Flowering - Floral Induction

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.

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

• 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 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

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

Long and Short Day Plants May Flower at the Same time

•

PHOTOPERIODISM• Some plants need several days at the proper

daylength. Winter & Summer Solstices

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.)

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

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.

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

PHOTOPERIODISM

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

Photomorphogenic Responses

Photomorphogenic Responses

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 Responses • Phytochrome is ubiquitous in plants - found in all

tissues. Has been isolated and purified.• Phycocyanin like

Photomorphogenic Responses • Phytochrome Action Spectra:

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 Responses

• (3) Chromoproteins (chromatophore & apoprotein):– Phytochromes (5) PR & PFr

– Cryptochromes Blue & UV– Photochromes Blue & UV

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

Photomorphogenic Responses

Photomorphogenic Responses

• Less etiolation with higher amount of PFr

• Chenopodium alba “lamb’s quarter”

Bud Dormancy

• Wareing (1950’s) Fagus beech tree– initiated by short days– relieved by long days

– reception site: leaf bud scales

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• 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 Dormancy• Stratification

– cold treatment of seeds

• Ambient Factors:– 1.) temperature (near freezing, -2--> 7

degrees C)– 2.) time (7 --> 12 weeks …)

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

• 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/Stratification

• Petkus Rye - – winter annual

Deveralization/Destratification

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