55 Jasmonic acids (JA) that are known to activate many defense responses in plants are biosynthesized in chloroplast and peroxisome. Which one of the following reactions is confined to perosoxisome only during biosynthesis of JA?

(1) Conversion of 12, 13-epoxy linolenic acid to 12- oxo-phytodienoic acid by the action of allene oxide cyclase.

(2) Conversion of 12-oxo-phytodienoic acid to 3-oxo2(2′[z]-pentenyl) cylopentane-l-octanoate by the action of oxo-phytodienoate reductase.

(3) Conversion of linolenic acid to beeta-hydroperoxy linolenic acid by lipoxygenase.

(4) Conversion of 13-hydroperoxy linolenic acid to 12, 13-Epoxy linolenic acid by allene oxide synthase

Correct answer: (2) Conversion of 12-oxo-phytodienoic acid to 3-oxo-2(2′[Z]-pentenyl) cyclopentane-1-octanoate by the action of oxo-phytodienoate reductase.

Explanation:

• Jasmonic acid (JA) biosynthesis begins in the chloroplast where linolenic acid is converted by lipoxygenase, allene oxide synthase, and allene oxide cyclase to 12-oxo-phytodienoic acid (12-OPDA).

• The reduction of 12-oxo-phytodienoic acid to OPC-8:0 (3-oxo-2(2′[Z]-pentenyl)cyclopentane-1-octanoate) by oxo-phytodienoate reductase (OPR) occurs specifically in the peroxisome. This is a key peroxisomal step in JA biosynthesis, followed by β-oxidation cycles to form JA.

• Other steps such as conversion of linolenic acid to beta-hydroperoxy linolenic acid by lipoxygenase, and conversion of 13-hydroperoxy linolenic acid to 12,13-epoxy linolenic acid by allene oxide synthase occur in the chloroplast.

Option details:

• (1) Allene oxide cyclase reaction: chloroplast, not peroxisome.

• (2) Oxo-phytodienoate reductase reaction: peroxisome-specific.

• (3) Lipoxygenase reaction: early chloroplast step.

• (4) Allene oxide synthase reaction: chloroplast step.

  Jasmonic acid is synthesized through complex enzymatic reactions beginning in the chloroplast and culminating in the peroxisome where oxo-phytodienoate reductase catalyzes a crucial conversion step, vital for producing this important plant signaling molecule.