Secrets of plant intelligence

 

Secrets of plant intelligence

We all know the plants do respond to stimuli as proved by the Eminent Scientist, Prof. Acharya Jagadish Chandra Bose. Not only Prof. Bose proved this phenomenon through various experiments, he further drew several similarities between the life of plants with animals by using his invented plant growth measuring instrument, the crescograph, and the resonant recorder. 

However, do we know about the brain, senses, and thinking power of plants or rather say plant intelligence? The matter is very intriguing and still a point of research to Scientists. If you think a little about it, one plant called “touch-me-not” (Mimosa Pudica) may easily come to your mind whose leaves fold when touched. One may get more examples from either some plants whose flower petals open with the sunrise and some insectivorous plants (e.g., Venus flytrap) that show quick response in the presence of insects and catch them as prey. Surprisingly, if the leaf-eating larvae of an insect come and start eating the leaves, then immediately the larvae-resistant toxic chemicals begin to form in every cell of the plant. Aren’t the fascinating examples of plant intelligence? Even more bizarre, scientists have found, is that even if the plant is run in front of the larvae by recording the sound of leaf food, the larvae-resistant toxic chemicals soon begin to form in the plant! Scientists speculate that even though the plant has no visual senses, it can sense external stimuli better. All of these events are just witness to the response of plants to stimuli and well-proven cases of plant intelligence. 

If we look at the history of science, we can see that many years ago, in the year 1880, legendary naturalist Charles Darwin gave an interesting idea by observing the behavior of plants. He stated the very interesting fact that the tip of the plant root which originates from the seed ‘radical’ can control the movement and function of the plant. The plant root is a highly intelligent organ that judges the quality of water and soil. In the soil, while absorbing water and mineral salts, plant roots do outstanding jobs in controlling the water balance, nutrition, growth, acid-base balance, and hormonal functions in the plant body. This indicates plants’ actions are also guided by some super-intelligent brain, much like the case of animals where the brain controls and manages all the bodily functions. Such minute observations were recorded by Darwin in his book “The Power of Movements in Plants” which many may not be fully aware of people.

Subsequently, many scientists researched in this field of plant intelligence and sensitivity towards stimuli and concluded that touch, sound, melody, resonance, etc from the surrounding environment plays a significant role in the same! However, the question arises that don't the plants need an improved and active nervous system to respond to such direct and indirect stimuli (viz. touch, sound, temperature)? And if so, where are the so-called nerves and nervous systems located in the plants? A lot of research has so far revealed many new facts and information. 

Firstly, some special glutamate receptor proteins have been found in plants, which act just as ‘neurotransmitters’ present in the animals. Surprisingly, several plant proteins including, G-box protein, 14-3-3, has been found to even stimulate the function of neurotransmitters in animals. Furthermore, some special proteins have been discovered in both plants and animals, which play crucial roles in nerve conduction.

With the discovery of the currently high magnification electron microscope, scientists have further successfully observed not only the presence of neurotransmitter-type proteins in the plant cell but also a full circular sac-like ‘synapse’ structure present there. These synapses can transmit stimuli from one plant cell to another in the vicinity. Besides, the phloem tissue inside the plant's circulatory system also acts as the nervous-like system extends throughout the plant's body - delivering water and food to specific places and at specific times according to the plant's needs. 

Of note, the well-known plant hormone called ‘auxin’ is considered to be a chemical of the ‘neurotransmitters' class according to scientists. Recently, Dr. Frantisek Baluska (University of Bonn, Germany) tested and proved that the auxin hormone in plants is transported through special sacs, in the same way, that neurotransmitters work in animal cells. However, exactly how or in what mechanism this phenomenon occurs in plants has not yet been fully discovered.

Many scientists also believe that the perception of plants is very advanced. Evidence suggests that many microorganisms and fungi, like animals, form friendly symbiotic relationships with plants, and that the plants can 'consider' which microorganisms or fungi will be useful for their own survival. In hostile environments, a variety of characteristic adaptations of plants are observed, which can only be found in organisms with advanced, sensitive nervous systems.

One may also wonder about the time-maintenance by the plants, like the time of the day a plant decides to bloom its flowers or start the process of photosynthesis or time to form nectar with the arrival of pollinated animals! In fact, with the understanding of the time of the day when it's really hot, they can set up a special 'temperature protection system'. We know that in animals there runs a special intrinsic rhythm of time, called a 'circadian rhythm'. A clear pattern of ‘circadian rhythm’ can also be seen in plants and scientists have revealed certain proteins regulating it specifically in plants. Scientific studies have shown that plants have the ability to regulate the circadian rhythm of each cell! 

Conclusion

Scientist Claude Bernard (1813-1878) believed that as the environment changes, so does the sensitivity of plants. He showed that by applying anesthesia on plants, changes in germination, photosynthesis, movement, etc. of plants can be seen, just like the animal body which becomes unresponsive following anesthesia. Henceforth, every cell in a plant is just as sensitive as the nerve cells in an animal. Yet many of the behaviors of plants, the techniques of their various physiological work are mysterious but definitely give us strong hints of plant intelligence. Research is still going in this field so that we get answers in the near future.

 

Dr. Juni  Banerjee

Former Scientist and Asst. Professor (Amity University, Delhi, India),

 Postdoctoral Research Fellow (University of Pennsylvania, Philadelphia, USA).

Ph.D. Degree Holder (Jadavpur University, Kolkata, India)

 

References:

1. Tandon PN. Jagdish Chandra Bose & plant neurobiology. Indian J Med Res. 2019

May;149(5):593-599.

2. Baluska F, Mancuso S, Volkmann D, Barlow PW. The 'root-brain' hypothesis of

Charles and Francis Darwin: Revival after more than 125 years. Plant Signal

Behav. 2009 Dec;4(12):1121-7.

3. Brenner ED, Stahlberg R, Mancuso S, Vivanco J, Baluska F, Van Volkenburgh E.

Plant neurobiology: an integrated view of plant signaling. Trends Plant Sci. 2006Aug;11(8):413-9.

4. Lam HM, Chiu J, Hsieh MH, Meisel L, Oliveira IC, Shin M, Coruzzi G.

Glutamate-receptor genes in plants. Nature. 1998 Nov 12;396(6707):125-6.

5. Baluska F, Samaj J, Menzel D. Polar transport of auxin: carrier-mediated flux

across the plasma membrane or neurotransmitter-like secretion? Trends Cell Biol. 2003 Jun;13(6):282-5.

6. Trewavas A. Green plants as intelligent organisms. Trends Plant Sci. 2005

Sep;10(9):413-9.

7. Robinson G., Hawes C,  Hillmer S,  Jürgens G,  Schwechheimer C,  Stierhof YD,  Viotti C, Plant Physiol. 2018 Mar; 176(3): 1884–1888.