plant hormones for Biology, Botany and biochemistry students

1. GIBBERELLINS
DR. R. RENUKA, M.SC.,M.PHIL.,PH.D.
ASSOCIATE PROFESSOR OF BIOCHEMISTRY
V.V.VANNIAPERUMAL COLLEGE FOR WOMEN
VIRUDHUNAGAR
TAMILNAD, INDIA.

2. GIBBERELLINS
GIBBERELLINS (GAS) ARE A CLASS OF DITERPENE
PLANT HORMONES THAT REGULATE VARIOUS
DEVELOPMENTAL PROCESSES INCLUDING STEM
ELONGATION, GERMINATION, DORMANCY, FLOWERING,
FLOWER DEVELOPMENT, AND LEAF AND
FRUIT SENESCENCE.

3. DISCOVERY OF GIBBERELLINS
• FIRST DISCOVERED BY A JAPANESE PLANT
PATHOLOGIST KUROSAWA IN 1928.
• HE OBSERVED RICE PLANTS INFECTED BY THE FUNGUS
GIBBERELLA FUJIKUROI (G. MONILIFORMIS) SHOWED
EXCESSIVE STEM ELONGATION (DEVOID OF NATURE OF
SEEDS).
• THIS DISEASE IS CALLED ‘BAKANAE DISEASE’ MEANING
FOOLISH SEEDLINGS.
• THE SUBSTANCE WAS LATER NAMED AFTER THE FUNGI

5. DISCOVERY OF GIBBERELLINS
• THE SUBSTANCE WAS EXTRACTED AND PURIFIED FROM THE
CULTURE FILTRATE OF G. FUJIKUROI. THE CHEMICAL WAS
NAMED AS GIBBERELLIC ACID.
• 72 FORMS OF GA ARE KNOWN’.
• OUT OF THESE 15 HAVE BEEN ISOLATED FROM G.fugikuroi.
• 3 FORMS GA5,GA6 AND GA8 ARE EXTRACTED FROM BEAN
SEEDS.
• GA3 IS FROM FUNGI AND IS COMMON GIBBERELLIC ACID.
• COMMERCIALLY AVAILABLE GIBBERELLINS ARE GA3,GA4 AND

6. DISTRIBUTION OF GIBBERELLIN
• WIDELY DISTRIBUTED IN NATURE.
• THEY ARE REPORTED FROM ALGAE, MOSSES, FERNS,
GYMNOSPERMS AND ANGIOSPERMS.
• THEIR PRESENCE ARE ALSO REPORTED FROM SOME SPECIES OF
BACTERIA AND FUNGI.
• IN HIGHER PLANTS GIBBERELLINS ARE PRESENT IN
MERISTEMATIC REGIONS LIKE STEM TIP, ROOT TIP, BUDS,
EXPANDING ORGANS, EMBRYOS AND SEEDS.
• THERE ARE 2 FORMS OF GIBBERELLINS
• ACTIVE (FREE FORM) AND INACTIVE (CONJUGATED FORM AS

7. CHEMISTRY OF GIBBERELLINS
TETRACYCLIC DITERPENE ACIDS WHICH HAVE COMMON STRUCTURE CALLED GIBBANE RING

8. GIBBERELLIN LIKE SUBSTANCES
• SOME SUBSTANCES WHICH HAVE NO GIBBANE RING SHOW
GIBBERELLIC ACID ACTIVITY
• HELMINTHOSPORAL- EXTRACTED FROM FUNGUS
HELMINTHOSPORIUM SATIVUM
• PHASEOLIC ACID – FROM SEEDS OF PHASEOLUS
• ECDYSONE – STEROID HORMONE OF INSECTS

9. BIOSYNTHESIS OF GIBBERELLIN

10. GIBBERELLIN TRANSPORT
• GIBBERELLINS ARE PRODUCED IN MERISTEMATIC REGIONS LIKE STEM
APEX, ROOT APEX,BUDS,EXPANDING ORGANS, EMBRYOS AND SEEDS.
• TRANSPORT OCCURS THROUGH XYLEM, PHLOEM AND CELL TO CELL.
• PHLOEM SEEMS TO BE MOST IMPORTANT TRANSPORT ROUTE.
• TRANSPORT IS NON-POLAR.

11. PHYSIOLOGICAL ROLE OF GIBBERELLINS
1. STEM ELONGATION – ELONGATION OF INTERNODES

12. • GIBBERELLINS ENHANCE THE GROWTH OF
INTERNODES AND INCREASES THE CROP
PRODUCTIVITY AND SUGAR YIELD OF THE SUGARCANE
CROP.

13. 2. BOLTING AND FLOWERING
• PLANTS WHICH ARE HAVING ROSETTE PATTERN OF GROWTH
SUCH AS CABBAGE, HENBANE ETC SHOW REMARKABLE GROWTH
AFTER TREATMENT WITH THE GIBBERELLINS.
• GIBBERELLINS INDUCE STEM ELONGATION IN THESE TYPES OF
PLANTS. THIS EFFECT IS CALLED AS BOLTING EFFECT (STEM
ELONGATION) AND ALSO INDUCE FLOWERING IN ROSETTE
PLANTS.
• PROMOTE THE FLOWERING OF
LONG DAY PLANTS IN SHORT DAYS.
• EG. HYOSCYAMUS NIGER

14. 3. BREAKING SEED DORMANCY
• SEEDS OF LETTUCE AND TOBACCO GERMINATE ONLY
AFTER THE EXPOSURE TO LIGHT (LIGHT SENSITIVE)
• IF SUCH SEEDS ARE TREATED WITH GA3, LIGHT
REQUIREMENT IS ALLEVIATED. SUCH SEEDS GERMINATE EVEN IN DARK.
• SEEDS OF TEMPERATE SPECIES SUCH AS APPLE, PEACH DO NOT GERMINATE
TILL THEY EXPOSED TO LOW TEMPERATURE (1-7DEGREES) FOR FEW DAYS.
APPLICATION OF GA OVERCOMES THIS. THEREFORE, GA REPLACES LIGHT AND
LOW TEMPERATURE REQUIREMENT FOR SEED GERMINATION.

15. BREAKING BUD DORMANCY
• IN TEMPERATE REGIONS THE BUDS FORMED IN AUTUMN
REMAIN DORMANT UNTIL NEXT SPRING DUE TO SEVERE
COLD. THIS CAN BE BROKEN BY GIBBERELLIN
TREATMENT.

17. BREAKING TUBER DORMANCY
• IN POTATO ALSO THERE IS A DORMANT PERIOD AFTER
HARVEST BUT, THE APPLICATION OF GIBBERELLIN SPROUTS
THE EYES VIGOROUSLY.

18. 4. PARTHANOCARPY
• GA PRODUCES PARTHENOCARPIC FRUITS WHICH ARE
SEEDLESS AND MORE FLESHY. EG. TOMATO, GRAPES,
STONE FRUIT ETC

19. 5. INCREASE THE SIZE AND NUMBER OF
FRUITS
• EG. GRAPES, APPLE, LEMON ETC.

20. 6. SEX EXPRESSION
• INDUCTION OF MALENESS IN DIOECIOUS PLANTS
• GIBBERELLINS PROMOTE THE FORMATION OF MALE
FLOWERS IN THE PLACE OF FEMALE FLOWERS IN
MONOECIOUS PLANTS LIKE CUCURBITS OR IN
GENETICALLY FEMALE PLANTS.

21. 7. INDUCE THE SYNTHESIS OF - AMYLASE
GIBBERELLIN INDUCE THE SYNTHESIS OF
IN THE ALEURONE LAYER SURROUNDING THE
ENDOSPERM OF CEREAL GRAINS DURING GERMINATION.
 THIS ENZYME HYDROLYSIS STARCH IN THE
ENDOSPERM INTO SIMPLE SUGARS AND
TRANSLOCATED TO GROWING EMBRYO
TO PROVIDE ENERGY SOURCE.
•

22. 8. REVERSAL OF DWARFISM
.
This is the most striking effect of gibberellins.
Gibberellins elongate the genetically dwarf
varieties of plants such as corn and pea

23. 9. LEAF EXPANSION
When some plants are treated with gibberellin , their
leaves become broaden and elongated. Broder leaves
have more photosynthetic area which finally increase
the height of the plant.

24. 10. SUBSTITUTION FOR VERNALIZATION
• TREATMENT WITH GIBBERELLIC ACID INDUCES EARLY
FLOWERING IN CERTAIN BIENNIAL PLANTS IN THE SAME
SEASON AND THUS REPLACES THEIR NORMAL LOW-
TEMPERATURE REQUIREMENT. IN THESE BIENNIAL PLANTS,
EXTENSION GROWTH AND FLOWERING GO HAND IN HAND,
AND IT IS QUITE LIKELY THAT GIBBERELLIC ACID REPLACES
VERNALIZATION TREATMENT.
• BY DOING THIS GIBBERELLIN CONVERTS BIENNIALS TO
ANNUAL PLANTS.

25. 11. MALT YIELD
• WHEN WE PROVIDE GIBBERELLINS TO
GERMINATING BARLEY GRAINS REMARKABLE
MALT PRODUCTION NOTICED WHEN USED IN
BREWING INDUSTRIES.

26. 12. DELAYED RIPENING OF FRUITS
gibberellins delayed ripening of citrus fruits. thus
extending the harvest season by 2–3 weeks. It is
useful for safe and prolonged storage of fruits.
 GA3 has an inhibitory effect on strawberry fruit
ripening, evidenced by a decrease in the respiratory
activity and a delay in anthocyanin synthesis and
chlorophylls degradation.

27. 13. INCREASE THE SIZE AND NUMBER OF
FLOWERS
GA3 AND CA7 ARE EFFECTIVE IN INDUCING EARLY FLOWERING,
INCREASE THE SIZE AND NUMBER OF THE FLOWERS.
•