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Microscale Thermo-Fluid Lab Microflow through Plant Phloem


Biological systems have long been of interest for scientists in search of phenomenon to apply in engineering systems. For instance, scientists have applied Characean cells for mixing, shark skin for drag reduction, artificial leaves to extract water, and sucrose transporters to actuate. The sucrose transporter proteins from phloem have been shown to be capable of generating enough fluid displacement to deform the cover plate of an actuator. Plants are capable of self-sustained pumping; where nutrients are transported from sources such as leaves through stems to sinks, including roots and fruits without external pressure or power. Nutrients such as sugars are transported through vascular networks called phloem built up by cells, including sieve elements for fluid transport, parenchyma cells with specialized companion cells for sieve biological support, and additional structural supporting cells. In this work we present a phloem model, combining protein level mechanics with cellular level fluid transport. Fluid flow and sucrose transport through a petiole sieve tube are simulated using the Nernst–Planck, Navier–Stokes, and continuity equations. The governing equations are solved, using the finite volume method with collocated storage, for dynamically calculated boundary conditions. The effects of reaction rates and leaf sucrose concentration are investigated to understand the transport mechanism in petiole sieve tubes [1]. This study reveals that increasing companion cell side deprotonation rate significantly enhances the sieve tube sugar concentrations, which results in much higher water transport. Lower apoplast pH increases the transport rate, but the flow control is less noticeable for a pH less than 5. A more negative membrane electrical potential difference will significantly accelerate the transporter proteins’ ability to pump water and nutrients. Higher companion cell and sieve element membrane hydraulic permeability also promotes flows through the phloem; however, the flow difference is less noticeable at higher permeabilities when near typical plant cell membrane ranges.

  1. Sze, T.J., Liu, J. and Dutta, P., 2013, “Numerical Modeling of Flow through Phloem Considering Active Loading” ASME Journal of Fluids Engineering, Vol. 136, pp 021206.
  2. Sze, T.J., and Dutta, P., and Liu, J., 2013, “Study of Protein Facilitated Water and Nutrient Transport in Plant Phloem” in Press ASME Journal of Nanotechnology in Engineering and Medicine.