Gibberellins are a group of plant hormones that regulate growth processes such as stem elongation, germination, and flowering, first discovered in relation to a rice disease in the 1920s. These hormones, particularly gibberellic acid (GA3), are involved in various developmental functions and can be applied in agriculture to enhance fruit size and yield in crops like grapes and cherries. The physiological effects of gibberellins are influenced by their structure and can vary based on the plant species.

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Regulators of Plant Height
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2. GIBBERLINS:
Regulators of Plant Height
Any of a group of plant hormones that stimulate stem elongation,
germination, and flowering.

3. In 1926, Japanese E. KUROSAWA investigated a rice disease that
is known as the ‘foolish seedling’.
• Grow extremely fast, look spindly and pale and break off
• Grow extremely fast, look spindly and pale and break off
• It is detected that this abnormal growth is caused by a
chemical secreted from a fungi, Gibberella fujikuroi.
•
It was first isolated in 1935 by Teijiro Yabuta and Sumuki,
from fungal strains (Gibberella fujikuroi) provided by
Kurosawa. Yabuta named the isolate as GIBBERLLINS.
•
LESLIE PALEG identified these gibberllins contain GIBBANE
SKELETON having biological activity of cell elongation or cell
division or both.
• Gibberllin A isolated in 1938 is a mixture of atlest 6
gibberllins (GA1, GA2, GA3, GA4, GA7, GA9.)
• Today, there are more than 110 gibberellins. 30% of them are
biologically active.
GIBBERLLINS: Gibberllins are Endogenous plant harmones that
regulate growth and influence various developmental processes,

4. including stem elongation, germination, dormancy, flowering, sex
expression, enzyme induction, and leaf and fruit senescence.
• They are found in all parts of the plant body, especially in
roots, shoots, buds, leaf, young fruits, and germinating seeds
are all rich in gibberllins.
• Different gibberellins differ in structure and biological activity.
• In a plant, different gibberellin types can be found. They can
be both active or inactive.
• Convertion to active form happens at root tips, inactive
Gibberellin is transported to root and after convertion, it goes
back to shoot.
• gibberellins are classified on the basis of structure as well as
function. All gibberellins are derived from the entgibberellane skeleton. The gibberellins are named GA1....GAn
in order of discovery. Gibberellic acid, which was the first
gibberellin to be structurally characterised , is GA3.
• Gibberellic acid (also called Gibberellin A3, GA, and GA3) is
a hormone found in plants. Its chemical formula is C19H22O6.
When purified, it is a white to pale-yellow solid.
• Gibberellic acid is a very potent hormone whose natural
occurrence in plants controls their development. Since GA
regulates growth, applications of very low concentrations can
have a profound effect while too much will have the opposite
effect. It is usually used in concentrations between 0.01 and
10 mg/L.
• Gibberellins are produced in greater mass when the plant is
exposed to cold temperatures.
• Gibberellin induces stem elongation in rosette plants. Cabbage
is a rosette plant with profuse leaf growth and retarded
internodal length. Just prior to flowering, internodes elongate

5. enormously. This is called bolting. Bolting needs either long
days or cold nights. When a cabbage head is kept under warm
nights, it retains its rosette habit. Bolting can be induced
artificially by the application of gibberellins under normal
conditions.
The mechanism of action of gibberllic acid appears mainly to
induce activity of gluconeogenic enzymes during early stages
of seed germination and this specificity ensures a rapid
conversion of lipid to sucrose , which is further used in
supporting growth and development of the embryonic axis to
a competent root and shoot system. It is also found that
gibberllins induce the synthesis of
α-amylase and other
hydrolytic enzymes during germination of monocot seeds .
they are also involved in mobilising seed storage reserves
during germination and seedling emergence.

6. APPLICATIONS OF GIBBERLLINS
• It is also widely used in the grape-growing industry as
a hormone to induce the production of larger bundles
and bigger grapes, especially Thompson
seedless grapes.
• Gibberellic acid is used extensively to increase the
sucrose yield of sugarcane.
• Gibberellic acid is also used to boost cherry
production. Sweet, bing cherries are sprayed 4 to 6
weeks before harvest to increase fruit size.
Application of GA3 to tart cherries increases yield
through enhanced bearing.
• The use of gibberlins in lower dose has shown
increased yield of digitalis glycosides per shoot .
the harmone tried with leaf and root culture of
digitalis , showed higher production of digoxin.
•
In case of Tinnevelly senna , GA shows a little positive
effect on dry wieght of shoot , but reduction in sennoside
content of leaves.
•
It is observed that GA treatment can cause an increase in
hieght of castor plant upto five times , but does not show any
changes in fixed oil content .
• The treatment significantly causes reduction in alkaloid
content of Vinca, Datura, Hyoscyamus, etc.

7. •
Dwarf pea plant treated with gibberellin:
“Foolish seedling disease” in rice

8. External application of gibberellins can
also enlarge fruit size in grapes:
• GA can induce parthenocartpy and fruit enlargement
Functions of Gibberellins:
Active gibberellins show many physiological effects, each depending
on the type of gibberellin present as well as the species of plant.

9. • Stimulate stem elongation by stimulating cell division and
elongation.
• Stimulates bolting/flowering in response to long days.
• Breaks seed dormancy in some plants which require
stratification or light to induce germination.
• Stimulates enzyme production (a-amylase) in germinating
cereal grains for mobilization of seed reserves.
• Gibberellins promote the production of male flowers, either in
place of female flowers in monoecious plants or in genetically
female plants such as cucurbits. (sex expression).
• Can cause parthenocarpic (seedless) fruit development.
• Can delay senescence in leaves and citrus fruits. This helps in
storing the fruits.