The paper that I’ll be discussing today is Jagdish Chandra Bose and Plant Neurobiology by Prakash Narain Tandon, a celebrated Indian scientist.
When I was a school student in India, I often came across JC Bose’s claims of plants being sentient beings, having nervous systems, etc. However, these things were never part of the official curriculum (i.e. we never had to learn these things for tests). Bose’s statements in this matter have always been considered to be something of a not-completely-scientific, “the whole universe is connected by prāna”-type of claim by the larger scientific community. This paper assets that despite initial rejection, most of Bose’s claims have been proven to be correct by modern science in recent times.
By the time Bose retired from Presidency College, he was a world renowned physicist who was known to have studied radio waves even before Marconi (although the primacy debate is a complex one, there is evidence to suggest that there were scientists in Europe who had studied radio waves even before Bose). After retiring, Bose started working at Bose Institute (which he founded), and guided by his “Unity of Life” philosophy, started studying the effect of radio waves on inorganic matter. Finding their response to be “similar to animal muscle”, he now started studying plant physiology (the nervous system of plants). He would expose plants to various stimuli, and record their response through the use of ingenious instruments that he himself designed. His conclusion was that the nervous impulses of plants were similar to those of animals.
Bose studied both large plant parts and individual plant cells. He would connect microelectrodes to these cells, and record their response to stimuli. He concluded that plants contain receptors of stimuli, nerve cells that code these stimuli electrically and propagate these messages, and also motor organs that purportedly helped in carrying out a response to the stimuli. In this, he concluded that plants and animals have similar nervous systems. Bose said that the nervous system in plants was responsible for things like photosynthesis, ascent of sap, response to light, etc.
Bose said that the action potential of plant neurons follows the unipolarity of animal neurons. But what is Action Potential? This is an amazing video explanation of what it is. Action Potential is the electric potential via which neurons transmit messages. In resting state, the electric potential difference between the inside and the outside of neurons is -70 mV (the inside is negatively charged). When neurotransmitters activate the neuron (because a message is to be passed), this negative potential difference is destroyed by a stream of positive sodium ions that comes into the neuron from the outside. This causes lots of changes to the neurons, including inducing it to release neurotransmitters to activate the next neuron in line. The electric potential difference becomes positive, and then becomes negative again because the neuron loses a lot of potassium ions to the outside. The sodium-potassium pump on the cell membrane expends energy to exchange sodium and potassium ions to ensure that the neuron returns to its previous state before it was excited. Thus, the neuron enters the resting state again. This is the chemical mechanism by which a neuron conducts a message.
Where can one find the “nerves” of plants? Bose localized the nervous tissue in the phloem, which conducted both efferent and afferent nervous impulses. He also measured the speed of the nervous impulse, which he found to be 400 mm/sec. Although Burdon-Sanderson and Darwin had previously reported on nerve impulses in insectivorous plants, Bose’s studies over the next three decades were far wider and deeper. Although ignored after the 1930s, his studies have been found to be correct by modern experiments. The author claims that Baluska et al have not only confirmed Bose’s major findings, but have also advanced these further utilizing molecular biology, genomics, etc. Baluska seems to have published this paper in a journal that he himself is the editor of. Hence, these claims perhaps need to be investigated further.
Along with Action Potentials (APs) (common to plants and animals), Slow Wave Potentials (SWPs) or Variation Potentials (VPs) (found only in plants) are also used by plants to transmit nerve impulses. These SWPs do not propagate electrically, but by hydraulic pressure exerted by tissues found in the xylem. Some plants like Dionaea flytraps were found to possess unidirectional APs similar to those found in cardiac myocytes (cadiac muscle cells). This prompted Bose to poetically state that plants possess hearts that beat as long as they live.
At the molecular level, plants possess voltage gate channels (membranous proteins that are activated by change in electric potential and allow the exchange of ions), a vesicular trafficking apparatus (for the transport of proteins and other molecules within the cell plasma) etc, all of which are also found in animal cells. Trewavas also observed that water soluble ions were responsible for intra-cell communication, and also inducing changes in plants as a response to environmental conditions. We now know that there exist many such water-soluble (these are called cystolic) messengers in plants, as they do in animals.
Darwin had pointed out that the tip of the radicle (found in the roots) is endowed with sensitivity, and also directs the movements of adjoining parts. In this, it is like the brain.
Bose elaborated on this by saying that the radicle is stimulated by friction and the chemical constitution of the surround soil. The cells undergo contraction at appropriate times, causing their liquid contents to go up. This causes the ascent of sap. Baluska et all carried these claims even further, and stated that within the root apex of the maize plant, there is a “command centre” which facilitates the long distance travel of nervous impulses, and instructs the plant to move towards positive stimuli (and away from negative stimuli). Tandon rejects the notion that such a command centre is anywhere near as complex as an animal brain.
Bose found the nerve cells in plants to be elongated tubes, and the dividing membrane between them to be the synapse (the gap between animal neurons where messages are transmitted between neurons). This claim has been substantiated by Barlow, who said that plant synapses share many characteristics with animal synapses. Plants also use many of the same neurotransmitters as animals like acetylcholine, glutamate and -aminobutyric acid.
Plant Memory, Learning and Intelligence
Bose claimed that plants are intelligent, have memory, and are capable of learning. Tandon makes the claim that Trewavas describes a large number of protein kinases in plant neural pathways, and hence finds their nervous system to be similar to that of animals. On skimming Trevawas’ paper however, I mostly found it to say that although there do exist protein kinases in plants, the neural systems found in plants differ from that of animals in important ways.
In another paper, Trewavas claims that one important difference between plant and animal nervous systems is the timescale of response- plants respond much more slowly to external stimuli. Hence, we need time scale photography to properly study the plant neural response. Also, if intelligence can be thought of as “a capacity for problem solving”, then plants show signs of intelligence as they change their architecture, physiology and phenotype in order to compete for resources, forage for food, and protect themselves against harsh elements of the environment.
Barlow substantiates these arguments, claiming that plants rapidly convert external stimuli to electrochemical signals, which cause them to change their physiology. He also claims that plants do have memory, as their decision making would involve recollection of previously stored memories. Barlow also says that roots experience four stimuli at once (touch, gravity, humidity and light), and have to decide how to obtain the optical mix of all. Hence, plants do possess the decision making aspect of intelligence.
With regard to plant intelligence, Baluska et al make the following claim:
‘Recent advances in chemical ecology reveal the astonishing communicative complexity of higher plants as exemplified by the battery of volatile substances which they produce and sense in order to share with other organisms information about their physiological state”
Gruntman and Novoplansky from Israel also claim that B. Dactyltoides are able to differentiate between themselves and other plants, and if a plant has multiple roots, each set of roots identities the other as belonging to the same plant (and hence these roots don’t compete with each other for resources). But how do plants recognize themselves and others? The authors claim that this is from the internal oscillations of hormones like auxin and cytokines. The frequency of this oscillation is unique to each plant, and can be measured externally by roots.
Bose claimed that
“these trees have a life like ours……they eat and grow…….face poverty, sorrows and sufferings. This poverty may……induce them to steal and rob…….they help each other, develop friendships, sacrifice their lives for their children”
The author finds that this sentiment is not yet fully supported by the scientific data collected by Bose. However, these claims may be further ratified when more experiments are done in this realm.
Bose single-handedly created the field of Plant Neurobiology. Although the establishment of this field has its opponents, even the most vocal of these opponents cannot find fault with any of Bose’s scientific claims. The author hopes that plant and animal neuroscientists communicate better with each other in the future, and find the time and resources to study this field more. Hopefully, such studies will ratify even more of Bose’s revolutionary ideas and claims.