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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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www.thefreedictionary.com/companion+cell
www.thefreedictionary.com/companion+cell
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Britannica online encyclopedia article on companion cell (plant anatomy), ...sieve cells, showing more primitive structural features, perform the same function. ... In other vascular plants, parenchyma cells function in the same way as companion cells (that is, as the sieve cell’s living protoplasm), but they are not...
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www.britannica.com/EBchecked/topic/129561/companion-cel...
www.britannica.com/EBchecked/topic/129561/companion-cell
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Of all the intricate cell–cell interactions in nature, those between the sieve element (SE) and its companion cell (CC) rank among the most complex and mysterious. ... A central tenet is that the SE-CC complex must function in several roles, including phloem loading and ... These cells differentiate in vertical files,
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www.plantcell.org/cgi/content/full/11/4/739
www.plantcell.org/cgi/content/full/11/4/739
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A generalized plant cell type, parenchyma cells are alive at maturity. They function in storage, photosynthesis, and as the bulk of ground and vascular tissues. Palisade parenchyma cells are elogated cells located in many leaves just below ... Companion cells retain their nucleus and control the adjacent sieve cells.
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www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANT...
www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTANAT.html
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Its main function is to transport sugars and other food materials such as amino acids (see protein) from the leaves, ... Phloem is composed of sieve elements and their associated companion cells, together with some sclerenchyma and parenchyma cell types. Sieve elements are long, thin-walled cells joined end to end,
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encyclopedia.farlex.com/Companion+cells
encyclopedia.farlex.com/Companion+cells
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The sieve tube elements of angiosperms (mono- and dicots), but not those of pteridophytes and gymnosperms are associated with companion cells. In Ginkgo and other gymnosperms their function is taken over by specialized parenchyma cells, that resemble companion cells in structure: the albuminous cells.
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www.biologie.uni-hamburg.de/b-online/e06/06d.htm
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Substantial symplastic continuity appears to exist between companion cells (CCs) and sieve elements of the phloem, which suggests that small solutes within the CC are subject to indiscriminate long-distance transport via ... Solutes may also diffuse across membranes as a function of their permeability coefficients.
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www.plantphysiol.org/cgi/content/full/131/4/1518
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Quantification of Plasmodesmatal Endoplasmic Reticulum Coupling between Sieve Elements and Companion Cells Using Fluorescence Redistribution after Photobleaching1,[W] ... According to the main function, phloem can be divided into collection phloem, transport phloem, and release phloem (van Bel, 2003 ). Table I summarizes...
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www.plantphysiol.org/cgi/content/full/142/2/471
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In contrast to plants expressing GFP from the strong SUC2 promoter, in RolC-controlled expression GFP is retained in companion cells. The 3'-UTR of SUT1 affected intracellular distribution of GFP but was insufficient for trafficking of SUT1, GFP or their fusions to SEs.
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www.biomedcentral.com/1471-2229/3/8
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