1. Cytoplasmic Male Sterility in maize is due to-
(1) Cytoplasm (2) Plastid
(3) Mitochondria (4) Ovary
Introduction
Cytoplasmic Male Sterility (CMS) in maize is a condition that causes the plant to fail in producing functional pollen, leading to male sterility. This phenomenon is crucial in hybrid seed production and is caused by genetic factors outside the nucleus, specifically in the cytoplasmic organelles.
Explanation of the Correct Cause: Mitochondria
CMS in maize is primarily due to mutations or rearrangements in the mitochondrial DNA. Mitochondria, the energy-producing organelles in the cytoplasm, contain their own genome, and mutations there can disrupt pollen development. In maize, male sterility is linked to specific mitochondrial genes, such as the T-cytoplasm type associated with a mitochondrial gene called T-urf13. This mitochondrial gene leads to male sterility by affecting pollen viability, and the sterility trait is maternally inherited because mitochondria come from the female parent only.
Explanation of Options
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Cytoplasm: Cytoplasm includes all the cellular content outside the nucleus, including organelles like mitochondria and plastids. While CMS is called “cytoplasmic” because the genes involved are extranuclear, the specific cause is mitochondrial, not the entire cytoplasm.
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Plastid: Plastids are another type of cytoplasmic organelle (including chloroplasts) involved in photosynthesis and other functions. Plastid genes generally do not cause CMS; the male sterility is not due to plastid DNA mutations.
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Mitochondria: These organelles are the correct answer. CMS arises from mutations or unusual expressions of mitochondrial genes that interfere with pollen development.
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Ovary: The ovary is a part of the flower’s female reproductive system and has no role in causing male sterility.
Cytoplasmic Male Sterility in maize is specifically caused by defective mitochondria, making option (3) the correct choice. The mitochondrial genome mutations impede functional pollen formation, resulting in male sterility inherited through the maternal line. This trait is widely utilized in hybrid maize production to facilitate cross-pollination without manual emasculation.
