38. Double haploids in plants can be induced by
(A) Mitomycin-C
(B) Mirin
(C) Colchicine
(D) 5-Azacytidine

Double haploids represent a breakthrough in plant breeding, enabling rapid development of homozygous lines for faster variety improvement. This SEO-optimized guide explores the correct method to induce double haploids in plants, with a detailed breakdown of options like colchicine, mitomycin-C, and more. Ideal for plant biologists, researchers, and students preparing for exams in genetics and plant biotechnology.

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Double haploids (DHs) in plants are invaluable tools in modern breeding programs. They allow scientists to create completely homozygous lines in just one generation, skipping the time-consuming self-pollination steps needed in traditional methods. This accelerates the development of superior crop varieties with traits like disease resistance or higher yield.

The process typically starts with haploid cells—often from gametes or haploid embryos—that undergo chromosome doubling to form fertile diploids. But which chemical induces this doubling? Let’s dive into the multiple-choice question and evaluate each option.

Correct Answer: (C) Colchicine

Colchicine is the gold standard for inducing double haploids in plants. Extracted from the autumn crocus (Colchicum autumnale), it binds to tubulin proteins, preventing microtubule polymerization. This disrupts spindle fiber formation during mitosis, halting chromosome separation and leading to cells with doubled chromosome sets (e.g., from $n$ to $2n$).

In practice, colchicine is applied to haploid explants, microspores, or young embryos via soaking, spraying, or culture media. Common concentrations range from 0.1-0.5% for 24-48 hours. It’s widely used in crops like wheat, rice, barley, and maize, boosting DH production efficiency up to 80-90% in optimized protocols.

For example, in anther culture, colchicine treatment post-haploid regeneration ensures fertile DH plants, cutting breeding cycles from 6-8 years to 1-2 years.

Why Not the Other Options?

Each alternative has a specific role in biology but fails for DH induction:

• (A) Mitomycin-C: This is an antibiotic and DNA cross-linking agent used primarily as an antineoplastic drug in cancer therapy. It alkylates DNA, inhibiting replication and causing cell death—ideal for mutagenesis but destructive for chromosome doubling. No role in plant DH production; it would kill haploid cells rather than double their chromosomes.

• (B) Mirin: A small-molecule inhibitor targeting the MRE11-RAD50-NBS1 (MRN) complex, mirin blocks homologous recombination in DNA double-strand break repair. It’s a research tool in genotoxicity studies and CRISPR off-target analysis but doesn’t affect mitosis or microtubules. Useless for inducing polyploidy or DHs in plants.

• (D) 5-Azacytidine: This cytidine analog incorporates into DNA and RNA, inhibiting DNA methyltransferases to cause hypomethylation. It promotes gene expression changes, used in epigenetic studies or cancer research, but doesn’t interfere with spindle apparatus or chromosome segregation. Occasionally applied in tissue culture for morphogenesis, it won’t reliably produce double haploids.

Applications and Tips for Plant Breeders

Colchicine’s specificity makes it indispensable, though alternatives like oryzalin or trifluralin are emerging for lower toxicity. Success rates depend on genotype, concentration, and exposure time—always optimize via dose-response curves.

In Indian contexts, like rice (Oryza sativa) breeding at institutions such as ICAR-IIRR, colchicine has revolutionized hybrid seed production.

For lab protocols:

1. Isolate microspores or anthers.

2. Culture on induction medium.

3. Treat with 0.2% colchicine for 24 hours.

4. Regenerate and select DH plants via flow cytometry.

This method underscores colchicine’s unmatched efficacy in “double haploids in plants induced by colchicine.”