Histochemical analysis of the root tuber of Polygonum multiflorum Thunb. (Fam. Polygonaceae).

Authentication is the first priority in quality evaluation of Chinese herbal medicines (CHMs). The most commonly used authentication methods are morphological identification and microscopic identification. Unfortunately, these two methods cannot provide the chemical information needed to assess the quality of CHMs. In this study, a combination of fluorescence microscopy and high performance liquid chromatography-mass spectrometry (HPLC-MS) was used to analyze the chemical profiles of the tissues of the raw root tubers of Polygonum multiflorum Thunb. The results showed that the cork cells, cortex, and vessels in transverse sections of the raw root tuber of P. multiflorum fluoresced differently. Further analysis by HPLC-MS revealed that anthraquinones are mainly distributed in the cortex, and 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucopyranoside could be found in all tissues of the raw root tubers of P. multiflorum with its relative content as cork > cortex > xylem of allotype vascular bundles > xylem of central vascular bundles. Moreover, the fluorescence characteristics of the tissues from the steamed root tuber of P. multiflorum were compared and showed different fluorescence from those of raw material. From these results, it can be deduced that the root tuber of P. multiflorum with a broader cortex and fewer vascular bundles visible in a transverse section should be of better quality. The different fluorescence characteristics can be used to differentiate raw root tubers of P. multiflorum from those that have been steamed.