Control and Co-ordination in Plants

Control and Coordination in plants:-

Coordination is the ability to use different parts of the plant together, smoothly and efficiently. In plants, coordination is due to the result of a chemical system, wherein plant hormones or phytohormones have a major role.

Movement in plants

Plants exhibit two types of movements.

1. Growth-dependent movements called the Tropic Movements. ( towards or away from a stimulus)
2. Non-growth dependent movements called the Nastic Movements. ( independent of stimulus)

Tropic movements

These can be classified again into 5 types. They are:

• Phototropism (light)
• Geotropism (gravity)
• Hydrotropism (water )
• Chemotropism (chemicals)
• Thigmotropism (touch)

1. Phototropism – It is the movement of plants in response to light. The shoot system of a plant exhibits this characteristic. The shoot moves towards the light.
2. Geotropism – It is the movement of a plant part towards the soil. This is a characteristic of the root system. The roots always move in the direction of the earth’s gravity.
3. Hydrotropism– It is the movement of a plant towards the water. The stimulus here is water.
4. Chemotropism – It is the movement of plants in response to a chemical stimulus. A classic example of this type of movement is the growth of the pollen tube towards the ovule, during fertilization, in a flower.
5. Thigmotropism – It is a directional movement in plants in response to touch. For e.g. the plant tendrils climb around any support which they touch.

Nastic Movements

Nastic movements in plants are not directional movements. They are not dependent on stimulus and are growth independent. For example, the leaves of a touch me not plant (Mimosa pudica), fold up immediately when touched. These kinds of changes occur due to the changes in the amount of water in the leaves. Depending on the quantity, they either swell up or shrink.

Control and Co-ordination in Plants:

Movements in plants and plant harmones. Co-ordination in Plants: Unlike animals, plants do not have a nervous system. Plants use chemical means for control and co-ordination. Many plant hormones are responsible for various kinds of movements in plants. Movements in plants can be divided into two main types:

• Tropic movement

• 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 which 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.

Plant hormones: Plant hormones are chemical which help to co-ordinate growth, development and responses to the environment.
Type of plant hormones: Main plant hormones are

• Auxin: (Synthesized at shoot tip).
  Function: Helps in growth.
  Phototropism: more growth of cells towards the light.

• Gibberellin: Helps in the growth of the stem.

• Cytokinins: Promotes cell division.

• Abscisic acid: Inhibits growth, cause wilting of leaves. (Stress hormone)