To those having problems with plant action potentials:
I am sorry that the action potential experiment using Mimosa is
giving you some trouble. Especially since it is really great when it works.
A lot depends on the state of the plants. They must be healthy,
well-watered and moved to the demonstration site in advance.
Silver wire is available from several places (I usually get it from
our Physics Department stockroom): Sigmund Cohn, 123 South Columbia, Mt.
Vernon, NY and The Matrone Group in Millburn, NJ 07041. You will need
several feet of very fine wire to make the connections. The "connector box"
is simply a means to connect the very-expensive silver wire to the usual
connnector wire with appropriate jacks for the recorder. The box can be
eliminated if you find a way to make a good connection without it. A short
piece of about 1-mm-thick silver wire is needed to stick into the soil; fine
silver wire is wound around the end and connected to the connection
box/recorder. I am not sure that the companies cited will sell small
amounts of the wire. If you have no other source, I can send it to you at
our cost plus shipping and handling.
I think someone else answered the question about Elmer's glue. It
is a water based glue that contains lots of NaCl. We apply it just before
dropping the hooked, fine silver wire over the petiole about half way
between the pulvinule and the leaflets. There is no need to let it dry. If
the leaf bends down during the application of glue and wire, try another one.
The trickiest part is setting the correct voltage on the recorder
and finding the right zero point. The action potentials generated will
probably be more than 10 mV but considerably less than 100 mV. I have an
old B and L recorder that allows me to use an "uncalibrated" setting between
the two. It would be best to try this out in advance and find the best
setting. In any case I would never take a lab into the classroom without
trying it first.
Good luck and please contact me if there are any more questions.
Section of Plant Biology
Ithaca, NY 14853
hcr1 at cornell.edu