Plant hormones

In the earlier chapter we see various terms related to plants and animals. In this chapter also we will learn some interesting facts about plants and humans. So lets start our discussion with plant hormones.

Plant hormones

Plant hormones also called as phytohormones because phyto means plants. These plant hormones are the complex organic compounds which have ability to synthesize in plant body. These hormones synthesized at one site and perform their functions at another site.

These plant hormones can major role such as growth and development.

There are 2 types of movement which generally see in plants :

1.) Directional movement : This type of movement called polar movement. They are of 2 types such as basipetal in which movement occurs from apex to base and acropetal in which movement occurs from base to apex.

2.) Non directional movement: This movement is non polar movement.

There are 5 types of major hormones such as

A.) Auxin

B.) Cytokinin

C.) Gibberellin

D.) Ethylene

E.) Abscisic acid

Lets start with our discussion with every hormones and their functions:

1.) Auxin :Auxin it was first discovered by scientist Charles Darwin when he was studying the movement mechanism in plants. Auxin have polar movement and specially basipetal that means it synthesized at apex and will be transported to the base via phloem. Tryptophan is one of the amino acid is precursor of auxin. For the synthesis of auxin tryptophan is required. The auxin is also called as IAA (Indole Acetic Acid).

Functions of auxin

  1. The major function is cell elongation.
  2. It have ability of apical dominance. The term apical dominance means it inhibits lateral bud formation.
  3. It breaks the dormancy.
  4. It helps in delay of leaf and fruit abscission (falling off).

2.) Cytokinin :Cytokinin was first discovered from coconut that is liquid part of that endosperm later on it was found in the maize plant. Therefore previously it was known as zeatin. Precursor of cytokinin is adenine. For the formation of cytokinin adenine is required. It is mainly produced in roots and transported to other parts via xylem. These cytokinin have non polar and bidirectional movement.

Functions of cytokinin :

  1. Cytokinin helps in cell division.
  2. Cytokinin carry out seed germination.
  3. Cytokinin responsible for nutrient mobilization or movement.
  4. It helps in chloroplast division.

3.) Gibberellin :The hormone was first discovered in Japan while studying the disease Bakanae disease in rice. The hormone was discovered by Japanese scientist Kurosawa. Gibberellin hormone produced in shoot tip, leaves and germinating seeds. The hormone transports via phloem to other parts of plant and the movement is non polar.

Functions of Gibberellin :

  1. It promotes cell division.
  2. Induce cell elongation.
  3. Helps in stem/ internode elongation.
  4. They inhibit flowering in short day plants.

4.) Ethylene :This hormone is called as gaseous hormone. The hormone can be synthesized in all parts of the plants but specially produced in meristematic region. This hormone is produced during stress condition. Methionine is the precursor of ethylene, that means for formation of ethylene the methionine which is an amino acid is important. It transports through xylem.

Functions of ethylene :

  1. It carry out fruit ripening.
  2. It breaks the bud and seed dormancy.
  3. It gives the triple response to plants that is inhibition and swelling of hypocotyl, inhibition of root elongation and apical hook formation.
  4. It increases the leaf senescence.

5.) AbscisicAcid :It is also called as stress hormone. The ABA can be synthesized in all cells and specially in which chloroplast is present. ABA is transported via both xylem and phloem

Functions of ABA :

  1. ABA causes maturation of embryo.
  2. ABA increases bud dormancy.
  3. Helps in induction of seed germination.
  4. ABA causes to increase the leaf senescence.

 

Questions and answers :

1.) Define plant hormones.

Answer :- Plant hormones also called as phytohormones because phyto means plants. These plant hormones are the complex organic compounds which have ability to synthesize in plant body. These hormones synthesized at one site and perform their functions at another site.

These plant hormones can major role such as growth and development.

2.) Enlist the names of plant hormones.

Answer :-There are 5 types of major hormones such as

  1. Auxin
  2. Cytokinin
  3. Gibberellin
  4. Ethylene
  5. Abscisic acid

3.) Explain auxin in detail.

Answer :-Auxin it was first discovered by scientist Charles Darwin when he was studying the movement mechanism in plants. Auxin have polar movement and specially basipetal that means it synthesized at apex and will be transported to the base via phloem. Tryptophan is one of the amino acid is precursor of auxin. For the synthesis of auxin tryptophan is required. The auxin is also called as IAA (Indole Acetic Acid).

4.) Describe gibberellin hormone.

Answer :-The hormone was first discovered in Japan while studying the disease Bakanae disease in rice. The hormone was discovered by Japanese scientist Kurosawa. Gibberellin hormone produced in shoot tip, leaves and germinating seeds. The hormone transports via phloem to other parts of plant and the movement is non polar.

5.) What are the functions of cytokinin.

Answer :-

  1. Cytokinin helps in cell division.
  2. Cytokinin carry out seed germination.
  3. Cytokinin responsible for nutrient mobilization or movement.
  4. It helps in chloroplast division.

6.) What is ethylene.

Answer :-This hormone is called as gaseous hormone. The hormone can be synthesized in all parts of the plants but specially produced in meristematic region. This hormone is produced during stress condition. Methionine is the precursor of ethylene, that means for formation of ethylene the methionine which is an amino acid is important. It transports through xylem.

7.) What are the functions of ABA.

Answer :-

  1. ABA causes maturation of embryo.
  2. ABA increases bud dormancy.
  3. Helps in induction of seed germination.
  4. ABA causes to increase the leaf senescence.

8.) What are the movement of hormones ?

Answer :- There are 2 types of movement which generally see in plants :

  1. Directional movement : This type of movement called polar movement. They are of 2 types such as basipetal in which movement occurs from apex to base and acropetal in which movement occurs from base to apex.
  2. Non directional movement: This movement is non polar movement.

9.) What is the function of gibberellin ?

Answer :-

  1. It promotes cell division.
  2. Induce cell elongation.
  3. Helps in stem/ internode elongation.
  4. They inhibit flowering in short day plants.

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