Seasonal and within-stem variations of neutral lipids in silver birch (Betula pendula) wood.
Seasonal and within-stem variations of neutral lipids in silver birch (Betula pendula) wood.
复制标题
银桦（Betula pendula）木材中性脂质的季节性和茎内变化。
作者：
R. Piispanen;P. Saranpää
对 7 年树龄无性系的茎材和五棵 35-70 年树龄的成熟银桦树 (Betula pendula Roth) 的中性脂质进行了分析。在幼树和老树的成熟木材中，游离脂肪酸含量低于三酰甘油 (TG) 浓度的 5%。游离亚油酸浓度在3月幼树休眠时最低，盛夏和9月最高。在成熟树木中，TG浓度向髓部方向增加，表明靠近髓部的活的薄壁细胞具有较大的TG储存能力。幼树中的 TG 浓度（平均为木材干重的 0.51 +/- 0.02%）全年保持恒定，而主要游离甾醇 β-谷甾醇（平均为总游离甾醇的 82.5 +/- 0.4%）的浓度在春季和初夏温度逐渐升高时下降，并在秋季树木进入休眠时升高。在幼树中，我们检测到β-谷甾醇和菜油甾醇的游离形式和酯化形式之间以及角鲨烯和betulaprenol-7之间的甾醇酯部分之间存在季节性相互转化。酯化甾醇/类异戊二烯的浓度异常高，尤其是在成熟茎材的内部区域（平均为木材干质量的 0.6 +/- 0.03%）。没有检测到心材形成。
Neutral lipids were analyzed in stem wood of a 7-year-old clone and in five 35-70-year-old mature trees of silver birch (Betula pendula Roth). In young trees and in mature wood of old trees, the free fatty acid fraction comprised less than 5% of the concentration of triacylglycerols (TG). The concentration of free linoleic acid was lowest in March when the young trees were dormant and highest during midsummer and September. In mature trees, the TG concentration increased toward the pith, indicating that living parenchyma cells close to the pith have a large TG storage capacity. The TG concentration (mean 0.51 +/- 0.02% of wood dry mass) remained constant throughout the year in young trees, whereas the concentration of beta-sitosterol, the dominant free sterol (mean 82.5 +/- 0.4% of total free sterols), decreased during spring and early summer when the temperature gradually increased, and increased during autumn when the trees became dormant. In young trees, we detected a seasonal interconversion between the free and esterified forms of beta-sitosterol and campesterol, and within the steryl ester fraction between squalene and betulaprenol-7. The concentration of esterified sterols/isoprenoids was exceptionally high, especially in the inner regions of mature stem wood (mean 0.6 +/- 0.03% of wood dry mass). No heartwood formation was detected.