Hassan Aref Memorial Lecture & Fall Fluid Mechanics Symposium Invited Lecture*

Sap Flow and Sugar Transport in Plants

Thursday, November 21, 2013

11:00-12:00, Assembly Hall, The Inn

Dr. Tomas Bohr

Technical University of Denmark

 Plants have highly effective vascular systems, which can transport fluid over large distances. The xylem system carries water from the roots up to the leaves and the phloem system carries sugar solutions from sources (leaves) to sinks (roots, fruits etc.) and thus provides the necessary material for growth. There are many important fluid dynamical problems connected with these flows, and I shall discuss some of them. In the 1920’ies, Ernst Münch proposed that sugar transport in the phloem is driven by passive osmotic pressure gradients generated by loading and unloading sugar into the phloem tubes (sieve elements) of the leaves. It has been strongly debated whether this hypothesis can actually account for long distance translocation, e.g., from canopy to root of a large tree. In the lecture, I will argue that optimization of the efficiency of the sugar transport leads to a universal scaling of the width of the phloem tubes with the loading (leaf) length and the translocation (stem) length in plants. These predictions have been tested for plants ranging from 10 cm herbacious plants to 60 m trees – both hardwood and conifers – and provide the first quantitative test of Münch’s ideas. For both the xylem and the phloem, the leaves provide the driving force for the sap flow, and I shall discuss current ideas how this complex feat is accomplished.

The lecture is partly based on recent papers:

K. H. Jensen, J. Lee, T. Bohr, H. Bruus, N. M. Holbrook & M. A. Zwieniecki: Optimality of the Münch mechanism for translocation of sugars in plants, Journal of the Royal Society Interface 8, 1155–1165 (2011)

K. H. Jensen, T. Bohr & H. Bruus:  Osmotically driven flows in microchannels separated by a semipermeable membrane, Lab on a Chip 9, 2093-2099 (2009)

K. H. Jensen, J. Liesche , T. Bohr & A. S. Schulz: Universality of phloem transport in seed plants, Plant, Cell & Environment 35, 1065-1075 (2012)

K. H. Jensen, K. Berg-Sørensen, S. Friis & T. Bohr: Analytic solutions and universal properties of sugar loading models in Münch phloem flow, Journal of Theoretical Biology 304, 286-296 (2012)

K.H. Jensen, D.L. Mullendore, N.M. Holbrook, T. Bohr, M. Knoblauch & H. Bruus: Modeling the hydrodynamics of phloem sieve plates, Frontiers in Plant Science 3, article 151 (2012)

L. S. Haaning, K. H. Jensen, C. Hélix-Nielsen, K. Berg-Sørensen & T. Bohr: Efficiency of osmotic pipe flows, Physical Review E 87, 053019 (2013)

*This is a joint seminar co-sponsored by the Department of Engineering Science and Mechanics, the Department of Mechanical Engineering, and the MultiScale Transport in Environmental and Physiological Systems (MultiSTEPS) program.

Renee Pietsch’s To Fly or Not to Fly Article

Teaching Advanced Secondary School Students about Principles of Flight in Biological Systems’ has been accepted for publication in the Journal of Biological Education. Renee is the first author on the paper, along with Cindy Bohland at the Roanoke Valley Governor’s School.  This work came out of her MultiSTEPs rotation in David Schmale’s lab. What a great way to demonstrate the added value of the rotations!

MultiSTEPS trainee Renee Pietsch featured in VT News

High school biology students learn about the physics of flying by studying flight paths of animals and microbes


A flight lab for biology students at the Roanoke Valley Governor’s School was developed by Renee Pietsch, a MultiSTEPS trainee in biological sciences, while working with Dr. David Schmale, an associate professor of plant pathology, physiology, and weed science, during one of her MultiSTEPS research rotations.

IEEE Life Sciences Grand Challenges Conference

The IEEE Life Sciences Grand Challenges Conference will be held October 4-5, 2012 at the National Academy of Sciences Auditorium in Washington DC


The Conference will conduct strategic discussions and debates on grand challenges facing the scientific community in the interface of engineering and life sciences. The anticipated outcome of conference shall be identified grand challenges on how engineering can be better interfaced with life sciences to understand the mechanisms of biological systems and major diseases, and to lead to improved healthcare.

The Conference will consist of a series of plenary presentations by thought leaders in academia, government and industry, and interactive panel discussions and small group discussions by all meeting participants. Plenary sessions include: Brain Disorder and Nervous Systems; Heart Diseases and and Cardiovascular Systems; Cancer; Education and Training; Translation – From Bech to Bedside.

Due to room capacity, participation is limited and interested participants will be first come first served. To reserve your seat, please register ASAP.