The contributions of apoplastic, symplastic and gas phase pathways for water transport outside the bundle sheath in leaves
The contributions of apoplastic, symplastic and gas phase pathways for water transport outside the bundle sheath in leaves
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DOI：
10.1111/pce.12372
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发表时间：
2015-01-01
影响因子：
7.3
通讯作者：
Buckley, Thomas N.
中科院分区：
文献类型：
--
作者：
Buckley, Thomas N.
人们对水从木质部到气孔的运动知之甚少。关于质外体途径还是共质体途径更重要，目前尚未达成共识，最近的研究表明蒸汽扩散也可能发挥作用。本研究的目的是使用基于可测量的解剖学和生物物理参数的新型分析框架来估计由质外体、共质体和气相途径贡献的束鞘外水力传导的比例。这里提出的计算表明，在大多数情况下，质外体途径提供了束鞘外的大部分电导，而共质体途径只贡献了一小部分。质外体和气相途径的贡献取决于几个关键但鲜为人知或高度可变的参数，即质外体整体流动的有效泊肃叶半径、细胞壁的厚度和叶内的垂直温度梯度。当叶中心变得比表皮更温暖时，气相电导率应强烈增加 - 在 0.2K 的温度梯度下提供高达 44% 的垂直水输送。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。木质部外水分运动的途径知之甚少。这项研究得出了一个分析框架，用于根据可测量的解剖学和生物物理参数计算束鞘外水平和垂直水输送的质外体、共质体和气相路径的电导。结果表明，束鞘外的大多数电导是质外体，但当叶子中心和表皮之间存在大的温度梯度时，气相运输在垂直水运动中可以发挥类似的重要作用。评论：
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 0.2K. These results may help to explain how leaf water transport is influenced by light absorption, temperature and differences in leaf anatomy among species.The pathways for water movement outside the xylem are poorly known. This study derived an analytical framework to compute conductances of apoplastic, symplastic and gas phase pathways for horizontal and vertical water transport outside the bundle sheath from measurable anatomical and biophysical parameters. The results suggest most conductance outside the bundle sheath is apoplastic, but that gas phase transport can play a similarly large role in vertical water movement when large temperature gradients exist between the center of the leaf and the epidermis. Commentary: