Q.55 In naturally occurring cytoplasmic male sterility, the molecular determinant is located in
(A) Chloroplast (B) Endoplasmic reticulum
(C) Golgi complex (D) Mitochondria
Cytoplasmic Male Sterility: Molecular Determinant Revealed
Cytoplasmic male sterility (CMS) enables hybrid seed production by producing pollen-sterile plants through maternal inheritance. Question 55 pinpoints the organelle housing CMS’s genetic cause—critical for plant biotech and breeding exams.
Correct Answer: (D) Mitochondria
CMS molecular determinants are mitochondrial genes or chimeric ORFs causing pollen abortion.
Mitochondrial genome rearrangements create novel open reading frames (e.g., orf239 in bean, orf79 in rice) expressed during anther development. These disrupt respiration/ATP supply to tapetum/microspores, triggering programmed cell death. Maternal inheritance ensures stable cy toplasm transmission; nuclear Rf genes restore fertility.
Why Other Options Wrong: Organelle Breakdown
Wrong choices misattribute CMS genetics to non-genomic or irrelevant organelles.
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(A) Chloroplast: Plastid genome is maternal but governs photosynthesis/chlorophyll—not pollen viability. No CMS-linked rearrangements observed.
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(B) Endoplasmic reticulum: ER handles protein folding/lipid synthesis; lacks DNA. CMS is genome-based, not transient organelle function.
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(C) Golgi complex: Processes vesicles/carbohydrates for pollen wall (sporopollenin); DNA-free. Sterility precedes wall defects in CMS.
Organelle Roles Table
| Option | Organelle | Has Genome? | CMS Link? | Primary Function Affected |
|---|---|---|---|---|
| (A) | Chloroplast | Yes | No | Photosynthesis |
| (B) | ER | No | No | Protein/lipid trafficking |
| (C) | Golgi | No | No | Vesicle modification |
| (D) | Mitochondria | Yes | Yes | Respiration/pollen ATP |
Breeding Application
CMS systems (e.g., maize T, rice Wild Abortive) produce F1 hybrids: A-line (CMS) × B-line (maintainer) → sterile hybrid; R-line restores. 95% of sunflower hybrids use CMS. Key exam fact: Mitochondrial, not chloroplast.
