INRA, U.M.R. 547 PIAF, F-63100 Clermont-Ferrand, France.
Tree Physiol. 2010 Jan;30(1):89-102. doi: 10.1093/treephys/tpp103. Epub 2009 Dec 2.
Bud break pattern is a key determinant of tree architecture. The mechanisms leading to the precedence of certain buds over the others are not yet fully explained, but the availability of soluble sugars may play a significant role, especially those in the xylem sap at the onset of the growing period. Here, we measured carbon availability in the different tissues (bud, xylem and bark). To assess the capacity of buds to use the xylem sap carbohydrates, the fluxes between xylem vessels and parenchyma cells, bark and buds of walnut (Juglans regia cv 'Franquette') were measured during the rest period until bud break. This uptake capacity varies according to the temperature, the sugar and the position on the branch of the fragment studied. Between December and March, in xylem tissues, the active component of sucrose uptake was predominant compared with diffusion (90% of the total uptake), whereas the active component accounted for more moderate amounts in buds (50% of the uptake). The active uptake of hexoses took place belatedly (April) in xylem. The flow rates between xylem vessels and buds increased 1 month before bud break and reached 2000 microg sucrose h(-)(1) g DW(-)(1). Fluxes seemed to depend on bud position on the branch. However, this study strongly suggests that they were mainly dependent on the sink strength of the buds and on the sink competition between bud, xylem parenchyma and bark.
芽休眠模式是树木结构的一个关键决定因素。导致某些芽优先于其他芽的机制尚未完全解释清楚，但可利用的可溶性糖可能起着重要作用，特别是在生长初期木质部汁液中的糖。在这里，我们测量了不同组织（芽、木质部和树皮）中的碳可用性。为了评估芽利用木质部汁液碳水化合物的能力，我们在休眠期直到芽休眠期间测量了核桃（Juglans regia cv 'Franquette'）芽、木质部和树皮之间的木质部导管和薄壁细胞之间的通量。这种吸收能力根据温度、糖和研究片段在树枝上的位置而变化。在 12 月至 3 月期间，在木质部组织中，与扩散相比，蔗糖吸收的活性成分占主导地位（总吸收的 90%），而在芽中，活性成分的比例适中（吸收的 50%）。己糖的主动吸收较晚（4 月）发生在木质部。木质部导管和芽之间的流速在芽休眠前 1 个月增加，达到 2000μg 蔗糖 h(-)(1)gDW(-)(1)。通量似乎取决于芽在树枝上的位置。然而，这项研究强烈表明，它们主要取决于芽的库强和芽、木质部薄壁组织和树皮之间的库竞争。
