The Phloem Sieve Tube as a Dynamic Carrier of Water and Sugars

• Author / Creator

  Ryan Stanfield

• This dissertation delves into the anatomy and physiology of the phloem plant vascular tissue. Two primary topics are investigated in this thesis: (1) The cellular localization and response of aquaporin protein water channels in phloem sieve tubes and (2) the mathematical modeling of phloem sieve plates and radial water flows on the hydraulic resistance and pressure profiles of sieve tubes in balsam poplar (Populus balsamifera L.). In the first study, I use immunohistochemistry experiments to identify the distribution and cellular location of aquaporins in the phloem within different organs of the poplar tree. I found that throughout the entire transport pathway from source to sink, sieve tube plasma membranes contain two subfamilies of aquaporin proteins. The first type, PIP1, facilitates the transport of water and some uncharged molecules through the plasma membrane. The second type, PIP2, is the primary water carrying channel in plants. I found that PIP1 aquaporins are mostly found within internal cellular compartments of the sieve tube. This contrasts with PIP2 aquaporins which were found mostly in the plasma membrane. The second study followed the results of the first and looked at how the application of a cold block affected the expression of selected PIP1 and PIP2 genes in phloem tissue. It was found that cold block application transiently increased the abundance of PIP2 aquaporins in the plasma membrane of sieve tubes and altered the abundance of aquaporin mRNA transcript. Overall, aquaporins in sieve tubes may be an important regulator in supporting long distance sugar transport due to turgor pressure maintenance, especially in trees. The third study was a computational model assessing the impact of sieve plate pores as well as radial flows on the resistance of fluid flow through sieve tubes. It was found that non-circular pores add significant resistance to the sieve tube conduit, and that radial water flows may ease some of the resistance encountered due to sieve plates.

• Subjects / Keywords

  • 3D-SIM
  • Cold Inhibition
  • Aquaporins
  • Sieve Tubes
  • Sieve Plates
  • Phloem Transport
  • Plant Physiology
  • Plant Anatomy

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-xmrt-he75

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.