Beyond APs and VPs: evidences of chaos and self-organized criticality in electrical signals in plants

Abstract

Studies on plant electrophysiology are mostly focused on specific traits of action potentials (APs) and/or variation potentials (VPs), often in single cells. Inspired by the complexity of the signaling network in plants and by analogies with some traits of neurons in human brains, we have sought for evidences of high complexity in the electrical dynamics of plant signaling, beyond APs and VPs responses. Thus, from EEG-like data analyses of soybean plants, we showed consistent evidences of chaotic dynamics in the electrical time series. Furthermore, we have found that the dynamic complexity of electrical signals is affected by the plant physiological conditions, decreasing when plant was stressed. Surprisingly, but not unlikely, we have observed that, after stimuli, electrical spikes arise following a power law distribution, which is indicative of self-organized criticality (SOC). Since, as far as we know, these were the first evidences of chaos and SOC in plant electrophysiology, we have asked follow-up questions and we have proposed new hypotheses, seeking for improving our understanding about these findings.

Plant “electrome” can be pushed toward a self-organized critical state by external cues: Evidences from a study with soybean seedlings subject to different environmental conditions

“…Moreover, we have confirmed that the temporal dynamic of the electrical signaling shows a complex non-linear behavior with long-range correlation (memory). 12 At least hypothetically for now, the persistence of the electrical signals observed in our study could support the hypothesis of a plant electrical memory, as claimed by Volkov et al 27 in a study proposing a mechanism of short-term electrical memory in the Venus flytrap. Actually, memory has been considered an essential attribute allowing plants to face environmental stresses and to improve their learning responses in the future (such as acclimation or priming responses).…”

“…As previously suggested 12,15 the dynamic of global electrical signals in plants, emerging from the integration of local (cell-tocell) electrical activity, is not a pure stochastic noise (white noise), and can be related to the physiologic state of the plants under different environmental conditions. A variety of natural phenomena are well described by 1/f btype noises, with b ranging from 0 (white noise) to > 2 (reddened noise)., 19,23,24 In our study, the interval of the b exponents values (often from 1.5 up to 3) of the PSD functions (Fig.…”

“…human brains have showed evidences of SOC, 21,22 as well as in plant electrophysiology. 12 We have suggested that SOC behavior could have the role to improve the efficiency of dissipation of disturbances, avoiding a catastrophic collapse of the whole system.…”

“…5,7,8,9 However, quite often mixed electrical potential waves are recorded, for instance, as result of overlapping APs and VPs (among other voltage variations), creating a complex web of systemic information in which several electrical signals may be layered on top of each other in time and space, 10 which makes hard accessing a proper signal analysis. 11 Recently, Saraiva et al 12 have demonstrated that electrical signals in plants, measured as time series of low voltage variations in whole tissues, can exhibit high complex dynamic patterns (actually, chaotic behavior instead purely white noise). Moreover, the complexity of the electrical signals showed dependence of the environmental stimulation (osmotic stress), exhibiting burst of electrical spikes following a power law (i.e.…”

“…Herein, to work on a specific framework to settle this type of the study, we are adopting the term "electrome" 13 as a reference to the non-local electrophysiology measurements. Accordingly, in this study we have used EPG technique with sub-dermal electrodes inserted in 15-days-old seedlings, 12 supposedly representing the electrome of the whole plants insofar the measurements were performed in tissues (from epidermis to vascular vessels) located between root and shoot, accounting for a significant part of each individual seedling. Moreover, taking into account the non-linear dynamic of the plants electrophysiology, we have hypothesized that the stimuli, as applied uniformly producing a constant tension in the plants, could push the system to a critical state, exhibiting spikes without a characteristic size.…”