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Do Plants Feel?

posted Jan 27, 2015, 1:10 AM by ranmini@charliesresearch.com   [ updated Jan 10, 2017, 6:37 PM by Upali Salpadoru ]

 How do they feel pain?  

No nerves; no brain; so they most probably do not feel any pain. But they see, they hear, smell and feel the touch, they are even capable of remembering events and communicate with other plants.

After very carefully planned experiments of Charles Darwin 1809- 1882 to investigate plant behavior, noteworthy researches on plant sensitivity were conducted by the famous physicist, Sir Jagadish Chandrabose 1858 – 1937 (Br.India). He showed that the injured plants quiver using one of his own inventions; a crescograph which could amplify plant movements up to 10,000 times.

How they see?

Charles Darwin and his son Francis Darwin showed by a series of experiments that the plant’s photosensitive region is at the growing tip of a stem. We see with rods and cones present in the eye.  There are photoreceptor proteins that get excited on receiving light. These are present in two kinds of cells called rods and cones.

  1. Rhodopsin (light sensitive proteins called ‘visual purple’) for monochromatic vision. (Sensitive even for feeble light.)
  2. Photospins in cones for red, blue and green light. (Needs brighter light)
  3. Cryptochrome to regulate our internal clocks.

Plants have neither rods nor cones; but they also have similar or even more advanced photoreceptors. (Chlamydomonas; Algae has an eye spot)  They can detect a wider part of the spectrum than most animals; For example UV rays and Infrared rays for which we are blind.

Plants not only detect light and colour , they can also recognize the short nights and long night variations that determine seasons. This has been termed ‘photoperiodism’. This is influenced by the RED light available at sun set. Julius von Sachs has shown that, the red light switches on certain genes while FAR RED or deep red switches them off. Employing these technique horticulturists can control the time of flowering in certain plants, showed that growing towards light is as a response to BLUE light.

Do they smell?

Smelling is showing a response to certain chemicals in the air. If you cut an onion you might sneeze. When sweet volatile oils reach your nose you may be pleased. "Plants know when their fruit is ripe, when their [plant] neighbor has been cut by a gardener's shears, or when their neighbor is being eaten by a ravenous bug; they smell it," Daniel Chamovitz writes. He says Caascuta  (dodder) can smell the difference between a tomato and a stalk of wheat. It will choose one over the other, based only on...smell".

Sense of touch

All are familiar with the vines that creep and crawl on the hardy stems nearby. Again Darwin was the first to show that growing plants exhibit a very slow rotatory movement.  When a creeper or their tendrils rotate, touches a stick it turns and twist hard and fast around it. Large number of plants distinctly exhibits the sense of touch. Touch me not (Mimosa pudica), Venus fly trap, and sundew, telegraph plant are a few of them. Botanists have also discovered that constant touch; by animals or other phenomenon such as the wind activate certain genes in a plant that retards the growth.


“Legumes have a specific swelling called pulvinus at the base of their leaves. This organ triggers rapid movements (of less than a second), as a reaction to touch or light variations”.


Fig.  Touch me not , Mimosa pudica (Sin. Nidi kumba)



“In thigmotropism, the plant responds directly to the direction of the source of the stimulus. For example, contact of tendrils stimulates the coiling response caused by differential growth of cells on opposite sides of the tendril. In thigmonasty, the response is unrelated to the direction of the source of stimulus. An example of thigmonasty is the movement of the leaves of sensitive plants”.

Communication

Fig. Prof. Dianna Bowles. (York Uni)

Dianna Bowles has shown that when a leaf of a tomato plant is burnt, electrical signals are sent to other parts of the plant. Despite the lack of nerves plants do transfer electrical signals. When a parasite attacks a plant it usually produces volatile substances which help the other plants of the same specie to fortify them.

Can the plants remember?

“Yes ! They can” is the answer of the present day botanists. Mark Jaffe has conducted some experiments that confirm this idea. When a tendril of a pea plant is rubbed on a side it curls round; thigmotropism.   This activity does not occur in darkness. So his experiment was to rub such a tendril in darkness and expose it to light after a few hours. As the light was shown the tendril curled up without being touched again.  This is one of the observations which clearly indicated that plants have a memory. 

Reference: What a plant knows by Daniel Chamovitz. 2012.

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