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What Bose proved 100 years ago, AI proves again – Plants produce sounds to stimuli

21 April, 2023 08:58:13
What Bose proved 100 years ago, AI proves again – Plants produce sounds to stimuli

Last week international scientists proved through Artificial Intelligence that plants produce sounds, inaudible to human ears and gave a stamp to the research done by Jagadish Chandra Bose a century ago. The researchers at the Tel Aviv University of Israel thanked Bose’s research and acknowledged him 100 years later for the ways in which Bose through gross scientific instruments, had proved how plants respond to external stimuli and produce their own neuro responses. Their emitted sounds are similar to human speech but at ultrasonic frequencies, which we cannot hear but is audible to bats, insects, and mice.

They used machine learning algorithms that learned to distinguish between different plants and different stress types and recorded sounds emitted by plants in the form of airborne waves similar to popcorn pops. It’s amazing to note how a century ago Bose used a simple crescograph, a measuring tool he invented to track growth in plants by magnifying the process 10,000 times. He did not have any sophisticated machines like today and not just that being an Indian, he was not even allowed access to the science labs by the British. Still, Bose proved plants have a well-defined nervous system. He found that their growth changed according to different stimuli: pleasant sounds spurred it while harsh ones retarded it. He went on to test how plant tissues react to seasonal changes, chemical inhibitors, and temperature variations, and how they feel pain and understand affection.

Born in the Munshiganj district of Bangladesh (then part of India) in 1858, Bose was a physicist, botanist, and even an author during his lifetime—all this even though he was not allowed access to science labs under racist British rule. Amazingly his wireless transmission, the world’s first, for which Marconi got the Nobel Prize and Bose was denied for being an Indian under colonisers, had also recently attracted international attention when Marconi’s grandson gave the credit to Bose. Similarly, the Tel Aviv study published in the International Journal ‘Cell’ on Thursday last week gives credit to Bose. Their study on cactuses, corn, tomatoes, tobacco, and wheat suggests that plants typically emit sounds under stress from dehydration or from having their stems severed. They also found that each type of stress is associated with a specific and distinct type of sound. Unstressed plants emitted less than one sound per hour, while plants under stress -- either dehydrated or injured because their stems were severed -- emitted between 30 and 50 sounds per hour. For example, in a dehydrating tomato plant, the sounds become noticeable by the second day, peak by the fifth day of dehydration, and stop when the plant is completely dehydrated.

As K.R. Shivanna, a plant scientist at the Ashoka Trust for Research in Ecology and Environment, Bangalore said: “Bose was much ahead of his time, and over the decades, there has been growing evidence that plants themselves perceive and respond to sounds.” When Jagdish Chandra Bose, then a renowned physicist, devoted himself entirely to research in botany, after his superannuation at Presidency College, it came as a surprise to many. The research on the plant nervous system by Bose during this period was pioneering, and recognized by recent plant biologists globally as the first in the field. His findings were so revolutionary at the time of their proclamation that they aroused disbelief and contradiction. Surprisingly, not many at that time took up such investigations, and once accepted with reluctance, there was practically very little activity in the field for the next several decades. More than a hundred years later, recent advances in molecular biology, genomics, ecology, and neurophysiology have led to renewed interest, confirming most of Bose’s observations. 

Between 1900 and 1935, Jagdish Chandra Bose, working in Calcutta at the Presidency College and later at the Bose Institute, established by him after his retirement, dedicated himself to research solely in the field of plant physiology. This, no doubt, was something unexpected and unusual for a distinguished physicist who had already attained international recognition for his work on the optical properties of radiowaves and wireless transmission ahead of Guglielmo Marconi. His observations and findings transformed him into a plant physiologist. He devised several ingenious instruments enabling him to record the plant responses to a variety of stimuli. Notwithstanding some opposition, ridicule, disbelief, and criticism initially, his observations in the early 1900s ultimately found general acceptance by eminent biologists and plant physiologists globally. He forcefully presented his claim through lecture demonstrations across the UK and Europe that the nerve impulses in all types of plants were similar to those in animals.

From the general electrical response of different parts of the plant, he proceeded to record responses from individual cells using a microelectrode recording system devised by him. In those early years, prior to the 1920s, such microelectrode studies had not yet been initiated on single neurons in animals. Bose reported, “Plants also have receptors for stimuli, conductors (nerves) which electrically code and propagate the stimulus, and efferent or terminal motor organs.” He established the nervous impulse and its transmission in plants, responsible for the control of many physiological functions including growth, the ascent of the sap, respiration, photosynthesis, motor activity, and response to the environment - light, heat, trauma, shock, and drugs and toxins. 

Bose became the first to use the term ‘Plant Nerve.’ The continued elaboration of the diverse aspects of neurotransmission by Bose for the next three decades has no parallel in the history of plant nervous system research. While there were some references to the plant nervous system and activity in the 1930s, there were limited reports on the subject till after the 1950s. However, later publications in the field confirmed most of his findings and acknowledged Bose's contributions in this field as the most important pioneering work.

Baluska et al not only confirmed Bose's major observations but also advanced these further by utilizing tools and techniques of modern molecular and cellular biology, chemical ecology and genomics. Though molecular biology was not yet a distinct discipline during Bose's time, in 1918, in his lecture on ‘Control of Nervous Impulse’, he stated, “The propagation of nervous impulse is a phenomenon of the transmission of molecular disturbance.”

Today advances in this field have led to the introduction of the term ‘Plant Neurobiology’ as a distinct discipline. Plant Neurobiology is a newly initiated field of plant biology that aims to understand how plants perceive their circumstances and respond to environmental input in an integrated fashion taking into account the combined molecular, chemical and electrical components of intercellular plant signaling and no doubt the Father of all these is none other than Bose. In his talk at Guildhouse in London on June 30, 1929, Bose poetically described this phenomenon, “In many other ways we are able to find that plant has a heart that beats continuously as long as life remains.”At the molecular level, plants have many, if not all, components found in the animal neuronal system. There are voltage-gated channels, a vesicular trafficking apparatus sensitive to calcium signals and other components of the neuronal cell infrastructure.

Bose also pointed out the sensory functions of the roots “Fine rootlets in contact with the soil are stimulated by friction and the presence of chemical substances. The cells thus undergo contraction forcing their liquid contents into others higher up.” Bose attributed the ascent of sap to this sensory-motor activity of the rootlets. It appears that Bose used the term nerve for nerve cells (or neurons) because the nerves do not have synapses. It may be pointed out that the term ‘neuron’ had not yet been coined then.

Bose’s lifelong research contributed to an overall conclusion that plants have an electromechanical pulse, a nervous system, a form of intelligence, and are capable of remembering and learning. A century later, some of these concepts entered mainstream literature.

Source: Some data taken from Indian Journal for Medical Research

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