Date: Mon, 06 Sep 1999 13:36:50 -0500 From: Lloyd Davidson <Ldavids@nwu.edu> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg3163$foo@default> Subject: Venus fly trap closure
I spoke a bit hastily on the mechanism of VFT closure. It is more complex
than simple turgor pressure changes, although such changes certainly
provide the major force for the movement. Here is a response from Dr.
Wayne Fagerberg, one of the very few experts on the subject:
"THE EXACT NATURE OF THE CLOSING MECHANISM HAS NOT BEEN WORKED
OUT AS FAR AS I KNOW BUT MAY INVOLVE CELL EXPANSION, CELL
SLIDING AND TURGOR COLLAPSE. THE FAST CLOSURE INVOLVES MOSTLY
THE CELLS AT THE MARGIN OF THE TRAP ALTHO THERE IS SOME MOVEMENT
OF CELLS AT THE BASE. THE FULL CLOSURE IS QUITE COMPLEX SO I WILL
GIVE YOU REFERENCES TO 2 OF OUR PAPERS FOR THE DETAILS:
Fagerberg,W.R. and D. Allain. 1991. A quantitative study of tissue dynamics
during closure in the traps of Venus's flytrap Dionaea muscipula (Ellis).
American Journal of Botany. 78: 647-657.
Fagerberg,Wayne R. 1992. Insectivorous Plants. McGraw-Hill Yearbook of
science and technology. McGraw-Hill, Inc. New York. p. 211-213.
Fagerberg, W.R. and D.G. Howe. 1996. A quantitative study of tissue
dynamics in Venus's flytrap Dionaea muscipula (Ellis). II. Trap
reopening. American Journal of Botany 83: 836-842. "
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The fact that some of the cells involved enlarge may have led to the belief
that cell growth was involved, but this enlargement is caused by a change
in turgor pressure, not growth. It would appear that this enlargement is
allowed in part by cell wall loosening caused by acidification of the cell
cytoplasm (caused by an increase in hydrogen ions). Turgor pressure, the
force behind the enlargement, increases when ions (charged molecules or
atoms) are caused to move into the cell and water flows in to balance the
osmotic pressure with that outside. According to the 1992 McGraw-Hill
Yearbook article, "It is the differential enlargement of specific motor
tissues within the trap that powers closure." The email above suggests
that cell collapse (loss of turgor pressure) may also play a
role. Apparently there are three stages to the closure and different
mechanisms may govern or predominate in each one. If anybody does not have
access to the McGraw Hill Yearbook article and is interested in seeing it,
I could send an efax to you. It is a good summary about what was known up
to that time and I don't believe a great deal has been done since. I don't
have ready access to the cited issues of the American Journal of Botany.
Lloyd
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