Jasmonic acid (JA) is an
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
found in several plants including
jasmine
Jasmine ( taxonomic name: ''Jasminum''; , ) is a genus of shrubs and vines in the olive family (Oleaceae). It contains around 200 species native to tropical and warm temperate regions of Eurasia, Africa, and Oceania. Jasmines are widely culti ...
. The molecule is a member of the
jasmonate
Jasmonate (JA) and its derivatives are lipid-based plant hormones that regulate a wide range of processes in plants, ranging from growth and photosynthesis to reproductive development. In particular, JAs are critical for plant defense against her ...
class of
plant hormones. It is biosynthesized from linolenic acid by the
octadecanoid pathway. It was first isolated in 1957 as the methyl
ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...
of jasmonic acid by the Swiss chemist Edouard Demole and his colleagues.
Biosynthesis
Its
biosynthesis starts from the fatty acid
linolenic acid
Linolenic acid is a type of naturally-occurring fatty acid. It can refer to either of two octadecatrienoic acids (i.e. with an 18-carbon chain and three double bonds, which are found in the '' cis'' configuration), or a mixture of the two. Linol ...
, which is oxygenated by
lipoxygenase (13-LOX), forming a
hydroperoxide
Hydroperoxides or peroxols are compounds containing the hydroperoxide functional group (ROOH). If the R is organic, the compounds are called organic hydroperoxides. Such compounds are a subset of organic peroxides, which have the formula ROOR. ...
. This peroxide then cyclizes in the presence of allene oxide synthase to form an
allene oxide. The rearrangement of allene oxide to form 12-oxophytodienoic acid is catalyzed by the enzyme
allene oxide cyclase. A series of
β-oxidations result in 7-iso-jasmonic acid. In the absence of enzyme, this iso-jasmonic acid isomerizes to jasmonic acid.
Function
The major function of JA and its various metabolites is regulating plant responses to abiotic and biotic stresses as well as plant growth and development. Regulated plant growth and development processes include growth inhibition,
senescence
Senescence () or biological aging is the gradual deterioration of functional characteristics in living organisms. The word ''senescence'' can refer to either cellular senescence or to senescence of the whole organism. Organismal senescence invol ...
,
tendril coiling, flower development and leaf abscission. JA is also responsible for
tuber
Tubers are a type of enlarged structure used as storage organs for nutrients in some plants. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing ...
formation in potatoes and yams. It has an important role in response to
wounding of plants and
systemic acquired resistance. The Dgl gene is responsible for maintaining levels of JA during usual conditions in ''
Zea mays'' as well as the preliminary release of jasmonic acid shortly after being fed upon. When plants are attacked by insects, they respond by releasing JA, which activates the expression of
protease inhibitors, among many other anti-herbivore defense compounds. These protease inhibitors prevent proteolytic activity of the insects' digestive proteases or "salivary proteins", thereby stopping them from acquiring the needed nitrogen in the
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
for their own growth. JA also activates the expression of
Polyphenol oxidase
Polyphenol oxidase (PPO; also polyphenol oxidase i, chloroplastic), an enzyme involved in fruit browning, is a tetramer that contains four atoms of copper per molecule.
PPO may accept monophenols and/or ''o''-diphenols as substrates. The ...
which promotes the production of
quinolines. These can interfere with the insect's enzyme production and decrease the nutrition content of the ingested plant.
JA may have a role in pest control. Indeed, JA has been considered as a seed treatment in order to stimulate the natural anti-pest defenses of the plants that germinate from the treated seeds. In this application jasmonates are sprayed onto plants that have already started growing. These applications stimulate the production of protease inhibitor in the plant. This production of protease inhibitor can protect the plant from insects, decreasing infestation rates and physical damage sustained due to herbivores. However, due to its antagonistic relationship with
salicylic acid (an important signal in pathogen defense) in some plant species, it may result in an increased susceptibility to viral agents and other pathogens. In ''
Zea mays'',
salicylic acid and JA are mediated by NPR1 (nonexpressor of pathogenesis-related genes1), which is essential in preventing herbivores from exploiting this antagonistic system.
Armyworms (
Spodoptera spp.), through unknown mechanisms, are able to increase the activity of the
salicylic acid pathway in maize, resulting in the depression of JA synthesis, but thanks to NPR1 mediation, JA levels aren't decreased by a significant amount.
Derivatives
Jasmonic acid is also converted to a variety of derivatives including the
ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...
methyl jasmonate
Methyl jasmonate (abbreviated MeJA) is a volatile organic compound used in plant defense and many diverse developmental pathways such as seed germination, root growth, flowering, fruit ripening, and senescence. Methyl jasmonate is derived from ...
. This conversion is catalyzed by the jasmonic acid carboxyl methyltransferase enzyme.
It can also be conjugated to amino acids in some biological contexts. Decarboxylation affords the related fragrance
jasmone.
References
*
{{DEFAULTSORT:Jasmonic Acid
Plant hormones
Acetic acids
Cyclic ketones
Alkene derivatives
Cyclopentanes