Abscisic acid

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Abscisic acid
Chemical name	[S-(Z,E)]-5-(1-Hydroxy-2,6,6-trimethyl- 4-oxo-2-cyclohexen-1-yl)-3-methyl- 2,4-pentanedienoic acid[1]
Chemical formula	C15H20O4
Molecular mass	264.32 g/mol
CAS number	[14375-45-2]
Density	? g/cm³
Melting point	161–163 °C
Boiling point	120 °C (sublimes)
SMILES	O=C1CC(C)(C)C(O)(/C=C/C(C)=C\C(O)=O)C(C)=C1
Disclaimer and references

Abscisic Acid (ABA), also known as abscisin II and dormin, is a plant hormone. It was given its names because it was once thought to be pivotal in abscission and in bud dormancy.^[2]

[edit] Location, Characteristics and Occasions for Synthesis Induction

• Released during desiccation (of vegetative tissues)
• Found to peak at night
• Synthesized in green fruit and seeds at the beginning of the wintering period
• Moved within the leaf and 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
• Capable of being synthesized by all cells.

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

Abscisic acid is named so because it was believed that this plant growth regulator caused the abscission of leaves from deciduous trees in the fall. The plant's growth slows down, and then assumes a dormant state. This is the complete opposite of what auxin, gibberellins, and cytokinins, the other plant hormones, 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 plant growth regulator 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 is produced in the roots in response to decreased soil water potential. It travels to the leaves where it is rapidly metabolised and alters the osmotic potential of the guard cells of the leaf, causing them to collapse and the stomata to close. This prevents transpiration from occurring and prevents further water loss from the leaves in times of low water availability.

[edit] Effects

• Stimulates stomatal closure, in order to reduce transpiration and prevent water loss.
• Inhibits fruit ripening
• Encourages seed dormancy by inhibiting cell growth – inhibits seed germination
• Inhibits the uptake of Kinetin
• Activates the pathogen resistance response defense
• Induces senescence in already-damaged cells and their proximate neighbours
• 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 threatens their survival (speculative)
• Decreases metabolism in response to a newly-developing deficiency of nutrient or adverse environmental condition, such that the 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 its presence indicates unusable or unsurvivable levels of Water, Sugar, Minerals and/or essential gases (speculative)

[edit] References

1. ^ Abscisic Acid Chemical Name
2. ^ Plant Physiology: Abscisic acid