Plant tissue culture terminology — In micropropagation and in vitro culture, what does “organogenesis” specifically refer to?
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AFormation of callus tissue (an undifferentiated mass of cells)
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BFormation of new roots and/or shoots from callus or directly from explant tissues
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CBoth formation of callus and formation of organs from callus
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DGeneral genesis of organs in any context, not necessarily in vitro
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ESomatic embryogenesis leading to whole plantlets
Answer
Correct Answer: Formation of new roots and/or shoots from callus or directly from explant tissues
Explanation
Introduction / Context:In plant tissue culture and micropropagation, organogenesis describes the developmental process by which discrete organs such as shoots and roots are induced to form under controlled conditions. It is a core route for clonal propagation and regeneration after transformation.
Given Data / Assumptions:
- Explants or callus are grown on media with defined auxin/cytokinin ratios.
- Callus refers to an undifferentiated cell mass.
- Organogenesis yields recognizable organs (shoots, roots) rather than whole embryos.
Concept / Approach:Organogenesis can be direct (organs arise from the explant without an intervening callus phase) or indirect (organs arise from prior callus). The hormonal balance concept is key: high cytokinin relative to auxin favors shoot organogenesis, whereas higher auxin favors root organogenesis.
Step-by-Step Solution:
Recognize that “callus formation” alone is not organogenesis; it is a precursor in indirect routes.Identify organ formation (shoots/roots) as the defining feature of organogenesis.Match the correct statement to this definition: formation of roots and/or shoots from callus or directly from explants.Verification / Alternative check:Protocols demonstrate that altering the auxin:cytokinin ratio switches between callusing and organ formation. The presence of meristematic centers and subsequent organ primordia confirms organogenesis.
Why Other Options Are Wrong:
a) Callus formation is dedifferentiation, not organogenesis.c) Mixing stages obscures the definition; organogenesis is specifically organ formation.d) Too broad; not specific to in vitro regeneration.e) Somatic embryogenesis is a different pathway that produces embryo-like structures.Common Pitfalls:Equating callus induction with complete regeneration; forgetting that direct organogenesis can bypass callus.
Final Answer:Formation of new roots and/or shoots from callus or directly from explant tissues.