11. Essential component of chloroplast photosynthetic apparatus for photosynthesis is coded by
(1) Nuclear gene
(2) Chloroplast gene
(3) Nuclear and chloroplast gene
(4) Chloroplast and mitochondrial genes

The essential components of the chloroplast photosynthetic apparatus are coded by (3) Nuclear and chloroplast genes. Both genomes are required: the chloroplast genome codes for certain core proteins, while most subunits and regulatory factors are nuclear-encoded and imported into the chloroplast.​

Genetic Control of the Photosynthetic Apparatus

Introduction

Key phrase: genetic coding of chloroplast photosynthetic apparatus nuclear and chloroplast genes

Plant photosynthesis depends on a sophisticated apparatus containing large complexes like Photosystem I, Photosystem II, cytochrome b6f, and ATP synthase. The proteins making up these complexes come from both the nuclear genome and the smaller, circular chloroplast genome—a result of evolutionary endosymbiosis and ongoing genetic integration.​

Explanation of Each Option

• (1) Nuclear gene

  • Incorrect alone. While the majority of photosynthetic apparatus proteins are nuclear-encoded and imported into the chloroplast, some essential and catalytic subunits are encoded by the chloroplast genome itself.​

• (2) Chloroplast gene

  • Incorrect alone. Chloroplast DNA encodes critical components (like the large subunit of RuBisCO, certain PSI and PSII subunits), but the full apparatus cannot assemble without nuclear-encoded components.​

• (3) Nuclear and chloroplast gene

  • Correct. The photosynthetic machinery is a genetic collaboration. Complexes like PSII, PSI, cytochrome b6f, and ATP synthase all contain subunits encoded by both nuclear and chloroplast DNA. This sharing is essential for proper assembly, repair, and regulation of photosynthetic function.​

• (4) Chloroplast and mitochondrial genes

  • Incorrect. Mitochondrial genes primarily code for proteins used in cellular respiration, not for the chloroplast photosynthetic apparatus. There is no direct mitochondrial genetic contribution to core chloroplast photosynthetic complexes.​

Quick Facts on Genetic Coding for Photosynthesis

• Chloroplast DNA codes for several key proteins and some rRNAs/tRNAs.

• Most regulatory and structural proteins are nuclear-encoded.

• Nuclear-encoded proteins are imported into the chloroplast via targeting sequences, ensuring correct assembly.

• Genetic collaboration between the two genomes governs photosynthetic function and adaptation.​