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Flowering - Floral Induction

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  1. Flowering - Floral Induction

  2. 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)

  3. 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

  4. 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

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

  6. Long and Short Day Plants May Flower at the Same Time • Henbane (11 hrs.), Cocklebur (15 hrs.)

  7. Long and Short Day Plants May Flower at the Same time

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

  9. 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.)

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

  11. 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.

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

  13. PHOTOPERIODISM

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

  15. Photomorphogenic Responses

  16. Photomorphogenic Responses

  17. 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)

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

  19. Photomorphogenic Responses • Phytochrome Action Spectra:

  20. 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)

  21. Photomorphogenic Responses • (3) Chromoproteins (chromatophore & apoprotein): • Phytochromes (5) PR & PFr • Cryptochromes Blue & UV • Photochromes Blue & UV

  22. Photomorphogenic Responses • Control of Gene Activation: • Actinomycin inhibits transcription & stops light responses

  23. Photomorphogenic Responses

  24. Photomorphogenic Responses • Less etiolation with higher amount of PFr • Chenopodium alba “lamb’s quarter”

  25. Bud Dormancy • Wareing (1950’s) Fagus beech tree • initiated by short days • relieved by long days • reception site: leaf bud scales

  26. 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

  27. 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

  28. Seed Dormancy • Stratification • cold treatment of seeds • Ambient Factors: • 1.) temperature (near freezing, -2--> 7 degrees C) • 2.) time (7 --> 12 weeks …)

  29. Dormancy • Lange 1950’s • Hyoscyamous niger “henbane” • annual and biennial types • varied time and temperature of treatment for biennial • shorter vernalization, longer to flowering

  30. 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

  31. Vernalization/Stratification • Petkus Rye - • winter annual

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