07 Plant Growth and Mineral Nutrition - part 11 - Growth Harmone - Cytokinin

07 Plant Growth and Mineral Nutrition - part 11 - Growth Harmone - Cytokinin


Cytokinin : 
  • Growth hormone that promotes cell division. 
  • Letham coined the term cytokinin. 
  • The first cytokinin was discovered by Skoog and Miller (1954) during investigation of nutritional requirements of callus tissue culture of Nicotiana tabacum (Tobacco).
  • They observed that the callus proliferatedwhen the nutrient medium was supplemented with coconut milk and degraded sample of DNA (obtained from herring sperm). 
  • They named it as kinetin. 
  • Chemically kinins are 6-furfuryl amino purine. 
  • First natural cytokinin was obtained from unripe maize grains by Letham et al. It is known as Zeatin. 
  • 6-benzyl adenine is a synthetic cytokinin hormone. 
  • Seven different types of cytokinins are recorded from plants. 
  • Natural cytokinins are also reported from plants like Banana flowers, apple and tomato fruits, coconut milk, etc.

Physiological effects and applications of cytokinin :
  • Besides cell division, it also promotes cell enlargment. 
  • High cytokinin promotes shooting A low ratio of cytokinin to auxin induces root developmentbut a high ratio causes buds and shoot to develop. 
  • Cytokinin and auxin ratio and their interactions controls morphogenic differentiation. 
  • Promotes the growth of lateral buds and controls apical dominance by cell division. 
  • Delays the senescence or ageing and abscission processes in plant organs. This was reported by Richmond and Lang (1957). 
  • Formation of interfasicular cambium and expansion of cells are other functions. 
  • Also breaks dormancy and promotes the germination of seeds. Cytokinin reverses apical dominance effect. 
  • Induces RNA synthesis and formation ofinterfascicular cambium.

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