photobiology
DESCRIPTION
Photobiology. 3 rd Year Student of biophysics. Prepared By Prof. Dr. Mohammed Naguib Abd El-Ghany Hasaneen. Professor Of Plant Metabolism And Biotechnology Academic Year 2005 - 2006. Contents. Introduction Radiation Visible light Ultraviolet light Ultraviolet light damage - PowerPoint PPT PresentationTRANSCRIPT
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