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GIBBERELLINS

  • First of all Japanese farmers observed peculiar symptoms in rice seedlings & called the bakanae disease (foolish seedling disease)

  • Rice plants become thin, tall & pale due to infection of Gibberella (Ascomycetes) or Fusarium (Deuteromycetes) confirmed by Kurosawa & Swada. 

  • Yabuta and Sumiki 1938 were the first to extract a crystalline substance from the Gibberella fungus , which they named as Gibberellin.

  • Gibberellin, is an acidic & possess a gibbon ring structure, are able to overcome genetic dwarfism in plants.

  • 100 type of Gibberellins (GA1, GA2 GA3 ............ GA100) are known. GA3 [C19H26O6] is representative of all gibberellins.
    Gibberellins | Capsule course of Botany for NEET

  • GA found in all groups of plants (algae, to angiosperms, but as a flowering hormone acts only in angiosperms.

  • Biosynthesis of gibberellin takes place by mevalonic acid pathway (Kaurene→GA)


Physiological effects and applications

(1) Stem/internode elongation :- GA induces internode elongation, leaf expansion & used in sugarcane cultivation.

Gibberellins induce stem elongation in rosette plants (Cabbage) this phenomenon known as bolting effect. (Elimination of rosette habit in some plants by gibberellins action is bolting)

(2) Elongation of genetic dwarf plants :- When gibberellin are applied to dwarf maize, Pisum & Vicia faba, then they become tall. The rosett plant of sugar beet indicate an extreme dwarfism, this habit can be eliminate by GA.

(3) Flowering in LDP, in short light duration :- (Shortening of life cycle)

(4) Parthenocarpy :- Like auxin, exogenous use of GA also induces the formation of seedless fruits.

(5) Substitution of cold treatment or vernalisation :- The biennials plants form their vegetative body in the Ist year. Then they pass through a winter season & produce flower & fruits in IInd year. GA induces flower in first year.

(6) Breaking of dormancy :- GA breaks the dormancy of seeds, buds and tubers

(7) Seed germination :- Gibberellin induce the synthesis of hydrolysis enzymes like a-amylase, lipases, & proteases 

(8) Sex expression :- GA induces maleness in Cucumis, Cannabis. 

(9) Germination of photoblastic seeds :- Gibberellin treated light sensitive seeds can germinates in dark. Ex. Lettuce, Tobacco.

(10) Fruit & flower enlarger :- Size of grape fruits & bunch & Geranium flowers increased by GA

Pomalin ⇒ GA (GA4 + GA7) + CK (6 - Benzyladenine) - acts as an apple enlarger

(11) In fermentation :- More growth of yeast cells by GA.

(12) Increase height of Sugarcane plant :- (More sugar contents by IAA )

Bio–assay :– 

(1) a-amylase activity test in Barley endosperm 

(2) Dwarf Pea & Maize test

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FAQs on Gibberellins - Capsule course of Botany for NEET

1. What are gibberellins and what is their role in plant growth and development?
Ans. Gibberellins are a group of plant hormones that play a crucial role in regulating plant growth and development. They are involved in processes such as seed germination, stem elongation, flowering, and fruit development. Gibberellins promote cell division and elongation, leading to overall plant growth.
2. How do gibberellins affect seed germination?
Ans. Gibberellins break seed dormancy and promote germination by stimulating the production of enzymes that break down stored nutrients in the seed. They also enhance the water uptake by the seed, leading to swelling and activation of the embryo. Overall, gibberellins play a key role in initiating the germination process.
3. Can gibberellins be used to increase crop yield?
Ans. Yes, gibberellins can be used to increase crop yield. By applying gibberellin-based plant growth regulators, farmers can promote cell division and elongation, leading to increased plant height, larger leaves, and more branching. This can result in higher crop yields and improved quality of fruits or grains.
4. Are gibberellins only found in plants?
Ans. No, gibberellins are not exclusive to plants. They are also produced by some fungi, such as Gibberella fujikuroi, which is known for its high gibberellin production. However, the majority of the research and application of gibberellins focus on their role in plant growth and development.
5. Can excessive use of gibberellins have negative effects on plants?
Ans. Yes, excessive use of gibberellins can have negative effects on plants. Overapplication of gibberellins can lead to excessive stem elongation, weak stems, and reduced overall plant health. It can also disrupt the balance of other plant hormones, causing hormonal imbalances and affecting normal plant development. It is important to use gibberellins judiciously and follow recommended application rates to avoid negative effects on plants.
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