The Pigment That Controls Growth and Flowering In Many Plants phytochrome. 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” in 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

It’s all about Preferences! Photoperiodic Response: It’s all about Preferences! Long Day Plants flower when there is adequate PR Short Day Plants flower when there is adequate Pfr

Synthesis Destruction phytochrome. Pr Pfr Vegetative (Non-Flowering) 660 nm 740 nm Red Light Pr Pfr (Fast) Far Red Light Synthesis Destruction Dark Reversion (Slow) Vegetative (Non-Flowering) Reproductive (Flowering)

Long-Day Plants Need Low Pr! Mid-Summer Sunlight phytochrome. 660 nm 740 nm Red Light Pr Pfr (Fast) Far Red Light Synthesis Destruction Dark Reversion (Slow) Vegetative (Non-Flowering) Reproductive (Flowering) Long-Day Plants Need Low Pr!

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

Long-Day Plants Need Low Pr! Sunset or Far Red Light phytochrome. 660 nm 740 nm Red Light Pr Pfr (Fast) Far Red Light Synthesis Destruction Dark Reversion (Slow) Vegetative (Non-Flowering) Reproductive (Flowering) Long-Day Plants Need Low Pr!

Short-Day Plant Need Low Pfr! Mid-Summer Sunlight phytochrome. 660 nm 740 nm Red Light Pr Pfr (Fast) Far Red Light Synthesis Destruction Dark Reversion Reproductive (Flowering) (Slow) Vegetative (Non-Flowering) Short-Day Plant Need Low Pfr!

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

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

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

Night lighting disrupts reversion to Pr Night Break phytochrome. 660 nm 740 nm Red Light Pr Pfr (Fast) Far Red Light Synthesis Destruction Dark Reversion (Slow) Vegetative (Non-Flowering) Reproductive (Flowering) Night lighting disrupts reversion to Pr and maintains vegetative status!

Light Interruption of Darkness Affects Short- and Long-Day Plants Differently Continuous long, dark period Continuous short, dark period Interrupted dark period Photoperiod type Short-Day (Long-Night) Long -Day (Short-Night) 24-hour day cycle Critical day length

Questions?

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 !

To lengthen the night, plants are covered with a blackout shade cloth 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)

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.

SUPPLEMENTAL LIGHTING 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 Incandescent lamps are not desirable in greenhouse production because they have low efficiency and generate excess heat. In addition, their light spectrum consists of primarily red wavelengths, which causes excessive stem elongation in some plants. Fluorescent lamps are more efficient but are needed in large numbers to make up for their low power. They have a similar problem as the incandescent lights but they emit mostly blue wavelengths. Specially designed fluorescent lamps with better balanced spectrum also are available.

DAILY DURATION OF LIGHT 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.