Fatty acid synthesis in plant cells occurs primarily in plastids.

Option Breakdown

This question focuses on the primary site of de novo fatty acid chain elongation in plants, distinct from animals (cytosol) due to plastid evolution.

• Cytosol: Site of some lipid assembly or elongation in animals/plants, but not initial fatty acid synthesis (de novo chain building) in plants—that’s plastid-specific.

• Plastids: Correct answer—stroma of chloroplasts/leucoplasts hosts acetyl-CoA carboxylase and fatty acid synthase (Type II system with ACP), producing C16-C18 chains.

• Mitochondria: Involved in beta-oxidation (breakdown) or minor lipoic acid synthesis, not de novo fatty acid production.​

• Lysosome: Absent in plants (vacuoles instead); handles degradation in animals, irrelevant to synthesis.​

Fatty acid synthesis in plant cell plastids builds essential membrane lipids and oils from acetyl-CoA in the stroma, powering photosynthesis and storage.

Synthesis Pathway

Plastids use prokaryotic-like Type II fatty acid synthase: malonyl-CoA forms via ACCase, then KAS enzymes elongate to palmitate/oleate on ACP; exported as acyl-CoA for ER lipids.

Why Not Other Compartments?

Cytosol handles cytosolic ACCase and TAG assembly (eukaryotic pathway); mitochondria oxidize fats; plants lack true lysosomes, using vacuoles for hydrolysis instead.

Plant-Specific Role

This plastid localization supports thylakoid membranes (prokaryotic pathway) and seed oils; mutants disrupt growth, highlighting its metabolic centrality.