Alyson,
We tried this with Mimosa in the semester just gone with our first year
plant phys students. It was a disaster! We weren't able to get any Elmer's
glue but used conductive epoxy instead. This may have been part of the
problem, but we did seem to have an electrical connection to the petiole.
However, using our recording apparatus (MacLab A/D interface) we had a high
level of noise - so much so that the signal was not detectable. On advice
from our resident animal neurophysiologist (Ian MacFarlane - an ex St.
Andrews man) we connected the silver wire by stabbing it through the
petiole - thus giving a better connection. Although this improved things -
the signal/noise ration was still very poor and whether we saw anything
which we could describe as an action potential was very hit and miss.
Needless to say this did not have the desired effect on our students'
perception of plant physiology, and we ended up dropping the experiment out
of the circus quite early on.
We had to make educated guesses about how to connect the apparatus as the
illustration in the textbook is not very helpful, so it is quite possible
that we got something wrong. One problem which we did identify is that if
you are trying to measure an action potential as it propagates down the
petiole, then you want your electrode to have a single, narrow point of
contact with the petiole. If you use a salt-bridge as you describe then you
may be trying to measure an average of the action potential across a
substantial length (in cellular terms) of the petiole. I would guess that
this would reduce your chances of seeing anything at all.
I'll send this reply to the list in case someone can shed some light on
these problems - in principle this seemed like an interesting experiment -
in practice we wish we hadn't tried it at all!
Regards,
Cris
>We are about to try- for the first time- the experiment described in Carol
>Reiss's book which measures action potentials in Mimosa and Venus Fly trap.
>The apparatus involves connecting silver wire to the petiole with Elmers
>glue. Can anyone tell me what this is and where I might obtain some from.
>Is there anything else that would work- e.g. soaking cotton wool in KCl to
>act as a bridge between plant and electrode. My other query is with the
>junction box. Is this simply a means of connecting the silver wire to the
>copper wire or am I missing something here? Any tips from anyone who has
>run this lab would be much appreciated.
>Alyson Tobin
___________________________________________________________________________
: Dr. Cris Woolston :
: Department of Applied Biology :
: University of Hull, Cottingham Road, Hull HU6 7RX, UK :
: RFC-822: C.J.Woolston at applied-biology.hull.ac.uk :
: Tel: +44 1482-465549 Fax: +44 1482-465458 :
___________________________________________________________________________
