Flowering - Floral Induction

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Flowering - Floral Induction
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Flowering - Floral Induction(branch bud ----gt
flower bud)

• violets, roses, chrysanthemums
• Chailakhan 1920s Russian
• Florigen
• Amount of light and photoperiods already known to
  be important.

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Photoperiodismthe ability of the plant to
respond to different lengths of light treatment

• W. W. Garner H. A. Allard - U. S. Ag. Dept.
  1918
• Maryland Mammoth
• large-leaved mutant
• lack of flowering
• greenhouse plants various stages
• most flowered in early December!
• DAYLENGTH critical factor
  Short Day, Long Day, Day Neutral plants

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Short Day Plants

• Flower only when day length is shorter than some
  critical value.
• Pointsetta, cocklebur, soybean.. - qualitative
• will not flower without a critical photoperiod
• wheat, rye, .. - quantitative
• will flower without a critical photoperiod but
  will take longer

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Short Day Plants

• Flower only when day length is shorter than some
  critical value.
• soybean.. - qualitative

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Long and Short Day Plants May Flower at the Same
Time

• Henbane (11 hrs.), Cocklebur (15 hrs.)

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Long and Short Day Plants May Flower at the Same
time

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PHOTOPERIODISM

• Some plants need several days at the proper
  daylength. Winter Summer Solstices

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PHOTOPERIODISM

• K. Hamner (U of Cal.) and J. Bonner (CIT) 1938
• Sensitive light receiving system (pigment) at
  work.
• Cocklebur
• 15 hrs of light/9 hrs dark flowers
• 15.5 hrs of light/8.5 hrs dark no flowers
• 15 hrs of light/9 hrs dark with interrupted dark
  no flowering
• (Dark period is more critical than light period
  for Floral Induction - initiation of floral
  primordia.)

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PHOTOPERIODISM

• K. Hamner (U of Cal.) and J. Bonner (CIT) 1938

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PHOTOPERIODISM REDEFINED

• K. Hamner (U of Cal.) and J. Bonner (CIT) 1938
• Short Day Plants
• uninterrupted darkness must be of a certain
  duration.
• (so much darkness or more)
• Long Day Plants
• uninterrupted darkness must be less than a
  certain maximum value.
• (so much darkness or less)
• Day Neutral Plants
• Flowers at a certain level of maturity or in
  response to some environmental factor other than
  the photoperiod.

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PHOTOPERIODISM

• K. Hamner (U of Cal.) and J. Bonner (CIT) 1938

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PHOTOPERIODISM
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PHOTOPERIODISM

• H. A. Borthwick and S. B. Hendricks 1950s US
  Ag

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Photomorphogenic Responses
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Photomorphogenic Responses
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Photomorphogenic Responses

• H. A. Borthwick and S. B. Hendricks 1950s US
  Ag
• Action spectra studies - flowering and others
• Subjected plants to various wavelengths during
  dark period ----gt responses
• All photomorphogenic responses studied had
  similar responses
• Predicted the photochrome pigment
• 2 forms - 1.) PR - red light absorbing form
• 2.) PFr - Far-red light
  absorbing form (Active Form)

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Photomorphogenic Responses

• Phytochrome is ubiquitous in plants - found in
  all tissues. Has been isolated and purified.
• Phycocyanin like

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Photomorphogenic Responses

• Phytochrome Action Spectra

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Photomorphogenic Responses

• Mechanism of Phytochrome Action
• PR ---------------------------------------------gt
  PFr
• Red Light
• PR lt---------------------------------------------
  PFr
• 
  Far-red Light
• Half Life of PFr 2.5 hours
• (based on conformational changes in phytochrome)

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Photomorphogenic Responses

• (3) Chromoproteins (chromatophore apoprotein)
• Phytochromes (5) PR PFr
• Cryptochromes Blue UV
• Photochromes Blue UV

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Photomorphogenic Responses

• Control of Gene Activation
• Actinomycin inhibits transcription stops light
  responses

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Photomorphogenic Responses
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Photomorphogenic Responses

• Less etiolation with
  
  higher amount of PFr
• Chenopodium alba
  
  lambs quarter

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Bud Dormancy

• Wareing (1950s) Fagus beech tree
• initiated by short days
• relieved by long days
• reception site
  leaf bud scales

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Bud Dormancy

• Initiation factors photoperiod, lack of water,
  cold treatment (vernalization).
• ABA - increases during bud
  dormancy
• GA - decreases during
  bud dormancy
• reception site leaf
  bud scales
• GAABA ratio
  a factor

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Seed Dormancy

• Hard Seed Coat
• prevents imbibition of water, gas exchange and
  growth
• helps maintain the seed bank
• Scarification
• any treatment that breaks the
  seed coat
• MECHANICAL (INSECTS)
• ACID
• FIRE

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Seed Dormancy

• Stratification
• cold treatment of seeds
• Ambient Factors
• 1.) temperature (near freezing, -2--gt 7 degrees
  C)
• 2.) time (7 --gt 12 weeks )

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Dormancy

• Lange 1950s
• Hyoscyamous niger henbane
• annual and biennial types
• varied time and temperature of treatment for
  biennial
• shorter vernalization, longer to flowering

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Vernalization/Stratification

• Petkus Rye - long day plant 15 1/2 wks to flower
• spring annual
• winter annual
• also needs vernalization (and/or stratification)
• flowers in 7 1/2 wks with cold treatment

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Vernalization/Stratification

• Petkus Rye -
• winter annual

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Deveralization/Destratification

• High temperatures (35 degrees C) are effective in
  devernalization/destratification if cold
  treatment is short.