07 Plant Growth and Mineral Nutrition - part 08 - Growth Hormones

07 Plant Growth and Mineral Nutrition - part 08 - Growth Hormones


Growth Hormones : 
  • Term `hormone' was coined first by Starling.
  • The internal factors that influence growth are called growth hormones or growth regulatorsas they inhibit, promote or modify the growth. 
  • Growth promoters are  -  
  1. Auxins, 
  2. Gibberellins (GA) and 
  3. Cytokinins (CK). 
  • Growth inhibitors in plants are - 
  1. Ethylene and 
  2. Abscissic acid (ABA). 
  • All phytohormones are growth regulators.
Know the Scientist : 

1. Charles Darwin (1886) 
  • The auxin is the first hormone to be discovered in plants. 
  • Discovery of auxins dates back to 19th century when Charles Darwin (1886) was studying tropism in plants. 
  • He exposed canary grass coleoptile to unilateral light. 
  • Conclusion : a growth stimulus is developed in the coleoptile tip and transmitted downwards to the growth zone. 
  • This has caused bending of the tip towards light. 
2. Boysen - Jensen (1910) 
  • The Danish plant physiologist Boysen - Jensen (1910) cut off the colepotile and inserted thin plate of gelatin beween the tip and the cut stump. 
  • Observation :  coleoptiles tip still bends towards unilateral light. 
3. Paal (1919) 
  • Paal (1919) cut off the tip of colepotile and replaced it asymmetrically on the cut coleoptile stump. 
  • He observed that the colepotile tip bent away from the side bearing tip even in dark.
4.  F.W. Went (1928)
  •  F.W. Went (1928) successfully isolated natural auxin from Avena coleoptile tips. 
  • He cut off the tip and placed them on small agar blocks. 
  • Then after certain period of time placed the agar blocks asymmetrically on cut coleoptile stump that caused bending. 
  • He demonstrated the presence of substance which could diffuse into agar blocks. 
  • Went named this substance as auxin.
5.  Thimann and Pincus (1948) 
  • According to Thimann and Pincus (1948) "Plant hormones are organic substances produced naturally in higher plants affecting growth or other physiological functions at a site remotefrom its place of production and active in very minute (optimum) amount".
6. Phillips 1971
  • Phillips 1971 : Hormones are transported through phloem parenchyma .

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