BY SIDDHARTH SANGHVI

GA3

The ‘bakane’ (foolish seedling) disease of rice seedlings, was caused by a fungal pathogen Gibberella fujikuroi. E. Kurosawa reported the appearance of symptoms of the disease in uninfected rice seedlings when they were treated with sterile filtrates of the fungus. The active substances were later identified as gibberellic acid

INFO

There are more than 100 gibberellins reported from widely different organisms such as fungi and higher plants. They are denoted as GA1 , GA2 , GA3  and so on. However, Gibberellic acid (GA3 ) was one of the first gibberellins to be discovered and remains the most intensively studied form.

All GAs are acidic.  Their ability to cause an increase in length of axis is used to increase the length of grapes stalks.  Gibberellins, cause fruits like apple to elongate and improve its shape.  They also delay senescence. Thus, the fruits can be left on the tree longer so as to extend the market period.

FUNCTIONS

FUNCTIONS

  ASSERTION : With Gibberellins sprey fruits can be left on the tree longer so as to extend the market period. REASON : Gibberellins, cause delay in fruits senescence. 

A & R

GA3  is used to speed up the malting process in brewing industry.  Sugarcane stores carbohydrate as sugar in their stems. Spraying sugarcane crop with gibberellins increases the length of the stem, thus increasing the yield by as much as 20 tonnes per acre. 

FUNCTIONS

FUNCTIONS

  ASSERTION : Spraying sugarcane crop with gibberellins increasing the yield by as much as 20 tonnes per acre. REASON : Gibberellins increases the length of the stem. (INTERNODE ELONGATION)

A & R

  ASSERTION : GA3  leading to early seed production IN CONIFERS. REASON : Spraying juvenile conifers with GAs hastens the maturity period. 

A & R

  Gibberellins also promotes bolting (internode elongation just prior to flowering) in beet, cabbages and many plants with rosette habit.

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PGR - Summary

Growth promoting Hormones

AUXIN

GA3

CK

03

Cytokinins

F. Skoog and his co-workers observed that from the internodal segments of tobacco stems the callus (a mass of undifferentiated cells) proliferated only if, in addition to auxins the nutrients medium was supplemented with one of the following: extracts of vascular tissues, yeast extract, coconut milk or DNA.

03

Cytokinins

Skoog and Miller crystalised cytokinesis promoting active substance and termed it KINETIN a modified form of adenine from autoclaved herring sperm DNA. Kinetin does not occur naturally in plants.

Kinetin does not occur naturally in plants.  * ZEATIN the naturally occurring cytokinin was isolated from corn-kernels and coconut milk.  Synthesised in regions of rapid cell-division like root apices, developing shoot buds, young fruits etc.

PROF. SIDDHARTH SANGHVI

Cytokinins helps to produce new leaves, chloroplasts in leaves, lateral shoot growth and adventitious shoot formation.  Overcomes apical dominance. Promote nutrient mobilisation so Helps delay LEAF SENESCENCE.

PROF. SIDDHARTH SANGHVI

PROF. SIDDHARTH SANGHVI

  ASSERTION : Cytokinins  delay LEAF SENESCENCE. REASON : Cytokinins helps in nutrient mobilisation

ETHYLENE

Cousins confirmed the release of a volatile substance from ripened oranges that hastened the ripening of stored unripened bananas. Later this volatile substance was identified as ethylene, a gaseous PGR

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>>> Ethylene-2

TRIPLE RESPONSE

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Influences of ethylene on plants include  horizontal growth of seedlings,  swelling of the axis  and  apical hook formation in dicot seedlings.

3

Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. 

4

Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called respiratory climacteric.

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Ethylene breaks seed and bud dormancy initiates germination in peanut seeds, sprouting of potato tubers. 

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Ethylene promotes rapid internode/petiole elongation in deep water rice plants. It helps leaves/ upper parts of the shoot to remain above water. 

PROF. SIDDHARTH SANGHVI

  ASSERTION : Ethylene protect deep water rice plants. It helps leaves/ upper parts of the shoot to remain above water. REASON : Ethylene promotes rapid internode/petiole elongation in deep water rice plants. 

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 Ethylene also promotes root growth and root hair formation, thus helping the plants to increase their absorption surface.

PROF. SIDDHARTH SANGHVI

  ASSERTION : Ethylene helps the plants to increase their absorption surface. REASON : Ethylene promotes root growth and root hair formation.

06

Ethylene is used to initiate flowering and for synchronising fruit-set in pineapples.  It also induces flowering in mango. 

Since ethylene regulates so many physiological processes, it is one of the most widely used PGR in agriculture.

06

 The most widely used compound as source of ethylene is ethephon. Ethephon in an aqueous solution is readily absorbed and transported within the plant and releases ethylene slowly. 

06

 Ethephon hastens fruit ripening in tomatoes and apples and accelerates abscission in flowers and fruits (thinning of cotton, cherry, walnut). It promotes female flowers in cucumbers thereby increasing the yield.

Other stories

01

AUXIN

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02

ABA

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