Part 4 - The In vitro Environment

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Part 4 - The In vitro Environment
Richard R Williams
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Control of plant growth
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Manipulate the Environment to

• Control plant development
• Optimise growth rate
• maximise for production
• restrict for storage
• Optimes morphology
• Maintain plant quality
• Acclimatize plants

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Characteristics of the In vitro
Environment

• The same set of environmental factors but
• Limited volume
• Initially defined
• Controlled
• Plant in vitro generally more sensistive.

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Environmental factors
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Culture room ecosystem
Culture vessel ecosystem
Kozai Smith 1994
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The Aerial Environment

• Physical
• Light
• Temperature
• Gaseous composition
• Water vapour / humiditiy
• Gad diffusivity
• Pressure
• Chemical
• Biological

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Light
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Light
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Typical light intensities

• 
  ?mol.m-2s-1
• Typical fluoro PFD 10 - 50
• Compensation point 20
• Autotrophic cultures 65 - 250
• Glasshouse 100 - 1500
• Sunlight 2000

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Light
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The light (energy) spectrum
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Light
Photon flux
- Quantity
PPFD - ?mol.m-2 s-1
- Quality
Spectrum
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Carbohydrate supply in vitro
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CO2 limiting in closed system
Fujiwara and Kozai 1995
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Photo-inhibition

• PPFD beyond capacity to absorb
• Damage reduces p/s capacity further
• Avoid by
• - only short exposure at high PPFD
• - reduce sugar levels
• - filter blue light

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Light direction
(From Kozai et al)
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Light x hormone responses
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Carry over of light effect ex vitro
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Temperature
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Typical culture temperatures
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Effect of temp. on Citrus callus
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Warmer temperatures for roots
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Humidity
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Humidity and stomates
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The Root Environment ...

• Physical
• Temperature
• Water potential
• osmotic matric pressure
• Diffusivty of medium components
• Hardness / compactness of medium
• Light

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The Root Environment ..

• Chemical
• Macroelements
• Microelements
• Dissolved gases
• Organic elements
• pH

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Media Components ..

• Minerals - macro - micro
  Sugar
• Organic growth factors - amino
  acids, vitamins
• Growth regulators - auxins
  cytokinins
• Gelling agent
• Other additives - antioxidants,
  absobants

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Factors affecting mineral supply

• Concentration in the medium
• Mixture - precipitation
• pH
• Gelling agent
• Plant size and growth rate
• Plant tissue content

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Media Components ..

• Minerals - macro - micro

• Sugar
• Organic growth factors - amino
  acids, vitamins
• Growth regulators - auxins
  cytokinins
• Gelling agent
• Other additives - antioxidants,
  absobants

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Complicating factors!

• Water availability
• Interaction between ions
• Necessary vs luxury uptake
• Changes over time

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The Root Environment ..

• Biological
• Pathogens
• Non-pathogens
• symbiotic vs competitive
• The explant

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Changes in media over time...

• Genetic (somatic) variability
• Habituation to growth regulators
• Exhaustion of some nutrients
• Accumualtion of toxins
• Photochemical changes
• ph changes
• Water availability

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Acclimatization

• Water balance
• cuticle
• stomate function
• lack of roots
• Photosynthesis
• sucrose
• light
• gas exchange (CO2)
• chlorophyll
• Root growth function
• Pathogens (latent)

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End of part 4