Flavanols in the nuclei of the tea bush (<i>Camellia sinensis</i>) - broadening the perspectives to human health
Keywords:catechin, polyphenol, histone, chromatin, epigenetic regulation, DMACA
AbstractFlavanols as a small subclass of the flavonoids stain selectively blue with the special reagent p-dimethylaminocinnamaldehyde (DMACA). Because of the prominent blue colour it is easy to recognize the flavanols histochemically in the vacuoles of expanding and maturing cells. However, the cells of the tea shrub (Camellia sinensis L.) show those blue coloured flavanols also in the nuclei. Silenced interphase nuclei of mature parenchyma cells indicate a pronounced diffuse distribution of blue stained flavanols. By contrast, in activated nuclei the flavanols reflect a variable, mosaic-like blue patterning enclosed by white interchromatin spaces. Subnuclear expression of euchromatin displays relative tiny blue dots of flavanols as compared with the larger-sized blobs of heterochromatin. From metaphase to telophase, the chromosomes stain a fairly dark blue with a more or less diffuse appearance. Those nuclei running through mitotic interphases from G 1 to G 2 have well-defined flavanol-free nucleoli. The flavanol pattern of meristematic chromosomes found in the tea plant is basically also valid for herbaceous plants, such as Hyacinthus romanus, Tulipa gesneriana and Allium cepa, which genuinely do not contain nuclear flavanols. This was verified by incubation of their rootlets in solutions of green tea and epigallocatechin gallate (EGCG). Also human nuclei demonstrate an easy import of added flavanols and the resulting blue stained chromatin reflects in much the same way the structural modifications as already described for the plant nuclei. Possible roles of flavanols in organizing basic mechanisms of chromatin remodelling are discussed. Hereby, also the overall problem of easy oxidizable flavanols should be integrated. Flavanols have the potential to associate to the histone proteins of chromatin. Even small fragments of histones can aggregate to catechin as shown on the basis of kinetic measurements for the H4-core peptide HAKRKT and its acetylated product HAK(ac)RK(ac)T according to the epigenetic histone code.
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