My question is occasioned by the fact that plants grown from cuttings appear to have no old-age effects. I understand that trees die eventually of old age-caused by degradation of their DNA-their new cells eventually degrade and wither, much like the skin cells of elederly humans. However, if you take a bamboo cutting, and root it, it will grow up as a youthful plant-no evidence on age-related degradation. How does the plant DNA repair itself? If you clone an animal (as with the case of “Dolly”) the clone has age-defected DNA, and shows signs of old age even while young?
Does plant DNA have some way of resetting the clock? All plant clones (ie plants grown from cuttings) seem to have no age-related degardation.
How is this possible?
Don’t know the answer, but it’s a damn good question.
It should be pointed out that whether cloned animals really show signs of aging in youth is still not clear. They seem to show defects, but that may not be age related as such since most cloned foetuses show some sort of defects, havin two heads, that aren’t normally realted to aging.
I’m also not sure that ‘trees die eventually of old age-caused by degradation of their DNA’. AFAIK trees die because plants are obligate growers. The need to keep laying down cambial tissues as the old stuff wears out, and this necessitates physical growth. As a result trees keep getting bigger and bigger with larger and larger proportions od dead material. After a while the organism can’t suport itself. In trees that can propagate new trunks from root suckers or other vegetative means there doesn’t seem to be any evidence of DNA breakdown.
I’m guessing plants just don’t have the same apoptosis and telomere restriction mechanisms as animals.
Come on people. Someone must know.
Very interesting question. Unfortunately, I know next to nothing about either plant biology or aging.
Blake, I’m not sure I understand how you believe trees die.
What does this mean on a molecular level? If you have a cite regarding plants dying because they can’t stop growing, I’d be grateful to have it.
Plants are able to undergo programmed cell death, but I’m not sure whether this has anything to do with aging in these organisms.
http://www.bio.unc.edu/faculty/jones/lab/pcd/
Again, interesting question.
-Apoptosis
It is an interesting question in’t it.
Trees being unable to suport themselves isn’t something that occurs on a molecular level, it’s purely physical. They have to grow and keep on laying down phloem. If they get too tall they die when the soil moisture becomes so low they develop a break in the xylem fluid. If the get too large in girth the xylem, which is dead tissue, inevitably begins to decay and the tree can no longer support its own weight and snaps.
I’ll see if I can dig up the refernces for trees and obligate growth fatalities.
I think that the word the OP is looking for is “totipotency”. This is the ability of differentiated cells to revert back to an undifferentiated state and thus regenerate the entire organism. Actually a survey of the tree of life reveals that this is actually quite common - plants, fungi, protists and bacteria all exhibit it. [Technically, fungi are an undifferentiated mass of hyphae that are effectively immortal. Most protists and bacteria are single-celled, so there’s no surprise there.] The real question is why animals appear to have lost this ability.
But then again maybe they haven’t. Differentiated animal cells can revert to a less differentiated state, however this usually results in a tumorous mass. If you can figure out exactly how and why this happens, and how to stop it, then it’s Nobel Prize time for you. 
Sorry, Terminus Est, but someone’s been feeding you a lotta bogus information.
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Totipotency has nothing to do with a differentiated cell reverting to an undifferentiated state. Totipotent cells are, by definition, undifferentiated, and have the capacity to differentiate into any cell type of a given organism:
http://www.counterbalance.net/stemtp/stemc-body.html -
Totipotent cells only exist in multicellular organisms; there’s no such thing as an “undifferentiated” or “differentiated” single-celled organism.
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The processes a cell goes through while becoming cancerous are not commonly refered to as “revert[ing] to a less differentiated state.”
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None of this has anything to do with why plant cuttings are seemingly ageless.
-Apoptosis
My point is that it isn’t that plants are anything special or different by being seemingly ageless and regenerative. It’s that animals seem to have lost that ability.
And totipotency may indeed apply to differentiated cells. Check out these class notes for BIO 183 at NCSU:
Just Google on “plant totipotent”.
This doesn’t try to answer the question, it’s an example. Naval oranges don’t make seeds, and if a farmer anywhere in the world wants an orchard of naval oranges he uses cuttings.
This has been going on ever since people first noticed naval oranges on a ‘sport’, and decided they liked them and wanted more of the same. WAG, this began hundreds of years ago. Essentially, not counting other clones that started from other sports, there is one naval orange tree in the world.
But we aren’t talking about totipotency per se. We are asking why animal cells, even germ cells presumably, have a finite number of divisions avaialble bfore they start to show signs of aging.
AFAIK no plant cells show this trait with or without reverting to a different form. And I wanna know why.
Blake,
I understand what we are talking about has nothing to do with totipotency (see my point 4 above). I am merely trying to clear up a few points with Terminus Est.
Unfortunately, a great deal of what they teach you in your first year is so simplified that it may as well be incorrect. Here is the correct usage of the word “totipotent” in a plant context:
“The transition from a genetically totipotent meristematic precursor to different stages of a committed procambial cell, and its subsequent differentiation into a mature vascular element, involves developmental events whose molecular nature is still mostly unknown.”
Please give me some cites from PubMed to back up your Googled notes.
The facts remain that:
A. A differentiated cell is NOT totipotent.
B. It makes no sense whatsoever to describe single-celled organisms as totipotent.
C. The word the OP was looking for was not “totipotency.”
-Apoptosis
Gotta go with Terminus Est on this one. I too was taught that plant cells are totipotent, and the journals and textbooks seem to agree with that:
Ikeda-Iwai, M.; Umehara, M. et al. 2003
Stress-induced somatic embryogenesis in vegetative tissues of Arabidopsis thaliana
The Plant Journal Volume 34 Issue 1
Krikorian, A.; Simola, M. 1999
Totipotency, somatic embryogenesis, and Harry Waris (1893-1973)
Physiologia Plantarum
Volume 105
Raven, P.; Evert, R.; et al 1992
Biology of Plants
W. H. Freeman/Worth Publishers
Referring to a “transition from a genetically totipotent meristematic precursor” tells us nothing about the totipotency of other cells or the correct use of the term.
Interesting stuff, Blake. Thanks for that. I guess what set me off is that Terminus Est defined totipotency as the de-differentiation of differentiated cells. This, of course, is incorrect.
At this point, I could argue that semantics are on my side- that, by definition, a differentiated cell is not totipotent. Only when it is de-differentiated (and is obviously no longer a differentiated cell) does it become totipotent. I will refrain from making that argument on the grounds that I think I would lose it.
I apologize to everyone for derailing this very interesting question.
-Apoptosis
From working at a plant molecular biology facility for some years (Boyce Thompson Institute for Plant Research), I can say that the following is known to work:
It is possible to begin with differentiated plant tissue (stem or leaf) and induce it into an undifferentiated “callus” state. This can then be induced to produce a complete plant. Sometimes it is fairly routine. Sometimes it can take years to work out the details and drive professors to madness. Nevertheless, the basic ability is there.