Photobiology

3rd Year Student of biophysics

Prepared By

Prof. Dr. Mohammed Naguib Abd El-Ghany Hasaneen

Professor Of Plant Metabolism And Biotechnology

Academic Year2005 - 2006

Contents

• Introduction• Radiation• Visible light• Ultraviolet light• Ultraviolet light damage• Phytochrome concept• Distribution and translocation of phytochrome• Physiological effects of phytochrome

We see visible light (350-700 nm)

Plants sense Ultra violet (280) to Infrared (800)

Examples Seed germination - inhibited by light Stem elongation- inhibited by light

Shade avoidance- mediated by far-red light

There are probably 4 photoreceptors in plants

We will deal with the best understood; PHYTOCHROMES

Light in PlantsLight in Plants

IntroductionIntroduction

A Primer on Radiation

Some important plant responses to radiation

(“light” is only one form of radiation):

•Photosynthesis•Photomorphogenesis;• Photropism; Photoperiodism•Energy balance/temperature•respiration•enzyme activity•transpiration•UV-responses•mutagenesis

(note that there is a much more detailed table and discussion of responses of plants to light in chapter 1 of Hart: Light and Plant Growth)

In what form does energy from the sun travel to Earth?

• Energy travels to Earth in the form of electromagnetic waves• Electromagnetic waves are classified according to wave length• Radiation is the direct transfer of energy by electromagnetic waves

Most of the energy from the sun reaches Earth in the form of

• Visible light

• Infrared radiation

• A small amount of ultraviolet radiation

• The different colors of light make up the visible spectrum.

• Red has the longest wave length

• Violet has the shortest wave length

Infrared radiation has the following properties:

• Wavelengths longer than red light

• It is not visible

• It can be felt as heat

• Used to warm food or baby chicks in an incubator

Ultraviolet light has the following properties:

• Wave lengths shorter than violet light

• Can cause skin damage

• Can cause eye problems

Radiation and radiation lawsRadiation and radiation laws

The way we describe and quantify radiation, and the units used, vary depending on the kind of process we’re interested in

Properties of radiation that are important to plants include Quality, Quantity, Direction (including diffuse vs. direct) and Periodicity.

Radiation quality (or “color”, for visible light) is a function of its wavelength (or frequency) distribution

The symbol “” is often used for

wavelength

Note these two charts are arrayed in opposite directions – one by increasing wavelength/decreasing energy and the other by increasing frequency/increasing energy

Radiation quantity is measured in one of three ways, depending on the application:

1. Quantum measurements (numbers of photons)

2. Radiometric measurements (amount of energy)

3. Photometric measurements (light intensity, based on human perception)

Radiation measurementsRadiation measurements

The amount of radiation is expressed as fluence (also known as density; quantity per area), rate (also known as flux; quantity per time) or fluence rate (also known as flux density; amount per area per time) Parameter Term Energy units Quantum

units

Quantity per area

fluence J m-2 mol m-2

Quantity per time

rate

(or flux)

J s-1 (watt) mol s-1

Quantity per area per time

fluence rate (or flux density)

W m-2 mol m-2 s-1

For studies of photosynthesis and photomorphogenesis, the quantity of radiation is usually measured in quantum units (quantum flux density; quantum fluence rate):

mol m-2 s-1

usually, only the visible, or photosynthetically active part of the spectrum is measured, or in the case of photomorphogenesis, only specific wavelengths

PPFD = photosynthetically activephoton flux density

PAR = photosynthetically active radiation

(400-700 nm)

Note that “mol” refers to a mole of photons, and that 1 mol photons=1 Einstein. A quantum is one indivisible “package” of radiation, or one photon.

For energy balance studies, radiation is measured in radiometric units, for

example:

Watts m-2

(note: 1 Watt = 1 Joule s-1)

Radiometric and quantum units are interconverted based on the amount of energy in photons.

The energy of a photon is proportional to its frequency and inversely proportional to wavelength:

E = h hc/Energy per photon(joules)

Planck’s constant:6.63 x 10-34 joules s

Frequency (s-1)

Speed of light 3 X 108 m s-1

wavelength(in meters)

See link from website to “working with light” or p. 28 of the handout by Hart or any good reference on radiation for more information on this conversion)

Because most light sources contain a wide range of wavelengths, it is difficult to convert precisely between quantum and radiometric units. Usually an approximation is used that assumes a “typical” distribution of wavelengths for a particular light source

All objects emit radiation (i.e., they “radiate”) as a function of their temperature (in addition to the emissivity of the material). Temperature affects both the amount and the quality (wavelength) of radiation emitted.

Temperature of radiating body, in degrees Kelvin

max = 2897/T

Wien’s Law:

The “bulk” of solar radiation is “shortwave” (visible plus near

infrared)

Notice that the range of photosynthetically active wavelengths is very small

relative to the range of the solar spectrum

• visible = 400-700 nm, about 45% of incident insolation• solar IR = 700-5000 nm, about 46% of incident• UV = 190-400 nm, about 9% of incident

Spectral QualitySpectral Quality

• Restating this as a rough “rule of thumb”:

When the sky is clear, the photosynthetically active part of the solar spectrum accounts for about HALF of the total solar energy, IR accounts for the other half

Radiance vs. Irradiance:Radiance vs. Irradiance:

Radiance is the radiation that is emitted from an object

Irradiance is the radiation that impinges upon an object

In this case, radiation is commonly described as a flux (rate), or amount per unit time. This could be either a radiant flux or a quantum flux

In this case, radiation is commonly described as a flux density, or amount per unit time per unit area. Again, the flux could be quantified either with either radiometric or photometric units.

Direct irradiance

Diffuse irradiance

Irradiance usually has both direct and diffuse components:

The amount of energy in direct-beam irradiance is strongly affected by the angle between the surface and the beam

Lambert’s Cosine Law:

Solar angle and leaf angle can have a very big influence on irradiation, dramatically affecting photosynthesis, transpiration and leaf temperature

definitions:Heliotropic: “sun tracking”Paraheliotropic: leaf stays parallel to direct beam of sunDiaheliotropic: leaf stays perpendicular to direct beam

Connections between matter and energyConnections between matter and energy

A short, painless review of simple organic chemistry …… to develop the connection between cycles of organic biomass and cycles of energy

(Inorganic; not a hydrocarbon.This is a highly oxidized form of carbon)

CO2

methane

ethene

ethane

ethyne

(organic hydrocarbons. The molecules are becoming increasingly reduced)

incre

asin

g p

ote

ntia

l energ

y (e

nerg

y

store

d in

chem

ical b

onds)

general deterioration of #4 green

general deterioration of #4 green

shade from trees and tower

general deterioration of #4 green

shade from trees and tower

poor air circulation from trees and shrubs

concentrated traffic between trap and green

general deterioration of #4 green

shade from trees and tower

poor internal and surface

drainage

poor air circulation from trees and shrubs

concentrated traffic between trap and green

general deterioration of #4 green

shade from trees and tower

poor internal and surface

drainage

poor air circulation from trees and shrubs

concentrated traffic between trap and green

general deterioration of #4 green

shade from trees and tower

delicate turfgrass

poor internal and surface

drainage

O2-deficient rootzone

poor air circulation from trees and shrubs

hot, humid microenvironment

concentrated traffic between trap and green

Wavelength - ENERGY

• Photons in short wavelengths pack a lot of energy– Visible light (400-750nm):

• 1 mole of photons = 250kJ energy

– Ultraviolet light (< 400 nm):• 1 mole of photons = 500 kJ energy

• Photons in longer wavelengths do not– Infrared radiation (>750 nm)

• 1 mole of photons = 85 kJ energy

• What happens when sunlight hits the wall of a building?

– Some reflected back to space (no effect) (this depends upon the COLOR of the wall!)

– Most is absorbed. Then what?• Absorption of radiation makes the temperature of the object

rise• How hot?• The hotter the more radiation emitted (as infrared)• Heats until energy in = energy out• Or energy absorbed = energy re-radiated

The Thermal Environment

• Energy is gained and lost through various pathways:– radiation - all objects emit electromagnetic radiation and

receive this from sunlight and from other objects in the environment

– conduction - direct transfer of kinetic energy of heat to/from objects in direct contact with one another

– convection - direct transfer of kinetic energy of heat to/from moving air and water

– evaporation - heat loss as water is evaporated from organism’s surface (2.43 kJ/g at 30oC)

change in heat content = metabolism - evaporation + radiation+ conduction + convection

Organisms must cope with temperature extremes.

• Unlike birds and mammals, most organisms do not regulate their body temperatures.

• All organisms, regardless of ability to thermoregulate, are subject to thermal constraints:– most life processes occur within the temperature range of

liquid water, 0o-100oC

– few living things survive temperatures in excess of 45oC

– freezing is generally harmful to cells and tissues

So how do organisms regulate temperature?So how do organisms regulate temperature?

• Manipulating the energy balance equation!– Net radiation

• Color, Orientation to sun, Minimizing/maximize IR losses (insulation)– Conduction

• Use warm or cool surfaces– Convection:

• Minimize or maximize exposure to wind or water (boundary layers, exposure, immersion)

– Evaporation:• Minimize or maximize evaporation to control heat loss

– Metabolism: Generate or limit generation of heat!• These can be morphological, physiological, or behavioral adaptations

Conserving Water in Hot Environments

• Animals of deserts may experience environmental temperatures in excess of body temperature:– evaporative cooling is an option, but water is

scarce

– animals may also avoid high temperatures by:• reducing activity

• seeking cool microclimates

• migrating seasonally to cooler climates

Conserving Water in Hot Environments

• Desert plants reduce heat loading in several ways already discussed. Plants may, in addition:– orient leaves to minimize solar gain

– shed leaves and become inactive during stressful periods

The Kangaroo Rat - a Desert Specialist

• These small desert rodents perform well in a nearly waterless and extremely hot setting.– kangaroo rats conserve water by:

• producing concentrated urine

• producing nearly dry feces

• minimizing evaporative losses from lungs

– kangaroo rats avoid desert heat by:• venturing above ground only at night

• remaining in cool, humid burrow by day

Tolerance of Freezing

• Freezing disrupts life processes and ice crystals can damage delicate cell structures.

• Adaptations among organisms vary:– maintain internal temperature well above freezing– activate mechanisms that resist freezing

• glycerol or glycoproteins lower freezing point effectively (the “antifreeze” solution)

• glycoproteins can also impede the development of ice crystals, permitting “supercooling”

– activate mechanisms that tolerate freezing

Organisms maintain a constant internal Organisms maintain a constant internal environment.environment.

• An organism’s ability to maintain constant internal conditions in the face of a varying environment is called homeostasis:– homeostatic systems consist of sensors, effectors,

and a condition maintained constant

– all homeostatic systems employ negative feedback -- when the system deviates from set point, various responses are activated to return system to set point

Temperature Regulation: an Example of HomeostasisTemperature Regulation: an Example of Homeostasis

• Principal classes of regulation:– homeotherms (warm-blooded animals) -

maintain relatively constant internal temperatures

– poikilotherms (cold-blooded animals) - tend to conform to external temperatures

• some poikilotherms can regulate internal temperatures behaviorally, and are thus considered ectotherms, while homeotherms are endotherms

Homeostasis is costly.

• As the difference between internal and external conditions increases, the cost of maintaining constant internal conditions increases dramatically:– in homeotherms, the metabolic rate required to

maintain temperature is directly proportional to the difference between ambient and internal temperatures

Limits to Homeothermy

• Homeotherms are limited in the extent to which they can maintain conditions different from those in their surroundings:– beyond some level of difference between

ambient and internal, organism’s capacity to return internal conditions to norm is exceeded

– available energy may also be limiting, because regulation requires substantial energy output

Partial Homeostasis

• Some animals (and plants!) may only be homeothermic at certain times or in certain tissues…

• pythons maintain high temperatures when incubating eggs

• large fish may warm muscles or brain

• hummingbirds may reduce body temperature at night (torpor)

What are energy units?

• 1. umoles of photons per meter squared per second:– umol m-2 s-1

• Watts per meter squared: W m-2

• Sunny day in Colorado: solar input:– 2200 umol m-2 s-1

– 1100 W m-2

– Why no time unit for W? (W = 1 J s-1)

• Can you convert between the two units?– Not quite since the conversion depends on wavelength

Infrared Light and the Greenhouse Effect 1

• All objects, including the earth’s surface, emit longwave (infrared) radiation (IR).

• Atmosphere is transparent to visible light, which warms the earth’s surface.

Infrared Light and the Greenhouse Effect 2

• Infrared light (IR) emitted by earth is absorbed in part by atmosphere, which is only partially transparent to IR.

• Substances like carbon dioxide and methane increase the absorptive capacity of the atmosphere to IR, resulting in atmospheric warming.

Greenhouse Effect - SummaryGreenhouse Effect - Summary

• Greenhouse effect is essential to life on earth (we would freeze without it), but enhanced greenhouse effect (caused in part by forest clearing and burning fossil fuels) may lead to unwanted warming and serious consequences!

Ozone and Ultraviolet Radiation

• UV “light” has a high energy level and can damage exposed cells and tissues.

• Ozone in upper atmosphere absorbs strongly in ultraviolet portion of electromagnetic spectrum.

• Chlorofluorocarbons (formerly used as propellants and refrigerants) react with and chemically destroy ozone:– ozone “holes” appeared in the atmosphere– concern over this phenomenon led to strict controls on

CFCs and other substances depleting ozone

Clouds…

• What happens on a cloudy day?– Less radiation comes in…

• What happens on a cloudy night?– Less radiation goes out…

The Absorption Spectra of PlantsThe Absorption Spectra of Plants• Various substances (pigments) in plants have different

absorption spectra:

– chlorophyll in plants absorbs red and violet light, reflects green and blue

– water absorbs strongly in red and IR, scatters violet and blue, leaving green at depth

Plants Respond to LightPlants Respond to Light

Photomorphogenesis, Phototropism, Photomorphogenesis, Phototropism, PhotoperiodismPhotoperiodism

Phytochrome responses (red/far red)Phytochrome responses (red/far red)flowering and dormancy; branch

patterns; root growth

Blue light responsesBlue light responsesstomatal opening; phototropism;

chloroplast orientation

Plants Respond to LightPlants Respond to Light

Photomorphogenesis.Photomorphogenesis.

– nondirectional, light-triggered development• red light changes the shape of phytochrome

and can trigger photomorphogenesis

PhototropismsPhototropisms

• Phototropic responses involve bending of growing stems toward light sources.– Individual leaves may also display phototrophic

responses.• auxin most likely involved

Carbon vs. Energy

Plants convert LIGHT energy into CHEMICAL energy

They use the chemical energy to take CO2 from the atmosphere, and turn it into glucose, and other C-structures….

Seed location?

Red light from sun penetrates to seed.

No light from sun to this deep seed.

Seed germinates. No germination.

Red light to seed = near surface

Sun Exposure and UV damage

• Sunshine, essential for life, strikes the earth in rays of varying wavelengths. Long rays (infrared) are unseen but felt as heat. Intermediate length rays are visible as light. Shorter rays (ultraviolet) are also invisible and are further divided into the following groups:

• Ultraviolet (UVA) rays are beneficial in low doses, but may increase the chance of cancer in high doses. UVBs are primarily responsible for sunburn and cancerUVCs are the shortest and most dangerous UV rays contain enough energy to damage DNA in living skin and eye cells. DNA controls the ability of cells to heal and reproduce. The ozone layer allows life to flourish by passing the longer, beneficial wavelengths and effectively blocking almost all UVC, some UVB and a little UVA.

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 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.

Pr Pfr

The structure of PhytochromeThe structure of Phytochrome

660 nm

730 nm

Binds to membrane

A dimer of a 1200 amino acid protein with several domains

and 2 molecules of a chromophore. Chromophore

Signal Transduction of Phytochrome

PrPfr G

Ca2+/CaM cGMP

CAB, PS IIATPaseRubisco

FNRPS I

Cyt b/f

CHS

Chloroplast biogenesisAnthocyanin synthesis

bZIPMyb

?

Membrane

G protein subunit

Calmodulin

Guanylate cyclase Cyclic guanidine monophosphate

How Phytochrome Works

Promoter has 4 sequence motifs which participate in light regulation.If unit 1 is placed upstream of any transgene, it becomes light regulated.

IV III II I

-252 -230 -159 -131 +1

5’-CCTTATTCCACGTGGCCATCCGGTGGTGGCCGTCCCTCCAACCTAACCTCCCTTG-3’

bZIP Myb TranscriptionFactors

Unit 1

Light-Regulated Elements (LREs)

e.g. the promotor of chalcone synthase-first enzyme in anthocyanin synthesis

There are at least 100 light responsive genes (e.g. photosynthesis)

There are many cis-acting, light responsive regulatory elements

7 or 8 types have been identified of which the two for CHS are examples

No light regulated gene has just 1.

Different elements in different combinations and contexts control the level of transcription

Trans-acting elements and post-transcriptional modifications are also involved.

Light-Regulated Elements (LREs)

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 changes, affect how long the plants perceives each form of phytochrome. perceives each form of phytochrome.

R FR

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

660 nm

PrPr

Synthesis

Vegetative(Non-Flowering)

(Fast)

Red Light

Far Red Light

Dark Reversion

PfrPfr

(Slow)

740 nm

DestructionReproductive(Flowering)

(Fast)

Red Light

Far Red Light

Dark Reversion

PrPr

(Slow)

660 nm

Synthesis

Mid-Summer Sunlight

740 nm

PfrPfr

Destruction

Reproductive(Flowering)

Vegetative(Non-Flowering)

Long-Day Plants Need Low Pr!

(Fast)

Red Light

Far Red Light

Dark Reversion

(Slow)

PfrPfr

660 nm

Synthesis

PrPr

Vegetative(Non-Flowering)

740 nm

Destruction

Reproductive(Flowering)

Long Night

Long-Day Plants Need Low Pr!

(Fast)

Red Light

PfrPfrFar Red Light

Dark Reversion

(Slow)Vegetative

(Non-Flowering)

660 nm

PrPr

Synthesis

Reproductive(Flowering)

740 nm

Destruction

Sunset orFar Red Light

Long-Day Plants Need Low Pr!

Reproductive(Flowering)

Vegetative(Non-Flowering)

Red Light

Dark Reversion

PfrPfr

(Slow)

740 nm

Destruction

(Fast)

Far Red Light

660 nm

PrPr

Synthesis

Mid-Summer Sunlight

Short-Day Plant Need Low Pfr!

Short-Day Plant Need Low Pfr!

Vegetative(Non-Flowering)

Reproductive(Flowering)

(Fast)

Red Light

Far Red Light

Dark Reversion

(Slow)

660 nm

Synthesis

PrPr

Destruction

740 nm

PfrPfr

Winter Far Red

Light

660 nm

Synthesis

(Fast)

Dark Reversion

Red Light

(Slow)

Far Red Light

Reproductive(Flowering)

PrPr

Destruction

Vegetative(Non-Flowering)

740 nm

PfrPfr

LongNight

Short-Day Plants Need Low Pfr!

(Fast)

Red Light

Far Red Light

Dark Reversion

(Slow)

660 nm

Synthesis

740 nm

PfrPfr

Destruction

Vegetative(Non-Flowering)

Reproductive(Flowering)

PrPr

Black Cloth

Short-Day Plants Need Low Pfr!

Dark Reversion

(Slow)

660 nm

PrPr

Synthesis

Reproductive(Flowering)

(Fast)

Red Light

Far Red Light

Night Break

Night lighting disrupts reversion to Prand maintains vegetative status!

740 nm

PfrPfr

Destruction

Vegetative(Non-Flowering)

24-hour day cycle

Critical day length

Light Interruption of Darkness Affects Short- and Long-Day

Plants Differently

Photoperiod typeShort-Day(Long-Night)Long -Day(Short-Night)

Continuous long, dark period

Continuous short, dark period

Interrupted dark period

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. 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

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

Plants Respond to GravityPlants Respond to Gravity

• Gravitropism is the response of a plant to the earth’s gravitational field.– present at germination

• auxins play primary role

– Four steps• gravity perceived by cell

• signal formed that perceives gravity

• signal transduced intra- and intercellularly

• differential cell elongation

The pigment phytochrome

• Detects R and FR light• Provides information about environment• Answers 3 questions for plant

– Am I in the light?– Do I have plants as neighbors or above me?– Is it time to flower?

Why bother?

• Seeds store materials to start growth• Must reach light before running out of stored

materials• Small seeds

– Need to be very near surface

– Often need light for germination

• Germinating plants straighten & open leaves at surface, too

Plant neighbors?

Far red reflected from other plants.

Red absorbed by other plants.

Far red enriched = neighbors

Why does this matter?

• Neighboring plants are threats– Might grow taller, shade you

• Solution– Grow at least as tall as neighbors

– Need to know that you have neighbors

• Isolated plants typically shorter than crowded plants– Other reasons, too

Under other plants?

Red absorbed

by other plants.

Far red reflected from other plants or transmitted.

Far red enriched = understory

Why important?

• Best growth strategy for understory plants is different than for plants in open

• Need to know whether– Shaded by other plants

OR

– Just cloudy

OR

– Late in day (low light)

Right time to flower?

• Unreliable indicators of time of year– Temperature – Moisture – Light levels

• Reliable: length of day/night – Varies with season– Varies with latitude

Detected by phytochrome

• Red-absorbing phytochrome

• Far red absorbing phytochrome

• Interconverted• Two forms of the same compound• Total amount same

Phytochrome has 2 forms

Pfr

Pr

Pr Pfr

Pfr

In red light

Pr Pfr

Pr absorbs red light, changes to Pfr form.

Pfr doesn’t absorb red light, stays the same.

In far red light

Pr Pfr

Pfr absorbs far red light, changes to Pr form.

Pr doesn’t absorb far red light, stays the same.

Pr

Pr

In pure light

Pfr

In pure far red light, all the phytochrome ends up in the Pr form.

In pure red light, all the phytochrome

ends up in the Pfr form.

Sunlight

Mostly red

A little far red

Pr

Pfr

In sunlight

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

In sunlight most P gets converted to Pfr form.

Pr

Pfr

Start of night

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

Most P in Pfr form.

Pfr

In the dark

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

Pfr form changes gradually to Pr form.

Pr

Pr

Pr

Pr

Pfr

After a short night

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

Pfr still left.

Pr

Pr

Pr

Pr

LDP = SNP

• Needs short night• Needs Pfr still present at end of night• Pfr promotes flowering for LDPs

Pfr

Later in the night

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

PfrPfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

More Pfr changes to Pr.

Pr

Pr

Pr

Pr

Pfr

After a long night

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

All the Pfr is gone.

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Day dawns

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

Most P gets converted to Pfr form again.

SDP = LNP

• Needs long night• Needs Pfr gone at end of night• Pfr inhibits flowering for SDPs

LDP SDP

Long day: Pfr left at end of short night.

Pfr promotes flowering for LDPs.

Pfr inhibits flowering for SDPs.

Short day: Pfr gone at end of long night.

No Pfr to promote flowering for LDPs.

No Pfr to inhibit flowering for SDPs.

Waiting for the right time

• Plants grow leaves until it is time to flower• LDPs wait until the day is long enough

– Really night short enough

– Some time before June 21

• SPDs wait until the day is short enough– Really night long enough

– Some time after June 21

• Flower opening happens later

Day neutral plants

• Flower when mature enough• Maybe other environmental signals (temp?)• Day length (dark length) doesn’t matter

Through the year

May

JuneJuly

AugustSeptember

October

Specific flowers at specific times.

Phytochrome tells plants

• If they are near the surface• About their plant neighbors• Whether it is time to flower• And lots more

References• http://www.abdn.ac.uk/sms/ugradteaching/GN3502/GN3502_07

32005_1.ppt• http://www.warnercnr.colostate.edu/class_info/by220-indy/physi

cal_environment/Physical%20Environment,%20part%202%202004.ppt

• http://www.coe.unt.edu/ubms/documents/classnotes/Spring2006/256,1,Sensory Systems in Plants

• http://128.192.110.246/pthomas/Hort3140.web/Phytochrome%20lecture.ppt

• http://fp.uni.edu/berg/pp/downloads/PhytochromeAction.ppt• http://www.fsl.orst.edu/~bond/fs561/lectures/radiation.ppt• http://www.coe.unt.edu/ubms/documents/classnotes/Spring2006/

Plant%20Sensory%20Systems%201720_Chapter_40_2005.ppt• http://turfgrass.cas.psu.edu/education/turgeon/CaseStudy/BlueC

ourseGreen_01/Blue_Course_Green.ppt• http://siri.uvm.edu/ppt/warmweatherrinjuries/warmweatherrinjur

ies.ppt• http://www.cobb.k12.ga.us/~dickerson/ch%2016.ppt