56. Which of the following set of cell organelles are involved in the biosynthesis of jasmonic acid through octadecanoidsignalling pathway?

(1) Chloroplast and peroxisomes

(2) Chloroplast and mitochondria

(3) Mitochondria and peroxisomes

(4) Golgi bodies and mitochondria

Correct answer: (1) Chloroplast and peroxisomes

Explanation:

• Jasmonic acid (JA) biosynthesis occurs in two main cell organelles: the chloroplast and peroxisome.

• The biosynthesis begins in the chloroplast where linolenic acid is converted to 12-oxo-phytodienoic acid (OPDA) through the octadecanoid pathway involving enzymes like lipoxygenase, allene oxide synthase, and allene oxide cyclase.

• OPDA is then transported to the peroxisome, where it is further converted by oxo-phytodienoate reductase and undergoes β-oxidation to form JA.

• Mitochondria and Golgi bodies are not involved in JA biosynthesis.

Option-wise:

• (1) Chloroplast and peroxisomes — correct; main organelles for JA biosynthesis.

• (2) Chloroplast and mitochondria — incorrect; mitochondria not involved.

• (3) Mitochondria and peroxisomes — incorrect; mitochondria not involved.

• (4) Golgi bodies and mitochondria — incorrect; neither involved.

  Jasmonic acid production starts in the chloroplast and is completed in the peroxisome, highlighting the compartmentalized nature of plant hormone biosynthesis critical for plant defense and development.