Measurement of Phloem-Based Electrical Signals in Plants

Electrical signals are vital components of long-distance signaling in plants, enabling rapid systemic responses to environmental stimuli. These signals, which include action potentials (APs), variation potentials (VPs), and system potentials (SPs), that can also combine into electropotential waves (EPWs), are primarily propagated through the vascular system, with the phloem playing a central role. EPWs, encompassing APs, VPs, and SPs, are integral to systemic signaling and inter-organ communication via the phloem, and are closely associated with plant responses to pests and pathogens. The complex architecture of the phloem, embedded deep within plant tissues and surrounded by multiple cell layers, poses significant challenges for direct electrophysiological measurements. Traditional electrophysiological methods for studying electrical long-distance signals often require wounding, which can alter the physiological conditions being measured. The use of aphids as bio-electrodes offers a promising alternative, as it avoids mechanical wounding and allows for flexible selection of measurement points. This chapter highlights the advantages and limitations of various techniques available for studying electrical signals in intact plants, which is essential for understanding how plants respond to environmental stimuli.