- 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.
Physiological effects of gibberellins:
- Stem elongation by inducing cell division & cell elongation in the internodes and also causes leaf expansion. It has no effect on roots. This is used to increase the length of grape stalks thus increasing the number of grapes in a cluster. This is used to increase the length of sugarcane stem thus increasing the yield of sugar to as much as 20 tonnes/acre.
- It is capable of converting a genetically dwarf plant or a rosette plant into a tall one. E.g., beet, cabbage. This rapid elongation of the stem is called Bolting.
- Can cause flowering in long day plants under short day conditions.
- It can substitute cold treatment in biennials.
- Speeds up malting process by increasing α-amylase in germinating barley seeds. This is used in brewery industry.
- It is capable of breaking dormancy of buds, tubers, seeds etc.
- It is capable of delaying fruit maturity & senescence thus helping to store the fruit. E.g., Citrus.
- Spraying of gibberellins on juvenile conifers speeds up maturity thus leading to early seed formation.
- It controls fruit growth & development and can induce parthenocarpy. E.g., apple, pear. It also elongates the fruit.
- They promote formation of male flowers in Cannabis & cucurbits.
- It helps in germinating Photoblastic positive seeds e.g., Lettuce, Tobacco in dark.
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