Help, again!

Ross Koning koning at ecsuc.ctstateu.edu
Fri Jan 14 16:27:36 EST 2000


At 12:12 PM 1/12/0, "lawrence at lmli.freeserve.co.uk"
<lawrence at lmli.freeserve.co.uk wrote:
>Oh...the dilemma!!!
>I know I said I was going to do pH and Germination but I figure there is not
>really much depth in that topic...and someone suggested a study of plant
>hormones.
>One thing though, how do I make up the solutions?  I realised the
>concentration in Textbooks are measured in ppm (parts per million), how can
>I do that with school equipments?  Would I be able to use mung beans and
>cotton wool?
>Lawrence

If you are going to make dilute solutions for use in
school settings, you can of course go to the local
university and make up your stock solution with an
analytical balance and so on...but the on-site way
to do this is by serial dilution.  You weigh out what
you accurately can with the balance you have...then
dissolve into a solvent that allows that amount to be
in a reasonably small first container.  This first
solution might have to be in acetone or alcohol. You can
then make serial dilutions of the first stock to get
at the final solutions you need.  If you DO use acetone
for your first solution, be sure that you record the
weight before you put it away in a tight container.
You might need to restore volume when you come back
to it later...it is SOO volatile!  The other thing is
that you want your final solution to not have too much
acetone or alcohol.  If you have achieved at least 1000x
dilution, then you might be OK.  Plants can deal with
*low* concentrations of these solvents.

This method means you will be "using" a fairly large
amount of material for the stock solution, but particularly
if the stock is acetone or alcohol, it will "keep" for
future use...just be sure to account for evaporation
as mentioned above...and keep in a dark place.  I always
keep stocks in refrigeration.

BTW: when I do hormone labs, I find that 10x differences
in concentrations among the trials is reasonably useful
to show dose responses in most bioassays.  For GA or IAA
I typically use 10-4, 10-5, 10-6, and 10-7 M plus a distilled
water comparator. For cytokinins, you might have to use a
more-dilute series, depending on the system you are measuring.
10-3 M IBA is herbicidal to Mung Beans! I get nice rooting
in hypocotyl cuttings at 10-5 M IBA. For a GA spray on dwarf
peas I use 10-4 M (there isn't much toxicity with GA when in
excess).

Best wishes!

ross

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( )_______________________________)
 \ Ross Koning                     \
  \ Biology Department              \
   \ Eastern CT State University     \
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     \ Koning at ecsu.ctstateu.edu        \
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