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Flowering - Floral Induction. violets, roses, chrysanthemums Chailakhan 1920’s Russian Florigen Amount of light and photoperiods already known to be important. Flowering - Floral Induction (branch bud ----> flower bud).

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Flowering floral induction branch bud flower bud

violets, roses, chrysanthemums

Chailakhan 1920’s Russian

Florigen

Amount of light and photoperiods already known to be important.

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


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


Short day plants
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


Short day plants1
Short Day Plants

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

    • soybean.. - qualitative


Long and short day plants may flower at the same time
Long and Short Day Plants May Flower at the Same Time

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



Photoperiodism
PHOTOPERIODISM

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


Photoperiodism1
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.)


Photoperiodism2
PHOTOPERIODISM

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


Photoperiodism redefined
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.


Photoperiodism3
PHOTOPERIODISM

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



Photoperiodism5
PHOTOPERIODISM

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




Photomorphogenic responses2
Photomorphogenic Responses

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

    • Action spectra studies - flowering and others

    • Subjected plants to various wavelengths during dark period ----> 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)


Photomorphogenic responses3
Photomorphogenic Responses

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

  • Phycocyanin like


Photomorphogenic responses4
Photomorphogenic Responses

  • Phytochrome Action Spectra:


Photomorphogenic responses5
Photomorphogenic Responses

  • Mechanism of Phytochrome Action:

  • PR ---------------------------------------------> PFr

  • Red Light

  • PR <--------------------------------------------- PFr

  • Far-red Light

  • Half Life of PFr = 2.5 hours

  • (based on conformational changes in phytochrome)


Photomorphogenic responses6
Photomorphogenic Responses

  • (3) Chromoproteins (chromatophore & apoprotein):

    • Phytochromes (5) PR & PFr

    • Cryptochromes Blue & UV

    • Photochromes Blue & UV


Photomorphogenic responses7
Photomorphogenic Responses

  • Control of Gene Activation:

  • Actinomycin inhibits transcription & stops light responses



Photomorphogenic responses9
Photomorphogenic Responses

  • Less etiolation with higher amount of PFr

  • Chenopodium alba “lamb’s quarter”


Bud dormancy
Bud Dormancy

  • Wareing (1950’s) Fagus beech tree

    • initiated by short days

    • relieved by long days

    • reception site: leaf bud scales


Bud dormancy1
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

    • GA:ABA ratio a factor


Seed dormancy
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


Seed dormancy1
Seed Dormancy

  • Stratification

    • cold treatment of seeds

  • Ambient Factors:

    • 1.) temperature (near freezing, -2--> 7 degrees C)

    • 2.) time (7 --> 12 weeks …)


Dormancy
Dormancy

  • Lange 1950’s

  • Hyoscyamous niger “henbane”

    • annual and biennial types

    • varied time and temperature of treatment for biennial

    • shorter vernalization, longer to flowering


Vernalization stratification
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


Vernalization stratification1
Vernalization/Stratification

  • Petkus Rye -

    • winter annual


Deveralization destratification
Deveralization/Destratification

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


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