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Cytokinin
- 1. CYTOKININS DR. R. RENUKA, M.SC.,M.PHIL.,PH.D. ASSOCIATE PROFESSOR OF BIOCHEMISTRY V.V.VANNIAPERUMAL COLLEGE FOR WOMEN VIRUDHUNAGAR, TAMILNAD, INDIA.
- 2. CYTOKININ Cytokinins are a group of plant growth hormones that promote cell division or cytokinesis especially controlling the transition from G2 to mitosis in plant roots and shoots. They are primarily involved in cell growth and differentiation.
- 3. DISCOVERY OF CYTOKININS In 1954, when Miller and others working on tobacco pith culture , they found certain stimulation of cell division when it was treated with DNA of Herring sperm which was kept in laboratory for long time. It was believed that it was the DNA degradation product which caused cell division stimulation in tobacco pith culture and not DNA itself. They called this product as kinetin as it is caused cytokinesis.
- 4. CHEMICALS WHICH INDUCE CELL DIVISION IS CALLED AS CYTOKININS.
- 5. SYNTHESIS AND TRANSPORT PRIMARY SITE OF CYTOKININ SYNTHESIS IS ROOT TIPS.
- 6. OCCURRENCE OF CYTOKININ CYTOKININS OCCUR IN EVERY DEVELOPING PART OF PLANTS SUCH AS APICAL MERISTEMS, DEVELOPING SEEDS, ROOT NODULES, BACTERIAL TUMORS AND ALL REGIONS WHICH SHOW ACTIVE CELL DIVISION.
- 7. CHEMICAL NATURE OF CYTOKININ WHETHER THEY ARE NATUALLY OCCURRING OR SYNTHETIC, ALL CYTOKININS HAVE SOME STRUCTURAL SIMILARITIES. ALL ARE DERIVATIVES OF ADENINE – WHICH IS A PURINE BASE OF NUCLEIC ACIDS. HYDROGEN ATOM ON N6 OF ADENINE RING IS SUBSTITUTED BY EITHER BENZYL GROUP RESULTING IN BENZYL ADENINE OR BY FURFURAL GROUP FORMING KINETIN OR BY ISOPENTENYL GROUP FORMING ZEATIN.
- 8. STRUCTURE OF BENZYL ADENINE, KINETIN AND ZEATIN
- 9. PHYSIOLOGICAL ROLES OF CYTOKININS 1. CELL DIVISION -One of the most important biologic effects of kinetin on plants is to induce cell division in tobacco pith callus, carrot root tissue, soy bean cotyledon, pea callus etc. in the presence of sufficient amount of auxin. - Cell division occurs when both IAA and cytokinin is applied jointly rather than individually. - Secondary growth occurs in cambium cells due to cell division.
- 10. 2.CELL ELONGATION Like auxin and gibberellins, cytokinin also promotes cell enlargement. Significant cell enlargement has been observed after kinetin treatment in cortical cells of tobacco roots, tobacco pith cultures, leaf discs cut from etiolated leaves of pumpkin etc.
- 11. 3. INITIATION OF INTERFASCICULAR CAMBIUM Kinetin can induce formation of intrafascicular cambium and there by secondary growth. (This is actually shown by Sorokin et al in 1962 in pea stem sections).
- 12. 4.MORPHOGENESIS KINETIN ALSO HAS THE ABILITY TO CAUSE MORPHOGENETIC CHANGES IN AN UNDIFFERENTIATED CALLUS. RELATIVE CONCENTRATIONS OF IAA AND CYTOKININ DETERMINES THE FORMATION OF PARTICULAR ORGANS EITHER SHOOT OR ROOT FROM CALLUS. MORE AUXIN CONC. ROOT FORMATION MORE CYTOKININ CONC. SHOOT FORMATION APPROPRIATE CONC. OF BOTH ROOT AND SHOOT AUXIN AND CYTOKININ FORMATION
- 13. 5. DELAY OF SENESCENCE THE AGING PROCESS OF LEAVES USUALLY ACCOMPANIES WITH LOSS OF CHLOROPHYLL AND RAPID BREAK DOWN OF PROTEINS, CHO, NUCLEIC ACIDS, LIPIDS AND TRANSPORTATION OF THE PRODUCTS TO YOUNGER LEAVES OR TISSUES. THIS IS CALLED SENESCENCE. IN 1957, RICHMOND AND LANG SHOWED THAT THIS SENESCENCE COULD BE POSTPONED TO SEVERAL DAYS IN DETACHED XANTHIUM LEAVES BY KINETIN TREATMENT. THIS EFFECT OF KINETIN IN DELAYING THE SENESCENCE IS CALLED AS RICHMOND-LANG EFFECT.
- 14. Cytokinin mediated delaying of senescence is linked with its effect on translocation of metabolites. the cytokinin treated leaves withdraw nutrients from adjoining leaves and maintain their nutrition and vigour. Action of kinetin in senescence is might be due to maintenance of the protein synthesising machinery. At molecular level, cytokinin may act either by depressing protein degradation or by increasing protein synthesis and maintains the ratio of RNA or protein to DNA.
- 15. 6. COUNTERACTION OF APICAL DOMINANCE Apical dominance is caused by auxin. Cytokinins counter the action of auxins. Here, Cytokinins are antagonist to auxin. In the intact plants, apical bud causes a preferential withdrawal of root manufactured cytokinin towards it. This leads to cytokinin starvation in lateral buds. As cytokinin is essential for cell division, lateral buds are inhibited from growing. Exogenous application of cytokinin stimulates cell division in lateral buds hence, growth of lateral buds are promoted even if apical buds are intact and apical dominance is nullified.
- 17. 7. BREAKING SEED DORMANCY Cytokinin is effective in breaking dormancy of light sensitive seeds like lettuce and tobacco and promote seed germination. Thus, cytokinin substitutes the light. Further more the inhibitory effect of far red light treatment on the germination of above seeds is also overcome by kinetin treatment. Kinetin in combination with red light reverse the influence of certain inhibitors (coumarin and xanthyletin) of seed germination and breaks seed germination.
- 18. 8.TUBER FORMATION Cytokinins induce tuber formation and inhibit elongation of stolons of potato. Tuber formation in Begonia is also stimulated by cytokinin.
- 19. 9. Promote cell expansion Cytokinin promotes the expansion of excised cotyledons of several dicots. The mechanism is associated with increased plasticity of the cell wall.
- 20. 10. INFLORESCENCE GROWTH Cytokinins induce cell division in inflorescence tips. This leads to more flowering which in turn yields more fruit. Cytokinin oxidase regulates rice production (Ashikari et al.2005).
- 21. 11. Cytokinin increases anthocyanin in I. balsominia and Betacyanin in excised cotyledons of Amaranthus in light. 12. Cytokinin promotes chloroplast development in callus tissues of excised cotyledons. *****************
- 22. THANK YOU