Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853 USA.
Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Ancon Republic of Panama.
Am J Bot. 2017 Sep;104(9):1285-1298. doi: 10.3732/ajb.1700277.
The hydraulics of xylem has been widely studied in numerous species and organ types. However, comparatively little is known about how phloem and xylem are hydraulically coupled or about many of the basic structural properties of phloem (such as conducting cell numbers and conductive areas), which nevertheless have direct bearing on understanding phloem loading and unloading.
Using a combination of light, epifluorescence, confocal, and transmission electron microscopy, we quantified the hydraulic architecture of Ginkgo biloba leaf laminae and examined the scaling relationships between phloem and xylem in five fully mature leaves.
The conductive areas and lengths of sieve cells and tracheids increase basipetally toward the petiole in a manner that is consistent with Münch's pressure flow hypothesis for phloem transport. This trend holds true for individual veins, the sum of conductive areas across all veins at any distance from the petiole, and for individual sieve cells and tracheids. Further, the conductive areas of phloem and xylem are isometrically correlated across the entire vasculature of the leaf lamina. The data for conducting cell areas do not conform with the predictions of the hydraulic models of da Vinci and Murray.
The scaling of Ginkgo lamina hydraulics complies with that observed in leaves of other gymnosperms and most angiosperms and is inconsistent with theoretical models that assume that the volume of transported incompressible fluids is conserved.
木质部的水力学在众多物种和器官类型中得到了广泛研究。然而，关于韧皮部和木质部如何水力连接，以及关于韧皮部的许多基本结构特性（例如传导细胞数量和传导面积），人们知之甚少，而这些特性直接影响到对韧皮部装载和卸载的理解。
我们使用光、外荧光、共聚焦和透射电子显微镜的组合，定量了银杏叶片叶层的水力结构，并检查了 5 片完全成熟叶片中韧皮部和木质部之间的比例关系。
筛管细胞和导管细胞的传导面积和长度沿基端向叶柄方向增加，这与 Münch 提出的韧皮部运输压力流假说一致。这种趋势适用于单个叶脉、叶柄距离内所有叶脉的传导面积总和，以及单个筛管细胞和导管细胞。此外，整个叶片叶层的整个脉管系统中，韧皮部和木质部的传导面积呈等比相关。传导细胞面积的数据不符合达芬奇和默里水力模型的预测。
银杏叶片水力学的比例与其他裸子植物和大多数被子植物叶片的观察结果一致，与假设运输不可压缩流体体积守恒的理论模型不一致。
