Neurotransmitters, neuroregulators and neurotoxins in the life of plants

Abstract

Cao, J., Cole, I. B. and Murch, S. J. 2006. Neurotransmitters, neuroregulators and neurotoxins in the life of plants. Can. J. Plant Sci. 86: 1183-1188. Recent evidence has shown that neurologically active compounds play an important role in the physiology of higher plants. The human neurotransmitter melatonin (N-acetyl-5-methoxytryptamine) has been found in more than 140 different plant species and is associated with flower and seed development, reproductive capacity and root growth. Hyperforin, once thought to be characteristic of St. John's wort (Hypericum perforatum L.), has now been found in several other plant species and preliminary findings indicate that it may function as a modulator of plant cell polarity and ion flow. The excitotoxin, β-methylamino-L-alanine, has been used to selectively isolate glutamate receptor mutants in Arabidopsis, and these studies are leading to new understandings of plant cell development. The study of these and other plant neurochemicals may lead to a new understanding of plant signal transmission and the mechanisms by which plant cells sense, interpret and respond to environmental cues. Mots clés: Neuromédiateurs, mélatonine, hyperforine, plante médicinale Plant cells produce a wide range of common and uncommon chemical compounds that ensure the survival of the individual and the species. Most frequently, plant responsive compounds are thought of as secondary metabolites, compounds that are not essential for the growth and development of the plant, but that accumulate in response to environmental stressors. However, there is another group of phytochemicals that includes compounds historically classified as primary or secondary metabolites that are essential for the reallocation of resources in plants in response to changing environmental factors. Neurologically active compounds fall into this mixed category and include such diverse examples as indoleacetic acid, caffeine, epinephrine, acetylcholine, opiates, nicotine, levodopa, serotonin, melatonin, hyperforin and many others. In mammalian systems, neurologically active compounds mediate brain function so that external stimuli are translated into immediate responses. The human neurotransmitter melatonin (N-acetyl-5-methoxytryptamine) is a ubiquitous, highly conserved molecule associated with timing of circadian rhythms in many organisms, including higher plants. Other compounds such as hyperforin, now isolated from several plant species, may function as serotonin transport inhibitors or nonspecific cation channel activators in human brains and potentially in higher plants. A different group of neuroregulatory molecules produced by plants overstimulate human neurons, resulting in neuronal cell damage and death. Excitotoxins such as β-methylamino-L-alanine not only affect human health but are also regulatory molecules redirecting plant growth. Plants lack the "flight or flight" response common

Analytical tools for elucidating the biological role of melatonin in plants by LC‐MS/MS

“…In 1995, Dubbels et al and Hattori and colleagues demonstrated the presence of MT in plants. Since then, it has been found in more than 140 different plant species . MT has also been found in numerous taxa, including fungi, bacteria, protozoans, and invertebrates .…”

“…An elevation of MT in reproductive tissue, with declining MT level as the plant ages, was observed in Pharbitis nil [25]. The accumulation of MT in reproductive tissues, seeds and fruits, may be indicative of a mechanism for protection of the tissues from oxidative damage arising from drought, cold, heat, UV light, or environmental toxins [6,26].…”

Targeted and Untargeted Phytochemistry of Ligusticum canbyi: Indoleamines, Phthalides, Antioxidant Potential, and Use of Metabolomics as a Hypothesis-Generating Technique for Compound Discovery

“…Bip), skullcap (Scutellaria baicalensis Georgi), and devilʼs trumpet (Datura metel L.) [17,18]. Although the exact role for these neurochemicals is yet to be fully understood, potential roles for MEL and 5HT in plant and human tissues include detoxification of free radicals [19,20] and/or hormonal signaling pathways [21][22][23].…”

Microchip electrophoresis‐single wall carbon nanotube press‐transferred electrodes for fast and reliable electrochemical sensing of melatonin and its precursors

“…Thereafter, MT was considered exclusively as an animal hormone, specifically a neurohormone for nearly four decades until the discovery in plants. Since then, it has been found in more than 140 different plant species and foods [14][15][16][17][18][19][20][21][22][23][24]. MT usually appears in the presence of its precursors; therefore, their simultaneous determination may be extremely important to understand its biosynthesis pathway and biological function in plants.…”