Electrical Properties of Mimosa pudica and its Ability to Transmit Data at 2.4 GHz

  1. 1.  University of Cincinnati

Abstract

This project explored the electrical properties of the Mimosa pudica plant and its ability for conducting and transmitting 2.4 GHz frequency radio waves which are commonly used for wireless communications. Mimosa pudica was chosen as all of its cells are electrically excitable which would provide a great model and example for learning about plant electrical properties and attempting to transmit a 2.4 GHz frequency. Mimosa pudica is famous for its ability to be sensitive and respond to the environment by folding up its leaflets and folding its leaves down when stimulated. A wireless router was modified to have its antenna output go through a shielded cable and then a copper electrode that was placed in the soil and with direct contact to the stem of the Mimosa pudica. Results of this demonstrated that the Mimosa pudica works very well as a conductor of electricity, shown by both a near-instant folding of the leaflets and leaves, along with a significantly increased recovery time. Transmission was not seen to be effective as there was a significant increase in signal strength along with if placed between the router and a computer it would conduct the signal and prevent the computer from connecting, however a standard dipole antenna still gave a much greater signal. These results suggest that Mimosa pudica is a great conductor and may prove to be an important tool to learn more about action potentials and general organismal electricity.

Background

Electrical properties of plants have recently become a topic of interest given the advent and rapid adaptation of computers. Back in 1985, Francis Hart looked at the electrical properties, specifically capacitance and conductance, of Poinsettia stems with “50 frequencies from .35 to 350 Hz.” Hart found that the conductivity is direct current, carried through the xylem and phloem, and will decrease over time smoothly and linearly as occurs from a standard ionic conductor (Hart, 1985). This finding suggests that plants are capable of electric conductance from even extremely low frequency. Soil properties can influence conductivity at the root level as well, both in terms of soil chemical properties and hydraulics. Soil chemical properties are composed of ions and nutrients available along with any chemicals the plant places in the soil as well. Gholizadeh assessed field conditions of a Malaysian paddy field to attempt to make maps of high soil electrical conductivity areas. These were found to typically be areas in which nutrients were abundant and likewise allowed for apparent electrical conductivity (Gholizadeh, Amin, Anuar, & Aimrun, 2011). Showing that high-nutrient areas could allow for electrical conductivity would support the idea that electric current could be sent through the soil between roots of a plant and an electrical transmitter or conductor.

Along with chemical properties, hydraulic properties are an important consideration as well to aid in proper uptake into a plant. Gholizadeh measured electrical conductivity “within a Malaysian rice cultivation area using VerisEC sensor,” instead of measuring through the plant itself (Gholizadeh, Amin, Anuar, & Aimrun, 2011). Yan Li studied how water saturation can influence water transport from the soil into the root. Among various soil particle sizes ranging from zero to one millimeters were tested. Li showed that it is the total volume of water that influences water transport rather than just saturation itself, and thus volumetric readings should be the method in which water levels are measured (Li, Pan, & Xu, 2013). As hydraulic conductance is a product of the volume of water, this is an important factor for encouraging an electrical signal to be transmitted across roots and through the plant.

These measures are important when designing an electrical interface with a plant. Since plants have been shown to conduct an electrical current, if this were to be tested on a large scale then it may help to have a uniformly electrically excitable plant to assist with conductivity and even provide a visual response. Mimosa pudica happens to be an ideal species for this task as it is a plant that participates in rapid plant movement through action potentials and other electrochemistry. Baker tested “biologically closed electrochemical circuits in electrically and mechanically anisotropic pulvini” in the Mimosa pudica and found the mechanism of the plant’s movements as a function of electro stimulation (Baker & Volkov, 2011). Both Volkov and Sibaoka in 2010 and 1991 respectively found that this was a result of action potentials (Sibaoka, 1991), in very much the same way that neurons fire, using a “redistribution of K+, CL-, Ca2+, and H+ ions through voltage gated ion channels” (Volkov, Foster, & Markin, 2010). In fact, Volkov was even able to alter the resting membrane potential by stimulating the Mimosa pudica causing a hypersensitive response in the rapid plant movement, requiring much less stimulation to elicit a response.

Electrical properties shown by the Mimosa pudica suggest that it may be a prime candidate to send an electric signal through given the uniform excitability of its cells. As plants are good conductors of electric current, and that electric current can be passed through soil, there may be a mechanism in which a plant can act as a transmitter of electromagnetic radiation. Proper hydraulics and soil chemistry would be required to take up radiation through the roots, however if possible then this could provide a way to quickly bring the 2.4 GHz band, commonly used for transmitting wireless internet, to large public spaces simply by placing electrodes in the soil.

Materials and Methods

A single Mimosa pudica plant was purchased and grown under a GlowPanel 45 Grow Light. After one week of habituation to its new environment along with growth of another leaf, a Linksys Wireless-B Router was purchased and modified to enable transmission directly from the router to the Mimosa pudica. Antennas were removed from the router, and one antenna connector was capped and shielded with aluminum foil to prevent the wireless radio from leaking signal. The other antenna connector was hooked up to a shielded one foot long wire which then had its end stripped to show a copper wire which was then connected to a copper plate to create an electrode. The soil around the plant was kept fairly moist to allow for ideal conductivity and the electrode was placed in three locations: the soil, the stem, and a leaf. At each of these regions, a computer was recording signal strength using inSSIDer 3 wireless monitoring software. Data was collected at each of these three electrode locations and then was imported into Excel for data analysis via an ANOVA with follow-up t-tests for each treatment. With the observation of hypersensitivity and increased unfolding time, these were also measured and were subjected to t-tests.

Results

When the electrode was placed in the soil the plant would fold up, become hypersensitive and take longer to unfold, and the signal plummeted to a low strength (Table 1) that was significantly different (p < .05) from just the wire itself.

 

Table 1: 2.4 GHz Signal Strength from Soil Placement

Time After Placement

Signal Strength

Control Strength

Average Signal

30 Seconds

-85 dBm

 

 

60 Seconds

-82 dBm

 

 

90 Seconds

-79 dBm

 

 

120 Seconds

-86 dBm

 

 

150 Seconds

-77 dBm

 

 

180 Seconds

-78 dBm

 

 

210 Seconds

-80 dBm

 

 

 

 

-72 dBm

-81 dBm

 

The electrode placed on the stem still caused the plant to fold up, be hypersensitive, and take longer to unfold, and an increase in signal was seen (Table 2) that was significantly different from just the wire itself (p < .05).

 

Table 2: 2.4 GHz Signal Strength from Stem Placement

Time After Placement

Signal Strength

Control Strength

Average Signal

30 Seconds

-70 dBm

 

 

60 Seconds

-69 dBm

 

 

90 Seconds

-73 dBm

 

 

120 Seconds

-71 dBm

 

 

150 Seconds

-68 dBm

 

 

180 Seconds

-69 dBm

 

 

210 Seconds

-70 dBm

 

 

 

 

-72 dBm

-70 dBm

 

Leaf placement of the electrode caused that leaf to fold up, but there was not the same hypersensitivity or increase throughout the entire plant in unfolding time. There was a significant difference (p < .05) in signal when placed on the leaf versus just from the wire (Table 3).

 

Table 3: 2.4 GHz Signal Strength from Leaf Placement

Time After Placement

Signal Strength

Control Strength

Average Signal

30 Seconds

-63 dBm

 

 

60 Seconds

-62 dBm

 

 

90 Seconds

-60 dBm

 

 

120 Seconds

-59 dBm

 

 

150 Seconds

-60 dBm

 

 

180 Seconds

-61 dBm

 

 

210 Seconds

-58 dBm

 

 

 

 

-72 dBm

60 dBm

 

Mimosa pudica was found to fold up with a significantly higher sensitivity (p < .05) as on average the plant only required half the disturbing of an unstimulated plant to evoke a rapid plant response. In addition, Mimosa pudica took a significantly longer amount of time (p < .05) to unfold again after disturbance when stimulated by a 2.4 GHz signal (Table 4).

 

Table 4: Time to Recover after Rapid Plant Movement Stimulation

Electrode Location

Length of Electric Stimulation

Mechanical Stimulation Required to Elicit Response

Time Folded Up

None

N/A

Multiple Full Leaves

12 Minutes

Soil

5 Minutes

One Full Leaf

42 Minutes

Stem

5 Minutes

None, Leaves Already Folded

56 Minutes

Leaf

5 Minutes

Two Full Leaves

33 Minutes

 

Discussion

Even though the Mimosa pudica was found to effectively increase the transmission of data if the electrode was in the soil, on the leaf, or stem, when compared to an actual dipole antenna (p < .05), a plant is not a good replacement or supplement to current antennas. However, several interesting observations such as the Mimosa pudica becoming hypersensitive to the slightest touch after having been exposed to the 2.4 GHz signal, and the fact that the unfolding process of the plant took on average 44 minutes longer than when normally stimulated suggest that the plant is a fantastic conductor of electricity (Figure 1).

 

Figure 1: Various electrode locations resulted in Mimosa pudica showing its rapid plant movement for an extended period of time which were significantly different from no stimulation suggesting a mechanism similar to long-term potentiation as found in neurons..

 

This idea is also supported with the observation that if the plant is placed directly between the router and the computer, then it will randomly fold leaflets and cause a huge signal loss by the computer. As the Mimosa pudica was found to be such a great conductor and is electrically excitable, this plant may have been a poor choice for a transmission experiment since it directly uses electric potentials for basic cellular functioning. Despite this however, Mimosa pudica may be able to give an easy method of researching more about action potentials, cellular depression, long-term potentiation, and other neural and plant concepts related to electricity. Unlike other cells or membrane components, the Mimosa pudica is extremely receptive to external electrical sources which can change the membrane potential and would allow for a larger-scale and therefore less precise requirements to explore and demonstrate many topics related to action potentials. The plant shows very clear responses that a microscope isn’t even required to see, and from these observations plus what other researchers have seen, Mimosa pudica may provide an effective method at both the teaching of these concepts to students and researching more into how these work on a larger and more resilient scale.

References

Baker, K. D., & Volkov, A. G. (2011). Electrochemistry of Mimosa pudica pulvini. ABST\nRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 241.

Gholizadeh, A., Amin, M. S., Anuar, A. R., & Aimrun, W. (2011). Apparent Electrical Conductivity in Correspondence to Soil Chemical Properties and Plant Nutrients in Soil. Communications in Soil Science and Plant Analysis, 42(12), 1447-1461. doi:10.1080/00103624.2011.577862

Hart, F. X. (1985). The extremely low frequency electrical properties of plant stems. Bioelectromagnetics, 6(3), 243-256. doi:10.1002/bem.2250060305

Li, Y., Pan, L.-P., & Xu, G.-Q. (2013). On quantifying hydraulic conductance at the soil-root interface. Hydrological Processes, 27(14), 2098-2102. doi:10.1002/hyp.9744

Sibaoka, T. (1991). Rapid plant movements triggered by action potentials. The Botanical Magazine, 104(1), 73-95. doi:10.1007/BF02493405

Volkov, A. G., Foster, C. J., & Markin, V. S. (2010). Molecular electronics in pinnae of Mimosa pudica. Plant Signaling & Behavior, 5(7), 826-831. doi:10.4161/psb.5.7.11569

 

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