IA Watson Grains Research Centre, Faculty of Agriculture and Environment, The University of Sydney, Narrabri, New South Wales, 2390, Australia.
Plant Cell Environ. 2015 Jan;38(1):7-22. doi: 10.1111/pce.12372. Epub 2014 Jun 16.
Water movement from the xylem to stomata is poorly understood. There is still no consensus about whether apoplastic or symplastic pathways are more important, and recent work suggests vapour diffusion may also play a role. The objective of this study was to estimate the proportions of hydraulic conductance outside the bundle sheath contributed by apoplastic, symplastic and gas phase pathways, using a novel analytical framework based on measurable anatomical and biophysical parameters. The calculations presented here suggest that apoplastic pathways provide the majority of conductance outside the bundle sheath under most conditions, whereas symplastic pathways contribute only a small proportion. The contributions of apoplastic and gas phase pathways vary depending on several critical but poorly known or highly variable parameters namely, the effective Poiseuille radius for apoplastic bulk flow, the thickness of cell walls and vertical temperature gradients within the leaf. The gas phase conductance should increase strongly as the leaf centre becomes warmer than the epidermis - providing up to 44% of vertical water transport for a temperature gradient of 0.2 K. These results may help to explain how leaf water transport is influenced by light absorption, temperature and differences in leaf anatomy among species.
水分从木质部向气孔的运动机制还不太清楚。目前对于哪种质外体途径或共质体途径更为重要仍没有定论，而且最近的研究表明，水汽扩散可能也发挥了一定作用。本研究旨在利用基于可测量解剖学和生物物理参数的新分析框架，估算非维管束鞘中由质外体、共质体和气相途径贡献的导水率比例。本研究提出的计算结果表明，在大多数情况下，质外体途径在维管束鞘外提供了大部分导水率，而共质体途径的贡献很小。质外体和气相途径的贡献取决于几个关键但知之甚少或高度可变的参数，即质外体整体流动的有效泊肃叶半径、细胞壁的厚度和叶片内的垂直温度梯度。随着叶片中心的温度高于表皮，气相导水率应会强烈增加——对于 0.2 K 的温度梯度，垂直水分输送可高达 44%。这些结果可能有助于解释叶片水分运输如何受到光吸收、温度和物种间叶片解剖结构差异的影响。
