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Phloem structure

Wednesday 19 January 2005, by www.botanique.org

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The main function of phloem is to conduct metabolites, amino acids and sugars, mainly sucrose, from metabolite sources (production sites) to metabolite sinks (consumption sites). Metabolite translocation is powered by osmotic pressure.

Phloem cells are the following:

- sieve elements that are joined together to form sieve tubes,

- companion cells, transfer cells: companion cells perform metabolic functions for the sieve elements (ATP or proteins synthesis...); transfer cells help sieve elements to transfer metabolites,

- intermediary cells are sometimes present to help connections between bundle sheath, parenchyma cells and sieve elements.