If you do not believe in Dryads (figure 1) and Elves (figure 2) as spirits that live in plants, you may want to reconsider. Many people believe that plants do not feel as animals do but new research is proving this wrong.

Figure 1: Here Dryads live.
Image by Victoria Roshchina

In the mid-19th Century, the animal physiologist Claude Bernard, while pondering about the phenomenon of irritability as a fundamental property of all living organisms, suggested that the common mechanisms of perception and   quick reaction to external influences must be   present in all organisms including plants.

Figure 2: Little Elves inhabit as magic spirits within a flower.
Image by Vera Sidelnikova and Victoria Roshchina

In  Leçons sur les phénomènes de la vie  communs aux animaux at aux végétaux [1]  (1878), he writes: “the ability that makes up the essential condition of all phenomena of living plants and animals, as there is in the simplest way. This ability is irritability”. His conclusion was based in part on observations of the Mimosa sp. leaves. Some Mimosas are commonly known for their sensitive leaves, which react by contriving when touched. Bernard found that these plants behaved similarly to animals when exposed to anesthetics: the leaves stopped responding to touch as the anaesthetic blocked the excitation pulses. Further experiments have shown that electric impulses are transmitted both in animals and plants and are used in communication between parts within an organism. Moreover, while visiting the Sorbonne in 1926, the scientist, naturalist and physician Jagadish Chandra Bose proposed that there was an analogue to the animal neuronal system in plants acting on possible common nervous mechanisms. However, it was not until the second half of the 20th Century that the molecular mechanism of plant irritability, including the perception of an external stimulus, sparked mainstream scientific interest. Today, we know that plants in general are sensitive in a similar manner to Mimosas (figure 3) although their responses are not easily visible to the naked eye.

Figure 3: Response of Mimosa pudica leaves to mechanical irritation dependent on the presence of noradrenaline found in the specialized structures called pulvini.
Image by Victoria Roshchina

Once the message has been received, the part of the body affected will respond to the stimulus.  Plants also contain those compounds that act like neurotransmitters in animals. Their functions in plants, however, seem to be quite varied. For example, histamines common in animal inflammatory responses, are present in some plants as a defense against predators and was first discovered in stinging emergences of burning nettle (Urtica urens) (Emmelin & Feldberg 1947, 1949), and later in other plants (Saxena 1965, 1966). Buelow and Gisvold (1944), showed the presence of catecholamines in winged four o’clock (Hermidium alipes), while serotonin, noradrenaline, and other related compounds have been identified in bananas (Waalkes et al., 1958).

Interestingly, during stressful conditions one may see a red coloration on some plants (figure 4). For example, in Impatiens noli-tangere, a red roots may be observed if the plant is grown in narrow chinks, while in normal soil conditions their roots have no such coloration. Appearance of red in parts of the algae Chara vulgaris results from stress due to growing in highly dense areas vs. algae growing with free space in aquariums where no red is visible.

 Figure 4: The natural markers of stress include accumulation of dopamine in roots of Impatiens noli-tangere and in Chara vulgaris. Image by Victoria Roshchina
Figure 4: The natural markers of stress include accumulation of dopamine in roots of Impatiens noli-tangere and in Chara vulgaris. Image by Victoria Roshchina

In addition to specialized mediator functions in organisms that have nervous systems, the discovery that these molecules have other roles in plants has triggered new questions about their role in evolution. Traditional directions in the study of neurotransmitters present in plants have looked at regulation of differentiation and development. For example, serotonin and melatonin have been found to be both regulators of plant growth (Erland & Saxena, 2016, 2017). Further, a wide variety of experiments have found other functions of neurotransmitters in plants such as acting as growth promoters (Fluck & Jaffe, 1974; Hartman & Gupta, 1989; Tretin & Kendrick, 1991; Roshchina, 2001; Murch, 2006; Kulma & Szopa, 2007; Ramakrishna et al., 2011; Erland & Saxena, 2016, 2017; Ramakrishna & Roshchina, 2019).

New lines in these studies are looking at the many roles of neurotransmitters released by all living organisms from microorganism to plants and animals. Chemical signaling via neurotransmitters is used in communication across organisms (stinging nettle releases histamines that rigger pain in some animals warning them to stay away), and in between cells (Mimosa leaves close as a result of internal messages within the plant after being triggered by external touch) (Roshchina, 2001, 2010). Moreover, there is a bridge between human health and the presence of neurotransmitters and even anti-neurotransmitters in food and medicinal plants. Since plants contain neurotransmitters, they are promising sources for pharmaceuticals. For example, nettle leaves and stems are rich in acetylcholine, dopamine, serotonin and histamine; while banana peels are rich in dopamine and serotonin.

Another interesting aspect is that plants are sensitive to the same toxins and poisons that animals are. Treatment with many insecticides leads to damage and even plant death. Remember that neurotransmitter systems are similar across all organisms! Toxins harmful to the nervous system of animals seem to be equally dangerous for plants. Accumulation of some toxic compounds in plant foods is a hazard for humans. The presence of neurotransmitters in plants provide new opportunities in pharmacology and medicine as we look for new drugs. The discovery of these molecules in plants is allowing us to understand plants in better and exciting ways and it may not be farfetched to think that the Dryads and Elves are indeed speaking to us.

About the Author

Garden, refuge of thoughtful Dryads…
Alexander Pushkin “Eugenii Onegin”, chapter 2.

Dr. Victoria Roshchina is a senior scientist and Professor at the Institute of Cell Biophysics, Russian Academy of Sciences. She has published over 250 papers on plant cell biology with a special interest on neurotransmitters functions across the life cycle of plants, which has led her towards discussions of novel ideas such as plant intelligence and communication. She is the author of more than 250 publications, including several books on neurotransmitters in plants. She feels comfortable strolling around forests where Dryads and Elves may dwell.


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Posted by Shweta Dixit