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Coordination in Plants

Plants move by osmotic changes and differential growth. Rapid movements such as closing leaves involve changes in the turgor pressure in cells. Other plant movements are due to differential growth. Auxin produced at the tip flows down due to gravity and helps growth in the next cells. Auxins promote cell elongation, stimulate cell division in the cambium. They also stimulate root initiation in stem cuttings, suppresses growth of lateral buds, and delays fruit ripening.
Leaves originate from the shoot apical meristem, a small mound of undifferentiated tissue at the tip of the stem. Leaf formation begins with the selection of a group of founder cells in the so-called peripheral zone at the flank of the meristem, followed by the initiation of local growth. Auxins produced by the first leaf flow down and cause the second leaf bud to grow, auxins from second leaf causes the third leaf to grow which in turn causes fourth leaf to grow.
The other hormones are cytokinin this induces rapid mitosis in developing seedling, promote cell division ,stimulates the growth of lateral buds. Gibberellins which initiate stem and root growth, causes parthenocarpy (development of seedless fruits) Abscisic acid inhibits shoot growth in plants and promotes closure of stomata. Ethylene is a gaseous hormone which induces fruit ripening and flowering in plants.
A directional response is caused by differential growth. Growth can be induced by light, gravity or touch. The coils in the tendrils of some plants are the result of differential growth.
Plants Respond to Stimuli
Plants are not conscious, but they do respond to external stimuli such as light, touch, etc. Sensitive plant is so named because it shows a rapid motion response to various stimuli; for instance, the leaves close when lightly touched. Greater disturbance causes the petioles to droop as though wilted and ready to fall from the plant. If left undisturbed for about ten minutes, the leaves rise and open again. The leaves also fold and droop at night when exposed to cold. Sensitive plant is so sensitive that it may shed leaves after handling but it recovers quickly and is easy to grow. However, plants respond drastically to changes, it must be treated very cautiously with no extremes or sudden changes in environmental factors such as light, temperature, humidity, and soil moisture.



Immediate response to stimuli

The plants do not posses nervous system for the conduction of the impulse but still it shows immediate response to stimuli. The plant Mimosa pudica is well known for its rapid plant movement. In the evening the leaflets will fold together and the whole leaf droops downward. It then re-opens at sunrise. The leaves also close up under various other stimuli, such as touching, warming, or shaking. The stimulus can also be transmitted to neighbouring leaves. The movement is caused by "a rapid loss of pressure in strategically situated cells that cause the leaves to droop right before one’s eyes".

This type of immediate response in plants is conveyed by electrical chemical means.


Mimosa pudica with leaves open

Mimosa pudica with leaves closed

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