Metabolite diffusion into bundle sheath cells from c(4) plants: relation to c(4) photosynthesis and plasmodesmatal
H Weiner1, J N Burnell, I E Woodrow
1Division of Plant Industry, CSIRO, GPO Box 1600, Canberra City A.C.T. 2601, Australia.
Plant Physiology
|November 1, 1988
Summary
This study measured metabolite diffusion between C4 plant cells, finding it occurs via plasmodesmata. These findings quantify transport and reveal an 850-900 molecular weight limit for cell permeation.
Area of Science:
- Plant Physiology
- Cell Biology
- Biochemistry
Background:
- C4 plants utilize specialized cell types (mesophyll and bundle sheath) for efficient photosynthesis.
- Understanding metabolite exchange between these cells is crucial for optimizing photosynthetic efficiency.
Purpose of the Study:
- To quantify the resistance to diffusive flux of metabolites between mesophyll and bundle sheath cells in C4 plants.
- To investigate the mechanism and characteristics of metabolite transport across the symplast.
Main Methods:
- Measurement of diffusive flux by monitoring metabolic transformation of metabolites within isolated bundle sheath cells.
- Determination of diffusion constants using cytosolic enzymes with high velocities and favorable equilibrium constants.
- Assessment of the effect of various compounds and treatments on metabolite diffusion.
Main Results:
- Rapid metabolite fluxes were observed, indicating transport through functional plasmodesmata.
- Diffusion constants varied based on metabolite molecular weight and bundle sheath cell source, ranging from 1-5 µmol/min/mg chlorophyll/mM gradient.
- Diffusion was unaffected by inhibitors, ions, or hormones but blocked by plasmolysis.
- A molecular weight exclusion limit of 850-900 Da for bundle sheath cell permeation was established.
Conclusions:
- Functional plasmodesmata mediate rapid metabolite diffusion between mesophyll and bundle sheath cells in C4 plants.
- Bundle sheath cells offer a quantitative model for studying plasmodesmatal transport.
- The identified molecular weight exclusion limit provides insights into the size selectivity of plasmodesmata.
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