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The Phloem Sieve Tube As a Dynamic Carrier of Water and Sugars by Ryan Stanfield a Thesis Submitted in Partial Fulfillment of Th

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The Phloem Sieve Tube As a Dynamic Carrier of Water and Sugars by Ryan Stanfield a Thesis Submitted in Partial Fulfillment of Th The Phloem Sieve Tube as a Dynamic Carrier of Water and Sugars by Ryan Stanfield A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Forest Biology and Management Department of Renewable Resources University of Alberta © Ryan Stanfield, 2019 ABSTRACT 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. ii PREFACE This thesis is an original work by Ryan Stanfield. Chapter 2 of this thesis has been published as R. C. Stanfield, U.G. Hacke and J. Laur, “Are phloem sieve tubes leaky conduits supported by numerous aquaporins?” American Journal of Botany, vol. 104, 719-732. I equally shared contribution towards this manuscript with U.G. Hacke for the design, literature review, writing and planning of this work. J. Laur performed the Western Blot analysis. I performed all other experiments. Chapter 3 of this thesis was by R. C. Stanfield, U.G. Hacke and J. Laur “Aquaporins Respond to Chilling in the Phloem by Increased Protein Abundance and Altered mRNA expression”. I designed the experiment, performed the literature review and wrote the chapter. J. Laur performed the qrtPCR analysis. I performed all other experiments. Chapter 4 of this thesis has been published as R.C. Stanfield, P. J. Schulte, K.E. Randolph and U.G. Hacke “Computational models evaluating the impact of sieve plates and radial water exchange on phloem pressure gradients.” Plant, Cell and Environment. I shared equally the planning, literature review and writing with U.G. Hacke. P.J. Schulte did the computional modeling work and wrote significant portions of the manuscript. K.E. Randolph contributed sieve plate callose blockage models. I obtained all the images used for mathematical modeling. Chapter 5 of this thesis has been submitted as a book chapter in Methods in Phloem Research as R.C. Stanfield and A. Schulz “Super-Resolution Microscopy of Phloem Proteins”. I performed the experiments and troubleshooting to write the protocol. A. Schulz wrote the introduction. I collected the images. iii “There's another disadvantage to the use of the flashlight: like many other mechanical gadgets it tends to separate a man from the world around him. If I switch it on my eyes adapt to it and I can see only the small pool of light it makes in front of me; I am isolated. Leaving the flashlight in my pocket where it belongs, I remain a part of the environment I walk through and my vision though limited has no sharp or definite boundary.” ― Edward Abbey iv ACKNOWLEDGEMENTS I would like to thank my supervisor Dr. Uwe Hacke for all the help given to me throughout the duration of my thesis. Through your guidance, I have significantly developed as a researcher over the past four years and owe a lot of my success to your dedication in mentoring the work that has gone into this dissertation. I will always have gratitude and respect for the work we did together. I thank the members of my supervisory committee, Dr. Barb Thomas and Dr. Enrico Scarpella who helped with obtaining balsam poplar cuttings and imaging techniques on the confocal microscope, respectively. Thank you to Robert Turgeon and Janusz Zwiazek for being thesis committee examiners. I have many people to thank that made this research possible. Thank you to Dr. Joan Laur for being my #1 tech support person for all my aquaporin labeling experiments (and failures). Thanks to Dr. Paul Schulte for the extremely valuable contribution towards the sieve plate modeling study, as well as all the great hospitality shown when I visited UNLV. Thanks to Arlene Oatway for the valuable tips and conversations in the microscopy lab. Thank you to Kelley Dunfield for making my T.A. appointments a whole lot of fun. Thank you to my lab mates Rachel Hillabrand, Jaime Azcona, Cayla Brocious, and Lauren Sinclair for helping to get through the tough times and celebrating during the best times. v TABLE OF CONTENTS List of tables ............................................................................................................................... x List of figures ............................................................................................................................. xi I. General Introduction and Literature Review ............................................................... 1 1. Phloem structure and function ......................................................................................... 2 a. Anatomy and cell biology ............................................................................................ b. Movement of sap through the phloem and cycling of water ........................................ 5 c. The analysis and complications associated with sampling phloem sap ...................... 10 2. Aquaporins .................................................................................................................... 12 a. Aquaporin structure and function ............................................................................. 12 b. Aquaporin response to environmental stress ............................................................. 16 3. Characteristics of study species: balsam poplar .............................................................. 18 4. Summary ....................................................................................................................... 20 5. Research objectives ....................................................................................................... 21 6. References ..................................................................................................................... 24 II. Are phloem sieve tubes leaky conduits supported by numerous aquaporins? .......... 33 1. Introduction ................................................................................................................... 34 2. Materials and methods ................................................................................................... 36 a. Plant material ........................................................................................................... 36 b. Tissue sampling and fixation .................................................................................... 37 c. Sectioning, staining, and immuno-labeling ............................................................... 37 d. Super-resolution microscopy .................................................................................... 39 e. Confocal laser scanning microscopy (CLSM) .......................................................... 40 f. Light microscopy and image analysis ....................................................................... 41 g. Diurnal experiment .................................................................................................. 41 h. Sieve element dimensions ....................................................................................... 42 3. Results ........................................................................................................................... 42 vi a. Detecting PIP1 aquaporins in the phloem and xylem using CLSM ........................... 43 b. Detecting PIP2 aquaporins in the phloem and xylem using CLSM ........................... 46 c. Characterizing cellular distribution of sieve element aquaporins using 3D-SIM ...... 46 d. Diurnal cycling of PIP1 aquaporins in sieve elements .............................................. 50 4. Discussion ..................................................................................................................... 50 a. PIP2s are markers of sieve tubes in poplar
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