polyploid transformants

MeyerowitzE meyerowitze at STARBASE1.CALTECH.EDU
Fri Dec 27 01:07:49 EST 1991

Elizabeth:  They are probably tetraploids.  A lot of cells in Arabidopsis are
apparently tetraploid, and one often obtains 4N regenerants which are simplex
for the introduced genes.  There are many ways to check: seed size is larger
for tetraploids (one easy way to see this is to drop 20 seeds into a capillary
that lines them up the long way, and a population of 2N and 4N plants will give
a bimodal distribution of length of capillary filled with seeds).  Chromosome
counts are simple: a lacto-acetic orcein squash of roots (and probably any
other stain, as well) shows centromeric heterochromatin even in interphase. 
One sees 6-10 spots in diploids, 14-20 in tetraploids.  If you catch any in
metaphase, the extra chromosomes are really apparent.
     Segregation of tetraploids is funky, as well, but is not usually an
appropriate way to see if the plants are tetraploid, because it takes a couple
of generations.  One simple genetic way to check, if you have time to wait 2
generations, is to cross the suspected tetraploids to known diploids, then self
the F1.  The F1 will be mostly sterile, and have lousy seed set, if one of the
parents was tetraploid, because the F1s are triploid, and necessarily have a
lot of nondisjunction.  This is how trisomics are usually made.  
     There are other ways to check, also.  In many plants, stomata are bigger
in tetraploids.  I have never looked in Arabidopsis, but I'm certain that
someone has.  Et cetera.  If you wish, I will dig for references on tetraploid
Arabidopsis: 4N Arabidopsis plants have been described several times in the
literature, but I don't recall offhand by whom.  
     Best regards (and happy new year to all).  Elliot Meyerowitz

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