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Journal of Plant Physiology 168 (2011) 109–120
Contents lists available at ScienceDirect
Journal of Plant Physiology
journal homepage: www.elsevier.de/jplph
Complete hunting cycle of Dionaea muscipula: Consecutive steps
and their electrical properties
Alexander G. Volkova,∗, Monique-Renée Pinnocka, Dennell C. Lowea,
Ma’Resha S. Gaya, Vladislav S. Markinb
aDepartment of Chemistry and Biochemistry, Oakwood University, 7000 Adventist Blvd., Huntsville, AL 35896, USA
bDepartment of Neurology, University of Texas, Southwestern Medical Center, Dallas, TX 75390-8813, USA
article info
Article history:
Received 19 April 2010
Received in revised form 17 June 2010
Accepted 17 June 2010
Keywords:
Charged capacitor method
Electrical circuits
Electrical signaling
Electrophysiology
Plant cell electrostimulation
Venus flytrap
abstract
The total hunting cycle of the Venus flytrap consists of five stages: 1. Open state →2. Closed state →3.
Locked state →4. Constriction and digestion →5. Semi-open state →1. Open state. The opening of the
trap after digestion consists of two steps: opening of the lobes, and changing of their curvature from
concave to convex shape. Uncouplers carbonylcyanide-4-trifluoromethoxyphenyl hydrazone (FCCP) and
carbonylcyanide-3-chlorophenylhydrazone (CCCP) inhibit the trap from opening for two weeks and
antracene-9-carboxylic acid inhibits the trap from constricting. Different stages of the hunting cycle
have different electrical characteristics. The biologically closed electrochemical circuits in the Venus fly-
trap are analyzed using the charged capacitor method. If the initial voltage applied to the Venus flytrap is
0.5 V or greater, changing the polarity of the electrodes between the midrib and one of the lobes results in
a rectification effect and in different kinetics of discharge capacitance. These effects can be caused by the
fast transport of ions through ion channels. The electrical properties of the Venus flytrap were investi-
gated and equivalent electrical circuits within the upper leaf were proposed to explain the experimental
data.
© 2010 Elsevier GmbH. All rights reserved.
Introduction
The response of the Venus flytrap (Dionaea muscipula)to
mechanical stimulation has been known for quite some time
(Brown, 1916; Burdon-Sanderson, 1873; Darwin, 1875; Lloyd,
1942). All plants react to mechanical stimuli (Volkov and Brown,
2006), but only certain plants with rapid and highly noticeable
touch-stimulus response mechanisms, such as the Venus flytrap
and Mimosa pudica L., have received much attention (Volkov et al.,
2010). The trap closure was investigated by electrical stimulation
between the lobes and midrib of the Venus flytrap (Markin et al.,
2008; Volkov et al., 2008a, 2009a). Time and speed of closing do not
depend upon the type of stimuli: both mechanically and electrically
stimulated traps close in 0.3 s (Volkov et al., 2007).
Abbreviations: A-9-C, anthracene-9-carboxylic acid; C, capacitance; CCCP,
carbonylcyanide-3-chlorophenylhydrazone; DPDT, double pole double throw
switch; FCCP, carbonylcyanide-4-trifluoromethoxyphenyl hydrazone; PXI, PCI
eXtensions for Instrumentation; Q, charge of capacitor; R, resistance; t, time; ,
the circuit time constant; TEACl, tetraethylammonium chloride; U, voltage; U0, the
initial voltage of a capacitor.
∗Corresponding author. Tel.: +1 256 726 7113; fax: +1 256 726 7113.
E-mail address: agvolkov@yahoo.com (A.G. Volkov).
Touching trigger hairs protruding from the upper epidermal
layer of the Venus flytrap’s leaves activates mechanosensitive ion
channels. As a result, receptor potentials are generated which in
turn induce a propagating action potential throughout the upper
leaf of the Venus flytrap (Benolken and Jacobson, 1970; Jacobson,
1965; Volkov et al., 2007, 2008a). A receptor potential always pre-
cedes an action potential and couples the mechanical stimulation
step to the action potential step of the preying sequence (Jacobson,
1965). A possible pathway of action potential propagation to the
midrib includes vascular bundles and plasmodesmata in the upper
leaf (Buchen et al., 1983; Ksenzhek and Volkov, 1998).
Upon closure, the cilia protruding from the edge of each lobe
form an interlocking wall that is impenetrable to all except the
smallest prey. The trap uses the double-trigger mechanism and
shuts when the prey touches its trigger hairs twice in succession
within a 25 s window of time. Partial closure allows the cilia to
overlap, however the lobes are still held slightly ajar. This partial
closure occurs in a fraction of a second, and several minutes may be
required for the lobes to come together fully. When prey is caught,
the lobes seal tightly and thus remain for 5–7 days, allowing diges-
tion to take place (Jaffe, 1973). The stalk and basal cells containing
lipid globules and the common wall between these two cells are
traversed by numerous plasmodesmata (Williams and Mozingo,
1971). Electron micrographs of the trigger hairs reveal three regions
0176-1617/$ – see front matter © 2010 Elsevier GmbH. All rights reserved.
doi:10.1016/j.jplph.2010.06.007
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110 A.G. Volkov et al. / Journal of Plant Physiology 168 (2011) 109–120
where the cells differ in size, shape, and cytoplasmic content. The
basal walls of the indentation cells contain many plasmodesmata.
Plasmodesmata found in anticlinal and podium cells pass through
constricted zones in the cell wall; there are numerous plasmodes-
mata in the peripheral podium cells (Mozingo et al., 1970).
The lobes of the Venus flytrap move because of changes in shape,
curvature, and volume of cells. In the case of the osmotic motor,
water flux and ion flux are linked to one another. If water follows
H+flux by osmosis, then the rate of flux will determine the rate of
volume change in the lobes. Rapid movement of each lobe requires
water cotransporters or contractile proteins (Morillon et al., 2001).
Water flux across biological membranes occurs as a passive dif-
fusion across the lipid bilayer (Volkov et al., 1997, 1998); it is also
facilitated by aquaporins, which may play a pivotal role in osmoreg-
ulation in both animals and plants. The rate of cellular movement
is determined by the water flux. This flux is induced by a rapid
change in osmotic pressure and is monitored by a fast and transient
opening of aquaporins. At the present time, the gating behavior of
aquaporins is poorly understood, but evidence is mounting that
phosphorylation, pH, and osmotic gradients can affect water chan-
nel activity (Tyerman et al., 2002).
The fast movement of the Venus flytrap has intrigued scientists
since it was first described by Darwin (1875), and since then it has
caused periodic bursts of research activity. Darwin was the first to
observe that the lobes of each trap are convex when held open and
concave when held shut. The underside of the lobes expands during
closure and the inner sides of the lobes increase upon reopening.
This model helps to explain the flipping action of “the most won-
derful plant” as described by Darwin (1875). By painting the surface
with dots, Darwin was able to prove that during the process of clos-
ing, the superficial layer of leaf cells contracts over the whole upper
surface.
The rapid trap closure of D. muscipula has been explained by a
loss of turgor in the upper epidermis or by a sudden acid-induced
wall loosening of motor cells. Another plausible explanation is
the expansion of the cell wall through acid growth (Williams and
Bennet, 1982). Several recent articles have linked trap closure with
a rapid decrease in pH; traps have been shown to close when
immersed in certain solutions, resulting in a decrease in pH to 4.5
and below. The low pH can activate enzymes that expand the lobes’
cell walls. Though action potentials are generated, leaves infiltrated
with neutral buffers at the pH above 4.5 do not close in response to
stimulation of their trigger hairs.
To close the trap, an electrical charge of 14 C can either be sub-
mitted as a single pulse, or be applied cumulatively as a sequence
of small charges over a short period of time (Volkov et al., 2008b).
Trap closure due to electrical stimuli obeys the all-or-nothing law;
there is no reaction due to stimuli under the required threshold,
and the speed of closing does not depend upon stimulus strength
above a particular threshold (Volkov et al., 2009a).
Uncouplers increase delay in trap closure and significantly
decrease the speed of closing. Ion channel blockers and aquaporin
inhibitors Hg2+, tetraethylammonium, and Zn2+ also decrease the
speed and increase the time of trap closure (Volkov et al., 2008c).
The possible mechanism of trap closure was developed by
Markin et al. (2008). When trigger hairs in the open trap receive
mechanical stimuli, a receptor potential is generated. Receptor
potentials generate action potentials, which can propagate in the
plasmodesmata of the plant to the midrib. Uncouplers and blockers
of fast anion and potassium channels can inhibit action poten-
tial propagation in the Venus flytrap. Once a threshold value of
the electrical excitation is attained, ATP hydrolysis and fast proton
transport begin, initiating aquaporin opening. Fast proton transport
induces transport of water and a change in turgor. The trap pos-
sesses curvature elasticity and consists of outer and inner hydraulic
layers where different hydrostatic pressures can build up. The open
state of the trap contains elastic energy accumulated due to the
hydrostatic pressure differences between the outer and inner lay-
ers of the lobe. Applied stimuli open water channels connecting the
two layers, water rushes from one hydraulic layer to another, and
the trap relaxes to the equilibrium configuration, its closed state.
The majority of publications concerning the Venus flytrap have
addressed the process of the trap closing, but few have discussed
the biochemistry of digestion and the secretory cycle of D. mus-
cipula (Fagerberg and Howe, 1996). The mechanism of the trap
opening is still unknown.
Affolter and Olivo (1975) monitored electrical signaling from the
Venus flytrap after live prey was captured. Stimulation of trigger
hairs after trap closure results in additional constricting of the trap.
Also, a greater force exerted by opposing lobes on one another is
observed (Burdon-Sanderson and Page, 1876).
Darwin (1875) found that mechanical stimulation of the trigger
hairs is not essential for digestion. The trap continues to narrow
and secrete digestive compounds whether the prey is alive or sub-
stituted by pieces of gelatin or meat. Scala et al. (1969) observed
phosphatase, proteinase, nuclease, and amylase in the digestive
secretion. Maximum secretion of the Venus flytrap enzymes occurs
within the first 5 days. A number of different enzymes are responsi-
ble for digestion and transport of amino acids. The adaxial surfaces
of the trap lobes possess an H+extrusion mechanism stimulated
by prolonged exposure to secretion elicitors during digestion (Rea,
1983). The acidity of the secretion may play an important role in
the facilitation of the carrier-mediated uptake of amino acids from
the trap cavity (Rea, 1984).
Lichtner and Williams (1977) found that in 50% of traps,
mechanical stimulation after closing leads to an additional narrow-
ing phase and secretion of viscous digestive substances with pH of
1.5–3.5 coating the interior of traps.
The trap is able to reopen after complete digestion and absorp-
tion of nutrients. Both opening and closing movements of the trap
are attributed to hydrostatic pressure changes in inner and outer
layers of lobes (Markin et al., 2008). In addition, the central layers
of parenchyma cells with their sustaining framework reflect the
elastic properties of the lobes (Stuhlman, 1948).
The goal of this study is the analysis of biologically closed elec-
trical circuits in the Venus flytrap using a new charged capacitor
method in the open, closed, and locked states of the trap, the eval-
uation of equivalent electrical scheme of the signal transduction
between a midrib and the lobes, and elucidation of additional steps
of lobes tightening before and during digestion after closing the
trap.
Materials and methods
Ag/AgCl electrodes were prepared (Volkov, 2000, 2006) from
Teflon-coated silver wires (A-M Systems). Following insertion of
the electrodes into each lobe and midrib, the traps closed due to
mechanical stimulation. We allowed the plants to rest until the
traps were completely open.
The Charge Injection Method was used for trap electrostimu-
lation between the midrib and lobes (Volkov et al., 2007, 2009b,
2010). A double pole double throw (DPDT) switch was used to con-
nect the known capacitor to the voltage source during charging, and
then to the plant during electrical stimulation. Since the charge of
the capacitor Qis related to the voltage source Vin the equation
Q=CV, we can precisely regulate the amount of charge using dif-
ferent capacitors and applying various voltages. By changing the
switch position, we can instantaneously connect the charged capac-
itor to the plant and induce an evoked response.
PCI eXtensions for Instrumentation (PXI) is a rugged PC-based
platform that offers a high-performance solution for measure-
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A.G. Volkov et al. / Journal of Plant Physiology 168 (2011) 109–120 111
Fig. 1. Photos of different stages of the trap closing stimulated by a cotton thread.
ment and automation systems. A NI-PXI-4071 digital multimeter
(National Instruments) connected to 0.2 mm thick nonpolarizable
Ag/AgCl electrodes was used to record the digital data. A NI-PXI-
4110 DC Power Supply (National Instruments) was the voltage
source for capacitor charging.
Mechanical stimulation was performed using a cotton thread to
gently touch one or two of the six trigger hairs inside the upper leaf
of the Venus flytrap. The thread was immediately removed before
the leaves closed.
Plants were fed a 5 mm×5mm×5mm cube of 4% (w/v) gelatin
and induced to close by stimulating the trigger hairs of the Venus
flytrap, as was suggested by Jaffe (1973).
Carbonylcyanide-3-chlorophenylhydrazone (CCCP); gelatin;
BaCl2; HgCl2; ZnCl2; carbonylcyanide-4-trifluoromethoxyphenyl
hydrazone (FCCP); and tetraethylammonium chloride (TEACl)
were obtained from Fluka (New York). Anthracene-9-
carboxylic acid (A-9-C) was purchased from TCI (Tokyo,
Japan).
Fig. 2. Photos of different stages of the trap closing, locking, and constricting induced by a piece of gelatin.
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Fig. 3. Photos of different stages of the trap closing by electrostimulation of D. muscipula (15 C, 1.5 V) using two Ag/AgCl electrodes located in a midrib (+) and in one of the
lobes (−).
A photo camera Nikon DX40DX with AF-S Micro Nikkor 105 mm
1:2.8 G ED VR lens (Nikon, USA) was used for the photography
of the Venus flytrap. Digital video recorders, Sony DCR-HC36 and
Sony HDR-XR500, were used to monitor the Venus flytraps and to
collect digital images, which were analyzed frame by frame. The
NTSC format consists of 30 interlaced frames of video per second,
which represents the maximum sampling frequency of parameters
extracted from the video stream.
Fifty bulbs of Dionaea muscipula (Venus flytrap) were purchased
for this experimental work from Fly-Trap Farm (Supply, North Car-
olina) and grown in a well drained peat moss in plastic pots at
22 ◦C with a 12:12 h light:dark photoperiod. The soil was treated
with distilled water. Irradiance was 700 E/m2s. All experiments
were performed on healthy adult specimens.
Results
Closing and tightening of the trap
Fig. 1 shows closing of the trap by mechanical stimulation using
a cotton thread. When thinking about mechanics of the trap clos-
ing, it might be tempting to compare the open trap with an open
book. If an insect sits on the page, one can catch it (actually squash
it) by quickly closing the book. This is not the case in the Venus fly-
trap hunting. In hunting with a book, the angle between the open
pages quickly changes from a certain initial value to zero with pages
remaining flat. In contrast to this in the Venus flytrap the angle
between the lobes at the middle of the midrib remains the same
during fast closing of the trap (Fagerberg and Allain, 1991; and our
observations – not shown). The Venus flytrap actually hugs the prey
quickly building the cage around it. This happens by bending the
lobes. The curvature of the lobes changes during closing of the trap.
The trap in the completely open state is convex and in the process
of closing, digestion, and opening has a concave configuration. The
trap changes from a convex to a concave shape (Fig. 3) in 100 ms.
There is a very small tightening of lobes during the first 5 min. Cilia
on the rims of the lobes bend over and lock the edges. The trap can
stay in such a position for a few hours before opening if the prey is
too small for digesting.
Fig. 2 shows different shapes of the Venus flytrap upper leaf
after a piece of a gelatin was put into the trap. In less than one s,
the open trap closes and locks in a few minutes (Fig. 2). The dis-
tance between the centers of lobes decreases during tightening of
the trap and digestion of a gelatin. After the lobes close, the trap
should be locked when cilia, finger-like protrusions, bend around
Fig. 4. Photo of the upper leaf of the Venus flytrap. Veins between the midrib and
cilia are shown.
the edges and overlap them. We call this third phase the locked
state. Next, the lobes flatten, constrict the prey, and seal the mar-
gins as a watertight chamber and digestion begins (Fig. 2). During
digestion, cilia from one lobe overlap the edges perpendicular to
lobes as cilia from another lobe stand up parallel to this lobe (Fig. 2).
This effect might be caused by a small difference in turgor between
constricted lobes. The trap starts to open after one week of diges-
tion; a day subsequent to it will be open with the convex shape
characteristic to the lobes.
Fig. 3 shows locking after closing the trap by electrostimulation
using the charged capacitor method. The trap closing has exactly
the same closing kinetics as in the case of a mechanical stimulation
of trigger hairs in the trap.
Fig. 4 shows veins between the midrib and cilia, which can play
an important role in water and ion transport during the trap closing,
sealing, digestion and opening.
Fig. 5 shows the kinetics of the trap closing after mechanostim-
ulation of a trigger hairs without a prey (Fig. 5a), electrostimulation
by 15 C charge using two Ag/AgCl electrodes located in a midrib
(+) and in one of the lobes (−)(Fig. 5b), and stimulation by a piece
of a gelatin as a prey (Fig. 5c). Traps closed in less than 1 s after
mechanical or electrical stimulation (Fig. 5a and b), but after the
tightening of the lobes, which takes place during 4–5 min, traps
can stay in this state for hours. We measured distance dbetween
the middle of the lobes outside the trap during the process of trap
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A.G. Volkov et al. / Journal of Plant Physiology 168 (2011) 109–120 113
Fig. 5. Kinetics of the trap closing after mechanostimulation of a trigger hairs (a); electrostimulation by 15 C charge using two Ag/AgCl electrodes located in a midrib (+)
and in one of the lobes (−) (b); and stimulation by a piece of a gelatin (c).
Fig. 6. Kinetics of the trap closing after electrostimulation by 15 C charge using
two Ag/AgCl electrodes located in a midrib (+) and in one of the lobes (−) and lobes
constricting after 1 s electrostimulation.
closing. Fig. 5c shows that if the trap is closed by a piece of gelatin,
there is additional slow kinetics of lobe constricting during a few
days of gelatin digestion.
Fig. 6 shows that if after closing the trap by electrical discharge
we submit an additional charge from the capacitor (the arrow,
Fig. 6), the significant and fast constricting of the lobes takes place
during 15 min. This tightening occurs about 200 times faster than in
the presence of a gelatin, probably because there is no mechanical
resistance from the prey inside the trap (Figs. 5c and 6).
The trap opening
The trap can be closed by electrostimulation of D. muscipula
(15 C, 1.5 V) using two Ag/AgCl electrodes located in a midrib (+)
and in one of the lobes (−)(Fig. 7a). In that case the trap opens in
24 h (Fig. 7b and c), but transformation from the concave to convex
shape (Fig. 7d) needs an additional 20 h. We tried to open the closed
trap by applying an electrical stimulus of opposite polarity. How-
ever, changing the polarity of electrodes and increasing the charge
up to 300 C did not result in the opening of the trap.
Inhibition of the trap opening
Earlier, we found that ion and water channel blockers such as
HgCl2, TEACl, ZnCl2, BaCl2, as well as uncouplers CCCP, FCCP, 2,4-
dinitrophenol, and pentachlorophenol decrease speed and increase
time of the trap closing (Volkov et al., 2008c). Blockers of ion
channels and uncouplers inhibit electrical signal transduction
in the Venus flytrap. Glycol-bis(2-aminoethylether)-N,N,N,N-
tetraacetic acid, A-9-C, neomycin, ruthenium red, lanthanum ions,
ethylene glycol-bis(-aminoethylether)-N,N,N,N-tetraacetic acid,
and NaN3, all inhibit the excitability of the Venus flytrap, which
indicates that ion channels are responsible for propagation of
action potentials. Uncouplers, which are soluble in both water
and lipid phases, permeate the lipid phase of a membrane by
diffusion and transfer protons across the membrane, thus elim-
inating the proton concentration gradient and/or a membrane
potential. Uncouplers create proton conductivity and block co-
transport of amino acids. Control plants were exposed to 10 mM
of KCl or CaCl2and no inhibitory effects of these salts on the
trap closure were found. Usually, concentration of salts in water
from lakes and ponds is much higher and varies from 100 mg/L
to 400 mg/L. Water from lakes, ponds, and rivers is the tradi-
tional source of water for the Venus flytrap in natural habitat
and in vivo.
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Fig. 7. The trap opening after electrostimulation of D. muscipula (15 C, 1.5 V) using two Ag/AgCl electrodes located in a midrib (+) and in one of the lobes (−).
We applied 20 L of one of the inhibitors to the midrib of the
Venus flytrap before the trap was closed by the addition of a small
piece of gelatin into the trap. Strong inhibition of the trap opening
was found in the Venus flytraps treated by 5 mM BaCl2,10МCCCP
or FCCP during 14 days after traps closing. Inhibitors of aquaporins
1 mM HgCl2, 10 mM TEACl and ZnCl2also showed some delaying in
the trap opening. 10 mM A-9-C, inhibitor of anion channels, showed
inhibition of the trap constricting. The Venus flytrap absorbs chem-
Fig. 8. Electrical discharge in the open trap of D. muscipula between electrodes located in a lobe (−a, b; + c, d) and a midrib (+ a, b; −c, d) connected to charged 1.0 F
capacitor and NI-PXI-4071 digital multimeter. The length of the midrib was 2 cm. These results were reproduced seven times on different Venus flytrap plants.
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A.G. Volkov et al. / Journal of Plant Physiology 168 (2011) 109–120 115
Fig. 9. Time dependence of voltage differences (a and b) during electrical discharge
in the trap between electrodes of different polarities connected to 1.0 F charged
capacitor.
ical compounds through leaf-surface glands by energy dependent
processes (Lloyd, 1942). There is the H+-co-transport of amino
acids by the digestive glands of the Venus flytrap (Rea, 1983, 1984).
Uncouplers can work as a shunt of H+-pump during the digestion
process or transport of amino acids.
Electrical circuits in the trap of D. muscipula
We used the Charged Capacitor Method to estimate with high
precision the amount of electrical energy necessary to induce a
response. A DPDT switch was used to connect the known capac-
itor to the NI-PXI-4110 DC Power Supply during charging, and then
to the plant during plant stimulation. Since the charge of a capacitor
Qconnected to the voltage source Uis Q=CU, we can precisely reg-
ulate the amount of charge using different capacitors and applying
various voltages. By changing the switch position, we can instan-
taneously connect the charged capacitor to the plant and induce
a response. If a capacitor of capacitance Cis discharged through a
resistor R, the capacitor voltage Uis then
UC(t)=U0×exp −t
,where =RC (1)
and
Q=CU0e−t/ =Q0e−t/ (2)
where Q0=CU
0is the initial charge on the capacitor. The capacitive
time constant RC governs the discharging process. At t==RC the
capacitor charge is reduced to CU0e−1, which is about 37% of its ini-
tial charge. For Rin ohms and Cin farads, the time constant RC is in
seconds. The voltage across the capacitor decreases exponentially
with the same time constant from the initial value U0to zero.
For electrostimulated closing of the trap both threshold volt-
age (1.5 V) and charge (9F) are required (Volkov et al., 2008a,b,c,
2009a,b). To avoid the trap closing, we selected 1 F capacitor for
our experiments, because if this capacitor is completely discharged,
only a small noninvasive charge up to 1.5 V ×1F = 1.5 C will be
transmitted to the Venus flytrap.
Fig. 8 shows time dependence of 1 F capacitor discharge
between Ag/AgCl electrodes located in the midrib and in a lobe at
different voltages from 0.05 V to 1.50 V when the trap is completely
open. Kinetics of the capacitor discharge depends upon the polarity
of the electrodes (Fig. 8a and c). If a positive electrode is located in
the midrib, the discharge is faster if the initial voltage is 0.5 V or
higher. This can be caused by a rectification effect due to openings
Fig. 10. Dependence of voltage on the 1.0 F capacitor during a discharge between electrodes located in a lobe (−a, b; + c, d) and a midrib (+ a, b; −c, d) connected to charged
capacitor and NI-PXI-4071 digital multimeter in the Venus flytrap on time. The trap was closed by a gelatin immediately before measurements of the capacitor discharge.
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116 A.G. Volkov et al. / Journal of Plant Physiology 168 (2011) 109–120
of ion channels. At low initial potentials of 100 mV or less, the kinet-
ics of the capacitor discharge does not depend upon the polarity of
electrodes. Differences between the capacitor discharge at differ-
ent voltages and polarities of two Ag/AgCl electrodes, located in
the midrib and a lobe, are shown in Fig. 9 which is a sum of exper-
imental results shown in Fig. 8a and c. At low potentials, the time
dependencies of the capacitor discharges are linear in logarithmic
coordinates (Fig. 8b and d) according to Eq. (1). At 0.5 V or higher
voltages there is a deviation from linear logarithmic dependence
(Fig. 8b and d), which cannot be described by Eq. (1).
Fig. 10 shows time dependence of 1 F capacitor discharge
between Ag/AgCl electrodes located in the midrib and in a lobe
at different voltages from 0.05 V to 1.50 V immediately after the
trap closing by insertion of small piece of gelatin in the trap. Again,
kinetics of the capacitor discharge depends upon the polarity of
electrodes (Fig. 10a and c). If a positive electrode is located in the
midrib, the discharge is faster if the initial voltage is 0.5 V or higher.
Fig. 11, which is the sum of experimental dependencies in Fig. 10a
and c, shows the difference between the capacitor discharge at
different voltages and polarities of electrodes.
After trap closing, the tightening of lobes begins. During diges-
tion of gelatin by the Venus flytrap, kinetics of capacitor discharge
after 24 h (Fig. 12), 48 h (Fig. 13), and 110 h does not depend more
so upon polarity of electrodes. Meaning that on this stage the ion
channels in the midrib are closed. ATP hydrolyzed in the midrib
during closing, (Jaffe, 1973) and the proton pump loses its activity
after tightening.
After a week of gelatin digestion, the trap begins to open. In
the beginning of this process, kinetics of the capacitor discharge
does not depend on polarity of electrodes (Fig. 15). The trap opens
in about a day, but the opening is not complete and the lobes have
concave shape. The transition from the concave to the convex shape
takes an additional day, signifying complete opening of the trap.
Fig. 11. Time dependence of voltage differences (a and b) during electrical discharge
in the trap between electrodes of different polarities connected to 1.0 F charged
capacitor.
Results shown in Figs. 8 and 13–15 can be also presented in
normalized coordinates (Fig. 16). Normalized coordinates were
obtained by dividing voltage by initial value. If the trap is com-
pletely open, the discharge of the capacitor is faster when the initial
voltage is 1.0 V or higher (Fig. 16a). This effect can be caused by
opening of ion channels. When the trap is closed and digests the
gelatin, discharge curves overlap because ion channels between a
midrib and lobes are in closed state (Fig. 16b–d).
Discussion
The closing process essentially involves a change of the leaf’s
geometry. The upper leaf is convex in the open state and con-
cave in its closed position. Trap closure is believed to represent
nonmuscular movement based on hydraulics and mechanics. The
Fig. 12. Dependence of voltage on the 1.0 F capacitor during a discharge between electrodes located in a lobe (−a, b; + c, d) and a midrib (+ a, b; −c, d) connected to charged
capacitor and NI-PXI-4071 digital multimeter in the Venus flytrap on time. The trap was closed by a gelatin 24 h before measurements of the capacitor discharge.
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A.G. Volkov et al. / Journal of Plant Physiology 168 (2011) 109–120 117
Fig. 13. Dependence of voltage on the 1.0 F capacitor during a discharge between electrodes located in a lobe (−a, b; + c, d) and a midrib (+ a, b; −c, d) connected to charged
capacitor and NI-PXI-4071 digital multimeter in the Venus flytrap on time. The trap was closed by a gelatin 48 h before measurements of the capacitor discharge.
Fig. 14. Dependence of voltage on the 1.0 F capacitor during a discharge between electrodes located in a lobe (−a, b; + c, d) and a midrib (+ a, b; −c, d) connected to charged
capacitor and NI-PXI-4071 digital multimeter in the Venus flytrap on time. The trap was closed by a gelatin 110 h before measurements of the capacitor discharge.
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118 A.G. Volkov et al. / Journal of Plant Physiology 168 (2011) 109–120
Fig. 15. Dependence of voltage on the 1.0 F capacitor during a discharge between electrodes located in a lobe (−a, b; + c, d) and a midrib (+ a, b; −c, d) of the Venus
flytrap connected to charged capacitor and NI-PXI-4071 digital multimeter in the Venus flytrap on time. The trap was closed by a gelatin 8 days before measurements of the
capacitor discharge. The trap opening started just before electrical discharge and 1 day before transformation of a concave to a convex shape of the trap.
Fig. 16. Normalized presentation of time dependencies of electrical discharge in the Venus flytrap between Ag/AgCl electrodes in a midrib and a lobe connected to 1 F
charged capacitor; experimental data was taken (a): from Fig. 8, (b): from Fig. 13, (c): from Fig. 14, and (d): from Fig. 15 U0is the initial capacitor voltage.
Author's personal copy
A.G. Volkov et al. / Journal of Plant Physiology 168 (2011) 109–120 119
Fig. 17. The schematic representation of the trap closing and opening.
nastic movement in various plants involves a large internal pres-
sure (turgor). It is quite likely that these movements are driven by
differential turgor that is actively regulated by the plants. Trap clo-
sure occurs via quick changes in the curvature of each lobe rather
than by movement of the leaf as a whole. The cell walls of the upper
and lower epidermis and adjacent mesophyll feature a preferential
microfibril orientation in the direction of the applied stress. These
anatomical features were selected as the basis of the hydroelastic
curvature model presented above.
The driving force of the closing process is most likely the elastic
curvature energy stored and locked in the leaves due to a pressure
difference between the upper and lower layers of the leaf (Markin
et al., 2008). The open state of the trap contains high elastic energy
accumulated due to the hydrostatic pressure difference between
the hydraulic layers of the lobe. The trigger signal opens the water
pores between these layers and the fluid transfers from the upper
to the lower layer. The leaf relaxes to its equilibrium state, corre-
sponding to the closed configuration. This process develops very
quickly; we found that it takes a fraction of a second. Markin et al.
(2008) derived equations describing this system based on elastic-
ity Hamiltonian and found kinetics of closing process. However, the
trap closing stage does not exhaust the whole process of catching
Fig. 18. Equivalent electrical circuits: E– battery, C1– external charged capacitor, C2,
Cm– membrane capacitance, R1– resistance in a lobe, R2,Rm– membrane resistance;
D– diode as a model of a voltage gated ion channel, DMM – digital multimeter, S –
electrical charge or voltage sensor and switch.
and digesting insects by the Venus flytrap. We found that the dis-
tance between the rims of lobes after closing is not equal to zero,
but remains in range of 15–20% of the initial distance between these
edges (Volkov et al., 2008a,b, 2009a,b). After closing, the trap should
be locked when cilia, finger-like protrusions, bend around the edges
and tighten the gap. We call this third phase the locked state. After
that the lobes flatten, depress the prey and the digestion process
begins. The trap starts to open after 5–7 days of digestion and after
a day it will be open with the concave shape of lobes. Additionally,
another day is required for changing of the trap from a concave to
a convex shape and the trap will be completely open. Therefore,
the total hunting cycle of the Venus flytrap consists of five stages:
1. Open state →2. Closed state →3. Locked state →4. Constriction
and digestion →5. Semi-open state →1. Open state.
Fig. 17 shows the sequence of events during the trap closing and
opening. The completely open trap with convex shape can be closed
by a prey, electrical or mechanical stimulation in less than 1 s. If the
trap is not completely open and has a concave shape, the trap clos-
ing will be slow. Locking and small tightening takes a few minutes.
If the prey was not captured, the trap will be subsequently open
and another day will be required for transition from the concave to
convex shape. If prey is captured by the Venus flytrap, constricting
and digesting takes at least 5 days and depends upon the size of a
prey. Partial opening of the trap takes place during 24 h and a trap
will be completely open the next day after a transition in shape.
Fig. 18 illustrates the equivalent electrical circuits in the trap
of the Venus flytrap. Fig. 18a corresponds to the passive electrical
circuits which can be described by Eq. (1).Fig. 18b shows the sim-
plest equivalent electrical circuit that can describe experimental
results presented in Figs. 9a and b and 10a and b.Fig. 18c presents
the equivalent electrical circuits describing experimental results
presented in Figs. 12–16.
Acknowledgments
This work was supported by the National Science Foundation
(Grant No. HRD0811507) and by Henry C. McBay Research Fellow-
ship (UNCF).
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