Plant Electrophysiology with Conformable Organic Electronics

Plant electrical signals are mediators of long-distance signaling and correlate with plant movements and responses to stress. Presently, these signals are studied with macro single surface electrodes that cannot resolve signal propagation patterns and integration, thus impeding their decoding and link to function. Unlike conventional extracellular electrodes, multielectrode (MEA) technology records the distribution patterns of electrical activity in cellular networks using a non-invasive, dense array of electrodes embedded in a substrate. The MEA technology is extensively used in brain and cardiac tissue research to decode the brain connectivity and potential propagation patterns in cardiac myocytes respectively. However, for plant electrophysiology the MEA technology remains fairly unexplored. Here we developed a conformable multielectrode array based on organic electronics for large-scale high-resolution plant electrophysiology. The MEA is developed with standard photolithography fabrication techniques, with parylene C as substrate and encapsulation layer resulting in total device thickness as low as 5 micrometers. The MEA is therefore highly conformable to the plant tissue leading to high Signal to Noise Ratio (SNR). With the conformable MEA we performed spatiotemporal mapping of the electrical activity of the carnivorous plant Dionaea muscipula a.k.a Venus Flytrap (VFT). VFT consists of a bilobed traps having three trigger hairs in each lobe which serve as mechanosensors. When the mechanosensitive hair is deflected, the mechanical stimulus is translated into an action potential (AP), by sensory cells at the base of the hair. Two action potentials (or two touches) in a short period (less than 30 secs) are required to induce closure of the trap. We found that the AP actively propagates through the tissue with constant speed and without strong directionality. We also found that spontaneously generated APs can originate from unstimulated hairs and that they correlate with trap movement. Finally, we demonstrate that the VFT circuitry can be activated by cells other than the sensory hairs. Our work reveals key properties of the AP and establishes the capacity of organic bioelectronics for resolving plants electrical signaling contributing to the mechanistic understanding of plants long-distance responses.