Abstract Detail



Anatomy and Morphology

Randolph, Katie [1], Schulte, Paul [1], Stanfield, RC [2], Hacke, Uwe [3].

Phloem sieve plates and the impact of sieve pore obstructions on flow.

The phloem, a tissue in vascular plants which distributes sugars and molecular signals throughout the plant, is functionally dependent on its structure.  Despite its significant role in growth and development, the physiological processes by which it functions are not yet fully characterized.  This study aims to generate basic quantitative data on how the structure of the sieve cells contributes to its functional state.  Specifically, we investigated the major contributors to flow resistance including the sieve plate, the constituents in the cell lumen, and sieve plate pores blocked by callose.  We utilized scanning electron microscope (SEM) images to build computational fluid models which enable the exploration of function under these various conditions.  We found that the sieve plate accounted for the majority of resistance to flow, giving a fractional resistance of 87% on average across our models, and conversely that the cell lumen provides minimal contribution to resistance.  One of the reasons the phloem remains so elusive is its sensitivity to manipulation.  The blockage of pores by callose may be an effect of disruption to the phloem in order to analyze it, or the blockage mechanism may exist as a form of fast regulation of phloem flow in response to environmental stimuli.  In either scenario, it is helpful to know how much these pore blockage effects can influence overall flow rates.  The modeled difference between pores obstructed by rings of callose compared to the same plate that had been digitally cleared of callose build-up showed that the flow rate would increase by 3.6 – 5.5 fold if the pores were unobstructed.  We concluded from this study that resistances generated from sieve plate pores are so substantial that obstructions not related to the sieve plate, such as plastids in the cell lumen, are not likely to make a significant impact to flow.


1 - University Of Nevada, School Of Life Sciences, Las Vegas, NV, 89154, United States
2 - University of Alberta, Edmonton, AB, Canada
3 - University Of Alberta, Department Of Renewable Resources, 442 Earth Sciences Building, Edmonton, AB, T6G 2E3, Canada

Keywords:
phloem
fluid dynamics
sieve plates
Navier-Stokes
hydrolic resistance.

Presentation Type: Oral Paper
Number:
Abstract ID:508
Candidate for Awards:Maynard F. Moseley Award


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