The Pigment That Controls Growth and Flowering In Many Plants

What Is Phytochrome ?  Phytochrome is a pigment found in some plant cells that has been proven to control plant development.  This pigment has two forms or “phases” it can exist in. P-red light sensitive (Pr) and P –far red light sensitive (Pfr) forms.  The actual plant response is very specific to each specie, and some plants do not respond at all.

Which Wavelengths Are Photoperiodic? The length of the night period plays a major role in determining which wavelength will be effective, as the phytochrome pigment tends to revert to Pr during long periods of darkness. Thus the length of exposure to light in a building, or if outdoors, the seasonal light changes, affect how long the plants perceives each form of phytochrome. R FR

Photoperiodic Response: It’s all about Preferences! Long Day Plants flower when there is a prolonged larger pool of Pfr Short Day Plants flower when there is prolonged larger pool of Pr

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering)

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Mid-Summer Sunlight Long-Day Plants Need/Sense Low Pr to Bloom!

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Long Night Long-Day Plants Sense/Need Low Pr!

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Sunset or Far Red Light Long-Day Plants Sense/Need Low Pr!

(Fast) Dark Reversion Red Light 740 nm660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Mid- Summer Sunlight Short-Day Plant Sense/Need Low Pfr to Bloom!

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Short-Day Plant Need Low Pfr! Winter Far Red Light

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Long Night Short-Day Plants Need Low Pfr!

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Black Cloth Short-Day Plants Need Low Pfr!

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Night Break Night lighting disrupts reversion to Pr and maintains vegetative status by keeping Pfr relatively high in short day plants!

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Synthesis and Reversion Help Tell Time

NightDay Max PFR Max PR Duration of Darkness 14 hours10 hours Ratio Of Forms Plants not only can differentiate Wavelength They can sense pigment ratios and duration of darkness!!! 660 nm 740 nm The Elegance of Photoperiod Impressive!

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Long Night Short-Day Plants Need Low Pfr!

Day Long Night Day Max PFr Max Pr Slow Decline 10 hours 14 hours 10 hours Sunrise Sunset Max reversion to Pr Form Max conversion to PFr Form Short Days = Long Nights = maximum PFr conversion ! The plant senses a high Pr Pool

(Fast) Dark Reversion Red Light 740 nm 660 nm Pr Pfr (Slow) Far Red Light SynthesisDestruction Vegetative (Non-Flowering) Reproductive (Flowering) Fall Extended Far Red Light Long-Day plants need to sense Low Pr! The increased far red light increases the Pr pool, causing the plants to go vegetative!

Day Short Night 16 Hour Day Max PFr Max Pr Slow Decline 16 hour 8 Hours Sunrise Sunset Partial Conversion to Pr Form = low Pr pool Max conversion to PFr Form Sunrise Long Days = Short nights which interrupts PFr conversion The plant senses a reduced Pr pool Partial Conversion to Pr Form = low Pr pool Max conversion to PFr Form

Types Of Photoperiodic Response Short Day Plants – Single Cycle……….Rice Requires only one short day cycle to initiate the photoperiodic response. Long Day Plants – Single Cycle………….Dill Requires only one long day cycle to initiate the photoperiodic response. Day Neutral Plants………………………………Cucumber Flower the same time under all day-lengths, least photoperiodic response. Ambiphotoperiodic Plants………………….Setaria These plants are inhibited by intermediate (Equinox) day-lengths. Short then Long Day Plants………………….Clover These plants are inhibited by intermediate (Equinox) day-lengths. Whereas many plants are photoperiodic, they do not all respond the same way. There are 10 distinct types, with many sub-responses to temperature within many of the groups.

Qualitative Long Day Plants………………Hibiscus Must have constant long days to initiate the photoperiodic response. Quantitative Long Day Plants…………..FoxGlove Requires a certain # of hours of LD’s to initiate the photoperiodic response. Qualitative Short Day Plants……….…..Poinsettia Must have constant short days to initiate the photoperiodic response. Quantitative Short Day Plants………..Chrysanthemum Requires a certain # of SD’s to initiate the photoperiodic response. Intermediate Day Plants……………………Sugar Cane Plants flower when days are neither too long or too short. (Equinox) Types Of Photoperiodic Response

The Phytochrome System Works Within The Apical Meristem Photoperiodicresponses are triggered in the meristem (both apical and axillary), long before the new branches develop. We can control development !

Photoperiodic shade cloth Light penetration through the shade cloth should not be more than 2 fc in order to prevent delay in flowering and/or disfigured flowers.

To lengthen the night, plants are covered with a blackout shade cloth. Applied in late afternoon and removed in the morning (5 pm to 8 am)

S UPPLEMENTAL L IGHTING  Light sources.  incandescent lamps emit large amounts of red light and are good for lighting mums (standard mum lighting)  mums flower when the day length decreases to 13.5 hrs or less  whenever the day length is longer than 14.5 hrs plants remain vegetative  split each long night in two short nights with supplemental light to prevent flowering

 The length of day has an effect on two plant processes  time of flowering  plant maturity  This light-induced response is called photoperiodism, and plants that flower under only certain day-length conditions are called photoperiodic. D AILY D URATION OF L IGHT

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