Practice question

Colchicine, an alkaloid from Colchicum autumnale, binds tubulin dimers and prevents microtubule polymerization essential for spindle fibre formation during mitosis and meiosis. Without functional spindle apparatus formed from microtubules organizing at kinetochores, sister chromatids or homologous chromosomes fail to separate to opposite poles at anaphase; nuclear membrane reforms around doubled chromosome complement. Cell undergoes endoreduplication producing diplochromosome and polyploid nucleus with doubled DNA content. Treatment of meristematic tissue or seedlings with 0.1-0.5% colchicine for 12-24 hours thus doubles chromosome number, converting haploid to diploid, diploid to tetraploid. Mechanism is antimitotic, not interfering with DNA replication or cytokinesis directly but blocking anaphase movement. Other agents like oryzalin, trifluralin and amiprophos-methyl target same tubulin pathway with less toxicity, widely used in doubled haploid and autotetraploid breeding programs for polyploid induction. Modern tubulin inhibitors like oryzalin bind plant-specific tubulin isotypes with lower mammalian toxicity, enabling safer polyploid induction in horticulture, while flow cytometry provides rapid confirmation of ploidy level by measuring nuclear DNA content, streamlining selection of stable polyploids for breeding programs and commercial cultivar development.