Scheda di revisione: Plant Tissue Culture

📋 Course Outline

1. Concept and Applications
2. Historical Development and Totipotency
3. Culture Medium Components
4. Medium Types and Physical Forms
5. Stock Solutions and MS Medium
6. Sterilization of Laboratory Materials
7. Surface Sterilization of Explants
8. Culture Facilities and Acclimatization
9. Aseptic Plant Preparation

📅 Key Dates

Date	Event
1902	Haberlandt proposed culturing isolated plant cells in vitro on an artificial medium and introduced the concept of totipotency.
1939	Carrot explants produced an undifferentiated callus mass that could undergo repeated subculture.
1950	Steward discovered embryogenesis in vitro through carrot culture and quantitative analysis of culture growth.
1952	Morel and Martin produced the first virus-free plant through shoot-tip culture of Dahlia.
1957	Skoog and Miller showed that a high kinetin level promotes shoot formation while a high auxin level promotes root formation.
1962	Murashige and Skoog developed the MS medium for tobacco tissue culture.
1964	Guha and Maheshwari obtained haploid plants from Datura anther culture, and in 1968 Niizeki and Oono obtained haploid rice plants.

📖 1. Concept and Applications

🔑 Key Concepts & Definitions

• Plant tissue culture : The culture of plant seeds, organs, explants, tissues, cells, or protoplasts on nutrient media under sterile conditions.

★ Must-know

• In vitro culture, in vitro propagation, micropropagation, and plant tissue culture refer to related techniques in which plant material grows on an artificial nutrient medium under aseptic and controlled conditions.

• Plant tissue culture is an asexual propagation method used by commercial growers to produce large quantities of clones of a particular plant.

Further detail

• Gottlieb Haberlandt is recognized as the father of plant tissue culture.

• Plant tissue culture can be used to culture stems, leaves, roots, flowers, tissues, cells, and protoplasts.

📖 2. Historical Development and Totipotency

🔑 Key Concepts & Definitions

• Totipotency : The capacity of separated plant organs, tissues, or cells to be manipulated in vitro and grown back into complete plants.

💡 Memory Hook

Haberlandt → Steward → MS medium → haploid plants

📖 3. Culture Medium Components

🔑 Key Concepts & Definitions

• Culture medium : An artificially prepared nutrient medium on which excised plant tissues and organs grow in vitro.

★ Must-know

• A general culture medium contains inorganic salts, an iron source, vitamins, amino acids, growth substances, and a carbohydrate supply.

📌 Macronutrients are inorganic salts needed in higher amounts, whereas micronutrients are essential inorganic salts needed in smaller amounts.

• Common auxins are IAA, 2,4-D, NAA, and IBA, while common cytokinins are kinetin, BAP, and zeatin.

Further detail

• Iron is commonly supplied as ferric-sodium ethylenediaminetetraacetate, or Fe-EDTA, which gradually releases iron as living cells utilize it.

• Common culture-medium vitamins include meso-inositol, nicotinic acid, pyridoxine, and thiamine, while glycine is the most commonly used amino acid.

• Sucrose is the usual carbohydrate supplied in plant tissue culture media.

📖 4. Medium Types and Physical Forms

★ Must-know

📌 A chemically defined medium has a known composition and concentration for every constituent, whereas a chemically undefined medium contains natural products whose exact composition and concentration are unknown.

• No single culture medium maintains optimum growth for every plant tissue, so the most suitable medium must be determined by trial and error and modified for the particular plant material.

• A solid medium contains 6–8% agar, a semisolid medium contains less agar, and a liquid medium contains no agar.

Further detail

• Complex additives used in some media include coconut milk, casein hydrolysate, yeast extract, watermelon juice, malt extract, potato extract, ripe tomato extract, and orange juice.

• Coconut milk may be added at 10–15% v/v because diphenylurea in it produces cytokinin-like responses.

• Solid and semisolid media are broadly prepared for callus culture, while liquid media are broadly used for cell suspension cultures.

📖 5. Stock Solutions and MS Medium

★ Must-know

• Concentrated stock solutions of macro salts, micro salts, vitamins, amino acids, and hormones are prepared because weighing every constituent immediately before medium preparation is time-consuming and inaccurate for small quantities.

• MS nutrient salts and vitamins are commonly prepared as 20X or 200X stock solutions, stored at 4°C, and mixed in the required amounts to prepare 1 litre of medium.

• The pH of MS medium is adjusted to 5.8 with either 0.1 N NaOH or 0.1 N HCl, with auxins dissolved in absolute ethyl alcohol and cytokinins dissolved in 1 N HCl.

Further detail

• MS macro salts include NH4NO3, KNO3, CaCl2·2H2O, MgSO4·7H2O, and KH2PO4.

• MS micro salts include H3BO3, MnSO4·4H2O, ZnSO4·4H2O, KI, Na2MoO4·2H2O, CoCl2·6H2O, and CuSO4·5H2O.

• The MS medium contains 30,000 mg sucrose per litre, and agar agar is added fresh at 8,000 mg per litre when a solid medium is required.

💡 Memory Hook

Prepare concentrated stocks → mix → add fresh components → adjust pH

📖 6. Sterilization of Laboratory Materials

★ Must-know

• Glassware and equipment are soaked in detergent, brushed and washed with tap water, rinsed with double-distilled water, dried at 60°C, wrapped, and autoclaved at 15 lb/in² and 121°C for 15–20 minutes.

• Prepared medium is placed in conical flasks or tubes, closed with non-adsorbent cotton plugs covered with paper or foil, and autoclaved at 15 lb/in² and 121°C for 15–20 minutes.

Further detail

• An alternative method for sterilizing glass goods and instruments is heating them in an oven at 150°C for 3–4 hours.

📌 Screw-capped glass vials must not be closed too tightly during autoclaving so expanding gases do not create an explosion risk.

💡 Memory Hook

Clean → wrap → autoclave

📖 7. Surface Sterilization of Explants

★ Must-know

• Explants are washed, treated with 5% liquid detergent for 10–15 minutes, rinsed, dipped in 70% ethyl alcohol for 60 seconds, treated with 0.1% mercuric chloride or 5–10% sodium hypochlorite for 10–15 minutes with shaking, and rinsed thoroughly with autoclaved distilled water.

• The detergent washing steps may be performed in the general laboratory, whereas the alcohol, sterilant, and sterile-water steps are performed inside a laminar-air-flow cabinet or pre-sterilized inoculation chamber.

📌 Surface sterilants must be removed by thorough rinsing with autoclaved distilled water because the sterilants are toxic chemicals that can damage plant tissues.

Further detail

• Common explant sterilants include sodium hypochlorite at 1–1.4% for 5–30 minutes, calcium hypochlorite at 9–10% for 5–30 minutes, hydrogen peroxide at 10–12% for 5–15 minutes, bromine water at 1–2% for 2–10 minutes, silver nitrate at 1% for 5–30 minutes, mercuric chloride at 0.01–1% for 2–10 minutes, and antibiotics at 4–50 mg/l for 30–60 minutes.

💡 Memory Hook

Wash → alcohol → sterilant → sterile-water rinses

📖 8. Culture Facilities and Acclimatization

★ Must-know

• Plant tissue cultures require controlled temperature, illumination, photoperiod, humidity, and air circulation.

• For most culture conditions, temperature control should maintain approximately 25 ± 2°C.

• Greenhouses provide a transition from controlled culture containers to field conditions, allowing regenerated plants to harden and develop root and leaf systems able to withstand the field environment.

Further detail

• Culture rooms may contain air conditioning, perforated shelves, fluorescent tubes, timing devices, dark areas, shakers, and batch or continuous bioreactors.

• Photon flux density for photosynthetically active radiation is expressed as μmol photons/m²/s, while irradiance is expressed as W/m².

📖 9. Aseptic Plant Preparation

🔑 Key Concepts & Definitions

• Aseptic inoculation : The placement of sterilized plant material onto culture medium under sterile conditions to prevent microbial contamination.

★ Must-know

• Seeds are surface sterilized and cultured on a simple basal nutrient medium so they germinate into aseptic seedlings whose explants can then be cultured without further surface sterilization.

Further detail

• Seed coats allow seeds to better resist the deleterious effects of toxic surface sterilants than exposed plant tissues.

📊 Synthesis Tables

Culture Medium Comparisons

Dimension	Chemically defined medium	Chemically undefined medium
Composition	All constituents and concentrations are known	Exact composition and concentrations are unknown
Main ingredients	Inorganic and organic chemicals	Natural products such as coconut milk
Variability	Composition is controlled	Composition varies with plant physiological and environmental conditions

Physical Forms of Medium

Medium form	Agar content	Broad application
Solid	6–8% agar	Callus culture
Semisolid	Reduced agar amount	Various culture techniques
Liquid	No agar	Cell suspension culture