on twice pre-developed plates, enabled a separation of proanthocyanidins according to their degree of polymerization [12]
After completion of the HPTLC-MS/MS analyses, the plate was documented with a DigiStore 2 system at white light illumination in order to connect the MS, MS2, and MS3 spectra with positions (RF on the plate). This is the first report about: (i) comparison of chromatographic fingerprints of leaves of Japanese, Bohemian and giant knotweed; (ii) quantification of total content of monomers and dimers proanthocyanidins in leaves of all three knotweed species; (iii) evaluation of all three knotweed species based on comparison of B-type proanthocyanidins total peak areas; (iv) identification of all B-type proanthocyanidins from monomers to decamers and some of their gallates in all three knotweed species; (v) analyses and identification of flavan-3-ols and proanthocyanidins in leaves of Bohemian knotweed by using mass spectrometry
Summary
Japanese knotweed (Fallopia japonica Houtt.; synonyms: Reynoutria japonica Houtt., Polygonum cuspidatum Sieb. & Zucc., Polygonum reynoutria Makino), giant knotweed & Zucc., Polygonum reynoutria Makino), giant knotweed Schmidt), and their interspecific hybrid Bohemian knotweed (Fallopia × bohemica (Chrtek & Chrtkova) J.P. Bailey; synonyms: Reynoutria x bohemica Chrtek & Chrtkova, Polygonum x bohemicum (Chrtek & Chrtkova) P.F. Plants 2020, 9, 118; doi:10.3390/plants9010118 www.mdpi.com/journal/plants
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