Abscisic acid

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Abscisic acid
Stereo, skeletal formula of abscisic acid
Names
Preferred IUPAC name
(2Z,4E)-5-[(1S)-1-Hydroxy-2,6,6-trimethyl-4-oxocyclohex-2-en-1-yl]-3-methylpenta-2,4-dienoic acid[3]
Other names
(2Z,4E)-(S)-5-(1-Hydroxy-2,6,6-trimethyl-4-oxo-2-cyclohexen-1-yl)-3-methyl-2,4-pentanedienoic acid; Dormic acid;[citation needed] Dormin[1][2]
Identifiers
3D model (
JSmol
)
3DMet
Abbreviations ABA
2698956
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.040.275 Edit this at Wikidata
EC Number
  • 244-319-5
MeSH Abscisic+Acid
RTECS number
  • RZ2475100
UNII
  • InChI=1S/C15H20O4/c1-10(7-13(17)18)5-6-15(19)11(2)8-12(16)9-14(15,3)4/h5-8,19H,9H2,1-4H3,(H,17,18)/b6-5+,10-7-/t15-/m1/s1 checkY
    Key: JLIDBLDQVAYHNE-YKALOCIXSA-N checkY
  • OC(=O)\C=C(\C)/C=C/[C@@]1(O)C(C)=CC(=O)CC1(C)C
Properties
C15H20O4
Molar mass 264.321 g·mol−1
Appearance Colorless crystals
Density 1.193 g/mL
Melting point 163 °C (325 °F; 436 K)[4]
log P 1.896
Acidity (pKa) 4.868
Basicity (pKb) 9.129
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H315, H319, H335
P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Abscisic acid (ABA or abscisin II[5]) is a plant hormone. ABA functions in many plant developmental processes, including seed and bud dormancy, the control of organ size and stomatal closure. It is especially important for plants in the response to environmental stresses, including drought, soil salinity, cold tolerance, freezing tolerance, heat stress and heavy metal ion tolerance.[6]

Discovery

In the 1940s, Torsten Hemberg, while working at the University of Stockholm, found evidence that a positive correlation exists between the rest period and the occurrence of an acidic ether soluble growth inhibitor in potato tubers.[7][8]

In 1963, abscisic acid was first identified and characterized as a plant hormone by Frederick T. Addicott and Larry A. Davis. They were studying compounds that cause abscission (shedding) of cotton fruits (bolls). Two compounds were isolated and called abscisin I and abscisin II. Abscisin II is presently called abscisic acid (ABA).[5]

In plants

Function

ABA was originally believed to be involved in abscission, which is how it received its name. This is now known to be the case only in a small number of plants. ABA-mediated signaling also plays an important part in plant responses to environmental stress and plant pathogens.[9][10] The plant genes for ABA biosynthesis and sequence of the pathway have been elucidated.[11][12] ABA is also produced by some plant pathogenic fungi via a biosynthetic route different from ABA biosynthesis in plants.[13]

In preparation for winter, ABA is produced in

primordia to develop scales to protect the dormant buds during the cold season. ABA also inhibits the division of cells in the vascular cambium
, adjusting to cold conditions in the winter by suspending primary and secondary growth.

Abscisic acid is also produced in the

stomata to close. The ABA-induced stomatal closure reduces transpiration (evaporation of water out of the stomata), thus preventing further water loss from the leaves in times of low water availability. A close linear correlation was found between the ABA content of the leaves and their conductance (stomatal resistance) on a leaf area basis.[15]

Seed germination is inhibited by ABA in antagonism with gibberellin. ABA also prevents loss of seed dormancy.[citation needed]

Several ABA-

stomatal regulation, and some mutants show stunted growth and brown/yellow leaves. These mutants reflect the importance of ABA in seed germination and early embryo development.[citation needed
]

pyridyl containing ABA activator) is a naphthalene sulfonamide hypocotyl cell expansion inhibitor, which is an agonist of the seed ABA signaling pathway.[16] It is the first agonist of the ABA pathway that is not structurally related to ABA.[citation needed
]

Homeostasis

Biosynthesis

Abscisic acid (ABA) is an

dioxygenation reaction yields the proximal ABA precursor, xanthoxin, which is then further oxidized to ABA. via abscisic aldehyde.[11]

Abamine has been designed, synthesized, developed and then patented as the first specific ABA biosynthesis inhibitor, which makes it possible to regulate endogenous levels of ABA.[17]

Locations and timing of ABA biosynthesis

  • Synthesized in nearly all plant tissues, e.g., roots, flowers, leaves and stems
  • Stored in
    chlorenchyma) cells where it is conjugated to glucose via uridine diphosphate-glucosyltransferase resulting in the inactivated form, ABA-glucose-ester [18]
  • Activated and released from the chlorenchyma in response to
    environmental stress, such as heat stress, water stress, salt stress[18]
  • Released during desiccation of the vegetative tissues and when roots encounter soil compaction.[19]
  • Synthesized in green fruits at the beginning of the winter period
  • Synthesized in maturing seeds, establishing dormancy
  • Mobile within the leaf and can be rapidly translocated from the leaves to the roots (opposite of previous belief) in the phloem
  • Accumulation in the roots modifies lateral root development, improving the stress response
  • ABA is synthesized in almost all cells that contain chloroplasts or
    amyloplasts

Inactivation

ABA can be catabolized to

P450 enzymes) or inactivated by glucose conjugation (ABA-glucose ester) via the enzyme uridine diphosphate-glucosyltransferase (UDP-glucosyltransferase). Catabolism via the CYP707As is very important for ABA homeostasis, and mutants in those genes generally accumulate higher levels of ABA than lines overexpressing ABA biosynthetic genes.[20] In soil bacteria, an alternative catabolic pathway leading to dehydrovomifoliol via the enzyme vomifoliol dehydrogenase
has been reported.

Effects

Signal cascade

ABA signal pathway in plants

In the absence of ABA, the phosphatase ABI1-INSENSITIVE1 (ABI1) inhibits the action of SNF1-related protein kinases (subfamily 2) (SnRK2s). ABA is perceived by the PYRABACTIN RESISTANCE 1 (PYR1) and PYR1-like membrane proteins. On ABA binding, PYR1 binds to and inhibits ABI1. When SnRK2s are released from inhibition, they activate several transcription factors from the ABA RESPONSIVE ELEMENT-BINDING FACTOR (ABF) family. ABFs then go on to cause changes in the expression of a large number of genes.[6] Around 10% of plant genes are thought to be regulated by ABA.[citation needed]

In fungi

Like plants, some fungal species (for example

Magnaporthe oryzae) have an endogenous biosynthesis pathway for ABA. In fungi, it seems to be the MVA biosynthetic pathway that is predominant (rather than the MEP pathway that is responsible for ABA biosynthesis in plants). One role of ABA produced by these pathogens seems to be to suppress the plant immune responses.[29]

In animals

ABA has also been found to be present in

macrophages) when stimulated. There are also conflicting conclusions from different studies, where some claim that ABA is essential for pro-inflammatory responses whereas other show anti-inflammatory effects. Like with many natural substances with medical properties, ABA has become popular also in naturopathy. While ABA clearly has beneficial biological activities[citation needed] and many naturopathic remedies will contain high levels of ABA (such as wheatgrass juice, fruits and vegetables), some of the health claims made may be exaggerated or overly optimistic. In mammalian cells ABA targets a protein known as lanthionine synthetase C-like 2 (LANCL2), triggering an alternative mechanism of activation of peroxisome proliferator-activated receptor gamma (PPAR gamma).[32] LANCL2 is conserved in plants and was originally suggested to be an ABA receptor also in plants, which was later challenged.[33]

Measurement of ABA concentration

Several methods can help to quantify the concentration of abscisic acid in a variety of plant tissue. The quantitative methods used are based on HPLC and ELISA. Recently, 2 independent FRET probes have been developed that can measure intracellular ABA concentrations in real time in vivo.[34][35]

References

  1. ^ O'Neil, Maryadele J; Heckelman, PE; Koch, CB; Roman, KJ (2006). The Merck Index, 14th.
  2. ^ 21293-29-8
  3. ^ "Abscisic Acid - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 22 October 2011.
  4. ^ "ChemSpider database - Abscisic acid - Properties". Retrieved 27 December 2012. The melting point is decided by experimental data by Tokyo Chemical Industry Ltd.
  5. ^
    PMID 16658017
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  6. ^
    PMID 24273463
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  8. S2CID 253856375
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  11. ^
    PMID 15862093
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  15. S2CID 30298332.[citation needed
    ]
  16. PMID 19407142
    .
  17. ^ US 7098365, Yoshida, Shigeo & Asami, Tadao, "Abscisic acid biosynthesis inhibitor", published 2006-08-29, assigned to Riken 
  18. ^ a b Zhang, Y., et al. (2021) ABA homeostasis and long-distance translocation are redundantly regulated by ABCG ABA importers. Science Advances.[1]
  19. ^ DeJong-Hughes, J., et al. (2001) Soil Compaction: causes, effects and control. University of Minnesota extension service
  20. PMID 24273463
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  21. doi:10.1093/jxb/38.7.1174
    .
  22. ^ Ralls, Eric (2023-06-27). "Plant leaves send signals to their roots on dry days telling them to keep digging deeper for water". www.msn.com/. Retrieved October 4, 2023.
  23. doi:10.1111/j.1399-3054.1979.tb01664.x
    .
  24. doi:10.1146/annurev.pp.45.060194.000553
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  30. PMID 21763293
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  31. PMID 20015036. Archived from the original
    on 2012-04-01. Retrieved 2018-09-30.
  32. PMID 21088297
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  33. PMID 19841654
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  34. PMID 24737861
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  35. PMID 24737862
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