companion-cell

companion cell

noun Botany.
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:
1885–90

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Based on the Random House Dictionary, © Random House, Inc. 2014.
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American Heritage
Science Dictionary
companion cell   (kəm-pān'yən)  Pronunciation Key 
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.
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