“When exposed to strong light, Karpinski explains, plants absorb more energy than they can use for photosynthesis—but he doesn’t think plants waste this excess energy. Karpinski says plants convert the energy to heat and electrochemical activity that can later trigger biological processes, like immune defenses. “It seems that plants can raise resistance against pathogens only using their light absorption system,” Karpinski says. “We found that electrochemical signaling is regulating this process. Electrical signaling in plants is known from the time of Darwin—it is nothing new. But what was not described is that light can induce action potentials. We have found there is a different signaling for blue, white and red light. If plants can signal differently different wavelengths of light, then plants can see colors as well.””
“Electrical excitability and signalling, frequently associated with rapid responses to environmental stimuli, are well known in some algae and higher plants. The presence of electrical signals, such as action potentials (AP), in both animal and plant cells suggested that plant cells, too, make use of ion channels to transmit information over long dis- tances. In the light of rapid progress in plant biology during the past decade, the assumption that electrical signals do not only trigger rapid leaf movements in ‘sensitive’ plants such as Mimosa pudica or Dionaea muscipula, but also physiological processes in ordinary plants proved to be correct. Summarizing recent progress in the field of electri- cal signalling in plants, the present review will focus on the generation and propagation of various electrical signals, their ways of transmission within the plant body and various physiological effects.”
JÖRG FROMM & SILKE LAUTNER “Electrical signals and their physiological significance in plants” Plant, Cell and Environment (2007) 30, 249–257 doi:10.1111/j.1365-3040.2006.01614.x
also includes “TECHNIQUES FOR MEASURING ELECTRICAL SIGNALS IN PLANTS” for extracellular and intracellular measurement
“surface measurements appear better suited as they are non-invasive and physically stable; they may also be performed simultaneously with other physiological methods such as gas exchange recordings (Fromm & Fei 1998). Such electrodes usually consist of Ag/AgCl wire, moistened with 0.1% (w/v) KCl in agar and wrapped in cotton to provide the appropriate contact with the plant surface (Fromm & Spanswick 1993), or of Ag/AgCl pelleted electrodes that can be connected to the plant surface by means of a conductive aqueous gel of the type commonly used in ECG (Mancuso 1999). At different positions of a plant surface, electrodes can be connected by screened cables to a high-input impedance electrometer with many channels. An identical electrode can either be placed on the distal region of a plant or in the soil to serve as a reference electrode (Fig. 1a). When all channels show stabilized potentials, the plant can be stimulated electrically at the apex (e.g. 3 V for 2 s) or by other stimuli (flaming, cold shock) applied to a leaf. Usually, the electrical responses to an apical stimulus can be shown by all electrodes, from top to bottom of the plant (Fig. 1a), indicating that the trans- mission of an electrical signal is occurring throughout the plant. For example, a similar experimental set-up has been used in sunflower to analyse the characteristics of APs and VPs (Stankovic et al. 1998).”
“Environmental stimuli such as spontaneous changes in temperature, light, touch or wounding can induce electrical signals at any site of the symplastic continuum.”
Toward an Understanding of Plant bioacoustics (doi:10.1016/j.tplants.2012.03.002) “a rationale as to why the perception of sound and vibrations is likely to have also evolved in plants” > pdf
Action Potential (AP) - rapidly propogating fixed amplitude signals, triggered with stimulus at threshold, do not vary with singal intensity, passivly propogating. signal duration/propogation in the order of seconds, with refractory periods in the order of 10s of seconds or minutes in some plants. amplitudes in the order of 100mV in mimosa.
Variation Potential (VP) - also refered to as 'slow wave potentials'. continuous, varying amplitude in relation to stimululus, non-self perpetualting, singal duration in the order of minutes, amplitude in similar range to APs, amplitude and speed of signals can decrease from the site of local stimulus.
Plant hearing: “THEY can “smell” chemicals and respond to light, but can plants hear sounds? It seems chilli seeds can sense neighbouring plants even if those neighbours are sealed in a box, suggesting plants have a hitherto-unrecognised sense.”