Summary of Biotechnologically Engineered Plants
Biotechnologically Engineered Plants: Molecular Markers Guide
Introduction
Plant tissue culture and micropropagation are plant biotechnology techniques that enable the multiplication, conservation, and study of plants under controlled in vitro conditions. They rely on the ability of many plant cells to divide and regenerate complete organs (totipotency). These techniques are used in clonal propagation, pathogen elimination, germplasm conservation, and the mass production of high-quality plant material.
Definition: Micropropagation is the rapid multiplication of plants from small explants in sterile nutrient media, through organogenesis or somatic embryogenesis.
Fundamentals and Stages of In Vitro Culture
Totipotency and Morphogenesis
- Totipotency: the ability of a single cell to regenerate an entire plant. Examples of maximum totipotency include protoplasts and microspores, which can produce haploid plants.
- Morphogenesis: the process of organ or embryo formation; it can occur:
- Directly from differentiated cells (direct organogenesis).
- From callus or dedifferentiated cell suspensions (indirect organogenesis or embryogenesis).
Definition: Organogenesis is the formation of organs (shoots or roots) from tissue cultured in vitro.
General Stages of Tissue Culture
- Explant selection and disinfection (asepsis and pathogen elimination).
- Establishment in an appropriate nutrient medium and growth conditions.
- Induction of proliferation (callus, shoots, or embryos).
- In vitro multiplication and rooting.
- Acclimatization and ex vitro transfer (adaptation to the external environment).
Definition: An explant is a piece of plant tissue isolated from the mother plant to initiate an in vitro culture.
Nutrient Media: Components and Functions
Comparative Table: Key Components
| Component | Primary Function | Typical Range / Notes |
|---|---|---|
| Water | Solvent and physical medium | Major component of the medium |
| Inorganic salts | Macro- and micronutrients (N, P, K, Ca, Mg, Fe, Cu, Zn, Mn, B, Mo) | e.g., MS medium as a reference |
| Sugar (sucrose) | Carbon and energy source | 20–30 g/L common; may vary depending on objective |
| Vitamins (e.g., thiamine) | Enzyme cofactors | B complex commonly used |
| Growth regulators (hormones) | Morphogenic control: auxins, cytokinins, gibberellins, ethylene, abscisic acid, others | Micromolar concentrations; auxin/cytokinin ratio crucial |
| Gelling agent (agar, Gelrite) | Solidifies the medium | Agar 6–8 g/L typical; Gelrite in smaller amounts |
| Antioxidants / adsorbents (ascorbic acid, PVP, activated charcoal) | Reduce browning and phenolic oxidation | Useful in woody species |
Definition: MS medium is a widely used nutrient medium (Murashige and Skoog) that contains a balanced mixture of salts and vitamins.
Growth Regulators (Practical Summary)
- Auxins (IAA, IBA, 2,4-D): promote callus and root induction; high doses can be herbicidal.
- Cytokinins (BAP, Kinetin, zeatin): promote shoot development and bud proliferation.
- Auxin/cytokinin ratio: determines whether callus, shoots, or roots are induced.
- Others: gibberellins (elongation), ethylene (senescence and stress), jasmonic acid, triacontanol (promoter in some woody species).
Aseptic Technique and Disinfection
- Washing and pre-sterilization: reduces surface microbial load.
- Common disinfectants: ethanol 75–95% (0.5–1 min), sodium hypochlorite 2.5–9% (5–20 min), hydrogen peroxide 2–10% (5–12 min), mercuric chloride 0.1–1% (restricted use due to toxicity).
- Antibiotics/antifungals in media to control internal contamination: carbenicillin, cefotaxime, nystatin, etc.; use with caution due to toxicity and effects on morphogenesis.
Definition: Asepsis is the set of procedures that prevent the entry of microorganisms during in vitro operations.
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Micropropagation and tissue culture
Klíčové pojmy: Totipotency: Each plant cell can, under appropriate conditions, regenerate a complete plant., Auxin/cytokinin ratio determines organogenesis: high auxin leads to roots/callus; high cytokinin leads to shoots., Sucrose (20–30 g/L) is the primary carbon source in culture media; its concentration affects morphogenic responses., Phenolic oxidation can hinder regeneration; use antioxidants (ascorbic acid, PVP, activated charcoal)., Aseptic technique: Explant disinfection and the use of a laminar flow hood and autoclave are essential., Cell suspensions and somatic embryogenesis allow for scaling up in bioreactors for mass production., Androgenesis produces haploid microspores useful for obtaining doubled haploids in breeding programs., Somaclonal variation can be a source of useful traits or a problem if clonal stability is desired., In vitro rooting typically uses IBA; reducing sucrose and adding supplements can improve rhizogenesis., Hyperhydration (vitrification) correlates with excess humidity and hormonal imbalance; adjust the medium and environmental conditions., Cryopreservation requires cryoprotectants and cold control to preserve germplasm long-term., Gradual acclimatization (light, humidity, substrate) is critical for successful ex vitro transfer.