layer of cells or layer of tissue

[planteome-user]

This is another parent term that Chris prpopsed on 11/25. Some other child structures would be spore sac, placenta, sterile jacket layer. The question is, when do you call something a layer of cells, and when is it a layer of tissue? This will hinge on our final definition of tissue, and probably has something to do with the organization of the cells and if there is an intercellular matrix. I suggest that if a structure is a layer of tissue, it can be a child of portion of tissue, but we may still want the subclass layer of tissue, to help classify tissue types. If a structue is a layer of less organized cells, it should be a layer of tissue, and we will need a new parent term for that.

Reported by: rlwalls2008

Original Ticket: obo/plant-ontology-po-term-requests/61

[planteome-user]

Examples please.

Original comment by: jaiswalp

[planteome-user]

Examples or layers of cells: Aleuron layer, meristem L2, sterile jacket layer, spore sac

Possible examples of layers of tissues: epigonium (used in mosses for protective layer surrounding embryo, may be outdated term), indusium (in ferns), placenta (in bryophytes, maybe other groups) but I'm not that keen on using layer of tissue as a parent term

Original comment by: rlwalls2008

[planteome-user]

From Dennis: "spore sac" has no meaning in botany and we should delete it if we are in fact using it.

Ramona's response: We are not currently using it. I took it from a book, in my search for possible new terms relating to non-angiosperms.

Original comment by: rlwalls2008

[planteome-user]

From Dennis: To follow up on my previous message: "spore sac" is an incorrect translation of German for sporogenesis tissue or simply sporangium in seed plants.

Original comment by: rlwalls2008

[planteome-user]

• priority: 7 --> 5

Original comment by: rlwalls2008

[planteome-user]

This raises an interesting issue. Take sporangium for an example. It will have sporogenesis tissue that will give rise to spores. The sporogensis tissue will be surrounded by a tapetum, often a single layer of cells that has a common origin with the sporogenesis tissue. The is layer of cells, but is it a tissue unto itself and what is its parent?

Original comment by: dws409

[planteome-user]

According to http://www.plantcell.org/cgi/content/full/17/10/2705 Jung et al The Plant Cell 17:2705-2722 (2005)

In angiosperm species, the floral meristem comprises three layers of cells with separate lineages: L1 (epidermis), L2 (subepidermis), and L3 (core) (Goldberg et al., 1993). During early anther development, archesporial cell division in the L2 gives rise to primary parietal cells and primary sporogenous cells (Scott et al., 2004). The primary sporogenous cell undergoes a small number of divisions to generate the meiocytes, which produce a tetrad of haploid cells that are released as free microspores (McCormick, 1993). The primary parietal cell divides periclinally to form an endothecial cell subjacent to the L1 and a secondary parietal cell. The latter again divides periclinally to generate a middle layer cell next to the endothecium and a tapetal cell adjacent to the sporogenous cells (Scott et al., 2004).

So its not a sporogenous tissue. The primary sporogenous cell giving rice to a MicrosporeMC, which divides meiotically to give rice to spores. These spores are collectively present in the sac. They are individual entities and each have a same developmental pipeline, but they all funcion as individual cells and never as collective similar to a mass of TISSUE and /or CELLs in a given cell LAYER.

So think in this way.

I suggest using the tissue as a organized mass of cells, well beyond a single layer. ALSO i think that a layer is a continuum and often completes a ring (may be truncated in patches as it developes but still has a ring like arrangement) around a group of another layer/tissue. Whereas tissue can be present as a discontinuum at a given location but never as a continuous layer/ring. If that makes sense making a definition on these lines would be okay.

Original comment by: jaiswalp

[planteome-user]

Having worked with tissue terms more, I now suggest that we don't use this term. It is better to classify layers of tissue under the type of tissue that they are made of, rather than in a bin called layer of tissue. I am rejecting this item, but leaving it open for comment, in case we want to revisit it.

Original comment by: rlwalls2008

[planteome-user]

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

Original comment by: rlwalls2008