Coordination in plants

Introduction

When all the nutrients are avialable to the plants , why plants have to move? Whether plants definitely need movement ? If yes, what is the mechnaism behind the movement  are some of the interseting things. The movement of higher plants are takes place in the form of bending, twisting, and elongation of certain plant parts or organs. In plant biology, movement of plants is meant to maitain coordination and growth however, unlike mammals, plants lack endocrinal, muscular and nervous system that assis in the process of movement . Plants move either spontaneously or by an atonomic force. This article is an attempt to explain the role of plant hormones and the way they exert control over plants to achieve coordination.

 

Movements in plants

Plants move and react to different stimuli in several ways. In some cases, plants demonstrate spontaneous movement even in the absence of external stimulus, for example spiralling tendrils exploring a safe place to fasten themselves. They may also exhibit induced movement in response to the action of plant hormone sucha s  Auxin. Auxin  can speed up the growth of a stem allowing the plant to slightly droop (a type of movement).The drooping (bowing) of plant is more likely towards whichever the side the Auxin is active. Movement of plants due to the external stimuli are divided into 2 types, tropism, and nasties.

 

Tropism

Tropism is the directional growth of  parts of plant as a result of some external factors. They move either towards or away from the stimulus depending upon the  influence of hormones. Accordingly, if the growth of a plant is in the same direction as the stimulus then it  is called positive tropism. On the other hand, a plant growing in the opposite direction of a stimulus is termed as negative tropism. Movement in a plant is largely influenced by light, gravity, chemicals, water, and touch, which we describe with the help of the terms phototropism, geotropism, chemotropism, hydrotropism and thigmotropism respectively.

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

  2. Geotropism is when the plant part moves in response to gravity. Accordingly, if the roots of a plant move downward, it is a positive geotropism whereas the movement  in the upward direction  is a negative geotropism.            

  3. Chemo tropism is the movement in response to a chemical stimulus such as pollen. For instance, growth of the pollen tube is directed towards the ovule during the fertilization process.

  4. Hydrotropism is the plant`s movement in response to the water where the roots of a plant move towards(positive hydrotropism) or away from the water (negative 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 the support which they come in contact with

 

 

Tropic and Nastic movements in plant

 

Nastic movement of plant

 

Tropic or directional movements

Stimulus

Response

Example

Light

Phototropism

Stem attempts to bend in the direction from where light is shed, for example, sunflower.

Gravity

Geotropism

Roots  grow in the direction of gravity but the shoot grow in the opposite direction.

Water

Hydrotropism

The roots always move towards water flow.

Touch

Thigmotropism

Pea plants climbs up around other plants

Chemicals

Chemotropism

Growth of pollen tubes towards ovules during the pollination

Nastic or non-directional movements

Touch

Thigmonasty

Leaves of a mimosa plant closes when someone touches them

Light

Photonasty

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

 

 

Chemical coordination in plants

Chemical coordination takes place with the help of phytohormones-plant hormones such as auxin and cytokinin .For example, auxin is responsible for the growth of the plants and cytokinin helps in the growth of a plant through rapid  cell division. Plants use a variety of techniques to perform movements. they are majorly classified into  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 aid in regulating the life processes such as germination of the seed, growth of the plant, the ripening of the fruit, pollination, flowering, etc. Plant hormones are otherwise known as the phytohormones that work like neurons in animals. The following illustration explains the classification and functions of phytohormones.

 

 

 

 

 

 

Read more

1 .      

 Introduction to plant nutrition 

2.

Respiration in plants

3.

Photosynthesis in higher plants

4.

Transportation in plants                                

5.

Plant breeding                                           

           

 

Important Questions

  1. A sunflower changes its movement in response to the sunlight, identify the type of movement in this case.

  2. Give an example of thigmotropism.

  3. Explain the different types of tropism in plants.

  4. How can hydrotropism help in plant nutrition?

  5. Enumerate the plant hormones and explain the role of Gibberlins.

 



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