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Optimal concentration for sugar transport in plants
Kaare H Jensen1, Jessica A Savage, N Michele Holbrook
1Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA. jensen@fas.harvard.edu
Journal of the Royal Society, Interface
|March 22, 2013
Summary
Vascular plants optimize sugar transport for efficient energy transfer. Optimal sugar concentrations balance flow rate and sap viscosity, with real-world data aligning with predictions for constant pressure transport.
Area of Science:
- Plant physiology
- Biophysics
- Biochemistry
Background:
- Vascular plants transport sugars from source (leaves) to sink (growth sites).
- Phloem sap flow rate and sugar concentration are key determinants of energy transfer.
- Both low and excessively high sugar concentrations can impede energy transfer efficiency.
Purpose of the Study:
- To determine the optimal sugar concentration for efficient mass flow in plant phloem.
- To compare theoretical predictions of optimal sugar concentration with empirical data.
- To investigate the role of active phloem loading in enhancing transport efficiency.
Main Methods:
- Literature review of over 50 experiments across 41 plant species.
- Analysis of reported phloem sap sugar concentrations.
- Comparison of empirical data with theoretical models predicting optimal concentrations under different pressure-concentration relationships.
Main Results:
- Theoretical models predict optimal sugar concentrations of 23.5% (constant pressure) and 34.5% (pressure proportional to concentration).
- Empirical data from literature show average phloem sugar concentrations ranging from 18.2% (all species) to 21.1% (active loaders).
- Observed concentrations align more closely with the theoretical optimum under constant pressure conditions.
Conclusions:
- Plant phloem vasculature appears optimized for efficient sugar transport at constant pressure.
- Active phloem loading mechanisms may have evolved to further enhance sugar transport efficiency.
- The findings suggest a balance between sugar concentration, sap viscosity, and flow dynamics for effective energy distribution in plants.
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