Rik Palmans, Voeren (Belgium)
----------------------------------------------------------------------
Stimulation of the trigger hairs generates an action potential-- two hairs
usually need to be stimulated simultaneously or in close succession, so
there is a kind of summation going on-- this triggers irreversible cell
elongation in at least some of the outer epidermal cells near the leaf
midrib by acidifying cell walls to pH 4.5 or so. During closure, nearly a
third of the ATP in these cells is dephosphorylated, presumably to pump H+
ions into the intercellular space.
Steve Williams <williams@lvc.edu> can give you more information about the
action potential generation-- the rest came from Raven et al, _Biology of
Plants_.
Michael A. Camann camann@lvc.edu
Dept. of Biology (717) 867-6172 voice
Lebanon Valley College (717) 867-6075 FAX
Annville. PA 17003
----------------------------------------------------------------------
Where's a real botanist when you need one?! It seems that VFT and mimosa
(sensitive plants) both operate by the same mechanism which involves rapid
transport of ions followed by osmotic movement of water out of specialized
cells. This results in a loss of turgor and a collapse of those cells
(pulvini?) which then results in a collapse of the leaf or a closing of the
trap. I would not stake my child's life on this one, but I believe it is
at least close to correct.
John Bohmfalk bohmfalk@tcgcs.com
Biology Dept.
Hastings College
Hastings, NE
----------------------------------------------------------------------
Dionaea muscipula, the venus-fly-trap, is certainly a fascinating plant. The
exact mechanism for the traps movement is not fully understood. There is a
definite action potential during the traps closing. Evidence also suggests
that the leaves have a ATP proton pump which allows hydrogen ions to move
across the membrane. The trap does not actually close like a bear trap;
instead there is a reversal of which surface is concave. Generally, each trap
can only close 3 to 4 times before the leaf dies. The number of trigger hairs,
the trap colour, and the overal petiole shape various from one plant to
another.
I hope this was of some help!
John peredur@usa.net