Changes in content and composition of phenolic acids during growth of xylem cells of Scots pine

Abstract

The content and composition of alcohol soluble phenolic acids (PhAs) were studied during cell xylem growth in course of wood annual increment formation in the trunks of Scots pine. Cells of the cambium zone, two stages of expansion growth, and outset of secondary thickening zone (before lignification) within the period of formation of early wood xylem were subsequently isolated from trunk segments of 25-year-old trees with constant anatomical and histochemical control. The amount of free and bound forms of phenolic acids extracted from tissues by 80% ethanol, as well as their ethers and esters, were calculated both per dry weight and per cells. The substantial alteration in content, proportion of fractions and composition of acids has been found between the cambium zone and the outset of secondary thickening of tracheids, and the character of variation depended on the calculation method. The amount of free and bound PhAs and esters and especially ethers calculated per cell had increased at the first stage of extension growth, reduced at the second, and increased in the outset of secondary wall deposition. The pool of bound acids was more than acids by 2–5 times depending on the stage of development of the cells. Sinapic and ferulic acids dominate among free hydroxycinnamic acids. The composition and the content of hydroxycinnamic acids in esters and ethers also depended on the stage of development of the cells. p-Coumaric and sinapic acids were the main aglycons in ethers in the cambium and sinapic and caffeic acids were in the other stages. The esters from cambium included mostly p-coumaric acid and those at other stages of development were sinapic and ferulic acids. The esters included benzoic acid at the first stages of growth. The pool of these esters decreased from the first phase of growth until the outset of cell wall thickening. The level of free benzoic acid increased respectively.