reaction wood

[planteome-user]

Suggest the addition of three new terms:

reaction wood (PO:0025472): A portion of secondary xylem (PO:0005848) found on either the upper or lower side of a shoot axis (PO:0025029) that is leaning or crooked, with specific anatomical characteristics that depend on whether it is compression wood (PO:0025473) or tension wood (PO:0025474).

Comment: Functions in restoring a leaning stem (PO:0009047) or branch (PO:0025073) to its original position. May be either compression wood, found on the lower side of a gymnosperm shoot axis or tension wood, found on the upper side of an angiosperm shoot axis.

compression wood (PO:0025473): A portion of reaction wood (PO:0025472) found on the lower side of a shoot axis (PO:0025029) that is leaning or crooked that has as parts heavily lignified tracheids (PO:0000301) that are rounded in transverse section and bear spiral cell wall checks.

Comment: Functions in restoring a leaning stem (PO:0009047) or branch (PO:0025073) to its original position. Found in gymnosperms.

tension wood (PO:0025474): A portion of reaction wood (PO:0025472) found on the upper side of a shoot axis (PO:0025029) that is leaning or crooked that has as parts gelatinous fiber cells (PO:0025422).

Comment: Secondary xylem tracheary elements (PO:0025445) in tension wood are often longer than the tracheary elements in non-tension wood of the same plant. Functions in restoring a leaning stem (PO:0009047) or branch (PO:0025073) to its original position. Found in angiosperms.

References: IAWA Mulitlingual Glossary (PO_REF:00012), Carlquist 2001 (ISBN:3540411739)

Reported by: rlwalls2008

Original Ticket: obo/plant-ontology-po-term-requests/459

[planteome-user]

Slightly modified definitions and comments from the POC meeting on 3-27-12:

reaction wood (PO:0025472): A portion of secondary xylem (PO:0005848) found on either the upper or lower side of a shoot axis (PO:0025029) that is angled away from vertical, with anatomical characteristics that depend on whether it is compression wood (PO:0025473) or tension wood (PO:0025474). Comment: Develops as a response to gravity (either tension or compression) and may function in restoring a stem (PO:0009047) or branch (PO:0025073) that is leaning to its original position. May be either compression wood, found on the lower side of a gymnosperm shoot axis, or tension wood, found on the upper side of an angiosperm shoot axis.

compression wood (PO:0025473): A portion of reaction wood (PO:0025472) found on the lower side of a shoot axis (PO:0025029) that is angled away from vertical and that has as parts heavily lignified tracheids (PO:0000301) that are rounded in transverse section and bear spiral cell wall checks. Comment: Develops as a response to gravity (either tension or compression) and may function in restoring a stem (PO:0009047) or branch (PO:0025073) that is leaning to its original position. Found in gymnosperms.

tension wood (PO:0025474): A portion of reaction wood (PO:0025472) found on the upper side of a shoot axis (PO:0025029) that is angled away from vertical and that has as parts gelatinous fiber cells (PO:0025422). Comment: Secondary xylem tracheary elements (PO:0025445) in tension wood are often longer than the tracheary elements in non-tension wood of the same plant. Develops as a response to gravity (either tension or compression) and may function in restoring a stem (PO:0009047) or branch (PO:0025073) that is leaning to its original position. Found in angiosperms.

Original comment by: rlwalls2008

[planteome-user]

From Frederic (via email): "The only thing you may add to the tension wood definition (according to the IAWA glossary of 1964) is the lack of cell wall lignification."

From RW: I think that it is only the G-layer where lignin is absent or very low. I don't have time to research it fully today, but I will modify the comment of tension wood to say: Develops as a response to gravity (tension ) and may function in restoring a stem (PO:0009047) or branch (PO:0025073) that is leaning to its original position. Found in angiosperms. Secondary xylem tracheary elements (PO:0025445) in tension wood are often longer than the tracheary elements in non-tension wood of the same plant. The gelatinous fiber cells found in reaction wood have a cell wall inner layer (G layer) that contains abundant cellulose and is poor in lignin.

Original comment by: rlwalls2008

[planteome-user]

From Rachel (via email):

1. Both types of rxn wood are found in normal branches and stems that look straight (but were leaning or crooked in the past), not just leaning axes, so it would more accurate to say something like "specialized for mechanical support". My main point is that although this type pf wood is specialized it is in fact very ubiquitous.

2. To my mind, one of the key characteristics of the c-wood tracheids is that they contain a specialized "S2" layer which contains more lignin and has a larger (more horizontal) microfibril angle. The microfibril angle is very important to its function). I would not have said that the spiral checks are that important or guaranteed to be present, but I may be wrong.

3. Also to my mind, the key characteristic of the tension wood gelatinous fiber is a greatly reduced lignin content, and increase in crystalline (as opposed to amorphous) cellulose content. I think they also have a more vertical microfibril angle.

4. The comment about tracheary element length in tension wood does not make sense to me. The first thing that comes to mind about reaction wood to me is that compression wood tracheids SHORTEN during cellular differentiation/maturation, whereas tension wood gelatinous fibers LENGTHEN during maturaion, and that this change in length is precisely what effects the stem movement.

Original comment by: rlwalls2008

[planteome-user]

Based on Rachel's and Frederic's comments, I am making the modifications below. I added "...is leaning..." to "...is or was leaning...", added a clause about the S2 layer to compression wood and removed the comment about spiral checks. I left in the part about tracheary elements being longer in tension wood for now, but I will look into that further.

reaction wood (PO:0025472): A portion of secondary xylem (PO:0005848) found on either the upper or lower side of a shoot axis (PO:0025029) that is or was angled away from vertical, with anatomical characteristics that depend on whether it is compression wood (PO:0025473) or tension wood (PO:0025474). Comment: Develops as a response to gravity (either tension or compression) and may function in restoring a stem (PO:0009047) or branch (PO:0025073) that is leaning to its original position. May be either compression wood, found on the lower side of a gymnosperm shoot axis, or tension wood, found on the upper side of an angiosperm shoot axis.

compression wood (PO:0025473): A portion of reaction wood (PO:0025472) found on the lower side of a shoot axis (PO:0025029) that is or was angled away from vertical and that has as parts heavily lignified tracheids (PO:0000301) with a specialized S2 layer that contains more lignin and has a larger (more horizontal) microfibril angle. Comment: Develops as a response to gravity (compression) and may function in restoring a stem (PO:0009047) or branch (PO:0025073) that is leaning to its original position. Found in gymnosperms.

tension wood (PO:0025474): A portion of reaction wood (PO:0025472) found on the upper side of a shoot axis (PO:0025029) that is or was angled away from vertical and that has as parts gelatinous fiber cells (PO:0025422). Comment: Develops as a response to gravity (tension) and may function in restoring a stem (PO:0009047) or branch (PO:0025073) that is leaning to its original position. Found in angiosperms. Secondary xylem tracheary elements (PO:0025445) in tension wood are often longer than the tracheary elements in non-tension wood of the same plant. The gelatinous fiber cells found in reaction wood have a cell wall inner layer (G layer) that contains abundant cellulose and is poor in lignin.

Original comment by: rlwalls2008

[planteome-user]

• labels: --> Request: New ontology term
• milestone: --> plant anatomy
• priority: 5 --> 1
• status: open --> closed-accepted

Original comment by: rlwalls2008