• Skoog & co-workers showed that callus formation occurred when internodal segments of tobacco are cultured. In the nutrient medium in addition to auxin, they provided extracts of yeast, vascular tissues, coconut milk or DNA.
  • Miller first discovered it from autoclaved Herring sperm DNA. He named it as kinetin.
  • Letham first obtained natural cytokinin from maize grain & coconut milk, it is referred as Zeatin.
  • Site of synthesis: Major source is roots & regions where rapid cell division occurs like meristems, root tip, buds, young leaves & developing fruits.
  • Transported through the xylem.
  • Derived from Adenine, it is 6-furfuryl aminopurine.

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  • A Japanese farmer in his rice field found a seedling that is extremely tall, he named it as Bakanae means ‘foolish seedling’.
  • Kurosawa showed that it was due to an infection by fungus Gibberella fujikorai (Fusarium monoliforme).
  • Yabuta & Sumuki isolated it & named it as Gibberellins.
  • Chemically it is Gibberellic acid (C19H22O6).
  • More than 100 different types of Gibberellins are known, of which GA3 is the most common.
  • Precursor of gibberellins: Mevalonic acid (derived from Acetyl CoA).
  • Site of synthesis: shoot buds, young leaves & developing seeds.
  • Transported by simple diffusion.

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