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.
- Rhodopsin (light sensitive
proteins called ‘visual purple’) for monochromatic vision. (Sensitive even for
feeble light.)
- Photospins in cones for red, blue
and green light. (Needs brighter light)
- 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.
