Coordination in plants

Plants though do not have nervous system or muscles but they also respond towards the stimulus. For example, when we touch Mimosa pudica (touch-me-not plant), its leaves fold up and droop. There are two types of movements in plants -dependent on growth and independent of growth. When we touch the Mimosa pudica, its leaves fold up but no growth occurs, so it does not involve any growth. But movement of seedling is due to growth. Plants convey information from cell to cell through electrical-chemical means.

Hormone produced by plants

 

Movement due to Growth

The most common example of movement of growth are tendrils. Tendrils are sensitive to touch. When they come in contact with some object, the part of tendril away from the object will grow fast compare to the part of tendril which is in contact with the object. So it is a directional movement and it appears as if the plant is moving.
Directional movements of the plants are known as tropic movements. The movement can be towards the stimulus or away from the stimulus. Examples of some movements in plants are mentioned below-

 Many plant hormones are responsible for various kinds of movements in plants. Movements in plants can be divided into two main types:

1. Tropic movement
2. Nastic movement

1. Tropic 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.

(i) Geotropic movement: 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.
(ii) Phototropic Movement: The growth in a plant part in response to light is called phototropic movement. Stems usually show positive phototropic movement, while roots usually show negative phototropic movement. If a plant is kept in a container in which no sunlight reaches and a hole in the container allows some sunlight; the stem finally grows in the direction of the sunlight. This happens because of a higher rate of cell division in the part of stem which is away from the sunlight. As a result, the stem bends towards the light. The heightened rate of cell division is attained by increased secretion of the plant hormone auxin in the is away from sunlight.
(iii) Hydrotropic Movement: When roots grow in the soil, they usually grow towards the nearest source of water. This shows a positive hydrotropic movement.
(iv) Thigmotropism Movement: The growth in a plant part in response to touch is called thigmotropism 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.
 

2. Nastic Movement: The movement which do not depend on the direction from the stimulus acts are called nastic movement. For example, when someone touches the leaves of 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.