Department of Organismic and Evolutionary Biology, Harvard University, 3119 Biological Laboratories, 16 Divinity Avenue, Cambridge MA 02138, USA.
Plant Cell Environ. 2011 Apr;34(4):690-703. doi: 10.1111/j.1365-3040.2011.02275.x. Epub 2011 Feb 18.
Measurements of diurnal diameter variations of the xylem and phloem are a promising tool for studying plant hydraulics and xylem-phloem interactions in field conditions. However, both the theoretical framework and the experimental verification needed to interpret phloem diameter data are incomplete. In this study, we analytically evaluate the effects of changing the radial conductance between the xylem and the phloem on phloem diameter variations and test the theory using simple manipulation experiments. Our results show that phloem diameter variations are mainly caused by changes in the radial flow rate of water between the xylem and the phloem. Reducing the hydraulic conductance between these tissues decreases the amplitude of phloem diameter variation and increases the time lag between xylem and phloem diameter variation in a predictable manner. Variation in the amplitude and timing of diameter variations that cannot be explained by changes in the hydraulic conductance, could be related to changes in the osmotic concentration in the phloem.
测量木质部和韧皮部的日直径变化是研究植物水力和木质部-韧皮部相互作用的一种很有前途的田间条件下的工具。然而，解释韧皮部直径数据所需的理论框架和实验验证都不完整。在这项研究中，我们分析评估了改变木质部和韧皮部之间的径向导水能力对韧皮部直径变化的影响，并使用简单的操作实验对理论进行了测试。我们的结果表明，韧皮部直径变化主要是由木质部和韧皮部之间的径向水流速率变化引起的。降低这些组织之间的水力导度会降低韧皮部直径变化的幅度，并以可预测的方式增加木质部和韧皮部直径变化之间的时间滞后。不能用水力导度变化来解释的直径变化幅度和时间变化可能与韧皮部中渗透浓度的变化有关。
