The development of proanthocyanidins (condensed tannins) and other phenolics in bark of Pseudotsuga menziesii

Abstract

The development and heterogeneity of proanthocyanidins in bark tissue of Pseudotsuga menziesii Franco (Douglas-fir) were analyzed chemically in extracts by means of the butanol–HCl reagent and histochemically with freehand sections by the nitroso reagent. About twice as much proanthocyanidin on a dry weight basis was found in the bark of mature hypocotyls as in the bark from 1- to 4-year-old stems and increment cores from 80-year-old trees. The proanthocyanidins were widely distributed in the vacuoles of epidermal cells, phellem, and the vascular cambial zone, but were randomly distributed in parenchyma cells within the phloem and the cortex. Only procyanidins were found in young, growing tissues, in parenchyma cells in the secondary phloem, in the vascular cambial zone, and in the bark of 80-year-old trees. Prodelphinidins were found in addition to procyanidins in the bark of 6-month-old hypocotyls and 1.5- to 4-year-old plants, possibly only in the cortical and phellem (cork) cells. Comparisons were made with nitroso reagent positive products in needles.