Plant electrical signals (ES´s) have become a multidisciplinary topic of interest in recent years. It is known that plants generate several types of ES´S when they face different kinds of stimuli [Sukhov et al., 2019]. At the cellular level, plants generate three main ES´S depending on the intensity of the stimulus. Non-critical stimuli, such as changes in temperature, light, salinity, soil moisture, and mechanical stimuli will produce a fast voltage curve known as action potentials (Ap´s) that relates to the depolarization and repolarization of the cell membrane. Critical stimuli, such as burning, cutting, puncture and flattening will trigger a voltage curve with a long repolarization time known as variation potentials (Vp’s). Lastly, critical, and non-critical stimuli will induce a system potentials (Sp´s) [Sukhov et al., 2019; Garcia-Servin et al., 2021].
However, ES´s are not only studied at the cellular level by measuring membrane potentials. Other investigations have analyzed the extracellular ES´s (EES´s) that plants generate under several stimuli as a systemic response [Fromm & Lautner, 2007]. EES´s measurements are used in diagnostic systems, for example, for determining the water conditions of plants, such as Persea americana, Prunus domestica, and Olea europea, this for developing irrigation systems that deliver water only when the plants need it, reducing the consume of water in crop [Rios-Rojas et al., 2014; Comparini et al., 2020]. EES´s measurements have been also used for the identification of the origin of a stimulus with the purpose of identifying risks as plagues or adverse environmental conditions in a remote mode just by sensing EES´s [Chatterjee et al., 2015; Pereira et al., 2018]. EES´s have also been studied for the comprehension of plant-to-plant electrical communication [Volkov & Shtessel, 2018; Volkov et al., 2019], and for the creation of acoustic art [Augustine, 2016].
Two types of electrodes are used for measuring ES´s, one type are electrodes of superficial fixation and the other perform by insertion [Xiaofei et al., 2009]. The superficial fixation electrodes have the advantage of not generating tissue damage and, in consequence, they help to diminish electrical interference in the plant [Xiaofei et al., 2009; Meder et al., 2021, Davies, 2006]. In 2021, Meder et al. demonstrated that a self-adhering electrode placed on the surface of a non-lignified plant tissue could measure ES´s with similar performance as the electrode insertion technique and its mechanical properties make it plausible to be placed on leaves. However, the insertion technique is most used for measuring EES´s in lignified and non-lignified plant research [Comparini et al., 2020; Volkov & Shtessel, 2018; Volkov et al., 2019; Saraiva et al., 2017]. It consists of the insertion of two or more electrodes, usually made of stainless steel, into the plant tissue to allow measuring its electrical properties, such as potential differences or impedance in the vascular tissue. Nevertheless, in this type of ES´s measurement, controlling the distance between electrodes and the depth of insertion is crucial for obtaining precise and robust measurements [Volkov & Shtessel, 2018; Volkov et al., 2019; Saraiva et al., 2017], besides that the ES´s measurement will be affected by the plant tissue and cell type where the electrodes are inserted and that could vary by the deep and angle of insertion [Perez-Garcia & Moreno-Risueno,2018], but methodologies that consider them or mechanism for that purpose are not observed. For this reason, in this work, was developed a mechanism that can be manufactured in different materials and sizes that allows the introduction of one or two electrodes into plant stems or branches perpendicular to the vascular bundles at the same variable depth and angle of insertion. The mechanism was implemented in an experiment for the identification of electrical signals related to drought stress, which could be differentiated through a neural network with an 84.91% of recognition rate. The drought stress electrical signals also presented a significant difference with the control signals with a p = 0.027. The mechanism is intended to facilitate electrode insertion and ensure equal distance, depth, and fixation.