Growth and Development of Horticultural Crops (1+1)

Discovery and Chemical Nature

• The discovery of auxins dates back to last quarter of the 19th century when Charles Darwin was studying tropisms in plants.
  
• Went (1926) was successful in isolating this growth substance from Avena coleoptile tips which still retained the growth promoting activity.
  
• He cut off the tips of the Avena coleoptiles and placed them on small agar-blocks for certain period of time and then placed the agar-blocks asymmetrically on cut coleoptile stumps.
  
• All the coleoptiles showed typical curvature even in dark.
• He also developed a method for determining the amount of this growth substance (i.e.,auxin) which is active in very small amounts in the Avena coleptile tips.
  
• This method or the bioassay is famous by the name of Avena Curvature Test.






http://image.wistatutor.com/content/plant-growth-movements/gibberellins-avena-test.jpeg

• Avena test (a) A piece of mica inserted on the shaded side prevented curvature of the coleoptile, (b) but not when it was inserted on the illuminated side, (c) when the tip was removed (d) but was put back with a block of gelatine, (e) normal phototropic curvature occurred.