CONTROL AND COORDINATION IN PLANTS
- Unlike animals, plants do not have a nervous system.
- Plants use chemical means for control and coordination.
- Many plant hormones are responsible for various kinds of movements in plants.
- The control and coordination in plants is done by plant hormones (or phytohormones)
There are four major types of plant hormones (or phytohormones) which are involved in the control and coordination in plants.
4. Abscisic acid (ABA)
- Auxins, gibberellins and cytokinins are the plant hormones which promote growth of plants.
- On the other hand, abscisic acid is a plant hormone which inhibits (or prevents).
- Movements in plants can be divided into two main types, viz. tropic movement and nastic movement
- The movements which are in a particular direction in relation to the stimulus are called tropic movements.
- Tropic movements happen as a result of growth of a plant part in a particular direction.
There are four types of tropic movements.
- The growth in a plant part in response to the gravity is called geotropic movement.
- Roots usually show positive geotropic movement, i.e. they grow in the direction of the gravity.
- Stems usually show negative geotropic movement.
- When roots grow in the soil, they usually grow towards the nearest source of water.
- This shows a positive hydrotropic movement.
- The growth in a plant part in response to touch is called thigmotropic movement.
- Such movements are seen in tendrils of climbers.
- The tendril grows in a way so as it can coil around a support.
- The differential rate of cell division in different parts of the tendril happens due to action of auxin.
- The movement of a plant part in response to light is called phototropism.
- If the plant part moves towards light, it is called positive phototropism. On the other hand, if the plant part moves away from light, then it is called negative phototropism
- The movements which do not depend on the direction from the stimulus acts are called nastic movement.
- For example; when someone touches the leaves of a mimosa, the leaves droop.
- The drooping is independent of the direction from which the leaves are touched.
- Such movements usually happen because of changing water balance in the cells.
- When leaves of mimosa are touched, the cells in the leaves lose water and become flaccid; resulting in drooping of leaves.