[NAFEX] Cloning

list at ginda.us list at ginda.us
Sun Mar 30 12:09:11 EST 2003

On Sunday, March 30, 2003, at 11:35  AM, Keith Benson wrote:

>>> Earlier fruiting may be tied to the advanced cellular clock of the 
>>> scion,
>>> but it does not seem to shorten the lifespan of the tree.
>>> Anyone know the reason?
> Does the cellular clock in plants, specifically pome fruits include 
> scenesce genes?  If not then the thing would essentially go on until 
> random mutations eliminated all of the cultuvars - and that could take 
> a while - especially with people culling off types (eliminating 
> mutations).
> There are those who even argue that there are some vertebrates that do 
> not become scenescent (larger turtles and tortoises for example).  Not 
> everyone may be pre-programmed to fall apart.
> Keith

In general, plant cells are not programmed to age and die (what Keith 
calls "senescence").  Plants tend to have lots of undifferentiated 
cells that are capable of becoming whole new plants, only different 
from the original plant due to random genetic damage.  Most animals are 
different.  Each of our cells is programmed to reproduce a fixed number 
of times and then die.  The only exceptions are new gametes and cancer 
cells.  (Cancer cells all have damage to the part of the genes that 
says "die now".)  There is something in a newly fertilized eggs that 
"resets" the clock, or it may happen earlier, when the germ cells that 
combine to form the fertilized egg are formed.  That's why people were 
watching Dolly for signs of premature aging - no one really knows what 
it takes to reset the clock.  (That's also one reason scientists are 
mostly more interested in fetal stem cells than adult stem cells - 
fetal stem cells still have a lifetime of reproduction in them.)

In simple terms, every plant cambium cell is similar to an animal fetal 
stem cell.  (Except the cambium cells are designed to turn off at a 
fixed time.)


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