Coordination in plants

Introduction

Most of us doubt whether plants need coordination as they don`t walk or run like animals, but a slight stationary movement is possible in plants. However, in botany, coordination is not about the locomotion but it is all about how the different internal processes complement each other to achieve survival and growth. Unlike mammals, plants do not have muscular system or nervous system. But, they are still able to show movement and coordination. Plants do not regulate their movements through the brain but they are achieved through their hormones known as phytohormones.

Table of Contents

1. Introduction

2. Movements in plants

3. Tropism

4. Chemical coordination in plants

5. Plant hormones

 

Movements in plants

Plants move as a result of many external stimuli. One such example is the influence of the plant hormone  Auxin resulting in speeding up of the growth of a stem allowing the plant to bend  (movement). The plant slightly bow towards whichever the side has more Auxin indicating the influence of plant hormones on the movement. Movement of plants in response to the external stimuli are divided into 2 types, namely tropism, and nasties.

 

Tropism

Tropism is the directional growth of a plant part as a result of some external factors. Movement can be in the direction of the stimulus or away from the stimulus. If the growth of a plant is in the same direction of the stimulus, it is known as positive tropism. On the other hand, if the growth of a plant is in the opposite direction of a stimulus, it is called a negative tropism. Factors such as light, gravity, chemicals, water, and touch are the 5 major stimuli that mediate the plant movements, and they are respectively termed as phototropism, geotropism, chemotropism, hydrotropism and thigmotropism.

  1. Phototropism is when a plant part moves in response to the light. When light is shed, the stem of a growing plant automatically moves towards the light,(positive phototropism). On the other hand, if the root of a plant moves away from the light  it is termed as negative phototropism.

  2. Geotropism is when the plant part moves in response to gravity. For instance, if the roots of a plant turn downward direction, it is a positive geotropism. On the contrary, if the stem moves in the upward direction, it is a negative geotropism.            

  3. Chemotropism is the plant movement in response to a chemical stimulus such as pollen. The growth of the pollen tube is directed towards the ovule during the fertilization process.

  4. Hydrotropism is the plant`s response towards the water. If the roots of a plant move towards the water, it is a positive hydrotropism.

  5. Thigmotropism is when a plant part exhibit directional movement in response to the touch of an object. For example, tendrils of a plant climb towards any support which they touch.

The following table illustrates the type of movement response based on the stimulus and examples for each

Tropic movements

Stimulus

Response

Example

Light

Phototropism

Stem tries to bend in the direction from where light is falling, for example, sunflower.

Gravity

Geotropism

Roots try to grow in direction of gravity, shoot tries to grow in direction opposite to gravity

Water

Hydrotropism

The roots always move towards water flow.

Touch

Thigmotropism

Pea plants climb up around other plants

Chemicals

Chemotropism

Growth of pollen tubes towards ovules

Nastic movements

Touch

Thigmonasty

Leaves of a mimosa plant closing due to touch

Light

Photonasty

Dandelion flower closes its petals during the daytime and closes during night-time.

 

Chemical coordination in plants

Different plants use different techniques to perform movements. For example, sunflower has the ability to sense the sunlight, so it faces against the sunlight. Similarly, touch me not plant respond by folding up its leaves when someone touches. Most of the plants respond by  2 types of movements; tropic and nastic. The directional movements are called tropic movements, while non-directional are termed as nastic.

 

Plant hormones

A hormone is a chemical messenger that regulates life processes such as seed germination, growth, ripening of the fruit, pollination, flowering, etc. Plant hormones are otherwise known as the phytohormones. In the case of plants, phytohormones work as the nervous system. The following illustration shows the classification and functions of phytohormones.

 

 

 

 

 





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