Articles
HISTOCHEMICAL LOCALIZATION OF CATECHINS AND PROCYANIDINS
Article number
381_116
Pages
797 – 802
Language
Abstract
As yet, different classes of polyphenolic compounds are not easily distinguished in histological sections.
This is mainly due to the limited selectivity of the staining reactions commonly employed.
We present two highly selective staining procedures for catechins (flavan-3-ols) and the corresponding oligomeric procyanidins that do not interfere with other phenolics such as hydrolysable tannins or phenolic acids.
The first procedure is based on the reaction of flavan-3-ols with p-dimethylamino-cinnamaldehyde (DMACA). This reaction yields a blue-coloured product and has been shown to be about thousandfold more sensitive against monomeric flavanols in comparison with the more common p-dimethyl-aminobenzaldehyde staining.
However, oligomeric flavan-3-ols (procyanidins) are stained less intensely.
These so-called "condensed tannins" can be localized in glycol methacrylate-embedded plant tissue by conversion to cyanidins via in situ-hydrolysis using hot sulphuric acid.
This treatment results in brilliant red staining of procyanidin-containing cells.
Depending on the degree of polymerization, this colour may shift to dark brown, since monomeric flavan-3-ols are not converted to red cyanidins but rather to insoluble brownish phlobaphenes.
Thus, in combination with the DMACA-staining for monomeric flavan-3-ols, the latter method provides a valuable means for rough estimation of the degree of polymerization of procyanidins at a cellular level.
This is mainly due to the limited selectivity of the staining reactions commonly employed.
We present two highly selective staining procedures for catechins (flavan-3-ols) and the corresponding oligomeric procyanidins that do not interfere with other phenolics such as hydrolysable tannins or phenolic acids.
The first procedure is based on the reaction of flavan-3-ols with p-dimethylamino-cinnamaldehyde (DMACA). This reaction yields a blue-coloured product and has been shown to be about thousandfold more sensitive against monomeric flavanols in comparison with the more common p-dimethyl-aminobenzaldehyde staining.
However, oligomeric flavan-3-ols (procyanidins) are stained less intensely.
These so-called "condensed tannins" can be localized in glycol methacrylate-embedded plant tissue by conversion to cyanidins via in situ-hydrolysis using hot sulphuric acid.
This treatment results in brilliant red staining of procyanidin-containing cells.
Depending on the degree of polymerization, this colour may shift to dark brown, since monomeric flavan-3-ols are not converted to red cyanidins but rather to insoluble brownish phlobaphenes.
Thus, in combination with the DMACA-staining for monomeric flavan-3-ols, the latter method provides a valuable means for rough estimation of the degree of polymerization of procyanidins at a cellular level.
Authors
M. Gutmann, W. Feucht
Keywords
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