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    Write any four physiological effects of gibberellins.

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    Updated on : 2022-09-05

    Gibberellin is one of the plant growth hormone which is required for the growth and development of the plants. The regulator is required for different processes.

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    The hormone causes elongation in the stem.

    The hormone is responsible for the bolting effect in the rosette plants.

    The regulator is externally used for the removal of dormancy in the case of seeds and buds.

    Ther hormone promotes and stimulates seed germination.

    The hormone can be used as an alternative to vernalization.

    They promote flowering in the long day plants.

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    Gibberellins

    Gibberellins are plant growth regulators, involved in stem elongation, germination, etc. Explore gibberellin function, structure, and uses only at BYJU'S.

    BiologyBiology ArticleGibberellins In Plants

    Gibberellins In Plants

    As, we humans have different types of hormones, a chemical messenger produced by the endocrine glands to perform several metabolic activities within the body.

    Like humans, plants also have five major types of plant hormones which are collectively called as plant growth regulators, promoters, inhibitors, and phytohormones.

    In this article let us learn more in detail about the Gibberellins – the largest known classes of the plant hormone.

    Gibberellins Definition

    “Gibberellins are any group of plant hormones that stimulate elongation of the stem, flowering and germination.”

    What are Gibberellins?

    Gibberellins are the plant growth regulators involved in regulating the growth and influencing different developmental processes which include stem elongation, germination, flowering, enzyme induction, etc.

    Gibberellins have different effects on plant growth and the stem elongation is the most dramatic amongst all.  The stem starts to grow when it is applied in low concentration to a bush. The internodes grow so long that the plants become indistinguishable from climbing. The Gibberellins overcome the genetic limitations in different dwarf varieties.

    There are more than 70 gibberellins isolated. They are GA1, GA2, GA3 and so on. GA3 Gibberellic acid is the most widely studied plant growth regulators.

    Also Read: Ethylene

    Gibberellin Structure

    Gibberellin Structure

    Gibberellin is a diterpenoid. It forms the basis of molecules such as vitamins A and E. The figure above shows the structure of the Gibberellin A1, the first identified gibberellin.

    The structure of all the gibberellins is the same with several side groups attached. These groups determine the unique functions of gibberellins in different tissues.

    Function of Gibberellins

    Gibberellin function in plants

    The important gibberellins function are mentioned below:

    Seed Germination

    Some seeds that are sensitive to light such as tobacco and lettuce exhibit poor germination in the absence of sunlight. Germination begins rapidly if the seeds are exposed to the sunlight. If the seeds are treated with gibberellic acid, the light requirement can be overcome.

    Also, read about Seed Germination

    Dormancy of Buds

    The buds that are formed in autumn stay dormant until next spring. This dormancy can be overcome by treating them with gibberellin.

    Root Growth

    Gibberellins have almost no effect on the growth of roots. However, some inhibition of growth can occur at a higher concentration in a few plants.

    Elongation of the Internodes

    Internodes elongation is the most pronounced effects of gibberellins on plant growth. In many plants such as dwarf pea and maize, the genetic dwarfism can be overcome.

    For example, the dwarf pea plants have expanded leaves and short internodes. But the internodes expand and look like tall plants when treated with gibberellin.

    Gibberellins exhibit their impact by altering gene transcription.

    The steps of gibberellin functions are mentioned below:

    The GA enters the cell and binds to a soluble protein receptor.

    This binds to a protein complex (SCF) that attaches ubiquitin to one or the other DELLA proteins.

    This activates the destruction of DELLA proteins through proteasomes.

    The destruction of DELLA proteins releases the inhibition and gene transcription starts.

    This procedure is amongst different cases in biology where the pathway is turned on by inhibiting the pathway. However, most of the proteins that are involved differ according to circumstances, both auxin and gibberellins influence gene expression by a common mechanism of repression relief.

    Uses of Gibberellins

    Gibberellin is commercially obtained from fungi. It is used to facilitate the germination of seeds.

    It is sprayed on the grapevines and used to enlarge them.

    It is used on cucumber plants to produce all-male flowers. This helps the farmers to obtain pollen of desired characteristics to be used for hybridization.

    Biennial plants produce flowers only during low temperatures. When gibberellin is applied, these plants will flower irrespective of the low temperatures.

    The dwarf varieties of plants which are genetic mutants can be made to grow by applying gibberellins to them.

    Also Read: Cytokinin

    Learn more about gibberellins, its definition, function, uses and other plant growth regulators @ BYJU’S Biology

    Frequently Asked Questions

    What is the main function of gibberellins?

    Gibberellins are plant growth regulators that facilitate cell elongation, help the plants to grow taller. They also play major roles in germination, elongation of the stem, fruit ripening and flowering.

    How do human use gibberellins?

    Gibberellins are utilized by the farmers to speed up the germination of seeds and to stimulate cell and stem elongation. These are applied externally to increase crop production.

    स्रोत : byjus.com

    9 Major Physiological Effects of Gibberellins

    ADVERTISEMENTS: Some of the major physiological effects of gibberellins are as follows: Gibberellins are weakly acidic growth hormones having gibbane ring structure which cause cell elongation of intact plants in general and increased internodal length of genetically dwarfed plants (e.g., Pea, Corn), in particular. ADVERTISEMENTS: The effect of gibberellins had been known in Japan for […]

    9 Major Physiological Effects of Gibberellins

    Article shared by : ADVERTISEMENTS:

    Some of the major physiological effects of gibberellins are as follows:

    Gibberellins are weakly acidic growth hormones having gibbane ring structure which cause cell elongation of intact plants in general and increased internodal length of genetically dwarfed plants (e.g., Pea, Corn), in particular.

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    The effect of gibberellins had been known in Japan for over a century where certain rice plants were found to suffer from bakanae (foolish seedling) disease. Such rice plants were thin, pale green, spindle shaped, longer by 50% than the healthy plants, and were sterile. The disease was found by Kurosawa (1926) to be caused by a fungus, Gibberella fujikori.

    The fungus is the perfect stage of Fusarium moniliforme. The active substance was separated and named gibberellin by Yabuta and T. Hayashi (1935). Gibberellic acid or GA3 was isolated in pure form by Brian et al, in 1955. Cross et al. (1961) worked out the structure of Gibberellic acid, GA3. More than 60 gibberellins have now been discovered in various fungi and plants (31 from seed plants) although no single species contains more than 15 (Phinney, 1971). GA1, GA3-8 and GA17-20 occur rather commonly; the others are found only in certain plants.

    Metabolism and Biological Action of Gibberellin:

    Gibberellins are isoprenoid compounds. Specifically, they are diterpenes synthesised from ac­etate units of acetyl coenzyme A by the mevalonic acid pathway. Geranylgeranyl pyrophosphate, a 20- carbon compound, serves as the donor for all gibberellin carbon atoms. Gibberellins are synthesised in the apical shoot buds (young leaves), root tips and developing seeds. Gibberellin transport occurs through simple diffusion as well as through conducting channels.

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    Many workers compare the action of GA to that of IAA in that both promote cell elongation and induce parthenocarpy; in some cells, both induce cell division also but they differ in their action too. While IAA is transported in a polar mariner, GA is not; while IAA prevents leaf abscission, GA has no effect; while IAA promotes root initiation, GA does not. But, on the contrary, GA tends to break dor­mancy while IAA does not; GA causes dwarf varieties of plants to grow tall but IAA cannot produce this effect and lastly, GA causes bolting in biennials but IAA does not.

    Physiological Effects of Gibberellins:

    1. Elongation of intact stems:

    Many plants respond to application of GA by a marked increase in stem length; the effect is primarily one of internode elongation.

    2. Dwarf shoots:

    Besides general increase in stem length, gibberellins specifically induce inter­nodal growth in some genetically dwarf varieties of plants like Pea and Maize. It appears that dwarf- ness of such varieties is due to internal deficiency of gibberellins.

    3. Bolting:

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    Gibberellins induce sub-apical meristem to develop faster. This causes elongation of reduced stem or bolting in case of rosette plants (e.g., Henbane, Cabbage) and root crops (e.g., Radish).

    4. Dormancy:

    Gibberellins overcome the natural dormancy of buds, tubers, seeds etc., and allow them to grow. In this function they are antagonistic to abscisic acid (ABA).

    5. Seed Germination:

    During seed germination, especially of cereals, gibberellins stimulate the production of some messenger RNAs and then hydrolytic enzymes like amylases, lipases and pro­

    teases. The enzymes solubilise the reserve food of the seed. The same is transferred to embryo axis for its growth.

    6. Fruit Development:

    Along with auxin, gibberellins control fruit growth and development. They can induce parthenocarpy or development of seedless fruits from unfertilized pistils, especially in case of pomes (e.g., Apple, Pear).

    7. Flowering:

    ADVERTISEMENTS:

    They promote flowering in long day plants during noninductive periods.

    8. Vernalization:

    Vernalization or low temperature requirement of some plants can be replaced by gibberellins.

    9. Application of gibberellins increases the number and size of several fruits, e.g., Grapes, To­mato; induce parthenocarpy in many species; and delay ripening of citrus fruits thus making storage safe.

    Related Articles:

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    5 Physiological Effects of Ethylene | Biology

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