Q.36 Jasmonic acid

1. is synthesized from linolenic acid
2. is growth promoter
3. delays leaf senescence
4. present in the mosses and ferns

Jasmonic acid is synthesized from linolenic acid via the octadecanoid pathway in plant chloroplasts and peroxisomes. This makes option 1 correct in Q.36, distinguishing it from incorrect claims about its growth promotion, senescence delay, or distribution in lower plants.

Correct Answer

1. Jasmonic acid is synthesized from linolenic acid. The biosynthesis begins with α-linolenic acid (18:3 fatty acid) from chloroplast membranes, oxygenated by lipoxygenase to form 13-hydroperoxylinolenic acid. This undergoes cyclization via allene oxide synthase and cyclase to 12-oxophytodienoic acid, followed by reduction and β-oxidation to yield jasmonic acid, a key stress hormone.

Option Explanations

• Synthesized from linolenic acid: Accurate; the octadecanoid pathway converts α-linolenic acid through lipoxygenase, allene oxide intermediates, and peroxisomal β-oxidation, triggered by wounding or pathogens.

• Is growth promoter: Incorrect; jasmonic acid primarily inhibits growth, promotes senescence, and mediates defense/stress responses rather than acting as a promoter like auxins or gibberellins.

• Delays leaf senescence: Incorrect; it accelerates leaf senescence and abscission, coordinating aging processes unlike cytokinins that delay it.

• Present in mosses and ferns: Partially true but not definitive; jasmonates occur across land plants including bryophytes like mosses and ferns, yet the option implies exclusivity, which is misleading as it’s widespread in vascular plants too.

Plant Hormone Role

Jasmonic acid regulates defense against herbivores/insects, male fertility, and root growth inhibition. Its synthesis pathway, conserved evolutionarily, starts in plastids and completes in peroxisomes. For exams, remember linolenic acid as the precursor differentiates it from other phytohormones like abscisic acid from carotenoids.