Dionée catch-fly

The Dionée catch-fly ( Dionaea muscipula ) is undoubtedly a carnivorous Plante, most known and emblématique. In 1763, Arthur Dobbs, then Governor of the North Carolina, drew for the first time the attention of the public and the European scientists to the plant. Around 1770, Carl von Linné, botanist Swedish, studied the plant and named it “Come flytrap” (“Venus catch-fly”) while taking as a starting point Venus, goddess of the love and the beauty in the Roman Mythologie. Nevertheless, one owes the valid description of the plant with Johh Ellis. The mechanism of capture of “Venus catch-fly” is amazing, and pushed Charles Darwin to be said dionée was “one of the most marvellous plants in the world”. The carnivority of dionée was shown, by Charles Darwin, only towards 1865.

It is a herbaceous plant of the family of the Droseraceae . It is the only species of the kind Dionaea . Its distribution is limited today to the North Carolina and the South Carolina on approximately: 45000 km ². It pushes on grounds low in Rock salt in the marshes Acide S (pH 3,5 to 4,9) and develops well in zones subjected to frequent fires.

The sheets of the Dionaea muscipula are laid out in rivet washer around a central axis, of a varying diameter from 10 to 15 centimetres with adult size, and are made up of a broad limb lower from 4 to 6 centimetres. The sheet is finished at its end by a kind of jaw made up of two lobes separate and connected by a thick central vein. With the periphery of the two lobes, one finds a series from 15 to 20 marginal teeth (" marginal trap spines" in English) slightly curved towards the interior. With the edge of the lobes and located on the inner face of the walls, the peripheral band comprises small sessile glands which secrete Glucides in order to attract the preys. The digestive surface (or intern surfaces) on which draw up three hairs laid out in triangle is in the center of the two lobes and is covered with a digestive gland multitude.

Origin of closing

The trap of Dionaea is closed again when one touches the interior of it. Consequently, that means that one of the elements of the trap is sensitive to any contact and actuates the mechanism of closing thereafter. Which is this element, the “release” of the process bringing to the movement of the two lobes? In fact the sensitive hairs are responsible for closing. Moreover, two stimulations of the trap are necessary so that this one is closed again, these last having to be carried out in a 20 seconds time interval. It is thought that this release in two times is a security measure which avoids with the trap of the useless closings, caused for example by the contact of dust, vegetable remains or especially of water drops.

As of 1873, measurements of potential were taken because a Electrical signal could a priori explain the speed of the closing of the trap. The fast closing of the trap is correlated with the release of at least two potentials of action (Pa): with each contact with the sensitive hair, a potential of action is released. But how is this potential of action generated?

In 1991, Fagerberg soaks the traps with a solution of ions Lanthane (La3+) and notes thereafter that the traps are anaesthetized and do not function even any more after two stimulations. However, a solution of ions lanthanum is strongly chelated by the channels of the ions Chlorure Cl. Indeed, the Lanthane is a Halogène: the Atome of Lanthane is thus very large and is blocked by the ionic Canal. This last is thus in its blocked turn. One can thus deduce that the potential of action which is emitted is in bond with channels chloride.

But before continuing, let us study the operation of an ionic channel: an ionic channel is a large protein made up of sub-units and located through a cellular membrane, forming a channel that ions, specific to each channel, borrow to enter and leave the cell. Under the effect of a stimulus, here mechanical stimulation, the structure of these sub-units is modified, opening a Pore over the entire length of the Protéine. When the ionic channels are closed, the ions cannot pass on both sides from the membrane. But when they are activated, each ionic channel becomes a passage opened by where the ions cross the cellular membrane.

In the case of the trap of Dionaea, the totality of the cells bathes in the interstitial liquid, container of many ions of various natures. However, the intracellular medium and this liquid are both rich person in ions, but with very different concentrations: the extracellular medium is concentrated much more in cations and more precisely in ions Calcium Ca2+ than the intracellular medium, him much richer in anions, here of the ions Chlorure Cl. In this situation, one says that the membrane is polarized. As we saw previously, the ionic channels calcium and chlorine open after stimulation of the trap: the loads carried by the extracellular and intracellular Milieu balance to obtain two neutral mediums, it is the Dépolarisation. It corresponds to an increase in the membrane potential (or rest) and makes the membrane less negative.

Another protein of the cellular membrane, the exchanging pump of ions, restores the electric charges on both sides membrane, it is the repolarization. To function, this protein uses the ATP (adenosine triphosphate), molecule used at all the organizations living to transport energy by providing ADP (Adénosine diphosphate) and an ion Phosphate.

The ionic channels specific to each nature of ion thus let pass from the Cations and of the Anions between the mediums will intra and extracellular after a stimulation until obtaining neutrality on both sides membrane. Thereafter, the exchanging pump of ions restores the initial order so that the process starts again. It is this variation, high-speed, of chemical and electric nature which forms the electrical signal, the loads thus being able to be propagated remotely

Before continuing, it is first of all necessary to define what is the potential of rest of a cell: it is a potential difference existing between the interior and the outside of the cell. Indeed, the interior of the cell is negative compared to an extracellular electrode of reference. Using an electrode on each side of the membrane, one measures a potential of rest around -70mV, standard value used. In the animal nervous cells, a brutal, fast and local modification of this potential of rest is able to be propagated and it is called the potential of action. One can thus suppose that the mechanism is completely comparable. Remain to include/understand how the signal is propagated, which occurs on arrival from the signal, that is what produces the movement, knowing that a plant does not have any muscular fabric. The cytological and physiological study largely exceeds our experimental competences and means. However, it remains us to observe and study all that occurs on a macroscopic scale.

Mechanism of closing

This disturbance of the potential of rest will then cause an electric wave which is propagated by the plasmic Membrane in all the cells of the trap. But how this electric wave is propagated within this one? The modification of the potential of rest of a first sensory cell thus causes a modification in the membranes of the close cells, creating a new potential of action and so on, until this electric wave arrives at the driving cells, responsible for the movement of the trap. This propagation is thus carried out thanks to a “chain reaction” where each cell intervenes, which makes it possible the electric wave not to lose in intensity.

The electric wave, arrived at the cells of the inner face of the trap, will allow the activation of a new enzyme intervening in the process of closing of the trap, the pump with protons. Once actuated, the pump, located at the level of the cellular membrane, will release from acidity in the form of H+ ions and will produce energy.

The pump with Proton S thus will transfer from the H+ ions and thus from the acidity of the interior of the cell of the inner face of the trap to the membrane of the cells of the external face of the trap. It also should be noted that this pump, although it is active after an electric stimulation, releases from the acid only after two stimulations. This thus explains the fact that one needs two stimulations for the level of the sensitive hairs so that the trap is closed again.

The H+ ions released by the pump with protons involve an acidification of the cells of the external face of the trap. Acidity then will act on the connections between fibers of the wall what causes a reduction in the ionic forces which are responsible for the assembly of the fibers (polymeric) which constitute the solid cellular wall around the cells. Consequently, the external walls will soften. The cells of the wall then will benefit from this softening of their “hull” to extend thanks to an entry from water in the intracellular medium and more precisely in the Vacuole. Is followed from there a resolidification of the walls of the lobe of the trap due to the lengthening of the cells which exert more pressure on this same wall (osmotic pressure), to the image of a faded sheet finding of water. The lobe of the trap is thus curved towards the interior, the cells of the external face of the lobe being lengthened than the cells of the inner face.

Dionée, mysterious plant by its appearance is also in its operation. Indeed, the “Venus's flytrap” still holds many secrecies: while passing a flame under the trap, this one is closed again. This experiment was discovered by chance by its author and it is not yet possible to connect the presence of a flame to the folding up of the trap using current knowledge. Proof, if it of it is need, that many other research is still necessary.

Cultivars

It is here about some cultivars but there are three times more, at least.

Akai Ryu = Red Dragon
“All Green”
“All Red” (" variety; ancienne" replaced by Royal Red or Akai Ryu)
“Bart Simpson”
“Chunky”
“Crossed Teeth”
“Cogs traps”
'Tooth of Requin" (different from “Shark Teeth”)
“Dutch”
“Filiformis”
“Fine Tooth X Red”
“Fused Tooth”
Various giant forms (South West Giant, Low Giant, Big Mouth…)
“Green Dragon”
“Jaws”
“Paradisia”
“Pink Come”
“Pompom” (false cultivar, three clones appeared separately then became normal)
“Red line”
“Red-Purple”
“Royal Red”
“Sawtooth” or “Dentata” (varieties considered as identical)
“Shark Teeth”
“White” (false cultivar, only one clone existed but is become again normal)
“Yellow”
“Red Piranha”

References

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