Gibberellins

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 i.e. Gibberellin

4. 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 GA7.

5. 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 GLUCOSIDES).

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

7. 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

8. BIOSYNTHESIS OF GIBBERELLIN

9. 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.

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

11. Gibberellins ENHANCE THE GROWTH OF INTERNODES AND INCREASES THE CROP PRODUCTIVITY AND SUGAR YIELD OF THE sugarcane CROP.

12. 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

13. 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.

14. 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.

15. Breaking tuber dormancy In potato also there is a dormant period after harvest but, the application of gibberellin sprouts the eyes vigorously.

16. 4. parthanocarpy Ga produces parthenocarpic fruits which are seedless and more fleshy. Eg. Tomato, grapes, stone fruit etc

17. 5. Increase the size and number of fruits Eg. Grapes, apple, lemon etc.

18. 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.

19. 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.  

20. 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

21. 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.

22. 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.

23. 11. Malt yield when we provide gibberellins to germinating barley grains remarkable malt production noticed WHEN USED IN BREWING INDUSTRIES.

24. 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.

25. 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.