Nerves or herbs?

 

 

 Illustrations’ source
 
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 «Beaucoup de gens ont un arbre planté dans la tête, mais le cerveau lui-même est une herbe beaucoup plus qu’un arbre. “L’axone et la dendrite s’enroulent l’un autour de l’autre comme le liseron autour de la ronce, avec une synapse à chaque épine”»/

 «Many people have a tree growing in their heads, but the brain itself is much more a grass than a tree. “The axon and dendrite twist around each other like bindweed around brambles, with synapses at each of the thorns of the bramble – the dendritic spines”»

– Deleuze and Guattari, “Mille Plateaux”
(quoting Steven Rose’s “The Conscious Brain
about the electrical nature of nerve signals).

 

«Recent advances in plant cell biology and neurosciences reveal surprising similarities between plants cells and neurons. (…) In plants, neuronal features are especially prominent in root cells of the transition zone interpolated between the apical meristem and elongation region. (…) Plant neurobiology experiences difficult start which is related to deeply-rooted, almost ‘dogmatic’, view of plants as passive creatures not in a need of any neuronal processes and capabilities. One can trace this strong belief back to Aristoteles, who makes clear that it will be rather tough to break this spell despite the fact that one of the first attempts to rehabilitate plants was done by nobody less than Charles Darwin. Charles Darwin proposed that the root apex represents the brain-like anterior pole of the plant bodyand our recent data support this proposal strongly. (…) Recent genomic analysis and projects resulted in surprising neuronal complexity which was not expected in these sessile (corals) or only slowly moving (Trichoplax) multicellular animals. As they are believed to lack brains (corals) and even neurons (Trichoplax) and, similarly as plants, considered not to be in any need of neurobiological apparatus due to sessile life-style; these data represent new challenge for the neurosciences. Until now, neurosciences typically associate complex neural systems with movements of evolutionary more advanced organisms; with humans at the top, being considered for the only organism having higher levels of consciousness. Importantly, as sessile multicellular animals show almost all ‘so-called’ plant-specific features, the profound differences between animals and plants are, in fact, rather secondary features of their sessile life-style. They do not represent, as generally accepted, the plant-animal schism, which can be traced back to Aristoteles and his philosophy. (…) Biological systems actively experience environment, both abiotic and biotic, and store (memorize) the obtained information in form of embodied knowledge. Via active accumulation of sensory-mediated experiences, sensory cells (neurons) change their structure, development, cell-cell communication (synaptic plasticity), as well as their activities and future fates. This important phenomenon is obvious already at subcellular levels such as cilium of sensory neuron which are not static structures but plastic antennae whose structure and function depends on the history of perceptions and signaling activities. As sensory perceptions and experiences represent non-genomic information; neurons, brains, plants and their cells, as well as bacteria and their colonies are phenotypically plastic. They are less hard-wired genetically but shaped structurally via experience-dependent neural processes based on sensory perceptions received from environment. As it is the case of developmentally open and plastic plants; also neurons, their networks, and animal brains are shaped besides genetically (Aristotelian bottom-top direction) also environmentally (Platonian top-down direction). This feature makes the essence of sensory networks for unique realm in biology, realm which is not reserved only for humans or animals, realm which spans across all biological levels, and realm which is evolutionarily as ancient as the life itself. Obviously, as stated also by Szentágothai and Érdi, the essence of neural needs revision and re-examination in biology. (…) Contemporary biology is still trapped in Aristotelian paradigm that plants differ profoundly from animals due to their insensitive nature and lacking the abilities to actively reconstruct environment from past sensory experiences in order to perform adaptive behavior allowing survival despite challenging environmental conditions. Recent advances in plant sciences have revealed that the sensory plants do not differ profoundly from the sensory animals. (…) Science is inevitably subjective human activity, which has produced our current anthropocentric world-views. As a consequence, this biological paradigm-shift necessary to escape from the Aristotelian trap might turn out to be even more complicated and difficult one as the physical paradigm shift. In fact, it started with Charles Darwin some 150 years ago and is still not completed. As Michael Pollan stated, the ‘disease of human self-importance’ is firmly rooted in our scientific thinking. We still did not ‘digested’ lessons from the Darwinian revolution 150 years ago that humans are only ‘one fiber in the fabric of life’ in which evolution and co-evolution is working on us in the same way as it is working on all others».

František Baluška and Stefano Mancuso

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«Electrical signaling, short-term memory and rapid closure of the carnivorous plant Dionaea muscipula Ellis (Venus flytrap) have been attracting the attention of researchers since the XIX century. We found that the electrical stimulus between a midrib and a lobe closes the Venus flytrap upper leaf without mechanical stimulation of trigger hairs. The closing time of Venus flytrap by electrical stimulation is the same as mechanically induced closing. Transmission of a single electrical charge between a lobe and the midrib causes closure of the trap and induces an electrical signal propagating between both lobes and midrib. The Venus flytrap can accumulate small subthreshold charges, and when the threshold value is reached, the trap closes. Repeated application of smaller charges demonstrates the summation of stimuli. The cumulative character of electrical stimuli points to the existence of short-term electrical memory in the Venus flytrap

– Alexander G. Volkov, Holly Carrell, Tejumade Adesina, Vladislav S. Markin and Emil Jovanov, “Plant electrical memory“, Volume 3, Issue 7, July 2008, pages 490-492, http://dx.doi.org/10.4161/psb.3.7.5684

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«[So the plant] has a specific memory for the light which builds its immunity against pathogens, and it can adjust to varying light conditions. Every day or week of the season has a characteristic light quality. Plants perform a sort of biological light computation, using information contained in the light to immunise themselves against diseases.»

– Prof. Stanislaw Karpinski, Warsaw University of Life Sciences, Poland.

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Charles Darwin and the plant root brain

Charles Darwin wrote that he was “always pleased to exalt plants in the scale of organised beings” and “felt an especial pleasure in showing how many and what admirably well adapted movements the tip of a root possesses”(1). Darwin went so far as to say that the root tip acts like a brain, located within the anterior end (sic) of the plant body, “receiving impressions from the sense organs and directing the root’s several movements”(2). What clearly impressed Darwin was the ability of the root to perceive, often simultaneously, multiple vectorial stimuli – touch, moisture, light, gravity – and then make a “decision” about which “final purpose”, or bending response, to follow.  It was very surprising because, as Darwin admitted, “plants do not of course possess nerves or a central nervous system”(2).

1.Darwin C. 1880. “The Power of Movements in Plants”. London: John Murray.
2.Darwin C. 1876/1983. “Autobiography”. In G de Beer, ed; Charles Darwin and TH Huxley, Autobiographies. Oxford: Oxford University Press. p 8-88.

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“Mimosa pudica” – Sensitive Plant

.

Plants’ sensibilia

A lotus flower opens as the day breaks and closes as darkness falls.

“The touch me not” plant, Mimosa pudica or Mimosa sensitiva, exhibits rapid leaf folding. The extent and speed of the response depends on how strong is the touch stimulus provided.

The “Venus fly trap”, Dionea, exhibits rapid trap closure when an insect comes in contact with it.

Desmodium gyrans, the famous Indian telegraph plant is an erect tropical Asian shrub which have one central and two small lateral leaflets. Darwin called the plant Hedysarum; modern botanists call it either Desmodium gyrans or, more correctly these days, Codariocalyx motorius; its common name is Telegraph plant or Semaphore plant after the leaf movements, which resemble semaphore signals. It is a leguminous plant, belonging to the family Papilionaceae (included in Leguminosae). The lateral leaflets of this plant show spontaneous jerking up and down a dance under the influence of sunshine. Darwin studied movements of the little leaflets of Desmodium gyrans, after borrowing a specimen from Sir Joseph D. Hooker, the director of the Royal Botanical Garden, Kew, England, a repository for thousands of plant species collected from all over the world. Hooker had obtained the specimen from Sikkim, a state in the northeast India in the Himalayan ranges. On Oct. 31, 1873, Charles Darwin wrote to Sir Joseph Hooker, “Now I want to tell you, for my own pleasure, about the movements of Desmodium [gyrans] (…). The little leaflets never go to sleep, and this seems to me very odd; they are at their games of play as late as 11 o’clock at night and probably later”. Darwin began studying Desmodium gyrans – or Hedysarum, as he sometimes called it – and the movements of its little leaflets as early as 1855, after borrowing one of Hooker’s specimens. “I do hope it is not very precious,” Darwin wrote, thanking Hooker for the loan, “for, as I told you, it is for probably a most foolish purpose. I read somewhere that no plant closes its leaves so promptly in darkness, and I want to cover it up daily for half an hour, and see if I can teach it to close by itself”. On July 24, 1878, he wrote to German researcher Fritz Muller: “I am working away as hard as I can at all the multifarious kinds of movements of plants and am trying to reduce them to some simple rules, but whether I shall succeed I do not know”. Characteristically, Darwin did succeed. Two years later, a book-length monograph titled “The Power of Movement in Plants” was published. It was the last book published during Darwin’s lifetime, representing more than two decades of research on moving plant species. During that time he performed round after round of experiments, measuring the movements of the leaves in all conditions, depriving the plants of light and nutrients, syringing water onto the leaves to simulate rainfall, subjecting them to extreme temperatures, and removing slices from the plants. Darwin’s Desmodium gyrans specimen moved when he syringed water onto the leaves. As the water landed on its pointed little leaflets, it set the plant twitching, and Darwin measured the movements. He wrote again to Muller in April 1881, and concluded that the movements were designed “to shoot off the drops of water”. “If you are caught in heavy rain”, he continued, “I should be very much obliged if you would keep this notion in your mind, and look to the position of such leaves”. Still, Darwin was not finished with the plant. On April 16, 1881, a year after the publication of “The Power of Movement in Plants”, Darwin dispatched a note to his friend Lord Avebury. The first line reads, “Will you be so kind as to send and lend me the Desmodium gyrans by the bearer who brings this note”. Once again, he was requesting a specimen; but Darwin never finished his research on Desmodium gyrans. He died a year later, on April 19, 1882. He was buried next to Sir Isaac Newton, beneath a flagstone in the north aisle of Westminster Abbey, and any theories he had secretly harbored about the plant were buried with him.

Jagadish Chandra Bose (1858-1937, D. Sc. from London University, 1896) was a Bengali polymath: a physicist, biologist, botanist, archaeologist, and writer of science fiction. His major contribution in the field of biophysics was the demonstration of the electrical nature of the conduction of various stimuli (wounds, chemical agents) in plants. These claims were experimentally proved by Wildon et al. (Nature, 1992, 360, 62–65). For his investigations, Bose invented several novel and highly sensitive instruments. In 1917, he invented the kreskograph – that could record a growth as small as 1/100,000 inch per second -, to show that plants responded to various stimuli as if they had nervous systems like the animals. Bose demonstrated that plant tissues under different kinds of stimuli like touch, presence, direction of light, mechanical vibrations, application of heat, electric shock, chemicals and drugs, produce electric response similar to that produced by animal tissues. He also tried to demonstrate that similar electric response to stimulation could be noticed in certain inorganic systems. Bose’s experiments on plants were mostly performed on Mimosa pudica and Desmondium gyrans (Indian Telegraph plant). He demonstrated that plants grow faster in pleasant music and their growth is retarded in noise or harsh sound. This was experimentally verified later on.  He also studied for the first time action of microwaves in plant tissues and corresponding changes in the cell membrane potential, mechanism of effect of seasons in plants, effect of chemical inhibitor on plant stimuli, effect of temperature etc. He claimed that plants can “feel pain, understand affection, etc.“, from the analysis of the nature of variation of the cell membrane potential of plants, under different circumstances. D.M. Bose, who succeeded Bose as Director of the Bose Institute, has pointed out “his model of an electric eye which records with electric signals messages received from outside world, his physical model of memory as a mechanism for storing information justified his being considered a precursor of the modern discipline of cybernetics”. It is now recognised that Bose had made very significant contributions to the field of chronobiology and circadian rhythms even before these two technical terms were coined.

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Gendun Chopel’s view that plants have conscience and are sentient beings

«”Yet, to be excessively proud, that is, to continually assert that even the smallest parts of all the explanations in our scriptures are unmistaken, seems beautiful only temporarily; it is a pointless stubbornness. Nothing will come from your being angry at me. If I am permitted to remain silent, I can control the peace of my own ears, but others are not benefited at all. For example, the followers of the new reasoning assert that the trees are sentient because they fold their leaves at night. [The traditional Buddhist response] was to say, “Well then, it must follow for you that pieces of leather are sentient because if they come near a fire, they shrink.” It is acceptable to say, however, that are flowers named Santeu and Venus [flytrap] that, as soon as an insect lands on them, grab it, suck its blood, hollow out the body, and discard it on the ground. Every Santeu kills more than two hundred insects every day, and the bodies just keep pilling up. Similarly, in another continent, there are many trees that suck blood when they catch humans or animals. This is clear to everyone. Since these are easy to understand, I have explained them, but recently, a Bengali scholar in India invented an electronic machine that actually recognizes the presence of life. If such a flower were brought before us, would we dare contest their claim? Would we say it is the nature of the plant? Even those who assert that insects and so forth are alive must at some point show various proofs for the existence of life. Would we describe the plant as a trifling hell? However, all types of those flowers are just like that. Look at the illustration I have drawn [not extant]. The Sinhalese scientists who are Buddhists say the Master had this in mind when he proibited [monks from] cutting plants. But that explanation is [only] temporarily convincing.”

He begins with the concession, relatively rare in the genre, that it is a short-sighted and stubborn to hold that every point of Buddhist doctrine is unmistaken and confirmed by modern science. Recognizing that such a statement might seem heretical to his readers, he asks for their indulgence. He obviously feels that what he has to say is important for Tibetans to hear. If he remains silent, he can preserve the peace of his ears, because he will not have to listen to the codemnations that his words will provoke. But if he remains silent, he will not be heard, and it is his conviction that his words are important.

He then begins a discussion of an important point on which Buddhism and Science disagree: the sentience of plants. This question also was a point of disagreement between the Buddhists and the Jains in ancient India. The Buddhists argued that there were six, and only six, types of sentiente beings, and hence six possibilities for rebirth: gods, demigods, humans, animals, ghosts,  and hell beings. Plants and inanimate objects did not have consciousness, and thus one could not be reborn as a plant or inanimate object. The Jains posited the existence of beings that had one sense organ (ekendriya), the sense of touch, which included plants, stones and water. Among the Jain evidence for the sentience of plants was that some plants fold their leaves at night. The Buddhists would counter with the absurd consequence that a piece of leather must be sentient because, when it is placed near a fire, it draws back.

Gendun Chopel was known as a skilled debater his days in the monastery. One of the marks by which this proficiency was measured in Tibet was the ability to successfully defend non-Buddhist (and hence wrong) position against Buddhist (and hence correct) position. Although he does not mention it here, Gendun Chopel was famous in his youth for having successfully upheld the Jain view that plants have consciousness. Arriving in India may years later, he seems to have found empirical proof. He consequently describes the Venus flytrap and another carnivorous plant called Santeu (perhaps the Nepenthes or ‘pitcher plant’ found in Sri Lanka) and also provided a drawing, which apparently has been lost. His claim that, “in another continent, there are many trees that suck blood when they catch humans or animals” seems to have passed over into the realm of the fantastic [Note: Though, Nepenthes rajah digests small vertebrates, mammals, birds, insects, frogs…]. What he refers to when he describes “a machine that actually recognizes the presence of life” is unclear. [Note: the commentator ignores the achievements of Jagadish Chandra Bose, 1858-1937] Gendun Chopel’s understanding of botany was such that he concluded that a Venus flytrap has consciousness because it consumes insects. For him, this is clear empirical evidence that the Buddhist view regarding the consciousness of plants is mistaken. His question, then, is how Buddhists should respond. One might concede that it is indeed the nature of the plant, and that the plant is sentient.

There is also a doctrinal loophole available to the Buddhist. Among the various forms of hell described in the Buddhist cosmographies are the trifling (pradesika) hells. Within these categories are beings temporarily born inside inanimate objects (rocks and brooms are sometimes mentioned) and who mistakenly identify such objects as their bodies. Thus, Gendun Chopel asks somewhat sarcastically whether the Buddhist might wish to uphold the position that plants lack consciousness by saying that a Venus flytrap is a case of a trifling hell. But this would not be an adequate response, because in his view all plants have consciousness.

Gendun Chopel mentions that Sinhalese scientists (who are also Buddhists) acknowledge that plants have consciousness and argue that the Buddha knew this because he prohibited monks from damaging plants. It is the case that damaging a living plant is one of the minor violations (to be expiated through confession) of the monastic code. The Buddha is said to have made this rule, however, because plants (especially trees) are sometimes the abodes of local spirits; the term translated as “plant” is bhutagama, “abode of a being”.»

– Donald S. Lopez, “Buddhism & science: a guide for the perplexed”, p. 122-124.

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