Theory:

Unlike the other hormones Abscisic acid (\(ABA\)) is a growth inhibitor which regulates abscission and dormancy. As it increases the tolerance of plants to various kinds of stress it is also known as stress hormone. It is found in the chloroplasts of plants.
 
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Abscisic acid
Physiological effects of abscisic acid:
  • It is a hormone that promotes abscission and wilting.
abscission.png
Senescence and abscission
  
The separation of leaves, flowers and fruits from the branch is known as abscission.
 
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Abscission of leaves
  • It initiates the closure of stomata during water stress and drought conditions.
Opening_and_Closing_of_Stoma.svg.png
Opening and closing of stomata
  • It promotes senescence in leaves by causing the loss of chlorophyll.
  • It induces bud dormancy in trees lie birch towards the approach of winter.
  • It is a potent inhibitor of tomato lateral bud growth.
Reference:
https://en.wikipedia.org/wiki/Abscisic_acid#/media/File:Abscisic_acid.svg
https://s3-us-west-2.amazonaws.com/treefruit.wsu.edu/wp-content/uploads/2016/01/02-Greene_Endo-Hormones101.pdf
https://en.wikipedia.org/wiki/Abscission#/media/File:Fall_Leaves.jpg
https://en.wikipedia.org/wiki/Guard_cell#/media/File:Opening_and_Closing_of_Stoma.svg