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.

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

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 Ambient Factors: cold treatment of seeds 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.