North American Fruit Explorers mailing list at ibiblio

[Joe and Ellen Hecksel <jhecksel@voyager.net>]

Thomas Olenio wrote:

> Hello,
>
> What is the difference between grafting fruit trees and Dolly the cloned
> sheep?
>
> I believe part of Dolly's problem was premature aging, due to her cellular
> clock being set from the starting point of a mature sheep.  Yet grafted
> trees do not seem to suffer the same fate.
>
> 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?


Darned good question.  I don't think anybody truly *knows* the answer. 
  I am willing to share my biases and beliefs.

I suspect that the major differences is that plant tissue is less 
differentiated than animal tissue.  Many trees, even very mature ones, 
will regenerate from root cuttings.  All of the normal tree parts from 
the roots.

One side effect of differentiation relates to the immune system.  Plants 
do not have active immune systems like animals.  They do not produce 
antibodies that gang-tackle foreign proteins.  One of signs of aging is 
that the immune system winds down and our bodies become more vulnerable 
to infections and cancer.

I currently think that the immune system winding down is actively 
programmed.  Our bodies are filling up with crud (protein chopped up by 
UV, bacteria and virus that are dormant-in-place, pre-cancerous cells 
that have not figured out how to sequester blood supply).  The 
collateral damages caused by a hyperactive immune system would outweigh 
the benefit of destroying relatively benign intruders.  As a frame of 
reference, the pathology of Arthritis, Lupus and Leprosy all have 
auto-immune components.

Another side effect relates to circulation and rate of healing.  I find 
that as an old geezer my cuts heal much more slowly than those of 
children.  I have no firm beliefs about "why", but it may have something 
to do with not triggering those pre cancerous cells into fully-blown 
cancer.

I write as though our bodies are constantly making rational, 
statistically optimized decisions.  That is silly, of course.  Rather, I 
think that those families (animal or human) that exhibited excessive 
healing rates or immune responses lost many members to cancer, etc. 
Loosing too many members makes the family fragile and they become 
extinct.  So there is a Survivor Bias toward those family lines that 
have immune system coast down rates that are near optimum.

The rate of healing in plants seems to be related more to site fertility 
and carbohydrate reserves.

My 2 cents.


> Later,
> Tom


--
-Joe Hecksel
My personal web site: http://my.voyager.net/~jhecksel

"March" is Latin for "Mud".  (Joke)  March/Mud will be welcome when it comes