Changes in the Partitioning of Carbohydrates in the Wood during Bud Break in Betula pendula Roth

Abstract

Summary Changes in the carbohydrates of the wood have been investigated during the growth and blossoming of catkins in branches of Betula pendula Roth collected in late winter and subjected to various temperature treatments (0°, 10°, and 21 °C). These changes were followed separately for the apoplast and for the symplast. The growth and blossoming of catkins was paralleled by a prominent resynthesis of starch (e.g. from 3.0 to 7.7 µmg−1 dwt) and a great decrease of sugars in the symplast (e.g. from 20.2 to 6.4 µgmg−1 dwt), a remarkable release of sugars into the apoplast (maximum content 8.98 gl−1), a steep rise in transpiration, and a sharp drop in the pH of the xylem sap (e.g. from 7.5 to 5.7). In the symplast, the ratio of starch to sugars changed from ca. 1:6 to 1:1 within 10 days while its sugar content decreased from 0.65 M to 0.2 M. During catkin growth and blossoming, the carbohydrate content of the branch wood decreased by about 50%. Because the amount of transpired water and its sugar content were found to account almost fully for the observed loss of carbohydrates from the symplast, the xylem pathway is attributed an essential role in translocating organic material in the early stage of spring. In the symplast, fructose, glucose, maltose, sucrose, and its galactosides raffinose and stachyose are abundantly found at 0°C with the contents lying between 2.3 and 7.2 µg mg−1 dwt. In the apoplast, in contrast, 97 to 98 % of the sugars are made up by fructose, glucose, and sucrose at the same time. Considerable changes in the absolute and the relative content of individual sugars are observed in the symplast during the storage periods. The physiological significance of the observed changes in carbohydrates, and of the xylem pathway are discussed.