In message , "David (in
Normandy)" writes
I notice there are some genetics experts on the forum. A question has gone
unanswered in my mind for a number of years because I didn't know who to ask
or where to look for the answer.

I've just grown a rhubarb plant from a cutting taken from my fathers plant
which is around 50 years old. I know my father took his as a cutting from my
grandfather. It may be possible that this too was from a cutting and so on,
hence the original "seed" based plant may be a hundred years or more old and
long since dead.
Can this process of taking cuttings of cuttings carry on indefinitely or
will the plant material eventually degrade or grow 'old' and die?

I vaguely recall that the aging process in animals is due in part to the
ends of chromosomes unravelling and not being copied correctly when cells
divide, a bit like analogue copies of copies of video tapes or audio
cassettes. And that the original undifferentiated 'stem cell' can only be
copied down around 60 generations (ie. copy of copy etc of original) before
the genetic material becomes too damaged for a viable cell to be formed by
division. I think this was also an issue regarding "Dolly the cloned
sheep" - there was speculation that she was born as old as her mother
genetically speaking because she wasn't cloned from a stem cell? I am
drawing a parallel here between animal cloning and vegetative cuttings - is
that valid?

So is there a limit to the viability of taking cuttings of cuttings of
cuttings etc? Is there any genetic 'age' associated with the plants?


Plants don't show the same distinction between soma and germ-line that
animals do - just about any plant cell, in the right circumstances (e.g.
tissue culture) can give rise to a new plant. In particular it is
possible to propagate plants from sports in a way that isn't true for
animals. (Imagine producing a new colour break of cat from a hair
follicle.)

In principle plant clones can live for a very long time - see Wollemia,
some tree/shrub in Tasmania (the name escapes my recollection), Opuntia
clonal microspecies in the US South West, aspens elsewhere in the US.
However clones do have a tendency to "age". I don't think it's due to a
lack of telomerase function (I don't know about the topic, but I suspect
that plant cells express telomerase). One known cause of "aging" is the
build up of virus infections - this can be reversed by passing the clone
through tissue culture. Another is the build up of detrimental
mutations, tho' this acts on a longer timescale.
--
Stewart Robert Hinsley