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Phloem Sap Sampling from Brassica napus for 3D-PAGE of Protein and Ribonucleoprotein Complexes
Published on: January 9, 2018
The evolution of minor vein phloem and phloem loading
R Turgeon1, R Medville, K C Nixon
1Department of Plant Biology, Cornell University, Ithaca, New York 14853 USA.
American Journal of Botany
|June 15, 2011
Summary
Phloem loading evolved with diverse companion cell types, including intermediary cells, appearing multiple times independently. Reduced plasmodesmatal connections are common but not universal in angiosperm evolution.
Area of Science:
- Plant Biology
- Evolutionary Biology
- Plant Anatomy
Background:
- Companion cells are crucial for phloem loading, but their phylogenetic relationships and structural diversity are poorly understood.
- Intermediary cells, implicated in symplastic phloem loading, represent a specialized companion cell type.
Purpose of the Study:
- To investigate the phylogenetic relationships of different minor vein companion cell types.
- To analyze the ultrastructure of minor veins in Euonymus fortunei and Celastrus orbiculatis (Celastraceae) and characterize their companion cells.
Main Methods:
- Phylogenetic analysis of minor vein phloem characteristics mapped onto a molecular tree.
- Ultrastructural analysis of minor veins in selected Celastraceae species.
- Comparative analysis of plasmodesmatal frequency and companion cell types across angiosperms.
Main Results:
- Intermediary cells, characterized by numerous plasmodesmata, have evolved independently at least 4-6 times in angiosperms.
- Extensive plasmodesmatal continuity between minor vein phloem and surrounding cells is ancestral.
- A general evolutionary trend towards reduced plasmodesmatal frequency exists, with exceptions like intermediary cells.
Conclusions:
- The evolution of phloem loading mechanisms is complex, with convergent evolution of intermediary cells.
- Caution is advised when generalizing phloem loading mechanisms, especially apoplastic loading, from model species.
- Transfer cells also exhibit numerous independent origins, not solely from lineages with reduced plasmodesmatal frequency.
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