Photobiology
3rd 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
•
•
•
•
•
•
•
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Introduction
Radiation
Visible light
Ultraviolet light
Ultraviolet light damage
Phytochrome concept
Distribution and translocation of phytochrome
Physiological effects of phytochrome
Introduction
Light in Plants
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
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 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
Note these two charts are
arrayed in opposite directions
– one by increasing
wavelength/decreasing energy
and the other by increasing
frequency/increasing energy
The symbol
“l” is often
used for
wavelength
Radiation measurements
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)
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
mmol m-2
Quantity per
time
rate
(or flux)
J s-1 (watt)
mmol s-1
Quantity per
area per time
fluence rate (or W m-2
flux density)
mmol 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):
mmol m-2 s-1
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.
usually, only the visible, or photosynthetically active
part of the spectrum is measured, or in the case of
photomorphogenesis, only specific wavelengths
PPFD = photosynthetically active
photon flux density
PAR = photosynthetically active radiation
(400-700 nm)
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:
Energy per photon
(joules)
Planck’s
constant:
6.63 x 10-34
joules s
E = hn = hc/l
wavelength
(in meters)
Frequency
(s-1)
Speed of light
3 X 108 m s-1
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.
Wien’s Law:
l
max
= 2897/T
Temperature of
radiating body,
in degrees Kelvin
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
Spectral Quality
• 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
• 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 is the radiation that is emitted from 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
Irradiance is the radiation that impinges upon an object
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.
Irradiance usually has both direct and diffuse components:
Direct irradiance
Diffuse irradiance
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
sun
Diaheliotropic: leaf stays
perpendicular to direct
beam
Connections 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)
methane
ethane
ethene
ethyne
(organic
hydrocarbons.
The molecules
are becoming
increasingly
reduced)
increasing potential energy (energy stored
in chemical bonds)
CO2
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
general
deterioration
of #4 green
concentrated
traffic between
trap and green
shade
from trees
and tower
poor air
circulation from
trees and shrubs
general
deterioration
of #4 green
concentrated
traffic between
trap and green
poor internal
and surface
drainage
shade
from trees
and tower
poor air
circulation from
trees and shrubs
general
deterioration
of #4 green
concentrated
traffic between
trap and green
poor internal
and surface
drainage
shade
from trees
and tower
poor air
circulation from
trees and shrubs
delicate
turfgrass
hot, humid
microenvironment
general
deterioration
of #4 green
O2-deficient
rootzone
concentrated
traffic between
trap and green
poor internal
and surface
drainage
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?
• 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
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 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 - 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…
Plants Respond to Light
The 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 Light
Photomorphogenesis, Phototropism,
Photoperiodism
Phytochrome responses (red/far red)
flowering and dormancy; branch
patterns; root growth
Blue light responses
stomatal opening; phototropism;
chloroplast orientation
Photomorphogenesis.
– nondirectional, light-triggered development
• red light changes the shape of phytochrome
and can trigger photomorphogenesis
Phototropisms
• 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.
Seed germinates.
No light
from sun
to this
deep
seed.
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 cancer
UVCs 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 specific to
each specie, and some plants do not respond at all.
The structure of Phytochrome
A dimer of a 1200 amino acid protein with several domains
and 2 molecules of a chromophore.
Chromophore
660 nm
730 nm
Pr
Pfr
Binds to membrane
Signal Transduction of Phytochrome
Membrane
Pfr
Ga
G protein a subunit
Pr
Guanylate cyclase
Ca2+/CaM Calmodulin
CAB, PS II
ATPase
Rubisco
FNR
PS I
Cyt b/f
Chloroplast biogenesis
cGMP
CHS
Cyclic
guanidine
monophosphate
bZIP
Myb
?
Anthocyanin synthesis
How Phytochrome Works
Light-Regulated Elements (LREs)
e.g. the promotor of chalcone synthase-first enzyme in
anthocyanin synthesis
Promoter has 4 sequence motifs which participate in light regulation.
If unit 1 is placed upstream of any transgene, it becomes light
regulated.
-252
-230
IV
III
-159
II
-131
+1
I
Unit 1
5’-CCTTATTCCACGTGGCCATCCGGTGGTGGCCGTCCCTCCAACCTAACCTCCCTTG-3’
Transcription
Factors
bZIP
Myb
Light-Regulated Elements (LREs)
 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.
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.
R FR
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.
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
740 nm
Pr
Synthesis
Red Light
(Fast)
Far Red Light
Vegetative
(Non-Flowering)
Dark
Reversion
(Slow)
Pfr
Destruction
Reproductive
(Flowering)
Mid-Summer
Sunlight
660 nm
740 nm
Pr
Red Light
(Fast)
Far Red Light
Synthesis
Dark
Reversion
Vegetative
(Non-Flowering)
(Slow)
Pfr
Destructio
n
Reproductive
(Flowering)
Long-Day Plants Need Low Pr!
Long Night
660 nm
740 nm
Red Light
Pr
(Fast)
Far Red Light
Synthesis
Pfr
Destruction
Dark
Reversion
Vegetative
(Non-Flowering)
(Slow)
Reproductive
(Flowering)
Long-Day Plants Need Low Pr!
Sunset or
Far Red Light
660 nm
740 nm
Red Light
Pr
(Fast)
Far Red Light
Synthesis
Pfr
Destruction
Dark
Reversion
Vegetative
(Non-Flowering)
(Slow)
Reproductive
(Flowering)
Long-Day Plants Need Low Pr!
MidSummer
Sunlight
660 nm
740 nm
Pr
Red Light
(Fast)
Far Red Light
Synthesis
Pfr
Destruction
Dark
Reversion
Reproductive
(Flowering)
(Slow)
Vegetative
(Non-Flowering)
Short-Day Plant Need Low Pfr!
Winter
Far Red
Light
660 nm
740 nm
Pr
Red Light
(Fast)
Far Red Light
Synthesis
Pfr
Destruction
Dark
Reversion
Reproductive
(Flowering)
(Slow)
Vegetative
(Non-Flowering)
Short-Day Plant Need Low Pfr!
Long
Night
660 nm
740 nm
Pr
Red Light
(Fast)
Far Red Light
Synthesis
Reproductive
(Flowering)
Dark
Reversion
(Slow)
Pfr
Destruction
Vegetative
(Non-Flowering)
Short-Day Plants Need Low Pfr!
Black Cloth
660 nm
740 nm
Pr
Red Light
(Fast)
Far Red Light
Synthesis
Dark
Reversion
Reproductive
(Flowering)
(Slow)
Pfr
Destructio
n
Vegetative
(Non-Flowering)
Short-Day Plants Need Low Pfr!
Night Break
660 nm
740 nm
Pr
Red Light
(Fast)
Far Red Light
Synthesis
Pfr
Destruction
Dark
Reversion
Reproductive
(Flowering)
(Slow)
Vegetative
(Non-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
(ShortNight)
24-hour day cycle
Critical day length
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
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.
Plants 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?
Red
absorbed
by other
plants.
Far red reflected
from 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
Phytochrome has 2 forms
• Red-absorbing phytochrome
Pr
• Far red absorbing phytochrome
Pfr
Pr
Pfr
• Interconverted
• Two forms of the same compound
• Total amount same
In red light
Prfr
Pr absorbs red light,
changes to Pfr form.
Pfr
Pfr doesn’t absorb red
light, stays the same.
In far red light
Pr
Pr doesn’t absorb far red
light, stays the same.
Prfr
Pfr absorbs far red light,
changes to Pr form.
In pure light
Pfr
In pure red light,
all the phytochrome
ends up in the Pfr form.
Pr
In pure far red light, all the
phytochrome ends up in the
Pr form.
Sunlight
Mostly red
A little far red
In sunlight
Pfrr
Pfrr
Pfr
Pfrr
Pfr
Pfr
Pfrr
Pfr
Pr
Pfr
Pfrr
Pfrr
Prfr
Pfr
Pfr
Pfr
Pfrr
Prfr
Pfrr
Pfr
In sunlight most P gets converted to Pfr form.
Start of night
Most P in Pfr form.
Pfrr
Pfrr
Pfr
Pfrr
Pfr
Pfr
Pfrr
Pfr
Pr
Pfr
Pfrr
Pfrr
Prfr
Pfr
Pfr
Pfr
Pfrr
Prfr
Pfrr
Pfr
In the dark
Pfr form changes gradually to Pr form.
Pfrr
Pfr
Prfr
Pfr
Pfr
Pfrr
Prfr
Pfrr
Pr
Pfr
Pfrr
Pfrr
Prfr
Pfr
Pfr
Prfr
Pfrr
Prfr
Pfrr
Prfr
After a short night
Pfr still left.
Pfrr
Pfr
Prfr
Pfr
Pfr
Pfrr
Prfr
Pfrr
Pr
Pfr
Pfrr
Pfrr
Prfr
Pfr
Pfr
Prfr
Pfrr
Prfr
Pfrr
Prfr
LDP = SNP
• Needs short night
• Needs Pfr still present at end of night
• Pfr promotes flowering for LDPs
Later in the night
More Pfr changes to Pr.
Pfrr
Prfr
Pfr
Pfr
Pfr
Pfrr
Pfr
Pfrr
Prfr
Pfrr
Prfr
Pfrr
Pfr
Pfr
Pr
Prfr
Pfrr
Prfr
Pfrr
Prfr
After a long night
All the Pfr is gone.
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Pr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Day dawns
Pfrr
Pfrr
Pfr
Pfrr
Pfr
Pfr
Pfrr
Pfr
Pr
Pfr
Pfrr
Pfrr
Prfr
Pfr
Pfr
Pfr
Pfrr
Prfr
Pfrr
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
Specific flowers at specific times.
May
June
September
July
August
October
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/by220indy/physical_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%2
0lecture.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/BlueCo
urseGreen_01/Blue_Course_Green.ppt
• http://siri.uvm.edu/ppt/warmweatherrinjuries/warmweatherrinjur
ies.ppt
•
http://www.cobb.k12.ga.us/~dickerson/ch%2016.ppt