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companion cell

noun, Botany
1.
any of a number of specialized parenchymal cells adjacent to a sieve tube in the phloem of flowering plants, believed to regulate the flow of nutrients through the tube.
Origin
1885-1890
1885-90
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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companion cell in Science
companion cell
  (kəm-pān'yən)   
A specialized parenchyma cell, located in the phloem of flowering plants and closely associated with the development and function of a sieve-tube element. Companion cells probably provide ATP, proteins, and other substances to the sieve-tube elements, whose cytoplasm lacks many structures necessary for cell maintenance.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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