IBG-2: Plant Sciences, Forschungszentrum Jülich Jülich, Germany.
IBG-2: Plant Sciences, Forschungszentrum Jülich Jülich, Germany ; Plant Sciences Division, Research School of Biology, Australian National University Canberra, ACT, Australia.
Front Plant Sci. 2013 Dec 26;4:531. doi: 10.3389/fpls.2013.00531. eCollection 2013.
Long-distance phloem transport occurs under a pressure gradient generated by the osmotic exchange of water associated with solute exchange in source and sink regions. But these exchanges also occur along the pathway, and yet their physiological role has almost been ignored in mathematical models of phloem transport. Here we present a steady state model for transport phloem which allows solute leakage, based on the Navier-Stokes and convection-diffusion equations which describe fluid motion rigorously. Sieve tube membrane permeability P s for passive solute exchange (and correspondingly, membrane reflection coefficient) influenced model results strongly, and had to lie in the bottom range of the values reported for plant cells for the results to be realistic. This smaller permeability reflects the efficient specialization of sieve tube elements, minimizing any diffusive solute loss favored by the large concentration difference across the sieve tube membrane. We also found there can be a specific reflection coefficient for which pressure profiles and sap velocities can both be similar to those predicted by the Hagen-Poiseuille equation for a completely impermeable tube.
长距离韧皮部运输是在源区和库区溶质交换伴随的水的渗透交换产生的压力梯度下发生的。但是，这些交换也沿着途径发生，然而它们的生理作用在韧皮部运输的数学模型中几乎被忽略了。在这里，我们提出了一个基于纳维-斯托克斯方程和描述流体运动的对流扩散方程的稳态模型，允许溶质泄漏。筛管膜对被动溶质交换的通透性 P s （以及相应的膜反射系数）强烈影响模型结果，并且必须处于为植物细胞报告的值的下限范围内，以使结果具有现实意义。这种较小的通透性反映了筛管元素的有效专业化，将筛管膜两侧的大浓度差所有利于的任何扩散溶质损失最小化。我们还发现，对于特定的反射系数，可以使压力分布和汁液流速与完全不可渗透管的哈根-泊肃叶方程预测的压力分布和汁液流速相似。
