Control and Co-ordination 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.

Plants exhibit two types of movements:

1. Growth-relevant movements are called the Tropic Movements. (towards or away from a stimulus)
2. Growth-irrelevant movements are called the Nastic Movements. (independent of stimulus)

Movement or growth of any part of the plant in response to an external stimulus is called ‘tropism’ or ‘tropic movement.’

1. Geotropic or Gravitropic 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 gravity. Stems usually show negative geotropic movement.
2. 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.
3. Hydrotropic Movement: When roots grow in the soil, they usually grow towards the nearest source of water. This shows a positive hydrotropic movement.
4. Thigmotropism Movement: The growth in a plant part in response to touch is called thigmotropism movement. Such movements are seen in the tendrils of climbers.
5. Chemotropic Movement: Movement shown by plants in response to specific chemicals is called ‘chemotropic movement’. A classic example of this type of movement is the growth of the pollen tube towards the ovule during fertilisation in a flower.

All the above-mentioned movements of plants are related to growth; hence, all such movements are collectively called 'growth-relevant movements’.

Nastic movements in plants are not directional movements. They are not dependent on stimulus and are ‘growth-irrelevant movements’. 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. Plants use electrochemical impulses for the transfer of information from one place to another. Plant cells change their shape by increasing or decreasing their water content and thereby bring about the movements of plants. As a response to changes in the surroundings, plant hormones bring about various movements in plants.

Plant hormones are chemicals that help to coordinate growth, development and responses to the environment. Main plant hormones are

1. Auxin: (Synthesised at the shoot tip).
   Function: Helps in growth.
   Phototropism: more growth of cells towards the light.
2. Gibberellin: Helps in the growth of the stem.
3. Cytokinins: Promotes cell division.
4. Abscisic acid: Inhibits growth, causes wilting of leaves. (Stress hormone)

Adaptations in Plants for Survival and Reproduction:

• In the plant called the Venus flytrap, there is a trap that appears and smells like flowers and deceives insects. When an insect visits that flower-like trap, the trap closes up and the trapped insect is digested by the plant.
• The lotus flower opens during the daytime, while that of the tuberose (Polyanthus) opens at night.
• Fibrils present on the leaves of the insectivorous plant Drosera bend inwards as soon as an insect lands on the leaves and surround the insect from all sides.
• In Balsam, the ripened fruit dehisces (bursts open) at the right time to disperse the seeds.

Various plants