Molecular electronics in pinnae of Mimosa pudica

Bioelectrochemical circuits operate in all plants including the sensitive plant Mimosa pudica Linn. The activation of biologically closed circuits with voltage gated ion channels can lead to various mechanical, hydrodynamical, physiological, biochemical and biophysical responses. Here the biologically closed electrochemical circuit in pinnae of Mimosa pudica is analyzed using the charged capacitor method for electrostimulation at different voltages. Also the equivalent electrical scheme of electrical signal transduction inside the plant''s pinna is evaluated. These circuits remain linear at small potentials not exceeding 0.5 V. At higher potentials the circuits become strongly non-linear pointing to the opening of ion channels in plant tissues. Changing the polarity of electrodes leads to a strong rectification effect and to different kinetics of a capacitor. These effects can be caused by a redistribution of K⁺, Cl⁻, Ca²⁺ and H⁺ ions through voltage gated ion channels. The electrical properties of Mimosa pudica were investigated and equivalent electrical circuits within the pinnae were proposed to explain the experimental data.Key words: electrophysiology, plant cell electrostimulation, charged capacitor method, electrical circuits, electrical signaling, Mimosa pudica     

Contractile Characteristics of Mimosa pudica L

The force-velocity characteristics of the primary pulvinus of Mimosa pudica have been determined using a new polytonic measurement technique. The contractile characteristics were determined from a modified form of Hill's equation (Hill, A. V. 1938. Proc. Roy. Soc. London B126: 136-195) describing the physiological contractile behavior of animal muscle. The values of the resulting Hill's constants were found to be remarkably similar to those of intact animal muscle and reconstituted contractile collagen.     

Mechanical and electrical anisotropy in Mimosa pudica pulvini

Thigmonastic or seismonastic movements in Mimosa pudica, such as the response to touch, appear to be regulated by electrical, hydrodynamical and chemical signal transduction. The pulvinus of Mimosa pudica shows elastic properties, and we found that electrically or mechanically induced movements of the petiole were accompanied by a change of the pulvinus shape. As the petiole falls, the volume of the lower part of the pulvinus decreases and the volume of the upper part increases due to the redistribution of water between the upper and lower parts of the pulvinus. This hydroelastic process is reversible. During the relaxation of the petiole, the volume of the lower part of the pulvinus increases and the volume of the upper part decreases. Redistribution of ions between the upper and lower parts of a pulvinus causes fast transport of water through aquaporins and causes a fast change in the volume of the motor cells. Here, the biologically closed electrochemical circuits in electrically and mechanically anisotropic pulvini of Mimosa pudica are analyzed using the charged capacitor method for electrostimulation at different voltages. Changing the polarity of electrodes leads to a strong rectification effect in a pulvinus and to different kinetics of a capacitor discharge if the applied initial voltage is 0.5 V or higher. The electrical properties of Mimosa pudica''s pulvini were investigated and the equivalent electrical circuit within the pulvinus was proposed to explain the experimental data. The detailed mechanism of seismonastic movements in Mimosa pudica is discussed.Key words: electrophysiology, plant electrostimulation, pulvinus, Mimosa pudica, charged capacitor method, electrical circuits, ion channels     

Ionic Fluxes from Pulvinar Cells during the Rapid Movement of Mimosa pudica L.

K^$ and Cl^- contents and the ratio of the fresh weight to dryweight of the abaxial halves of the main pulvini of Mimosa decreasedafter movement, but changes in the adaxial halves were not clear.Another experimental result showed that the solution ejectedfrom the pulvinar cells flowed both toward the stem and thepetiole. These transferred ions and water may flow back to thepulvinar cells during recovery. (Received January 30, 1984; Accepted June 12, 1984)     

Mimosa pudica,Dionaea muscipula and anesthetics

Some studies showed that anesthetics reduce the response of physical stimuli in Mimosa pudica and in Venus Flytrap (Dionaea muscipula), peculiar plants that have the ability to respond to touch stimuli. In this research we tested the effects of ketamine, lidocaine, diethyl ether, and amlodipine on the movements of Mimosa pudica and Venus Flytrap. With a literature review, we tried to bring elements to theorize about the interaction of these substances with these plants. The angular displacement in Mimosa´s petiole and in Dionaea leaves is what was measured to compare the drugs group with control groups.     

Rapid hydropassive opening and subsequent active stomatal closure follow heat-induced electrical signals in Mimosa pudica

In Mimosa pudica L., heat stimulation triggers leaflet folding in local, neighbouring and distant leaves. Stomatal movements were observed microscopically during this folding reaction and electrical potentials, chlorophyll fluorescence, and leaf CO(2)/H(2)O-gas exchange were measured simultaneously. Upon heat stimulation of a neighbouring pinna, epidermal cells depolarized and the stomata began a rapid and pronounced transient opening response, leading to an approximately 2-fold increase of stomatal aperture within 60 s. At the same time, net CO(2) exchange showed a pronounced transient decrease, which was followed by a similar drop in photochemical quantum yield at photosystem (PS) II. Subsequently, CO(2)-gas exchange and photochemical quantum yield recovered and stomata closed partly or completely. The transient and fast stomatal opening response is interpreted as a hydropassive stomatal movement caused by a sudden loss of epidermal turgor. Thus, epidermal cells appear to respond in a similar manner to heat-induced signals as the pulvinar extensor cells. The subsequent closing of the stomata confirms earlier reports that stomatal movements can be induced by electrical signals. The substantial delay (several minutes) of guard cell turgor loss compared with the immediate response of the extensor and epidermal cells suggests a different, less direct mechanism for transmission of the propagating signal to the guard cells.     

On the Phloem of Mimosa pudica L.

The phloem of Mimosa pudica L. was examined in view of somereports that the sieve elements in this plant show featuresnot previously described for these cells in Leguminosae. Inthe present study only a usual dicotyledonous type of sieveelement was recognized. The sieve elements pass through stagesof differentiation involving development and dispersal of P-proteinbodies, disintegration of nuclei, and appearance of plastidsstoring a starch staining red with iodine. Callose occurs onthe transverse or moderately oblique sieve plates. The phloemcontains secretory cells. They are wide and long and have transverseor more or less inclined end walls. In younger cells the endwall bears in the centre a conspicuous pit to which the protoplastsof the superimposed cells are firmly attached. In many oldercells the pit region is replaced by a perforation so that thecontents of superimposed cells may be completely merged. Itremains to be determined whether the perforation is presentin an intact plant or results from a rupture during sampling.The secretory cells accumulate material that gives a positivetest for carbohydrates and a negative test for proteins.     

Evaluation of Mimosa pudica Seed Mucilage as Sustained-Release Excipient

The present study was conducted to investigate the sustained-release properties of Mimosa pudica seed mucilage. Matrix tablets of diclofenac sodium containing different proportions of mucilage and dibasic calcium phosphate as diluent were formulated by wet granulation method. The tablets had uniform physical appearance, average weight, drug content, and adequate hardness. The results of in vitro release conducted using USP type II dissolution rate apparatus, in a dissolution media comprising of 900 mL of 0.1 N HCl for 2 h followed by phosphate buffer (pH 6.8) for 24 h at 37°C and 50 rpm, revealed that as the proportion of mucilage in the matrix was increased there was a corresponding decrease in the release of drug. Further, the matrix tablets were found to release the drug following Higuchi square root release kinetics, with the mechanism of release being diffusion for tablets containing higher proportion of mucilage and a combination of matrix erosion and diffusion for tablets containing smaller proportion of mucilage. The swelling and erosion studies revealed that, as the proportion of mucilage in tablets was increased, there was a corresponding increase in percent swelling and a decrease in percent erosion of tablets. The SEM photomicrographs showed gelling structures in tablets containing higher percentage of mucilage, while both pores and gelling structures were present on the surface of tablets containing smaller proportion of mucilage and commercial formulation. On comparative evaluation, the dissolution profile from formulation containing mucilage to drug in the proportion of 1:40 was found to be similar to the commercial sustained-release formulation of diclofenac.     

Light- and Auxin-Induced Leaflet Opening in Detached Pinnae of Mimosa pudica

Leaflet pairs from detached pinnae of Mimosa pudica opened afterthe pinnae had been irradiated with light (2 W·m^–2)of 726 or 403 nm, whereas they remained almost closed with lightof 585 or 656 nm. Light-induced leaflet opening was observedonly in the daytime, from 6:00 to 16:00. Application of IAAat more than 30 µg/ml to the cut end of the pinna rachisesmade the leaflets open even in darkness with almost constantlag times of about 100 min which were independent of the concentration.NAA and 2,4-D also made the leaflet open at lower concentrationsthan IAA. Auxin-induced leaflet opening showed diurnal variation.Application of IAA for 2 to 6 min, depending on the concentration,was enough to open the leaflets. Autoradiography showed thatIAA was transferred from the cut end of a rachis throughouta pinna within 4 min. ¹Present address: Biological Institute, Faculty of Science,Kobe University, Kobe 657, Japan. (Received September 24, 1982; Accepted March 4, 1983)     

Memory elements in the electrical network of Mimosa pudica L.

The fourth basic circuit element, a memristor, is a resistor with memory that was postulated by Chua in 1971. Here we found that memristors exist in vivo. The electrostimulation of the Mimosa pudica by bipolar sinusoidal or triangle periodic waves induce electrical responses with fingerprints of memristors. Uncouplers carbonylcyanide-3-chlorophenylhydrazone and carbonylcyanide-4-trifluoromethoxy-phenyl hydrazone decrease the amplitude of electrical responses at low and high frequencies of bipolar sinusoidal or triangle periodic electrostimulating waves. Memristive behavior of an electrical network in the Mimosa pudica is linked to the properties of voltage gated ion channels: the channel blocker TEACl reduces the electric response to a conventional resistor. Our results demonstrate that a voltage gated K⁺ channel in the excitable tissue of plants has properties of a memristor. The discovery of memristors in plants creates a new direction in the modeling and understanding of electrical phenomena in plants.     

Change in the actin cytoskeleton during seismonastic movement of Mimosa pudica

The seismonastic movement of Mimosa pudica is triggered by a sudden loss of turgor pressure. In the present study, we compared the cell cytoskeleton by immunofluorescence analysis before and after movement, and the effects of actin- and microtubule-targeted drugs were examined by injecting them into the cut pulvinus. We found that fragmentation of actin filaments and microtubules occurs during bending, although the actin cytoskeleton, but not the microtubules, was involved in regulation of the movement. Transmission electron microscopy revealed that actin cables became loose after the bending. We injected phosphatase inhibitors into the severed pulvinus to examine the effects of such inhibitors on the actin cytoskeleton. We found that changes in actin isoforms, fragmentation of actin filaments and the bending movement were all inhibited after injection of a tyrosine phosphatase inhibitor. We thus propose that the phosphorylation status of actin at tyrosine residues affects the dynamic reorganization of actin filaments and causes seismonastic movement.     

Cupriavidus taiwanensis bacteroids in Mimosa pudica Indeterminate nodules are not terminally differentiated

The beta-rhizobium Cupriavidus taiwanensis forms indeterminate nodules on Mimosa pudica. C. taiwanensis bacteroids resemble free-living bacteria in terms of genomic DNA content, cell size, membrane permeability, and viability, in contrast to bacteroids in indeterminate nodules of the galegoid clade. Bacteroid differentiation is thus unrelated to nodule ontogeny.     

Calmodulin Implication in the Glycine Uptake by Mimosa pudica Pulvinar Cells

Previous experiments have evidenced that calcium is functionallyimplicated in glycine uptake by pulvinar motor cells of Mimosapudica L. The present data show that compounds having anticalmodulinproperties, compound 48/80 and the sulfonamide W-7, inhibitedthe amino acid uptake suggesting that a step in this processmay be regulated by calmodulin. H⁺ excretion by the tissuesand transmembrane potential of the motor cells were not modifiedby these compounds, thus showing that the inhibition of aminoacid uptake was not an indirect consequence of a decrease inthe proton motive force energizing the glycine H⁺ cotransport.Therefore, the data argue for the implication of calmodulinin a specific Ca²⁺-regulated reaction. (Received March 2, 1994; Accepted May 6, 1994)