Introduction: What is Jasmonic Acid?
Jasmonic acid is a plant hormone that plays an important role in plant development and defence and regulates plant response to biotic and abiotic stress.
In the 1980s plant physiologists found that essential oils from some fragrant flowers such as jasmine and rosemary possess the activity of retarding root growth and promoting leaf senescence. The isolation of methyl jasmonate from jasmine oil obtained from the Jasminum grandiforum led to the discovery of Jasmonic acid and its derivatives. Jasmonic acid (JA) was first isolated from cultures of the fungus Lasiodiplodia theobromae. JA (“when doing voice over please say jasmonic acid, not JA”) and its derivatives occur throughout the plant kingdom.
How Plants Use Jasmonic Acid?
Jasmonates are derived from linolenic acid in a lipoxygenase- dependent process. Their structure is similar to mammalian eicosanoids, which are also derived from lipids through the action of lipoxygenase. The chemical formula of jasmonic acid is C12H18O3.
The level of JA in plant tissues varies as a function of tissue type, development, and external stimuli. The highest levels of JA/JAMe are reported in flowers and reproductive tissues, whereas much lower levels are found in roots and mature leaves. The highest levels of jasmonate accumulate in actively growing tissues such as hypocotyl hooks, flowers, and developing seed pods.Jasmonic acid (JA) and its methyl ester, methyl jasmonate (JAMe), are naturally occurring regulators of higher plant development, responses to external stimuli, and gene expression.
Changes in plant gene expression are induced by nanomolar to micromolar concentrations of JA/JAMe. Regulated plant growth and development processes include growth inhibition, senescence, tendril coiling, flower development and leaf abscission. JA is also responsible for tuber formation in potatoes and yams. It has an important role in response to the wounding of plants and systemic acquired resistance. It has also been shown to stimulate fruit ripening, likely through its action on ethylene biosynthesis.
When plants are attacked by insects, they respond by releasing JA, which activates the expression of protease inhibitors, among many other anti-herbivore defence compounds. These protease inhibitors prevent the proteolytic activity of the insects’ digestive proteases or “salivary proteins”, thereby stopping them from acquiring the needed nitrogen in the protein for their own growth. JA also activates the expression of Polyphenol oxidase, which promotes the production of Quinolines. These can interfere with the insect’s enzyme production and decrease the nutrition content of the ingested plant.
Under abiotic stress, JA is usually involved in physiological and molecular responses. Physiological responses often include
- activation of the antioxidant system
- accumulation of amino acids and soluble sugars
- regulation of stomatal opening and closing.
Molecular responses often involve
- the expression of JA related genes
- interactions with other plant hormones
- interactions with transcription factors.
Several bioassays have been used to estimate JA levels in plant tissues such as Oat leaf bioassay.
Recent insights into JA regulated plant defence cascade and better knowledge of key regulators of plant growth and development processes will help us to design future crops with increased stress resistance and better adaptability to the changing climate and increased attack from herbivores and pests. Thanks for reading!