The excitability of plant cells: With a special emphasis on characean internodal cells

Abstract

This review describes the basic principles of electrophysiology using the generation of an action potential in characean internodal cells as a pedagogical tool. Electrophysiology has proven to be a powerful tool in understanding animal physiology and development, yet it has been virtually neglected in the study of plant physiology and development. This review is, in essence, a written account of my personal journey over the past five years to understand the basic principles of electrophysiology so that I can apply them to the study of plant physiology and development. My formal background is in classical botany and cell biology. I have learned electrophysiology by reading many books on physics written for the lay person and by talking informally with many patient biophysicists. I have written this review for the botanist who is unfamiliar with the basics of membrane biology but would like to know that she or he can become familiar with the latest information without much effort. I also wrote it for the neurophysiologist who is proficient in membrane biology but knows little about plant biology (but may want to teach one lecture on "plant action potentials"). And lastly, I wrote this for people interested in the history of science and how the studies of electrical and chemical communication in physiology and development progressed in the botanical and zoological disciplines.

Plant intelligence and attention

“…26,28 As reaction times (and hence quick shifts from one focus within the context of attention to another) make a difference for the survival of an organism, the relative speed of intercellular communication in plants is crucial for their inclusion among attentive subjects. If plants are "fast biosensors for molecular recognition of the direction of light, monitoring the environment and detecting insect attacks," 27,30 then their attentional modulations are on the par with sudden changes in environmental conditions that make up the concrete context of their growth and development.…”

Electrophysiology of Woody Plants

“…Initially developed for animal cells, this technique was rapidly adopted for plant cell studies (Hedrich & Schroeder 1989). Voltage clamp techniques were introduced to demonstrate the contribution of various ion currents involved in the AP in Chara cells (Lunevsky et al 1983;Wayne 1994). To this day, charophytic algae have served as important research models for higher plant cells electric behavior studies.…”

Plant intentionality and the phenomenological framework of plant intelligence

“…Still, the dynamic nature of plant growth and adaptation requires plant cells that are "inherently excitable and sensory." 18,27,28,49 Even if cells do not circulate in the bodies of plants, as they do in animal bodies, they generate action potentials and synthesize the protein RHD3, responsible for the proper arrangement of root cell files underlying the direction of root growth. 29 It is this directionality of growth, along with its deliberate regulation, that will hold the clue to the intentionality inherent in plant life.…”

“…Still, the dynamic nature of plant growth and adaptation requires plant cells that are "inherently excitable and sensory." 18,27,28,49 Even if cells do not circulate in the bodies of plants, as they do in animal bodies, they generate action potentials and synthesize the protein RHD3, responsible for the proper arrangement of root cell files underlying the direction of root growth.29 It is this directionality of growth, along with its deliberate regulation, that will hold the clue to the intentionality inherent in plant life.At the origins of phenomenology, intentionality was conceived as "consciousness of..." or, in strikingly spatial terms, as "directedness toward…" To be conscious is to intend something, that is to say, to be directed toward the intended object (the metaphysical concept this notion supplants is "will"). In light of this definition, the intentionality of plants may be understood as the movement of growth, directed toward the optimal patches of nutrientrich soil and sources of light.…”