Re: Mutagens (Colchicine)
Sun, 22 Jan 1995 13:34:04 -0500


In response to your request. Colchicine is NOT something to play "Mad
Scientist" with. A bit of backround:
-Colchicine (hereafter:C) is derived from several Colchicum spp, several
Merendera spp and Gloriosa suberba.
-It is highly toxic and carcinogenic.
-It is in the class of Antimitotic agents, it mutates cells through a process
called endomitosis. This simply means that it halts cell division.
-Why does that cause mutation? Suppose when it halts cell division, the cell
is in the process of dividing (mitosis).The cell would have any percentage
between 0% and 100% extra chromosomes. Extra chromosomes=Polyploidy=mutation.
-This is not as simple as it sounds, you can have partial polypoids,
mutipolyploids (polyploids with are "redoubled") etc. And remember, this
takes place on the cellular level, the whole plant isn't affected, just
individual cells.
-With this understood, it is obvious that we need to treat material with the
fewest cells possible, so that if one favorabily mutates, it can develop into
something useful. Something like a seed or even better; callus or cell
suspension cultures.
To make this clearer. Suppose you were to spray a seedling with C. At best
only a small percentage of the billions of cells would mutate. An even
smaller percentage would mutate into something useful or noticiable. The
chances of any mutated celld falling in a place that would effect the
resulting growth of the plant (the apical or lateral buds) is nil. Sure you
might get a mutation for variegation, but if it happens to occur in the
middle of a leaf, you will only see a small variegated spot in an other wise
normal plant.
Therefore, is is not a magic bullet and it won't work miracles. Most times,
mutations obtained will only be useful in sexual breeding. If you are not put
off by that, here are some suggestions for treatment times and dosages:
The optimum time of treatment: The amount of time it takes the cell to
complete division (so you do not "remutate"). Practically: between 3 and 24
Dosages: varies with genus and species and is modified with duration of
exposure: Start with solution concentrations of .01% C and work up to .5% C.
Material to experiment with: I use TC material because I have access to it. I
have suggested to people to use seeds. The entire seed if it is small and has
little to no seed coat (ie Coleus or Orchids) or a pregerminated seed if it
is large (ie a Legume).
Finally, ever wonder how to tell if you actually have a polyploid? Either one
you've created or one you suspect? The easiest way to tell is with the Pollen
Measuring Technique. Simply collect pollen from several plants known or
suspected of being "normal" and the pollen of the suspected polyploid. Use a
hig powered Microscope and a Stage Micrometer and simply compare the pollen
grains. The polyploid should have larger pollen (scientist's: don't flame me.
I know there are drwbacks to this method, but it's fine for the hobbyist).

Hope this has answered some of your questions. Good Luck.

Another Pearl of Wisdom from:
( John Laroche