The Pigment That Controls Growth and Flowering In Many

Plants

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

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)

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

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.

DAILY DURATION OF LIGHT

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 The actual plant response is very specific to each specie, and some specific to each specie, and some plants do not respond at all. 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 Thus the length of exposure to light in a building, or if outdoors, the seasonal light building, or if outdoors, the seasonal light changes, affect how long the plants perceives changes, affect how long the plants perceives each form of phytochrome. each form of phytochrome.

R FR

(Fast)

Dark Reversion

Red Light

740 nm660 nm

PrPr PfrPfr

(Slow)

Far Red Light

Synthesis Destruction

Vegetative(Non-Flowering)

Reproductive(Flowering)

(Fast)

Dark Reversion

Red Light

740 nm660 nm

PrPr PfrPfr

(Slow)

Far Red LightSynthesis Destruction

Vegetative(Non-Flowering)

Reproductive(Flowering)

Mid-Summer Sunlight

Long-Day Plants Need/Sense Low Pr to Bloom!

(Fast)

Dark Reversion

Red Light

740 nm660 nm

PrPr PfrPfr

(Slow)

Far Red LightSynthesis Destruction

Vegetative(Non-Flowering)

Reproductive(Flowering)

Long Night

Long-Day Plants Sense/Need Low Pr!

(Fast)

Dark Reversion

Red Light

740 nm660 nm

PrPr PfrPfr

(Slow)

Far Red LightSynthesis Destruction

Vegetative(Non-Flowering)

Reproductive(Flowering)

Mid-Summer Sunlight

Short-Day Plant Sense/Need Low Pfr to Bloom!

(Fast)

Dark Reversion

Red Light

740 nm660 nm

PrPr PfrPfr

(Slow)

Far Red LightSynthesis Destruction

Vegetative(Non-Flowering)

Reproductive(Flowering)

Black Cloth

Short-Day Plants Need Low Pfr!

(Fast)

Dark Reversion

Red Light

740 nm660 nm

PrPr PfrPfr

(Slow)

Far Red LightSynthesis Destruction

Vegetative(Non-Flowering)

Reproductive(Flowering)

Night Break

Night lighting disrupts reversion to Prand maintains vegetative status by keeping

Pfr relatively high in short day plants!

Types Of Photoperiodic ResponseTypes Of Photoperiodic Response

Short Day Plants – Single Cycle……….RiceRequires only one short day cycle to initiate the photoperiodic response.

Long Day Plants – Single Cycle………….DillRequires only one long day cycle to initiate the photoperiodic response.

Day Neutral Plants………………………………CucumberFlower the same time under all day-lengths, least photoperiodic response.

Ambiphotoperiodic Plants………………….SetariaThese plants are inhibited by intermediate (Equinox) day-lengths.

Short then Long Day Plants………………….CloverThese plants are inhibited by intermediate (Equinox) day-lengths.

Whereas many plants are photoperiodic, they do not all respond thesame way. There are 10 distinct types, with many sub-responses to temperature within many of the groups.

Qualitative Long Day Plants………………HibiscusMust have constant long days to initiate the photoperiodic response.

Quantitative Long Day Plants…………..FoxGloveRequires a certain # of hours of LD’s to initiate the photoperiodic response.

Qualitative Short Day Plants……….…..PoinsettiaMust have constant short days to initiate the photoperiodic response.

Quantitative Short Day Plants………..ChrysanthemumRequires a certain # of SD’s to initiate the photoperiodic response.

Intermediate Day Plants……………………Sugar CanePlants flower when days are neither too long or too short. (Equinox)

Types Of Photoperiodic ResponseTypes Of Photoperiodic Response

Questions?