plant growth regulators : GA & cytokinin
Download as PPTX, PDF14 likes4,478 views
Gibberellins were discovered accidentally in 1926 when a fungus that causes rice diseases was found to promote excessive growth. The active compound was later isolated and named gibberellic acid. Over 112 gibberellins are now known. Gibberellins are synthesized in young leaves, shoot tips, root tips, and developing seeds. They cause cell enlargement by stimulating amylase production, which breaks down starch into sugars. Gibberellins promote stem elongation, bolting, flowering in long day plants, parthenocarpic fruit development, dormancy breaking, and high concentrations can cause abnormal growth.
More Related Content
Similar to plant growth regulators : GA & cytokinin (20)
plant growth regulators : GA & cytokinin
- 1. Prepared by- A. Naga tharun M. Sc. (Pl. Physiology) BACA,AAU,Anand
- 2. DISCOVERY OF GIBBERLLINS The discovery of gibberllins was quite accidental. Japanese worker kurasova(1926) in japan while conducting experiments on rice disease caused by gibberella fujikuroi causal organism for foolish seedling of rice or bakane disease observed that the fungus caused the excessive growth. He applied the fungal extracts to the healthy plants and observed enhanced growth Later yabuta and samuki named that active principle as gibberllin. Further it was purified ,crystallized and named it as gibberllic acid by Curtis and cross(1954). At present 112 types of gibberllins are known like GA1,GA2 & so on… GA3 is the most common type of gibberllin
- 3. gibberllin
- 4. Occurrence &site of synthesis Young leaves (major portion) Shoot tip Root tip Developing seeds
- 5. biosynthesis
- 7. transport Passive &non polar Gibberllins move both in xylem and as well as in phloem
- 8. Mode of action Gibberellins causes cell enlargement the effect is not considered to be direct. The effect is indirectly mediated through the formation of auxin,in turn is responsible for cell enlargement. Gibberllins has been known to cause synthesis of amylase in barley aleurone cells. This enzyme converts starch to reducing sugars resulting in an increase of osmotic pressure,causing entry of water into the cells and cell enlargement.
- 9. Causing cell enlargement in barley:
- 10. Role of gibberllins Stimulation of stem growth: • The most imp effect of GA is stem elongation when GA is applied the stem elongates markedly As a result such plants grow taller. • It causes intermodal elongation rather than increase in no. of nodes and intrnodes. • However, not all plants respond equally to GA application .it is only the genetic dwarf and rosette plants which show marked stem elongation.
- 11. Rice dwarf var:
- 12. Bolting: • Production of floral axis is called bolting. olting and flowering are induced normally after photo induction or vernalisation. • Bolting however can be induced without vernalisation(0-5⁰C) by the treatment of the plant with gibberellins.
- 13. Flowering in long day plants • Gibberllins promote flowering in long day plants under unfavorable SD conditions.eg niger
- 14. PARTHENOCARPIC FRUITS • Gibberellms have been found to be more effective than auxins in causing parthenocarpic development of fruits in plants like tomatoes, apples, pears and stone. • Gibberellin application promotes panicle exertion. Generally 30% of the panide is covered by leaf sheath. • Application of GA + Brassinosteroids is practically used in commercial seed production of Rice
- 15. Breaking in dormancy: • Gibberellins are effective in breaking the dormancy in potato tubers and in tree buds in winter. • In potato the tubers remain dormant for weeks after harvest. However when GA is applied the buds sprout soon after the tubers are harvested. • This will be useful to use the freshly harvested tuber for sowing. The seed material has to be dipped in 0.5 to 1.0 g of GA /lit of water for 10 - 20 mns then air dried at 15-25⁰c.
- 16. High conc leads to • Hair like sprouts • Poor emergence • A typical viens
- 17. CYTOKININS: Skoog and his coworkers discovered cytokinins when they were trying to identify a compound to initiate and sustain the proliferation of cultured tobacco pith tissue. Crystals of a cell division inducing substance was later isolated for the first time by Miller, from an autoclaved herring sperm DNA in 1951 and named it as Kinetin Letham (1963) extracted, purified and crystallized cytokinin from immature kernels of maize and named it as zeatin
- 18. Occurrence: as a component of RNA of plants, microorganisms and animals. root tips, shoot tips, developing fruits, xylem sap and germinating seeds
- 21. Biosynthesis: • There are two methods .the first is the direct pathway ,involving formation of isopentinyladenosine 5 monophosphate(IPAMP)from AMP and dimethylallylnpyrophosphate(DMAPP) to fom zeatin type compounds. • Another possibility is that they may be released by the hydrolysis of tRNA, first to mono nucleotides and then to free cytokinins
- 22. TRANSPORT: When cytokinin is applied to leaves and stems, the hormone does not move and the effect is localized. Cytokinin is carried passively along the transpiration stream in xylem from root. It moves in phloem via basipetal
- 23. Mode of action: Cytokinin is a structural component of transfer RNA molecule. They may help in binding of mRNA with tRNA - amino acid complex during protein synthesis. Cytokinins increase the synthesis of nucleic acid by increasing the enzyme t RNA synthatase and decrease the degradation by reducing the activity of ribonuclease. Cytokinin increases the incorporation of phosphorous in to nucleic acids and adenine into RNA.
- 24. Celldivision cytikinins are known to be regulators of cell division in mature cells. the most important effect of cytokinins is the stimulation of cell division in excised tissues. cytokinins alone does not produce celldivision. auxin is also essential
- 26. Morphogenesis: Root and bud differentiation Cytokinins in interaction with auxins control morphogenesis The ceils of tobacco pith do not either grow or differentiate when only auxin or only cytokinin is added to the medium. However when the medium contains both auxin and kinetin m the ratio of 10:1 pith cells grow and forms a mass of unorganized cells (callus) If ratio is more ,then more no. of roots are initiated. If ratio is less,then more no. of shoot buds are initiated
- 27. Anti senescence hormone: Cytokinins delay senescence. Generally, protein and chlorophyll content of the leaf decreases with the increase in age. Thus, when leaf becomes old. it turns in to yellow, become senescent and finally shed of. Senescence of leaves can be delayed by application of kinetin. Cytokinins delay senescence by increased synthesis of proteins. The delay of senescence of leaves and other organs of the plants by cytokinins is called as Richmond - Lang effect.
- 29. In an experiment, one of the two primarily opposite leaves of a bean plant was treated with Benzyl adenine. This treatment accelerated senescence of untreated leaf. This is because of mobilization of organic metabolites and minerals from untreated leaf to cytokinin treated leaf because of cytokinin acts as mobilizing centers. Green vegetables like cabbage, lettuce and celery deteriorate rapidly after harvest. Post harvest spray of Benzyl adenine at 10 to 40 ppm or post harvest dip of 10 ppm increase shelf life of these vegetables.
- 30. Promotion of lateral bud growth Application of cytotmins reduces apical dominance . The action of cytokinin is antagonistic to that of auxin in apical dominance The lateral buds of intact plants which otherwise remain arrested can be made to grow by applying kinetin. The pathogen Corynebacterium facians causes a disease called Witches broom in many plants This symptom is characterized by loss of apical dominance and emergence of numerous lateral branches which give the appearance of a broom.This effect is due to the secretion of cytokinin namely isopente the pathogen
- 32. Breaking of dormancy Lettuce seeds require the presence of red light for germination in addition to moisture, air and suitable temperature. However the seeds can be made to germinate in the dark by applying Kinetin. Thus. Kinetin replaces the red light requirement for germination. In cocklebur, each fruit (but) contains two seeds which are of unequal in size The lower one in largest and germinates while the upper seed is dormant. Here the dormancy is due to the presence of germination inhibitors. This dormancy is over come by the application of kinetin.
- 33. Cell enlargement: Cortical cells of tobacco root were observed to enlarge four times of their normal size in the presence of kinetin