Abscisic acid: Encyclopedia - Abscisic acid

Abscisic acid

Abscisic acid (ABA), also known as abscissin, is a plant hormone.

Abscisic acid - Location Characteristics and Occasions for Synthesis Induction

• Released during desiccation (of vegetative tissues)
• 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

Abscisic acid is defined as a plant hormone that mainly acts to inhibit growth, promotes dormancy, and to help the plant tolerate stressful conditions.

Abscisic acid is named so because it was believed that this hormone caused the abscission of leaves from deciduous trees in the fall. The plants growth slows down and then it will assume a dormant state. This is the complete opposite of what auxin, gibberellins, and cytokinins, the other plant hormones will do to the plant. Inside the terminal bud the hormone abscisic acid is produced. The slow growth and direction of leaf primordial develops scales to protect the dormant buds during the cold season.

This hormone inhibits the division of the cell in the vascular cambium. Also preparing for the winter by suspending primary and secondary growth. The most impressive effect of abscisic acid is the inhibition of growth and the maintenance done on the dormancy of buds. Yet this is not enough to keep the dormancy of buds up for the long term.

Abscisic acid - 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 (speculative)
• 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 (speculative)
• Possibly induces cell dormancy or senescence by a climactic increase or sustained level stimulating the synthesis of GA and/or Ethylene (speculative)
• 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 (speculative)

Auxins - Cytokinins - Ethylene - Gibberellins - Abscisic acid

Brassinosteroids - Jasmonates - Salicylic acid

Category: Plant hormones

Adapted from the Wikipedia article "Abscisic acid", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki