The document discusses gibberellins, a class of diterpenes that promote stem elongation and aid in seed germination by mobilizing endosperm reserves. It covers their discovery linked to 'foolish seedling' disease in rice, biosynthesis pathways, key active forms, and their effects on plant growth and gene expression regulation. Additionally, it highlights the role of gibberellins in crop advancements, such as the creation of high-yielding rice varieties.

1. PLANT PHYSIOLOGY
• PRESENTATION BY:-
• AHMED AQUIB
• B.TECH BIOTECHNOLOGY (C.B.S&H.)
GIBBERELLINS
DR. RAJENDRA PRASAD CENTRAL AGRICULTURAL UNIVERSITY

2. INTRODUCTION
Gibberellins are diterpenes, noted for their capacity
to stimulate hyper-elongation of intact stems,
especially in dwarf and rosette plants and stimulate
mobilization of endosperm reserves during seed
germination.
Terpenoids contain one or more 5- carbon isoprene
units.
Giberellins are synthesised in
● Developing seeds and fruits
● Young leaves
● The apical region of roots
Lacking
gibberellin
Moderate
gibberellin
High
Gibberellin

3. MORE ABOUT GIBBERELLINS
Gibberellins are large class of molecules but GA1 & GA4 are principal naturally
occuring active gibberelins in higher plants
GA3 is readily extracted from fungal source so also commercially available.
Gibberellins are related biosynthetically to carotenoid pigments, sterols, latex and
other isoprene derivatives.
Albeit unconciously, selective breeding of crops that were deficient in
gibberellin synthesis led to green revolution.

4. DISCOVERY OF GIBBERELLINS
The first inroads into the understanding of GAs were
developments from the plant pathology field, with
studies on the bakanae, or "foolish seedling" disease
in rice.
Foolish seedling disease causes a strong elongation
of rice stems and leaves and eventually causes them
to topple over. And produced little or no grain.
In 1926, Japanese scientist Eiichi Kurosawa
identified that foolish seedling disease was caused
by the fungus Gibberella fujikuroi. Bakane diseased
Rice

5. DISCOVERY OF GIBBERELLINS (CONTINUED..)
Later work at the University of Tokyo showed that a substance produced by this
fungus triggered the symptoms of foolish seedling disease and they named this
substance "gibberellin".
Workers at Imperial Chemical Industries in the UK and the Department of Agriculture
in the US both independently isolated gibberellic acid from fungal cultures.
The known effect of gibberellins on rice and several other plant systems indicated
that similar substances might be present in higher plants as well.
In the 1960s, development of a high-yielding semi-dwarf variety of rice is called IR8,
and it has a short height because of a mutation in the sd1 gene (GA deficiency)

6. DIFFERENT
GIBBERELLINS• ALL GIBBERELLINS ARE DITERPENES BASED ON THE 20-
CARBON ENT-GIBBERELLANE STRUCTURE. MORE THAN 135
HAVE BEEN FOUND.
• THE BIOACTIVE GAS ARE GA1, GA3, GA4, AND GA7.
• REQUIREMENTS FOR ACTIVITY:-
• A CARBOXYL GROUP AT CARBON-7 IS A FEATURE OF ALL GAS
AND IS REQUIRED FOR BIOLOGICAL ACTIVITY.
• C19-GAS ARE MORE BIOLOGICALLY ACTIVE THAN C20-GAS.
• THOSE GAS WITH 3-Β-HYDROXYLATION, 3-Β,13-
DIHYDROXYLATION, OR 1,2-UNSATURATION ARE GENERALLY
MORE ACTIVE.

7. BIOSYNTHESIS OF GIBBERELLINS
GIBBERELLINS ARE TERPENES, SHARING A CORE PATHWAY WITH
SEVERAL OTHER HORMONES AND A WIDE RANGE OF SECONDARY
PRODUCTS.
ACTUAL BUILDING BLOCK FOR TERPENOIDS ARE NOT ISOPRENE BUT TWO
PHOSPHORYLATED DERIVATIVES KNOWS AS ISO-PENTYL PYROPHOSPHATE
(IPP) AND ITS ISOMER DIMETHYLALYL PYROPHOSPHATE(DMAP).
IPP IS A PRODUCT OF TWO DIFFERENT BIOSYNTHETIC PATHWAYS, ONE LOCATED
IN THE CYTOPLASM AND ONE LOCATED IN CHLOROPLASTS.
AMO-1618 AND PHOSPHON ARE ANTIGIBBERELLINS THAT INHIBIT ENZYME
INVOLVED IN SYNTHESIS OF GIBBERELLINS. EFFECTS OF THESE CAN BE

8. BIOSYNTHESIS OF GIBBERELLIN (CONT.)
THE MEVALONIC ACID (MVA) PATHWAY IS LOCATED
IN THE CYTOPLASM
THE METHYLERYTHRITOL-4-PHOSPHATE (MEP)
PATHWAY IS LOCATED IN THE CHLOROPLAST
(3) Acetyl Co-A
Hydroxymethylglutaryl Co-A (6 Carbon)
Mavelonic Acid (6 Carbon)
IPP DMAP
2 NADPH
2 NADP+ + Co-A
Phosphorylations
G-3-P + Pyruvate
Methylerythritol-4-phosphate (5 Carbon)
IPP← ----> DMAP
NADP+
NADPH
CO2
Phosphorylations

9. BIOSYNTHESIS OF GIBERELLINS (CONT.)
CYTOPLASM
CHLOROPLAST
● Gibberellin is biosynthesised from geranylgeranyl
pyrophosphate (GGPP) to GA12-7-aldehyde.
● GA12-7-aldehyde is inactive, but serves as the precursor to all
other gibberellins.
● While the biosynthetic pathway up to GA12-7-aldehyde is the
same in all plants, subsequent pathways can vary substantially

10. INACTIVATION AND TRANSPORT
● GIBBERELLINS CAN BE INACTIVATED BY HYDROXYLATION AT THE C-2
POSITION OR BY CONVERSION TO INACTIVE CONJUGATE (EG. GA8
GLUCOSIDE)
● GIBBERELLINS HAVE BEEN DETECTED IN BOTH THE XYLEM AND PHLOEM
SAPS.
● TRANSPORT OF GIBBERELLINS IS NOT POLAR BUT MOVES ALONG WITH
OTHER PHLOEM TRANSLOCATED ORGANIC MATERIAL ACCORDING TO
SOURCE-SINK RELATIONSHIP.

11. GIBBERELLINS STIMULATE HYPER-ELONGATION
GIBBERELLINS PROMOTE ELONGATION ALMOST EXCLUSIVELY
ALMOST EXCLUSIVELY IN INTACT PLANTS.
A ROSETTE IS AN EXTREME CASE OF DWARFISM IN WHICH THERE
IS ABSENSE OF SIGNIFICANT INTERNODE ELOGATION. SO LEAVES
ARE CLOSELY PLACED. HYPER ELONGATION OF STEM IS
BROUGHT ABOUT BY SMALL AMOUNT OF GA
JUST BEFORE FLOWERING ROSETTES UNDERGO RAPID
INTERNODE ELONGATION (BOLTING) TRIGGERED BY
PHOTOPERIOD AND LOW TEMPRATURE. BOLTING CAN BE
INDUCED BY EXOGENOUS GA APPLICATION.
.
Spinach

12. NUTRIENT MOBILIZATION DURING GERMINATION
BARLEY HALF SEED EXPERIMENT
1. SEEDS OF CEREALS SUCH AS BARLEY ARE TRANSECTED TO PRODUCE TWO
HALF-SEED
2. ONE HALF-SEED CONTAINS THE EMBRYO AND THE OTHER HALF-SEED DOES
NOT.
3. WHEN IMBIBED, THE EMBRYO-CONTAINING HALF-SEED WILL PROCEED TO
SECRETE Α-AMYLASE AND OTHER HYDROLYTIC ENZYMES
4. THE HALF-SEED WITHOUT THE EMBRYO CANNOT, OF COURSE, GERMINATE
BUT NEITHER DOES IT PRODUCE ELEVATED LEVELS OF Α-AMYLASE.
5. TREATMENT OF THE EMBRYO-LESS HALF-SEED WITH GIBBERELLICACID,
HOWEVER, WILL STIMULATE THE HALF-SEED TO PRODUCE HIGH LEVELS OF Α-
AMYLASE.

13. GENE EXPRESSION
REGULATION BY
GIBBERELLINS
• DELLA PROTEINS ARE A CLASS OF NUCLEAR PROTEINS THAT
APPEAR TO FUNCTION AS REPRESSORS IN GIBBERELLIN SIGNALING.
•SOLUBLE GA RECEPTOR PROTEINS LIKE GA INSENSITIVE DWARF
1 (GID1), IN RICE.
•GID1 ENCODES A NUCLEAR PROTEIN THAT BINDS WITH GIBBERELLIC
ACID BOTH IN VITRO AND IN VIVO.
•GID1 RECEPTOR BINDS NOT ONLY WITH GIBBERELLIN, BUT ALSO WITH
THE DELLA PROTEIN TO FORM A GA-GID1-DELLA COMPLEX.
• THIS RESULTS IN THE DEGRADATION OF THE DELLA REPRESSOR
PROTEIN BY THE 26S PROTEASOME PATHWAY, THUS RELIEVING A
DELLA-IMPOSED REPRESSION AND ALLOWING EXPRESSION OF THE
GIBBERELLIN-RESPONSIVE GENE.

14. Thankyou