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Memristors in the electrical network of Aloe vera L. a

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Alexander G Volkov , Jada Reedus , Colee M Mitchell , Clayton Tucket , Victoria Fordea

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Tuckett , Maya I Volkova , Vladislav S. Markin & Leon Chua a

Department of Chemistry and Biochemistry; Oakwood University; Huntsville, AL USA

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Department of Neurology; University of Texas; Southwestern Medical Center; Dallas, TX USA c

Department of EECS; University of California, Berkeley; Berkeley CA USA Published online: 07 May 2014.

Click for updates To cite this article: Alexander G Volkov, Jada Reedus, Colee M Mitchell, Clayton Tucket, Victoria Forde-Tuckett, Maya I Volkova, Vladislav S. Markin & Leon Chua (2014) Memristors in the electrical network of Aloe vera L., Plant Signaling & Behavior, 9:7, e29056, DOI: 10.4161/psb.29056 To link to this article: http://dx.doi.org/10.4161/psb.29056

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Research Paper

Research Paper

Plant Signaling & Behavior 9, e29056; May; © 2014 Landes Bioscience

Memristors in the electrical network of Aloe vera L Alexander G Volkov1,*, Jada Reedus1, Colee M Mitchell1, Clayton Tucket1, Victoria Forde-Tuckett1, Maya I Volkova1, Vladislav S Markin2, and Leon Chua3 Department of Chemistry and Biochemistry; Oakwood University; Huntsville, AL USA; 2Department of Neurology; University of Texas; Southwestern Medical Center; Dallas, TX USA; 3Department of EECS; University of California, Berkeley; Berkeley CA USA

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Keywords: Electrostimulation, Memristor, Aloe vera, CAM plant, Plant electrophysiology

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Abbreviations: C, capacitance; CAM, crassulacean acid metabolism; CCCP, carbonylcyanide-3-chlorophenylhydrazone; DAQ, data acquisition; FCCP, carbonylcyanide-4-trifluoromethoxyphenyl hydrazone; I, electrical current; M, memristor; P, power; PXI, PCI eXtensions for Instrumentation; R, resistance; TEACl, tetraethylammonium chloride; q, charge; V, voltage; VFG, voltage of an function generator; VP, voltage between electrodes in a plant; VR, voltage on resistor R; f, magnetic flux

A memristor is a resistor with memory, which is a nonlinear passive 2-terminal electrical element relating magnetic flux linkage and electrical charge. Here we found that memristors exist in vivo. The electrostimulation of the Aloe vera 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 periodic sinusoidal or triangle electrostimulating waves. Memristive behavior of an electrical network in the Aloe vera is linked to the properties of voltage gated ion channels: the K+ 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.

Introduction Aloe vera (L.) is a member of the Asphodelaceae (Liliaceae) family with crassulacean acid metabolism (CAM). In the Aloe vera, stomata are open at night and closed during the day. CO2 acquired by Aloe vera at night is temporarily stored as malic and other organic acids, and is decarboxylated the following day to provide CO2 for fixation in the Benson-Calvin cycle behind closed stomata. Aloe vera is a model for the study of plant electrophysiology with crassulacean acid metabolism. The natural habitats of Aloe vera are the subtropical parts of the world. Aloe vera is considered to be intolerant of low temperatures. Its succulent leaves contain substances used for numerous medical and cosmetic applications. Recently, we analyzed anisotropy and nonlinear properties of electrochemical circuits in the leaves of Aloe vera.1,2 The newly developed DC charge stimulating method3,4 permits direct in vivo evaluation of the simplest electrical circuits in a cluster of cells or in a single cell. Using this method, we discovered strong electrical anisotropy of the Aloe vera leaf.1 Along the conductive bundles, the behavior of the Aloe vera leaf is strongly nonlinear. Electrostimulation by voltages higher than 2 V causes a drastic change in the leaf: the initial input resistance drops. These changes occur in the conducting bundles and are probably due to the opening of voltage gated ion channels in the Aloe vera leaf.

Chua5 postulated in 1971 the existence of the fourth basic electrical circuit element, memristor, a resistor with memory, which is a nonlinear passive 2-terminal electrical element relating magnetic flux linkage and electrical charge (Fig. 1). Memristor has the ability to recall the resistance of a previous current when turned off, and will remember that resistance when the current flow resumes. During the last decade different memristors were developed as solid state semiconductor devices, polymers, and modified electrodes.6-11 Analysis of the Hodgkin-Huxley axon model shows that voltage gated channels can be identified as a potassium ion-channel memristor and a sodium ion-channel memristor.12-16 Since plants have voltage gated K+ channels, it would be interesting to investigate the possible presence of memristors in plants. A memristor is a nonlinear element because its current-voltage characteristic is similar to that of a Lissajous pattern. No combination of nonlinear resistors, capacitors, and inductors can reproduce this Lissajous behavior of the memristor. Mathematically memristance can be described by equation:



(1)

*Correspondence to: Alexander G. Volkov; Email: [email protected]; [email protected] Submitted: 04/07/2014; Revised: 04/28/2014; Accepted: 04/29/2014; Published Online: 05/07/2014 Citation: Volkov AG, Reedus J, Mitchell CM, Tucket C, Forde-Tuckett V, Volkova MI, Markin VS, Chua L. Memristors in the electrical network of Aloe vera L.. Plant Signaling & Behavior 2014; 9:e29056; PMID: 24806097; http://dx.doi.org/10.4161/psb.29056

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Results Electrostimulation of the Aloe vera by bipolar periodic waves from a function generator Experimental setup is shown in Figure 2. Two methods were used for Aloe vera electrostimulation: function generator FG300 and potentiostat SI1287. Bipolar sinusoidal or triangle periodic waves with amplitude VFG were applied from a function generator. To measure electrical current we included in the circuit additional 10 kΩ resistor R, so that electrical current was found as I = V R /R. Potential difference, V P, between electrodes in plants is equal to V P = V FG – V R (3) V P is always less than V FG because of a voltage drop on a Figure 1. Relationships between a voltage, current, charge, and flux. resistor R (Fig. 2). Figure 3 shows how electrical current depends on the voltage Vp induced by bipolar sinusoidal wave from a function generator with frequency of 0.001 Hz, when platinum electrodes are inserted along the vascular bundles in a leaf of Aloe vera. There is a self-crossing between curves and a pinched point in hysteresis loop at low frequency of sinusoidal wave in the voltagecurrent plane when I = 0 μA and V P = 0 V, which is a typical sign of a memristor of a first kind (Fig. 3A). In some experiments there is a pinched point in hysteresis loop at low frequency of sinusoidal wave in the voltage-current plane when I = 0 μA and V P = 0 V without a self-crossing between curves, which is a typical sign of a memristor of a second kind (Fig. 3B). Increasing of a sinusoidal wave frequency to 1000 Hz leads to the disappearing of a pinched point in the complete agreement with characteristics of memristors, which had a small “parasitic” capacitor connected Figure 2. Two methods of cyclic voltammetry: (Method A) Block diagram of the data acquisition across the memristor. This capacitance can and electrostimulation system; (Method B) The SI1287 Advanced Electrochemical Interface was be a function of membrane, electrodes, and connected via the GPIB to PC and used in 2 terminal configuration for cyclic voltammetry. plant tissue capacitances. We found that a self-crossing between curves exists in 71% The power of a memristor is of experiments (Mean 71.43%, Std. Dec. 46.88%, Std. Err. P(t) = I2 (t)M(q(t)) (2) 12.53%, n = 14). The amplitude of electrical current increases where ϕ and q denote the flux and charge, respectively if the applied voltage amplitude to the leaf of Aloe vera increases. (Fig. 1). The simple possible equivalent electrical circuits are shown in The pinched hysteresis loop of memory elements, when inserts. subject to a periodic stimulus, can be self crossing (type I The power consumption characteristic can be estimated from memristor) or not (type II memristor).17 We found earlier that Figure 3 using equation: the electrostimulation of plants by bipolar sinusoidal or triangle P(t) = I(t)V(t). (4) periodic waves induces electrical responses in the Venus flytrap, At low frequencies of a bipolar periodic sinusoidal wave Mimosa pudica, and Aloe vera with fingerprints of memristors from a function generator, the power consumption is positive of type I or type II.18 The main goal of this article is to study (Fig. 4A). Memristance has positive values for passive devices memristive properties of the Aloe vera plant in vivo. Due to at all values of electrical charge. Figure 4B shows the power large size and thickness of Aloe vera leaf, it is possible to do consumption at high frequencies, which has high positive and electrostimulation in 3 dimensions – along the leaf, perpendicular, small negative values during electrostimulation of Aloe vera by and from top to bottom directions. a bipolar sinusoidal wave from a function generator. Capacitive

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Figure 3. Electrical current I vs. voltage VP applied to a leaf of Aloe vera. Frequency of sinusoidal voltage scanning was 0.001 Hz (A) and 1000 Hz (B). Position of Pt electrodes in a leaf of Aloe vera is shown. These results were reproduced 14 times. The simplest equivalent electrical circuits are shown in inserts.

currents cause this effect during charging and discharging processes (Fig. 4). Figure 5 shows electrical responses induced by bipolar sinusoidal wave from a function generator with frequency of 0.001 Hz (A) and 1000 Hz (B), when platinum electrodes are inserted on top and on bottom of the leaf of Aloe vera. There is a pinched point in hysteresis loop at low frequency of sinusoidal wave in the voltage-current plane when I = 0 μA and V P = 0 V, without a self-crossing between curves (Fig. 5A). This is a typical sign of a memristor of a second kind. There is low amplitude of the loop at positive voltages and level of signal to noise ratio is low. The pinched hysteresis disappears at high frequencies (Fig. 5B). For a plant tissue, the pinched hysteresis loop transforms to a non-pinched hysteresis loop instead of a single line I = V/R at high frequencies of the applied voltage because the amplitude of electrical current depends also on capacitance of a plant tissue and electrodes, frequency, and direction of scanning: (5)

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Figure 4. Electrical power P vs. time t estimated from Figure 3. Frequency of sinusoidal voltage scanning was 0.001 Hz (A) and 1000 Hz (B). Position of Pt electrodes in a leaf of Aloe vera is shown.

Electrostimulation of the Aloe vera by linear sweep cyclic voltammetry The cyclic voltammetry shows also memristive properties of Aloe vera (Figs. 6A, B, and 7A). At low frequencies of scanning at 10-4 Hz (Fig. 6A) and 10 -3 Hz (Fig. 6B), there is a pinched point with self-crossing between curves when I = 0 μA and V P = 0 V, which is a typical fingerprint of a memristor (Fig. 6A, B). Increasing the speed of scanning, from 20 mV/s (10 -3 Hz) to 1 V/s (5x10-2 Hz), leads to the disappearance of pinched points in the hysteresis loop (Fig. 6C, D). Effect of inhibitors and uncouplers on memristive responses According to theoretical calculations, voltage gated K+ ion channels are memristors.6,12-14 To verify this hypothesis, we used tetraethylammonium chloride (TEACl) as a chemical compound, which is known to block voltage gated K+ ion channels in plant and animal electrophysiology. Figure 7 shows the effect of tetraethylammonium chloride (TEACl) on electrical current induced by periodic bipolar sinusoidal wave when platinum electrodes are inserted along the pulvinus of Aloe vera. A 0.2 mL aliquot of 10 mM TEACl was injected in the Aloe vera leaf 25 h before electrical measurements. A 25 h delay was required because of the slow distribution of TEACl in the plant tissue. The

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of a bipolar periodic sinusoidal wave. Injection of 0.2 mL of distilled water or 10 mM CaCl2 solution in control experiments does not inhibit memristive properties of the Aloe vera leaf. Our results demonstrate that a voltage gated K+ channel in the excitable tissue of plants has properties of a memristor. Figure 8 shows the effect of uncoupler carbonylcyanide4-trifluoromethoxyphenyl hydrazone (FCCP) on electrical current induced by bipolar sinusoidal electrical waves at different frequencies when electrodes are inserted along the leaf of Aloe vera. The same results were obtained during electrostimulation by bipolar triangle wave. As in the previous case, 25 h delay between the plant treatment and electrostimulation experiments was required because of slow diffusion of FCCP to the plant tissue. FCCP decreases the amplitude of electrical responses at low and high frequencies. Similar results were obtained by substitution of FCCP by uncoupler CCCP (Fig. 9).

Discussion The memristor driven by the sinusoidal current generates I-V pinched hysteresis loop. The pinched hysteresis loop is a double-valued Lissajous figure of (V(t), I(t)) for all times t, except when it passes through the origin, where the loop is pinched. It was theoretically shown that the voltage gated potassium ion channels in axons are locally active memristors.12-15 Plants have the voltage gated potassium ion channels associated with plasma membranes. Figures 3, 5, and 6 show memristive properties of 2 types in the Aloe vera leaf. Figures 3 and 6 shows that plant tissue has properties of memristor type I and Figure 5 illustrates electrical characteristics of a memristor type II. A blocker of the voltage gated potassium ion channels, TEACl inhibits the memristive properties of the Aloe vera leaf. It means that the voltage gated potassium ion channels in the Aloe vera leaf are memristors. Figure 4 shows the power characteristics of the Aloe vera memristors at different frequencies of applied periodic bipolar sinusoidal wave. Uncouplers FCCP and CCCP decreases the amplitude Figure  5. Electrical current I vs. voltage VP applied to a leaf of Aloe vera. of a hysteresis loop by depolarizing of a plasma membrane Frequency of sinusoidal voltage scanning was 0.001 Hz (A) and 1000 Hz (B). and by decreasing of a membrane capacitance. Uncouplers, Position of Pt electrodes in a leaf of Aloe vera is shown. These results were which are soluble in both water and lipid phases, permeate reproduced 14 times. the lipid phase of a membrane by diffusion and transfer protons across the membrane, thus eliminating the proton pinched hysteresis loop (Fig. 7) disappears and the memristive concentration gradient and/or a membrane potential. Most system transforms to a resistance. Frequency of sinusoidal voltage protonophoric uncouplers widely used in photosynthesis research scanning was 0.001 Hz. (A) in Figure 7 is a response to a bipolar are oxidized by the manganese cluster of the Photosystem II periodic sinusoidal electrostimulating wave with frequency of O2-evolving complex in chloroplasts and inhibit photosynthetic 10-3 Hz and panels B shows the response to a bipolar periodic water oxidation. The membrane pool of plastoquinone can sinusoidal wave with frequency of 1000 Hz. reduce oxidized uncouplers, leading to formation of an artificial TEACl decreases the amplitude of electrical current between cyclic electron transfer chain around Photosystem II involving electrodes in the pulvinus of the Aloe vera. TEACl is known uncouplers as redox carriers. Uncouplers promote auto oxidation as a blocker of voltage gated potassium channels. TEACl, an of the high-potential form of cytochrome b559 and partially inhibitor of voltage gated K+ channels, transforms a memristor to convert it to lower potential forms. Protonophores uncouple a conventional resistor in plant tissue at low and high frequencies electron transport, accelerate the deactivation of the S-2 and S-3

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Figure 6. Cyclic voltammetry in a leaf of Aloe vera with a scanning rate of periodic triangle wave of 2 mV/s (A), 20 mV/s (B), 200 mV/s (C), and 1000 mV/s (D). Position of Pt electrodes in the Aloe vera is shown. These results were reproduced 14 times.

states on the donor side, and facilitate the oxidation of cytochrome b559 on the acceptor side of Photosystem II. By applying the periodic bipolar sinusoidal or linear periodic bipolar waves to the Aloe vera leaves, we found memristors of types I and 2 in vivo. Voltage gated potassium channels play a role of bio-memristors in plants. This study can be a starting point for understanding mechanisms of memory,20 learning,19 circadian rhythms,3 and biological clocks. Biological tissue in many organisms exhibit memristive behaviors. We found bio-memristors in different plants such as the Aloe vera, Venus flytrap,18 and Mimosa pudica.18 Gale et al. 21 found memristive properties of protoplasmic tubes of acellular slime mold Physarum polycephalum. Johnsen et al. 22 found that the sweat ducts in the skin are memristors. Hota et al.23 create transparent memristors from natural regenerated silk fibroin protein obtained from cocoons of Bombyx mori silkworm. We should expect the finding of bio-memristors in many different biological systems in the near future.

Materials and Methods Plants Aloe vera L. plants were grown in clay pots. Fifty plants were exposed to a 12:12 h light/dark photoperiod at 21 °C (Environmental Corporation, USA). Volume of soil was 2.0 L. Aloe vera plants had 25–35 cm leaves. The average humidity was 40%. Irradiance was 700–800 μmol photons m-2s-1. All experiments were performed on healthy adult specimens.

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Chemicals Tetraethylammonium chloride (TEACl), carbonylcyanide4-trifluoromethoxyphenyl hydrazone (FCCP), and carbonylcyanide-3-chlorophenylhydrazone (CCCP) was obtained from Fluka (New York). Data acquisition All measurements were conducted in the laboratory at constant room temperature of 22 °C inside a Faraday cage, which was mounted on a vibration-stabilized table. In order to estimate possible high frequency content of the responses evoked, a high performance National Instruments data acquisition system was used. High speed data acquisition of low-pass filtered signals was performed using microcomputer NI-PXI-1042Q (National Instruments) with simultaneous multifunction I/O plug-in data acquisition board NI-PXI-6115 (National Instruments) interfaced through a NI SCB-68 shielded connector block to electrodes. The system integrates standard low-pass anti-aliasing filters at one-half of the sampling frequency. The multifunction NI-PXI-6115 data acquisition board provides high resolution and a wide gain range. Any single channel can be sampled at any gain at up to 10 MSamples/s. Plant electrostimulation The function generator FG300 (Yokagawa, Japan) was interfaced to NI-PXI-1042Q microcomputer and used for electrostimulation of plants. Cyclic voltammetry The SI1287 Advanced Electrochemical Interface (Solartron, Hampshire, England) was connected via the

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Figure 8. Electrical current I vs. voltage VP applied to a leaf of Aloe vera. Frequency of sinusoidal voltage scanning was 0.001 Hz (A) and 1000 Hz (B). Two-hundred μL of 10 μM FCCP were injected by a syringe to the leaf 25 h before measurement. Position of Pt electrodes in a leaf of Aloe vera is shown. These results were reproduced 14 times. Figure 7. Electrical current I vs. voltage VP applied to a leaf of Aloe vera. Frequency of sinusoidal voltage scanning was 0.001 Hz (A) and 1000 Hz (B). 200 μL of 10 mM TEACl were injected by a syringe to the leaf 25 h before measurement. Position of Pt electrodes in a leaf of Aloe vera is shown. These results were reproduced 14 times.

All experimental results were reproduced 14 times on different plants. Software SigmaPlot 12 (Systat Software, Inc) was used for statistical analysis of experimental data. Disclosure of Potential Conflicts of Interest

GPIB to PC and used in 2 terminal configuration for cyclic voltammetry. Images A photo camera Nikon D3X (Nikon USA Inc, Melville, NY USA) with AF-S Micro Nikkor 105 mm 1:2.8 G ED VR lens (Nikon USA) was used for the photography. Statistics

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No potential conflicts of interest were disclosed. Acknowledgments

This article is based upon work supported in part by the National Science Foundation under Grant No CBET-1064160 and in part by the US Army Research Office under contract/ grant number W911NF-11-1-0132 (A.G.V.). L.C.’s research is supported by AFOSR grant number FA9550-13-1-0136.

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Volkov AG, Foster JC, Jovanov E, Markin VS. Anisotropy and nonlinear properties of electrochemical circuits in leaves of Aloe vera L. Bioelectrochemistry 2011; 81:4-9; PMID:21167797; http://dx.doi.org/10.1016/j.bioelechem.2010.11.001 2. Volkov AG, O’Neal L, Volkova MI, Markin VS. Electrostimulation of Aloe vera L., Mimosa pudica L. and Arabidopsis thaliana: Propagation and collision of electrotonic potentials. J Electrochem Soc 2013; 160:G3102-11; http://dx.doi. org/10.1149/2.018307jes 3. Volkov AG, Baker K, Foster JC, Clemmons J, Jovanov E, Markin VS. Circadian variations in biologically closed electrochemical circuits in Aloe vera and Mimosa pudica. Bioelectrochemistry 2011; 81:39-45; PMID:21334987; http://dx.doi. org/10.1016/j.bioelechem.2011.01.004 4. Jovanov E, Volkov AG. Plant electrostimulation and data acquisition. In: Plant Electrophysiology-Methods and Cell Electrophysiology. Volkov, AG, ed. Berlin: Springer, 2012: 45-67 5. Chua L. Memristor – The missing circuit element. IEE Transactions Circuit Theory 1971; 18:507-19; http://dx.doi.org/10.1109/TCT.1971.1083337 6. Chua L. Memristor, Hodgkin-Huxley, and edge of chaos. Nanotechnology 2013; 24:383001; PMID:23999613; http://dx.doi.org/10.1088/0957-4484/24/38/383001 7. Chua L. Resistance switching memories are memristors. Appl Phys, A Mater Sci Process 2011; 102:765-83; http://dx.doi.org/10.1007/s00339-011-6264-9 8. MacVittie K, Katz E. Electrochemical systems with memimpedance properties. J Phys Chem C 2013; 117:24943-7; http://dx.doi.org/10.1021/jp409257v 9. Strukov DB, Snider GS, Stewart DR, Williams RS. The missing memristor found. Nature 2008; 453:80-3; PMID:18451858; http://dx.doi.org/10.1038/nature06932 10. Borghetti J, Snider GS, Kuekes PJ, Yang JJ, Stewart DR, Williams RS. ‘Memristive’ switches enable ‘stateful’ logic operations via material implication. Nature 2010; 464:873-6; PMID:20376145; http://dx.doi.org/10.1038/nature08940 11. Smerieri A, Berzina T, Erokhin V, Fontana MP. Polymeric electrochemical elements for adaptive networks: Pulse mode. J Appl Phys 2008; 104:114513-8; http://dx.doi. org/10.1063/1.3033399 12. Chua L, Sbitnev V, Kim H. Hodgkin-Huxlew axon is made of memristors. Internat J Bifurcation Chaos 2012; 22:1230011-1-48 13. Chua L, Sbitnev V, Kim H. Neurons are poised near the edge of chaos. Internat J Bifurcation Chaos 2012; 22:1250098-1-49 14. Sah M, Kim H, Chua L. Brains are made of memristors. IEEE Circuits Systems 2014; 14:12-36; http://dx.doi.org/10.1109/MCAS.2013.2296414 15. Pershin YV, Di Ventra M. Experimental demonstration of associative memory with memristive neural networks. Neural Netw 2010; 23:881-6; http://dx.doi. org/10.1016/j.neunet.2010.05.001 16. Jo SH, Chang T, Ebong I, Bhadviya BB, Mazumder P, Lu W. Nanoscale memristor device as synapse in neuromorphic systems. Nano Lett 2010; 10:1297-301; PMID:20192230; http://dx.doi.org/10.1021/nl904092h 17. Adhikaru AP, Sah MPd, Kim H, Chua L. The fingerprints of memristor. IEEE Trans Circuits Systems 2013; http://dx.doi.org/10.1109/TCSI.2013.2256171 18. Volkov AG, Tucket C, Reedus J, Volkova MI, Markin VS, Chua L. Memristors in plants. Plant Signal Behav 2014; 9: http://dx.doi.org/10.4161/psb.28152, In press; PMID:24556876. 19. Pershin YV, La Fontaine S, Di Ventra M. Memristive model of amoeba learning. Phys Rev E 2009; 80:021926.0 20. Volkov AG, Carrell H, Baldwin A, Markin VS. Electrical memory in Venus flytrap. Bioelectrochemistry 2009; 75:142-7; PMID:19356999; http://dx.doi.org/10.1016/j. bioelechem.2009.03.005 21. Gale E, Adamatsky A, Costello BDL. Are slime moulds living memristors? arXiv 2013;1306.3414v1 22. Johnsen GK, Lütken CA, Martinsen OG, Grimnes S. Memristive model of electroosmosis in skin. Phys Rev E Stat Nonlin Soft Matter Phys 2011; 83:031916; PMID:21517534; http://dx.doi.org/10.1103/PhysRevE.83.031916 23. Hota MK, Bera MK, Kundu B, Kundu SC. A natural silk fibroin protein-based transparent bio-memristor. Adv Funct Mater 2012; 22:4493-9; http://dx.doi. org/10.1002/adfm.201200073

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Figure 9. Electrical current I vs. voltage VP applied to a leaf of Aloe vera. 200 μL of 10 μM CCCP were injected by a syringe to the leaf 25 h before measurement. Frequency of sinusoidal voltage scanning was 0.001 Hz (A) and 1000 Hz (B). Position of Pt electrodes in a leaf of Aloe vera is shown. These results were reproduced 14 times.

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Memristors in the electrical network of Aloe vera L.

A memristor is a resistor with memory, which is a non-linear passive two-terminal electrical element relating magnetic flux linkage and electrical cha...
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