companion cells and albuminous cells

[planteome-user]

companion cell (PO:0000071)

'''current definition:''' A specialized parenchyma cell associated with a sieve-tube member in angiosperm phloem and arising from the same mother cell as the sieve-tube member.

'''proposed definition:''' A parenchyma cell that is adjacent to a sieve-tube member and arises from the same mother cell as the sieve-tube member.

comment: Found in angiosperms. Compare to albuminous cells (PO:xxxx), which are found in gymnosperms.

Currently part_of primary phloem '''and''' part_of secondary phloem, which can't be true. Should change to part_of phloem.

Suggest that we add relation companion cell adjacent_to sieve tube element.

'''albuminous cell (new term)'''

'''proposed def.:''' A parenchyma cell that is morphologically and physiologically associated with a sieve cell but does is not derived from the same initial cell as the sieve cell.

comment: May be found in the rays and sometimes the axial system of gymnosperms. Compare to companion cells, which are found in angiosperms.

is_a parenchyma cell, part_of phloem, adjacent_to sieve cell.

Should we have a term for phloem parenchyma cell? Could be parent of companion cell and albuminous cell. Similar to term for wood parenchyma cell.

Reported by: rlwalls2008

Original Ticket: obo/plant-ontology-po-term-requests/442

[planteome-user]

• summary: parenchyma cells in vascular tissue --> parenchyma cells in phloem tissue

Original comment by: rlwalls2008

[planteome-user]

At the POC meeting on 2-21-12, we discussed the need to add terms for the different types of companion cells found in symplastic versus apoplastic phloem loaders.

New proposed terms and definitions:

'''companion cell (PO:0000400):''' A parenchyma cell (PO:0000074) that is adjacent to a sieve-tube element (PO:0000289) and arises from the same phloem mother cell (PO:0000400) as the sieve tube element.
comment: Companion cells are connected to sieve tube elements through plasmodesmata and may participate in phloem sucrose loading (GO:0009915). A sieve tube element may have one or more or no companion cells associated with it. This term should not be used for other types of parenchyma cells (PO:0000074) that do not arise from the same phloem mother cell as a sieve tube element. Companion cells are found in angiosperms while albuminous cells (PO:0025412) are found in non-angiosperm vascular plants. Companion cells may be specialized as transfer companion cells (PO:id), intermediary companion cells (PO:id), or ordinary companion cells (PO:id). Multiple types of companion cells may be found in the same plant.
adjacent_to sieve tube element, part_of phloem
synonym: minor vein companion cell

'''transfer companion cell (new term):''' A companion cell (PO:0000400) that is a transfer cell (PO:0000078) with many cell wall invaginations.
Comment: Plasmodesmata between a transfer companion cell and adjacent mesophyll cells may be few in number. Transfer companion cells are found in plants that use apoplastic phloem loading.
syn: transfer cell (broad)
is_a companion cell and is_a transfer cell. No way to set up transfer cell as a cross-product, so must have dual parentage for now.

'''ordinary companion cell (new term):''' A companion cell (PO:0000400) that lacks cell wall invaginations and has few or no plasmodesmata connecting it to adjacent mesophyll cells.
Comment: Found in plants that use apoplastic phloem loading.
syn.: regular companion cell, standard companion cell

'''intermediary companion cell (new term):''' A companion cell (PO:0000400) that has dense cytoplasm, a small vacuole, proplastids rather than chloroplasts, and abundant and highly branched plasmodesmata linking it to mesophyll cells.
Comment: Intermediary companion cells translocate high concentrations of raffinose-family oligosaccharides and are found in plants that use symplastic phloem loading.
syn.: intermediary cell

References:
[http://www.ncbi.nlm.nih.gov/pubmed/21669666 PMID:21669666] (Turgeon et al. 2001, AJB)
[[PO_REF:00011]] (Turgeon 2006, BioScience)

Original comment by: rlwalls2008

[planteome-user]

• summary: parenchyma cells in phloem tissue --> companion cells and albuminous cells

Original comment by: rlwalls2008

[planteome-user]

Revised comment for companion cell (PO:0000400), based on suggestions from Pankaj:

Def.: A parenchyma cell (PO:0000074) that is adjacent to a sieve-tube element (PO:0000289) and arises from the same phloem mother cell (PO:0000400) as the sieve tube element.

Comment: Companion cells are connected to sieve tube elements through plasmodesmata and function in phloem loading of small molecules, including photosynthate (either sucrose or raffinose-family oligosaccharides). May participate in phloem sucrose loading (GO:0009915). Molecules can be loaded into the companion cells from surrounding cells through either symplastic (via plasmodesmata) or apoplastic (transmembrane) transport. Unlike sieve tube elements, companion cells retain their nuclei and other organelles at maturity. A sieve tube element may have one or more or no companion cells associated with it. This term should not be used for other types of parenchyma cells (PO:0000074) that do not arise from the same phloem mother cell as a sieve tube element. Companion cells are found in angiosperms, as compared to albuminous cells (PO:0025412), which are found in non-angiosperm vascular plants. Companion cells may be specialized as transfer companion cells (PO:id), intermediary companion cells (PO:id), or ordinary companion cells (PO:id). Multiple types of companion cells may be found in the same plant.

Also, add to comment of other companion cell types: Unlike sieve tube elements, companion cells retain their nuclei and other organelles at maturity.

Original comment by: rlwalls2008

[planteome-user]

The definitions below were accepted at the POC meeting on 3-8-12. Definitions have been sent out for review.

Created new terms:

transfer companion cell (PO:0025458): A companion cell (PO:0000400) that is a transfer cell (PO:0000078) with many cell wall invaginations.
Comment: Plasmodesmata between a transfer companion cell and adjacent mesophyll cells may be few in number. Transfer companion cells are found in plants that use apoplastic phloem loading. Unlike sieve tube elements (PO:0000289), transfer companion cells retain their nuclei and other organelles at maturity.

ordinary companion cell (PO:0025459): A companion cell (PO:0000400) that lacks cell wall invaginations and has few or no plasmodesmata connecting it to adjacent mesophyll cells.
Comment: Found in plants that use apoplastic phloem loading. Unlike sieve tube elements (PO:0000289), ordinary companion cells retain their nuclei and other organelles at maturity.
intermediary companion cell (PO:0025460): A companion cell (PO:0000400) that has dense cytoplasm, a small vacuole, proplastids rather than chloroplasts, and abundant and highly branched plasmodesmata linking it to adjacent mesophyll cells.
Comment: Intermediary companion cells translocate high concentrations of raffinose-family oligosaccharides and are found in plants that use symplastic phloem loading. Unlike sieve tube elements (PO:0000289), intermediary companion cells retain their nuclei and other organelles at maturity.

Closing this item.

Original comment by: rlwalls2008

[planteome-user]

• priority: 5 --> 1
• status: open --> closed-accepted

Original comment by: rlwalls2008