Localization of proanthocyanidins using in situ-hydrolysis with sulfuric acid.

A valuable method for specific localization of proanthocyanidins in plant tissues is given. The specificity is based on the acid hydrolysis of condensed tannins in situ via hot sulfuric acid, yielding bright red anthocyanidins. This treatment did not cause noticeable damage of tissue embedded in glycol methacrylate prior to sectioning. Further proof of specificity was achieved by control staining with the flavan-3-ol-selective p-dimethylaminocinnamaldehyde (DMACA) reagent. In addition, comparison of adjacent sections stained with the DMACA reagent may give coarse information about the degree of polymerization of the proanthocyanidins.