Department of Forest Botany, Warsaw University of Life Sciences, Nowoursynowska 159, 02-776, Warsaw, Poland.
Department of Dendrometry and Forest Productivity, Warsaw University of Life Sciences, Nowoursynowska 159, 02-776, Warsaw, Poland.
Planta. 2022 Jul 29;256(3):52. doi: 10.1007/s00425-022-03966-4.
In Dracaena draco trunks, the primary and secondary xylem conduits co-function. Both are resistant to embolism; however, secondary conduits are mainly involved in mechanical support. Monocotyledonous dragon trees (Dracaena spp., Asparagaceae) possess in their trunks both primary and secondary xylem elements, organized into vascular bundles, that for dozens of years co-function and enable the plant to transport water efficiently as well as provide mechanical support. Here, based on the modified Hagen-Poiseuille's formula, we examined the functional anatomical xylem traits of the trunk in two young D. draco individuals to compare their function in both primary and secondary growth. We provided analyses of the: (i) conduits surface sculpture and their cell walls thickness, (ii) conduit diameter and frequency, (iii) hydraulically weighted diameter, (iv) theoretical hydraulic conductivity, (v) area-weighted mean conduit diameter, as well as (vi) vulnerability index. The conduits in primary growth, located in the central part of the trunk, were loosely arranged, had thinner cell walls, larger mean hydraulically weighted diameter, and significantly larger value of the theoretical hydraulic conductivity than conduits in secondary growth, which form a rigid cylinder near the trunk surface. Based on the vulnerability index, both primary and secondary conduits are resistant to embolism. Taking into account the distribution within a trunk, the secondary growth conduits seems to be mainly involved in mechanical support as they are twisted, form structures similar to sailing ropes and have thick cell walls, and a peripheral localization. D. draco has been adapted to an environment with water deficit by distinctive, spatial separation of the xylem elements fulfilling supportive and conductive functions.
在龙血树树干中，初生木质部导管和次生木质部导管共同发挥功能。两者都具有抗栓塞能力；然而，次生导管主要参与机械支撑。单子叶龙血树（龙血树属，天门冬科）在其树干中既有初生木质部元素，也有次生木质部元素，它们组织成维管束，这些维管束在几十年的时间里共同发挥功能，使植物能够有效地运输水分，并提供机械支撑。在这里，我们基于改进的哈根-泊肃叶公式，研究了两个年轻的龙血树个体树干的功能解剖木质部特征，以比较它们在初生和次生生长中的功能。我们对以下方面进行了分析：（i）导管表面的纹饰及其细胞壁厚度，（ii）导管直径和频率，（iii）水力加权直径，（iv）理论水力传导率，（v）面积加权平均导管直径，以及（vi）脆弱性指数。初生木质部导管位于树干中心部位，排列松散，细胞壁较薄，水力加权平均直径较大，理论水力传导率显著大于次生木质部导管，后者在树干表面附近形成刚性圆柱。根据脆弱性指数，初生和次生导管都具有抗栓塞能力。考虑到在树干内的分布，次生生长导管似乎主要参与机械支撑，因为它们扭曲，形成类似于帆船绳索的结构，并且具有较厚的细胞壁和外周定位。龙血树通过独特的木质部元素空间分离，适应了缺水的环境，这些元素分别履行支持和传导功能。
