Abscisic Acid is a plant hormone.

Location, Characteristics and Occasions for Synthesis Induction

• Released during desiccation
• Has been found to peak at night
• Synthesized in green fruit and seeds at the beginning of the wintering period
• As well as moving within the leaf it can be transferred to the leaf from the roots by the transpiration stream
• Rapidly translocated
• Produced in response to stress
• Synthesized in leaves and stems (particularly when water stressed)
• Released by cells in danger of not having enough nutrients locally or good enough environmental conditions to survive
• All cells capable of synthesizing

Effects

• Stimulates stomatal closure
• Fruit ripening inhibition
• Encourages seed dormancy by inhibiting cell growth – inhibits seed germination
• ABA inhibits the uptake of Kinetin
• Pathogen resistance response defense -
• Induces senescence in already damaged cells and their proximate neighbors
• Quickly puts a plant, organ, tissue or individual cell in a defensive posture (whatever this entails) in response to rapidly developing nutrient or environmental stress that threaten their survival
• Decreases metabolism in response to a newly developing deficiency of nutrient or adverse environmental condition, such that condition becomes survivable at the new lower level of metabolism (Not true in Theory II)
• Possibly induces cell dormancy or senescence by a climactic increase or sustained level stimulating the synthesis of GA and/or Ethylene (Not true in Theory II of plant hormones)
• A climactic rise or sustained level of ABA may be a prerequisite for the synthesis of any GA and/or Ethylene in that it presence indicates unusable or unsurvivable levels of Water, Sugar, Minerals and/or essential gases (Not true in Theory II)