1. Flowering - Floral Induction

2. 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.

3. Photoperiodism the 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 ) 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 Ambient Factors: cold treatment of seeds
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.