2Flowering - Floral Induction (branch bud ----> flower bud) violets, roses, chrysanthemumsChailakhan 1920’s RussianFlorigenAmount of light and photoperiods already known to be important.
3Photoperiodism 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 Mammothlarge-leaved mutantlack of floweringgreenhouse plants …various stagesmost flowered in early December!DAYLENGTH critical factor Short Day, Long Day, Day Neutral plants
4Short Day PlantsFlower only when day length is shorter than some critical value.Pointsetta, cocklebur, soybean.. - qualitativewill not flower without a critical photoperiodwheat, rye, .. - quantitativewill flower without a critical photoperiod but will take longer
5Short Day PlantsFlower only when day length is shorter than some critical value.soybean.. - qualitative
6Long and Short Day Plants May Flower at the Same Time Henbane (11 hrs.), Cocklebur (15 hrs.)
7Long and Short Day Plants May Flower at the Same time
8PHOTOPERIODISMSome plants need several days at the proper daylength. Winter & Summer Solstices
9PHOTOPERIODISM 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 = flowers15.5 hrs of light/8.5 hrs dark = no flowers15 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.)
10PHOTOPERIODISMK. Hamner (U of Cal.) and J. Bonner (CIT) 1938
11PHOTOPERIODISM REDEFINED K. Hamner (U of Cal.) and J. Bonner (CIT) 1938:Short Day Plantsuninterrupted darkness must be of a certain duration.(so much darkness or more)Long Day Plantsuninterrupted darkness must be less than a certain maximum value.(so much darkness or less)Day Neutral PlantsFlowers at a certain level of maturity or in response to some environmental factor other than the photoperiod.
12PHOTOPERIODISMK. Hamner (U of Cal.) and J. Bonner (CIT) 1938
17Photomorphogenic Responses H. A. Borthwick and S. B. Hendricks 1950’s US AgAction spectra studies - flowering and othersSubjected plants to various wavelengths during dark period ----> responsesAll photomorphogenic responses studied had similar responses …Predicted: the photochrome pigment2 forms ) PR - red light absorbing form2.) PFr - Far-red light absorbing form (Active Form)
18Photomorphogenic Responses Phytochrome is ubiquitous in plants - found in all tissues. Has been isolated and purified.Phycocyanin like