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01-11-2004, 09:37 PM

wrote in
oups.com:

Sean Houtman wrote:

There are a number of cases of an animal producing some chemical
substance that is deleterious to a plant. Many galls are formed
by an insect or other arthropod producing some toxin that the
plant deals with by growing tissue around it, thereby protecting
and feeding the buggie.

I always wonder that crown-gall formation in certain plants can be
regarded as cancer of the plant. Can this growth be included in
the definition of cancer. There is a local tree which produces
edible fruits (Zizyphus species), almost all tree tend to develop
tumour-like growth having a different color from the stem, I don't
know whether eating fruits of such infected plants is harmless for
humans for not?

I am going to be brave and opine that there is no homologue to
cancer in plants.

Here are my reasons for my opinion. Animal tissues are plastic, and
in the event of injury, cells from surrounding tissue can either
replace the injured cells, or grow some sort of scar tissue. Animal
cells generally need to be able to divide and grow at any time
during the life of the animal. Plant tissues are not plastic.
Generally, once a tissue differentiates, it stays that way, injury
does not produce healing by the way of replacement. Though plants
can recover from injury, it tends to be through either sequestering
the injury, or sloughing the effected part. There are times where
plants may begin to grow various sorts of undifferentiated tissue,
but the cells of that tissue are unable to invade other parts of the
plant. The source of that growth always seems to be from
meristematic tissue in the first place.

Sean