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Mitosis and Meiosis

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Postby MrMistery » Thu Mar 13, 2008 10:18 am

I know what primary meristems are, but as initials are said to be restricted to the RAM, I always assumed that mitosis only takes place there. However, I must admit that nobody has ever explained these things to me in detail, everything I know is from what I read in one book and in free articles around the internet.
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Postby MrMistery » Thu Mar 13, 2008 10:50 am

Ok, I just realized that by some strange coincidence I have a botany ebook on my sister's laptop. Here is a picture that would suggest that what I said earlier is accurate: the region of cell division is in the apical meristem, with the primary meristems being the place where the cells start to differentiate and which eventually give rise to the respective. Also, logically thinking, there would be no reason for the cells of the primary meristems to keep dividing as the cells are somewhat differentiated - it would be much easier to restrict division to the RAM.
Image
If I somehow got things mixed up, I welcome corrections.
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Postby Cat » Thu Mar 13, 2008 7:44 pm

“Also, logically thinking, there would be no reason for the cells of the primary meristems to keep dividing as the cells are somewhat differentiated - it would be much easier to restrict division to the RAM.” – No, it would not. If only apical meristem cells could divide, none of the plants would be able to grow in width – that is what primary and secondary meristems are for.

The region of cell division is identified as the major collection/concentration of dividing cells in one place. It does not preclude cell division from occurring everywhere else.

You are mostly correct though: apical meristems give rise to primary meristems, and primary to secondary… Each one is somewhat differentiated and set to produce only certain types of cells, just like adult stem cells in humans.

The main difference they have from human adult stem cells is that primary meristems can fairly easily dedifferentiate into apical meristem cells on some occasions. You can observe this when you try rooting a cutting. In absence of root, some cells from the stem primary meristem tissues would dedifferentiate into root apical meristem cells that would produce new roots.
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Re: Mitosis and Meiosis

Postby MrMistery » Thu Mar 13, 2008 9:32 pm

Let's leave out secondary meristems - i think we can agree mitosis takes place there, but I was referring to primary structure here.
Primary meristems are for growing in width? I honestly don't think that's the case. By looking at the structure, I can see cell lines(as in lines made out of cells on top of each other, not stabilized cell lines) radiating from the RAM. Which suggests to me that the cell divisions in the RAM take place in a particular way, with longitudinal divisions taking place much more frequently than horizontal ones. In fact, I even remember reading that somewhere(don't remember where though).

Sure, mitosis will occur in other places. It takes place in the perycicle giving rise to lateral roots and in the epidermis giving rise to trichomes etc. It may even take place once in a while in primary mersitems. But my hypothesis is that it takes place so rarely compared to cell divisions in the RAM that it is negligible, and that the natural course is the restriction of initials to the RAM. Sure, it's hard to draw a clear line between the RAM and primary meristems, but in general at least.
PS: I am enjoying the discussion :D
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Re: Mitosis and Meiosis

Postby Cat » Thu Mar 13, 2008 10:57 pm

I enjoy this discussion too. :D I hope Elvira does not mind...

O.K. Here is a better picture of the meristem locations in the root:

Image

Also, look at this website below and let me know what you think.

http://www.botany.uwc.ac.za/SCI_ED/grad ... rimary.htm

I understand there is some disagreement as to which meristematic tissues - primary or secondary - contribute more to annual plant growth in width. In the woody plants it is unanimously secondary (or lateral) meristems. In either case all meristems divide and more rapidly than those of the promeristem - heart of apical meristem.
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Postby Elvira » Fri Mar 14, 2008 10:28 am

Thanx a lot, you've been loads of help! :)
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Postby MrMistery » Sat Mar 15, 2008 4:10 pm

so the protoderm, ground meristem and procambium are part of the apical meristem? That does explain why I understood it the wrong way: cause everywhere it said that the apical meristem is the region where mitosis occurs - and then it said what tissue each primary meristem forms, never specifying the RAM is just one big mersitem complex... Maybe you should write a clear botany book that teacherless students like myself could learn from :lol:
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Postby Cat » Mon Mar 17, 2008 3:25 pm

I'll think about it...
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