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Tets and colchicine (touching several bases)


Colchicine is used for relief of gout, though in what concentrations I
do not know.  It is used on irises in concentrations of .033% or .05% or
so.  Newly germinated seedlings are treated for 24 hours at room temp
(or in a method developed by Sam Norris, up to three days at just above
freezing 34 F or 1-2 C).  For those who are interested in the actual
action, I understand it to actively bind to microtubules during mitosis
and effectively prevents the chromosomes from dividing after they
replicate. The colchicine is washed out of the cells at this point and
the cells continue onward in their replication and division, whith the
only difference being that the base number of chromosomes has
increased.  Oryzalin is an herbicide that is also a mitotic disrupter,
but I am not quite as clear how it works.
	I am under the understanding that many IB's are "triploid".  They are
marginally fertile, but I beleive this is because both parents do not
have the same base number of chromosomes originally.  TBs are tets,
SDB's are dips, but SDBs do not have half the number of TB chromosomes,
since they are different species.
	I versicolors in the wild are all typically natural tets, and I believe
Bee Warburton says somewhere near the beggining of the world of Iris
that they are a result of a natural interspecies cross occuring sometime
ago.  I setosa and I virginica are supposed to be the parents.  A number
of studies have been done on the similarities (genomically speaking) by
the japanese.  Interestingly, Tony Huber has done studies of chromosome
number in wild vericolor and found variation from 96-108 chromosomes, if
I remember correctly.  It should be noted that I have never done
chromosome counts, but what people tell me is that chromosome counts
that are that high are tough to do accurately.
	In my opinion, tetraploidy is not always the best thing for iris.  I
have a number of tet siberians and japanes whose foliage habits are a
bit ojectionable.  The foliage is just not as graceful, and the flower
are on stalks that do not sway in the breeze quite as nicely.  They do,
however, typically have a richer color saturation, which lends toward
deeper, more intense colors.
andrew wheeler
awheele2@abacus.bates.edu





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