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[[Image:SieveTube.png|thumb|right|[[Companion cell]] (left, light pink), nucleus (dark pink), sieve tube (right, solid green), sieve tube plates (dashed green), dissolved nutrients (yellow)]]
[[Image:SieveTube.png|thumb|right|[[Companion cell]] (left, light pink), nucleus (dark pink), sieve tube (right, solid green), sieve tube plates (dashed green), dissolved nutrients (yellow)]]


In plant anatomy, sieve cells and sieve tube members constitute sieve elements, which are conducting cells. They are specialized cells in the phloem tissue of flowering plants. <ref name=":0">{{Cite web|url=https://web.archive.org/web/20070807064315/http://www.biologie.uni-hamburg.de/b-online/e06/06d.htm|title=Botany online: Supporting Tissues - Vascular Tissues - Phloem|date=2007-08-07|access-date=2018-05-21}}</ref>
Phloem is highly organized tissue that contains many specialized cells including sieve elements. In plant anatomy, sieve cells and sieve tube members constitute sieve elements, which are conducting cells. They are specialized cells in the phloem tissue of flowering plants. <ref name=":0">{{Cite web|url=https://web.archive.org/web/20070807064315/http://www.biologie.uni-hamburg.de/b-online/e06/06d.htm|title=Botany online: Supporting Tissues - Vascular Tissues - Phloem|date=2007-08-07|access-date=2018-05-21}}</ref> Sieve elements' major function includes transporting sugars over long distance through plants by acting as a channel. Sieve elements elongate cells containing sieve areas on their walls. Pores on sieve areas allow for cytoplasmic connections to neighboring cells. Structurally, they are elongated and parallel to the organ or tissue that they are located in. Sieve elements typically lack a nucleus and contain none to a very few amount of ribosomes. <ref>{{Cite book|url=https://link.springer.com/chapter/10.1007/978-1-4684-8658-2_1|title=Phloem Transport|last=Lamoureux|first=Charles H.|date=1975|publisher=Springer, Boston, MA|isbn=9781468486605|series=NATO Advanced Study Institutes Series|pages=1–31|language=en|doi=10.1007/978-1-4684-8658-2_1}}</ref>


=== Sieve Tubes ===
=== Sieve Tubes ===
Main functions of sieve tube elements include maintaining cells and transporting necessary molecules with the help of companion cells. <ref>{{Cite journal|date=2018-06-01|title=The rendez-vous of mobile sieve-element and abundant companion-cell proteins|url=https://www.sciencedirect.com/science/article/pii/S1369526617301437|journal=Current Opinion in Plant Biology|language=en|volume=43|pages=108–112|doi=10.1016/j.pbi.2018.04.008|issn=1369-5266}}</ref> The sieve tubes are living cells (which do not contain a nucleus) that are responsible for transporting carbohydrates throughout the plant.<ref>{{Cite journal|last=Torode|first=Thomas A.|last2=O’Neill|first2=Rachel|last3=Marcus|first3=Susan E.|last4=Cornuault|first4=Valérie|last5=Pose|first5=Sara|last6=Lauder|first6=Rebecca P.|last7=Kračun|first7=Stjepan K.|last8=Rydahl|first8=Maja Gro|last9=Andersen|first9=Mathias C. F.|date=2018-02-01|title=Branched Pectic Galactan in Phloem-Sieve-Element Cell Walls: Implications for Cell Mechanics|url=http://www.plantphysiol.org/content/176/2/1547|journal=Plant Physiology|language=en|volume=176|issue=2|pages=1547–1558|doi=10.1104/pp.17.01568|issn=0032-0889|pmid=29150558}}</ref> As stated earlier, there are two categories of sieve elements and these are sieve cells and sieve tube members/elements.<ref name=":1">{{Cite web|url=https://web.archive.org/web/20070912193059/http://www.botany.hawaii.edu/faculty/webb/Bot410/410Labs/LabsHTML-99/SecPhloem/LabSecPhloem-99.htm|title=Secondary Phloem|date=2007-09-12|access-date=2018-05-21}}</ref> Sieve Tube elements are associated with companion cells which are cells that combined with sieve tubes create the sieve element-companion cell complex. This allows for supply and maintenance of the plan cells and allow for signaling between distant organs within the organism. <ref>{{Cite journal|date=2018-06-01|title=The rendez-vous of mobile sieve-element and abundant companion-cell proteins|url=https://www.sciencedirect.com/science/article/pii/S1369526617301437|journal=Current Opinion in Plant Biology|language=en|volume=43|pages=108–112|doi=10.1016/j.pbi.2018.04.008|issn=1369-5266}}</ref> Sieve tube members do not have ribosomes or a nucleus and thus need companion cells to act as transport molecules. Companion cells provide Sieve tube elements with proteins necessary for signaling and ATP. It is the companion cells that helps transports carbohydrates from outside the cells into the sieve tube elements. <ref>{{Cite journal|date=2018-06-01|title=Sieve-element differentiation and phloem sap contamination|url=https://www.sciencedirect.com/science/article/pii/S1369526617301541|journal=Current Opinion in Plant Biology|language=en|volume=43|pages=43–49|doi=10.1016/j.pbi.2017.12.008|issn=1369-5266}}</ref>
Main functions of sieve tube elements include maintaining cells and transporting necessary molecules with the help of companion cells. <ref>{{Cite journal|date=2018-06-01|title=The rendez-vous of mobile sieve-element and abundant companion-cell proteins|url=https://www.sciencedirect.com/science/article/pii/S1369526617301437|journal=Current Opinion in Plant Biology|language=en|volume=43|pages=108–112|doi=10.1016/j.pbi.2018.04.008|issn=1369-5266}}</ref> The sieve tubes are living cells (which do not contain a nucleus) that are responsible for transporting carbohydrates throughout the plant.<ref>{{Cite journal|last=Torode|first=Thomas A.|last2=O’Neill|first2=Rachel|last3=Marcus|first3=Susan E.|last4=Cornuault|first4=Valérie|last5=Pose|first5=Sara|last6=Lauder|first6=Rebecca P.|last7=Kračun|first7=Stjepan K.|last8=Rydahl|first8=Maja Gro|last9=Andersen|first9=Mathias C. F.|date=2018-02-01|title=Branched Pectic Galactan in Phloem-Sieve-Element Cell Walls: Implications for Cell Mechanics|url=http://www.plantphysiol.org/content/176/2/1547|journal=Plant Physiology|language=en|volume=176|issue=2|pages=1547–1558|doi=10.1104/pp.17.01568|issn=0032-0889|pmid=29150558}}</ref> As stated earlier, there are two categories of sieve elements and these are sieve cells and sieve tube members/elements.<ref name=":1">{{Cite web|url=https://web.archive.org/web/20070912193059/http://www.botany.hawaii.edu/faculty/webb/Bot410/410Labs/LabsHTML-99/SecPhloem/LabSecPhloem-99.htm|title=Secondary Phloem|date=2007-09-12|access-date=2018-05-21}}</ref> Sieve Tube elements are associated with companion cells which are cells that combined with sieve tubes create the sieve element-companion cell complex. This allows for supply and maintenance of the plan cells and allow for signaling between distant organs within the organism. <ref>{{Cite journal|date=2018-06-01|title=The rendez-vous of mobile sieve-element and abundant companion-cell proteins|url=https://www.sciencedirect.com/science/article/pii/S1369526617301437|journal=Current Opinion in Plant Biology|language=en|volume=43|pages=108–112|doi=10.1016/j.pbi.2018.04.008|issn=1369-5266}}</ref> Because sieve tube members do not have ribosomes or a nucleus and thus need companion cells to act as transport molecules. Companion cells provide Sieve tube elements with proteins necessary for signaling and ATP. It is the companion cells that helps transports carbohydrates from outside the cells into the sieve tube elements. <ref>{{Cite journal|date=2018-06-01|title=Sieve-element differentiation and phloem sap contamination|url=https://www.sciencedirect.com/science/article/pii/S1369526617301541|journal=Current Opinion in Plant Biology|language=en|volume=43|pages=43–49|doi=10.1016/j.pbi.2017.12.008|issn=1369-5266}}</ref>


Sieve tube elements and companion cells are connected through plasmodesmata. <ref>{{Cite web|url=https://web.archive.org/web/20070912193059/http://www.botany.hawaii.edu/faculty/webb/Bot410/410Labs/LabsHTML-99/SecPhloem/LabSecPhloem-99.htm|title=Secondary Phloem|date=2007-09-12|access-date=2018-05-21}}</ref> Structurally, the walls of sieve tubes tend to be dispersed with plasmodesmata grouped together and it is these areas of the tube walls and plasmodesmata that develop into sieve plates over time. Sieve tubes tend to be found largely in angiosperms. <ref name=":2" /> They are very long and have horizontal end walls containing sieve plates. Sieve plates contain sieve pores which can regulate the size of the openings in the plates with changes in the surroundings of the plants. <ref>{{Cite journal|last=Lu|first=Kuan-Ju|last2=Danila|first2=Florence R.|last3=Cho|first3=Yueh|last4=Faulkner|first4=Christine|date=2018-03-25|title=Peeking at a plant through the holes in the wall - exploring the roles of plasmodesmata|url=https://nph.onlinelibrary.wiley.com/doi/abs/10.1111/nph.15130|journal=New Phytologist|language=en|volume=218|issue=4|pages=1310–1314|doi=10.1111/nph.15130|issn=0028-646X}}</ref>
Sieve tube elements and companion cells are connected through plasmodesmata. <ref>{{Cite web|url=https://web.archive.org/web/20070912193059/http://www.botany.hawaii.edu/faculty/webb/Bot410/410Labs/LabsHTML-99/SecPhloem/LabSecPhloem-99.htm|title=Secondary Phloem|date=2007-09-12|access-date=2018-05-21}}</ref> Structurally, the walls of sieve tubes tend to be dispersed with plasmodesmata grouped together and it is these areas of the tube walls and plasmodesmata that develop into sieve plates over time. Sieve tubes tend to be found largely in angiosperms. <ref name=":2" /> They are very long and have horizontal end walls containing sieve plates. Sieve plates contain sieve pores which can regulate the size of the openings in the plates with changes in the surroundings of the plants. <ref>{{Cite journal|last=Lu|first=Kuan-Ju|last2=Danila|first2=Florence R.|last3=Cho|first3=Yueh|last4=Faulkner|first4=Christine|date=2018-03-25|title=Peeking at a plant through the holes in the wall - exploring the roles of plasmodesmata|url=https://nph.onlinelibrary.wiley.com/doi/abs/10.1111/nph.15130|journal=New Phytologist|language=en|volume=218|issue=4|pages=1310–1314|doi=10.1111/nph.15130|issn=0028-646X}}</ref>

Revision as of 07:23, 21 May 2018

Introduction

Companion cell (left, light pink), nucleus (dark pink), sieve tube (right, solid green), sieve tube plates (dashed green), dissolved nutrients (yellow)

Phloem is highly organized tissue that contains many specialized cells including sieve elements. In plant anatomy, sieve cells and sieve tube members constitute sieve elements, which are conducting cells. They are specialized cells in the phloem tissue of flowering plants. [1] Sieve elements' major function includes transporting sugars over long distance through plants by acting as a channel. Sieve elements elongate cells containing sieve areas on their walls. Pores on sieve areas allow for cytoplasmic connections to neighboring cells. Structurally, they are elongated and parallel to the organ or tissue that they are located in. Sieve elements typically lack a nucleus and contain none to a very few amount of ribosomes. [2]

Sieve Tubes

Main functions of sieve tube elements include maintaining cells and transporting necessary molecules with the help of companion cells. [3] The sieve tubes are living cells (which do not contain a nucleus) that are responsible for transporting carbohydrates throughout the plant.[4] As stated earlier, there are two categories of sieve elements and these are sieve cells and sieve tube members/elements.[5] Sieve Tube elements are associated with companion cells which are cells that combined with sieve tubes create the sieve element-companion cell complex. This allows for supply and maintenance of the plan cells and allow for signaling between distant organs within the organism. [6] Because sieve tube members do not have ribosomes or a nucleus and thus need companion cells to act as transport molecules. Companion cells provide Sieve tube elements with proteins necessary for signaling and ATP. It is the companion cells that helps transports carbohydrates from outside the cells into the sieve tube elements. [7]

Sieve tube elements and companion cells are connected through plasmodesmata. [8] Structurally, the walls of sieve tubes tend to be dispersed with plasmodesmata grouped together and it is these areas of the tube walls and plasmodesmata that develop into sieve plates over time. Sieve tubes tend to be found largely in angiosperms. [9] They are very long and have horizontal end walls containing sieve plates. Sieve plates contain sieve pores which can regulate the size of the openings in the plates with changes in the surroundings of the plants. [10]

Formed through the vertical connections between multiple sieve tube members, sieve tubes are directly responsible for the transport through the minimum resistance surrounding their walls. [11] By having the assistance of these pores that constitute a majority of the structure of sieve plates, the diameter of the sieve tubes can be regulated. This regulation is necessary for the sieve tubes to respond to changes in the environment and conditions within the organism. [5]

Sieve Cells

Sieve cells are long, conducting cells in the phloem that do not form sieve tubes. The major difference between sieve cells and sieve tube members is the lack of sieve plates in sieve cells. [9]They have a very narrow diameter and tend to be longer in length than sieve tube elements as they are generally associated with albuminous cells.[12] They have long, unspecialized areas with ends that overlap with those of other sieve cells. Sieve cells are also associated with gymnosperms because they lack the companion cell and sieve member complexes that angiosperms have. [13] Sieve cells are very uniform and have an even distribution across of sieve areas. Their narrow pores are necessary in their function in most seedless vascular plants and gymnosperms which lack these sieve-tube members. [9]

Just as Sieve tube elements have companion cells which form complexes and function together, sieve cells have albuminous cells that aid them in functioning. [1] These albuminous cells work between phloem and parenchyma. They connect parenchyma with mature sieve cells to help participate in transport of cells. There can be many of these albuminous cells that belong to one sieve cell, depending on the function of the tissue or organ. [9]

Sieve pores are very common in the areas that have overlapping sieve cells. In order to observe the activity of sieve cells and tubes, callose levels can be measured. Callose acts as a block to the sieve pores that are present in both of these sieve elements. A lack callose suggests that the sieve elements are more active and therefore can regulate their pores more actively in response to environmental changes. [14]

Discovery

The forest botanist Theodor Hartig was the first to discover and name these cells as Siebfasern (sieve fibres) and Siebröhren (sieve tubes) in 1837.

Origin

Companion cells and Sieve cells originate from meristems, which are tissues that actively divide throughout a plant's lifetime. They are similar to the development of xylem. [1]

See also

References

  1. ^ a b c "Botany online: Supporting Tissues - Vascular Tissues - Phloem". 2007-08-07. Retrieved 2018-05-21.
  2. ^ Lamoureux, Charles H. (1975). Phloem Transport. NATO Advanced Study Institutes Series. Springer, Boston, MA. pp. 1–31. doi:10.1007/978-1-4684-8658-2_1. ISBN 9781468486605.
  3. ^ "The rendez-vous of mobile sieve-element and abundant companion-cell proteins". Current Opinion in Plant Biology. 43: 108–112. 2018-06-01. doi:10.1016/j.pbi.2018.04.008. ISSN 1369-5266.
  4. ^ Torode, Thomas A.; O’Neill, Rachel; Marcus, Susan E.; Cornuault, Valérie; Pose, Sara; Lauder, Rebecca P.; Kračun, Stjepan K.; Rydahl, Maja Gro; Andersen, Mathias C. F. (2018-02-01). "Branched Pectic Galactan in Phloem-Sieve-Element Cell Walls: Implications for Cell Mechanics". Plant Physiology. 176 (2): 1547–1558. doi:10.1104/pp.17.01568. ISSN 0032-0889. PMID 29150558.
  5. ^ a b "Secondary Phloem". 2007-09-12. Retrieved 2018-05-21.
  6. ^ "The rendez-vous of mobile sieve-element and abundant companion-cell proteins". Current Opinion in Plant Biology. 43: 108–112. 2018-06-01. doi:10.1016/j.pbi.2018.04.008. ISSN 1369-5266.
  7. ^ "Sieve-element differentiation and phloem sap contamination". Current Opinion in Plant Biology. 43: 43–49. 2018-06-01. doi:10.1016/j.pbi.2017.12.008. ISSN 1369-5266.
  8. ^ "Secondary Phloem". 2007-09-12. Retrieved 2018-05-21.
  9. ^ a b c d "Botany online: Supporting Tissues - Vascular Tissues - Phloem". 2007-08-07. Retrieved 2018-05-21.
  10. ^ Lu, Kuan-Ju; Danila, Florence R.; Cho, Yueh; Faulkner, Christine (2018-03-25). "Peeking at a plant through the holes in the wall - exploring the roles of plasmodesmata". New Phytologist. 218 (4): 1310–1314. doi:10.1111/nph.15130. ISSN 0028-646X.
  11. ^ "Sieve-element differentiation and phloem sap contamination". Current Opinion in Plant Biology. 43: 43–49. 2018-06-01. doi:10.1016/j.pbi.2017.12.008. ISSN 1369-5266.
  12. ^ Cayla, Thibaud; Batailler, Brigitte; Le Hir, Rozenn; Revers, Frédéric; Anstead, James A.; Thompson, Gary A.; Grandjean, Olivier; Dinant, Sylvie (2015-02-25). "Live Imaging of Companion Cells and Sieve Elements in Arabidopsis Leaves". PLoS ONE. 10 (2). doi:10.1371/journal.pone.0118122. ISSN 1932-6203. PMC 4340910. PMID 25714357.{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link)
  13. ^ 1946-2004., Campbell, Neil A., (1996). Biology (4th ed ed.). Menlo Park, Calif.: Benjamin/Cummings Pub. Co. ISBN 0805319409. OCLC 33333455. {{cite book}}: |edition= has extra text (help); |last= has numeric name (help)CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  14. ^ Evert, Ray F.; Derr, William F. (1964). "Callose Substance in Sieve Elements". American Journal of Botany. 51 (5): 552–559. doi:10.2307/2440286.
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