Plant Physiology
Dr. Kneeland Nesius
MGB Room 108C
683 4193
knesius@odu.edu
Prokaryote cell
type: lacking many membrane structures: nuclear
membrane, E.R., mitochondria, chloroplast, etc; replicate by binary fission
Heterotrophic nutrition eubacteria
Autotrophic nutrition cyanobacteria
Eukaryote cell type:
advanced cell type (contain many types of membrane organelles); replicate
by mitosis
heterotrophic - animals, fungi, protistia (ameoba)
autotrophic - plants, protistia (algae)
Kingdoms
Archaebacteria (prokaryote),
Eubacteria (prokaryote),
Protista (eukaryote)
Plantae (eukaryote)
Fungi
(eukaryote)
Animalia (eukaryote)
Types of Plants:
Moss and Ferns- no seeds, fruit nor flowers- spores used for DNA distribution.
Gymnosperms (pine trees)- seed present, no fruit or flowers, seeds formed in cones, seeds used for DNA distribution.
Angiosperms (flowering
plants)- seeds, fruit, flowers present. Fruit and seeds are
used for DNA distribution.
Plant Cell Types
Meristematic - Apical meristems, vascular cambium, cork cambium
Parenchyma
Collenchyma
Sclerenchyma
Epidermis
Cork
Vascular Tissues: Transporting Tissue
Xylem- conducts water and solutes
Phloem conducts photosynthates
Plant Cells -
Unit Membrane
phospholipid bilayer with protein integral and peripheral
(selective absorption, specific recognition sites) page 8 in text
Membrane Bound Organelles
Nucleus (nuclear membrane, pores, chromatin, nucleolus - ribosome synthesis)
Heterochromatin (10%), Euchromatin (90%)
Review transcription and translation in text page 11
E.R. Smooth(secrete non protein) and Rough (secrete protein SRP receptor)
Golgi Apparatus (trans cisternae and cis cisternae), secretory vesicles
secrete non cellulose polysaccharides and glycoproteins (pectin
and hemicellulose)
Vacuoles (tonoplast)
Mitochondria cristae, lumen, inner and outer membranes (cristae, matrix
-
permeable to H+ protons) catabolic reactions, site of aerobic respiration,
breakdown of energy rich molecules forming biological energy ATP.
Plastids: Chloroplasts anabolic reactions, organelle
where photosynthesis occurs -
formation of energy rich molecules utilizing light energy.
Amyloplasts (Leucoplast) - stores starch,
Chromoplasts - contain colored pigments embeded in membranes
(thylakoids, stroma, nucleoid DNA)
Plastids are interconvertible - proplastids, etioplasts, prolamellar
bodies
Protochlorophyll - Chlorophyll
Mitochondria and Chloroplasts are semiautonomous Binary Fission, prokaryote
ribosomes
Microbodies:
Peroxisomes - removes hydrogen from organic molecules
forms hydrogen peroxide, photosynthetic cells
Glyoxysomes - converts fats into glucose via glyoxylate cycle
Oleosomes - store oils
Nonmembrane Bound Organelles
Ribosomes
Cytoskeleton consists of microtubules and microfilaments
Cell Wall - primary and secondary (review secondary cell wall of
vascular tissue)
(Consists of cellulose, pectins, hemicellulose and lignins)
Using web pages look up the structure of these compounds.
polycellulose polymers form microfibrils
Primary cell wall ( 25% cellulose, 25% hemicellulose, 35% pectins)
Present in all plant cells
Secondary (40% cellulose, 35% hemicellulose, 20% lignin)
Present in selected cells
Plasmodesmata Primay and Secondary ER, desmotubule
Symplast living part of a plant cell - cytoplasm
Apoplast - nonliing partof a plant cell - cell wall and intrcellular spaces
How Cell Walls Form
Cell division cell plate forms via microtubules - middle lamella laid down by golgi bodies deposited by vesicles.
Cell membrane forming
between the two cells comes from the vesicles depositing cell wall material.
Pectins are the
most soluble of the cell wall polysaccharides: This will act as the glue
in the middle lamella holding the two newly formed cells together.
Charged carboxyl
groups linked via Ca+2 ions will condense the pectin molecules. In the
laboratory on mineral nutrition calcium will be one of the essential elements.
Without this element plant cells can not divide. Why?
Primary cell wall laid down in the matrix being formed by the golgi secretions above.
Microfibrils will become embedded in the polysaccharide matrix (hemicellulose and pectins).
See figure with rossette given out in class.
Review (matrix formed in golgi, vesciles)
Cellulose microfibrils are synthesized at cell membrane.
Rossettes embedded in cell membrane contain many cellulose synthase.
After cell wall expansion, secondary cell walls, form in some plant cells.
More cellulose microfibrils which are aligned parallel to each other
Phenolic polymer, lignin, present
Seed Germination
Young forming seeds are in a quiescent state.
Quiescent - provide a satisfactory temperature, oxygen level, water germinate and grow
Seed
Dormancy - provide a satisfactory temperature, oxygen level, water
will not
germinate and grow
Read the handout on seed dormancy attaced to the first laboratory exercise.
Were your seeds in the laboratory dormant or quiescent?
Seed
Coat Dormancy - seed coat must be broken before embryo can grow.
example - persimmons must pass thrugh animal's gut
and expelled in feces, breaking down the seed coat, so
the embryo can grow
Embryo
Dormancy
Primary Dormancy seed with embryo must mature before growing
Induced Dormancy
1. after ripening - period of time for embryo matures and grows
2. Chilling - Stratification - seed must undergo a damp cool period
3. Light stimulates seed germination
Two Hormones
involved - 1. ABA (abscisic acid) inhibits seed germination
Example fruit contains ABA which prevents
seeds from germinating inside fruit
2. GA (gibberellic acid) stimulates seed germination
Synergic effect of two hormones Both hormones work together
What happens
when seeds are provided with water, oxygen at optimal temperature?
Imbibition -
Hydrate organelles
Activates Enzymes Present
Activates Enzyme Synthesis
Translocation of macromolecules
Respiration - provides ATP -energy
Activates Mitosis and Growth/Development
Chemical Composition
of Specific Seeds of Economic Importance - Chart given
out in lecture -
Activates Enzyme Synthesis
Translocation of macromolecules
Respiration - provides ATP -energy
Activates Mitosis and growth
Chemical Composition of Specific Seeds of Economic Importance - Chart given out in lecture-
Species
Family
Nature of
Percent Content
Reserve tissue Carbohydrate
Protein Lipid
_________________________________________________________________________
Maize
Gramineae Endosperm
51 - 74
10
5
(Zea mays)
Wheat
Gramineae Endosperm
75 80
13
2
(Triticum
vulgare)
Pea
Legum
Cotyledon
34 45
20
2
(Pisum sativum)
Peanut
Cotyledon
12 33
20 30 40 - 50
(Arachis
hypogaea)
Soybean
Cotyledon
14
37
17
(Glycine
sp)
Difference
in Composition of Soluble Nitrogen - Chart give out in class -
Note - Aspartic Acid, Glutamic Acid,
Glutamine, Asparagine
Amides nitrogen transporters
Parts of Seed
- endosperm, scutellum, cotyledon,
Changes in seeds during germination - Charts given out in class -
Movement of various macromolecules
Endosperm or Cotyledon translocated to growing axis.
Protein
-> amides ------->
Protein or Nucleic Acids
Protein
-> organic acids + ammonia -------> Protein or Nucleic Acids
Carbohydrates
-> glucose or sucrose -->
Carbohydrates, Lipids, Respiration
Lipids -> Organic Acids
-->
Carbohydrates, Lipids, Respiration
Roots (radicle) will begin the uptake of inorganic nutrients (elements) from soil.
Root structure - longitudinal section
from class or in book
See Figures In Text
corn and rice
- ammonium uptake at apex
barley calcium
uptake at apex
corn iron taken
up at apex or region of elongation
potassium, nitrate,
ammonium and phosphate absorbed freely at all locations
Mycorrhizal fungus improves uptake
phosphate
See Figures In Text
Inorganic elements present in plants -
handout given out in class
How do you determine which inorganic nutrients are essential?
Hydroponic growth system -
Water Culture or Sand
See Figures In Text
Macroelements - greater than 10 ug/g dry weight
N,Ca,K,Mg,P,S,Si
Microelements - less than 10 ug/g dry weight
Cl, Fe, B, Mn, Na, Zn, Cu, Ni, Mo
Essential elements required for growth - chart
1. Organic Molecules Structure CHNOP
2. Energy storage P in ATP
3. Ionic form K, Ca, Na
4. Redox reactions Fe, Cu
See Chart In Text
Hoaglands solution Contains essential elements
(1) in optimum concentration (2)
What were some of the forms of nitrogen in Hoagland's solution?
See Chart In Text
Chelating Agents form soluble complexes with insoluble
ions - EDTA or DTPA
Fe+3 insoluble, Fe+2 soluble
See Chart In Text
Did you use chelators in the laboratory?
Influence of pH on uptake of minerals
See Chart In Text
What was the pH of the solutions you made in the laboratory?
Relationship between growth and nutrient content
Chart: Deficiency zone, Adequate zone, Toxic zone, Critical concentration
See Chart In Text
Mineral elements classified on the basis of their mobility within a plant and the ability to retranslocate during deficiencies
Mobile Immobile elements
N, K, Mg,
Ca, S, Fe, B, Cu
P, Cl, Na,
Z, Mo
Activation of cell respiration:
See Class Handout "respiration rate various times during
germination"
Substrates for cellular respiration must be made available in the cotyledon.
Starch : polymers of glucose (alpha 1,4 linkage), straight chains
Amylopectin : polymers of glucose (alpha 1,4 linkage), branching (1,6 linkages)
Beta amylase nonreducing end
Alpha amylase interior part of starach
How did you measure amylase in the laboratory?
Starch phosphorylase - form glucose phosphates
Debranching enzyme breaks the 1, 6 linkage
Respiration - Oxidation of energy rich molecules (C6H12O6
) to energy poor molecules (CO2 and H2O)
with the energy being transferred into biological usable energy (ATP).
How and what substrates or products did you measure for detrmination of
respiration in the laboratory?
Glucose contains 686 kcal mol-
Aerobic Respiration Oxygen used during the process
Overall Equation:
36 ADP + 36 Pi + C6H12O6 + 6 O2 --------> 6 CO2 + 6 H2O + 36 ATP
Anaerobic Respiration Oxygen is not used during the process
Overall Equation:
2 ADP + 2 Pi + C6H12O6
--------> 2 CO2 + 2 C2H5OH
+ 2 ATP
Divided into three set of reactions:
Glycolysis, Citric Acid Cycle (TCA), Kreb
Cycle, and Cytochrome Electron Transport
System
Coenzymes used during these processes:
ATP Undergo hydrolysis to form ADP (structural formula)
NAD+ reduced to NADH (structural formula)
FAD reduced to FADH2 (structural formula)
Study Figures in Text
Cyclic Phosphorylation (how ATP is used as an energy source)
ATP + H2O ----------> ADP + Pi - 7.3 kcal mol-
Glucose ----------------> Glucose - 6- phosphate + 4.0 kcal mol-
Glucose-6-phosphate + Fructose ------> Sucrose + Pi
ADP + Pi ------------------> H 2O + ATP
+ 12 kcal mol-
Substrate Phosphorylation - acquire energy directly from a substrate - explain and give examples
Oxidative Phosphorylation - acquire energy through NAD being
reduced and then oxidized through the cytochrome system
explain and give examples
Glycolysis (cytosolic/plastidic processes)
The energy
conserving phase occurs in the cytoplasm; however, some of the substrates
forming during the initial
phase come
from plastids.
Examine the Figure in Text Concerning Glycolysis
SUMMARY BELOW
Glucose (6carbons) 686 kcal mol-
INITIAL PHASE
2 ATP -------------->
2 ADP
Fructose 1,6 biphosphate
ENERGY CONSERVING PHASE
PGAl PGAl
NAD+ ------- > NADH NAD+ ------- > NADH
PGA PGA (biphospoglycerate)
2 ADP ------> 2 ATP
2 ADP ------> 2 ATP
PEP PEP
Pyruvate (3carbons) Pyruvate(3 carbons)
Focus
on the carbon skeletons and amount of bioological energy being made available
during this pathway.
Initial Phase - Substrates from different sources are channeled into triose phosphates
Energy Conserving Phase Triose phosphate converted into pyruvate
Enzymes kinases and dehydrogenases identify where these occur
For each NADH coenzyme formed approximately 2 ATP may be generated via cytochrome
2 oxidative phosphorylation Identify location in pathway.
4 substrate phosphorylation
Total ATP = 8; Net ATP = 6
7.3 kcal mol- per ATP
43.8 kcal mol- / 686 kcal mol- X
100% = 6.4%
Glucogenesis formation of glucose through reversal of glycolytic pathway.
Not all steps are reversible.
STOP FOR EXAM 1
Reduction of pyruvate = fermentation - use up the
reducing power (NADH) formed
No oxygen required
Total ATP = 4; Net ATP = 2
7.3 kcal mol- per ATP
14.8 kcal mol- / 686 kcal mol- X 100% = 2.2%
Energy values and carbon skeletons
Examine
anaerobic equation above.
GLYCOLYSIS SUMMARY
CARBON SKELETONS
Initial substrates carbohydrates form triose phosphates.
Final products pyruvic acids - two/glucose
ENERGY TRANSFORMATION
four substrate phosphorylation/glucose
two oxidative phosphorylation/glucose
Gluconogenisis - Review
Pyruvate
Two options: 1. Low Oxygen (hypoxic/ anoxic)
Pyruvate is reduced forming CO2 + ethanol
(fermentation/ anaerobic respiration)
carbon skeletons/ energy net 2 ATP/glucose (no net NADH)
2. Ambient oxygen slightly lower or higher
Pyruvate is oxidized forming CO2 and water
(aerobic respriation)
Kreb Cycle/ TCA Cycle enzymes located in mitochondrion
Review semiautotomous organelles (DNA + ribosomes)
Enzymes are genetically coded by nuclear and mitochondria DNA
Examine the Figure in Text Concerning Kreb Cycle/TCA
Cycle FIG. 11.6
Enzymes are located in matrix of mitochondria
TCA SUMMARY
CARBON SKELETONS
Initial substrates pyruvic acid from cytosol.
Final products carbon dioxide and water
Carbon skeletons
- citrate, oxoglutarate, succinate , malate,
oxalate (OAA)
ENERGY TRANSFORMATION
one substrate phosphorylation/
Kreb Cycle (2 per glucose)
oxidative phosphorylation/
coenzymes 4 NADH (3ATP/NADH), 1 FADH2 (2
ATP/FADH2),
Total ATP = 15 per TCA
2 TCA per glucose; 6 per glycolysis = 36 ATP
7.3 kcal mol- per ATP
262.8 kcal mol- / 686 kcal mol-
X 100% = 38.6%
Examine the Figure in Text Concerning Kreb Cycle/TCA Cycle FIG. 11.6
Alternative pathways in plants - (A) malic enzyme
(B) PEP carboxylase and malate dehyrogenase
(C) Malate is stored in vacuoles
Examine Handout Given Out
in Class FIG. 11.7
Electron Transport System converts energy of reduced NADH and FADH2 into ATP
Involves membranes of mitochondria to form a proton gradient to run a proton pump (chemiosmotic hypothesis)
1. Electron Transport Chain will Catalyze a Flow of Electrons from
NADH to
Oxygen
Involves oxygen as end acceptor for hydrogen ions
Involve cytochromes to transport electrons
2. Involve ATPase
F factor (F0F1)
Examine the Figure in Text Concerning Cytochrome Electron Transport System
and ATP synthase FIG. 11.8
Oxidation of NADH and FADH2 can be uncoupled from oxidative phosphorylation
Inhibitors
Cyanide inhibits cytochrome oxidase
DNP dinitrophenol uncoulpler
How the substrates of glycolysis and citric acid cycle were determined.
C-14 labeling experiment
uniform labeling and specific labeling of carbon
continuous labeling experiment
pulse labeling experiment
Reactions of the oxidative Pentose Phosphate Pathway (cytosol)
(15% of ATP generated in some tissue)
1. Produces
NADPH energy source
2. Produces ribose- 5-phosphate
3. Erythrose-4-phosphate
(4 carbon) Forms with PEP to form phenolic
compouds (lignins) and aromatic amino acids
Examine the Figure in Text Concerning Oxidative Pentose Phosphate Pathway (PPP) FIG. 11.4
Cyanide- Resistant Pathway
Regulation of Respiration -
Phosphofructokinase
Pyruvate kinase (ATP)
PEP
ATP/ADP ratio
Examine the Figure in Text Concerning Control of Glycolysis,
Kreb and CETS FIG. 11.13
Mitochondrial Genome encodes many respiratory subunits.
MtDNA divided into two groups
A. translation components (tRNA, ribosome
proteins, rRNA) and B. oxidative phosphorylation complexes.
Nuclear DNA encodes citric acid cycle enzymes
Whole plant and tissue respiration.
Plant may respire over half of daily photosynthetic yield
Organs and Tissue vary is respiration rates
Effects of Temperature
Q10 = 2 between 0 and 30 centigrade
Climacteric Effect plant parts (fruits, leaves, etc) before they
senesce
the respiration rate greatly increases.
What would a graph showing the climacteric effect look like?
Pasteur Effect High concentrations of oxygen inhibits glycolysis
Carbon Dioxide has a limited direct inhibitory effect on respiration
3 - 5 % carbon dioxide slows down aerobic respiration.
Photosynthesis - Reduction of energy poor
molecules (CO2 and H2O) to energy rich molecules ( C6H12O6)
with the energy being transferred from light which is absorbed by chlorophyll
pigments. Oxygen is given off as a product.
Glucose contains 686 kcal mol-
Joseph Priestley - oxygen gas is produced during photosynthesis
Overall Equation: 6 CO2 +
6 H2O + 62 ATP + 36 NAHPH + H - -------->
62P + 36 NADP + 72H + 62 ADP + 62 Pi + C6H12O6
+ 6 O2
(chlorophylls a and b)
Light - 9 to 10 photons red and blue
1937 Robert Hill - Isolated chloroplast + iron salts
(ferric) - oxidants
Placed in light:
4 Fe+++ + H2O -----------.
Fe++ + O2
+ 4 H+
Hill reactions: Oxygen is cleaved from water.
We now know that the electron acceptor is the coenzyme:
NADP + H+ ------------------.> NADPH2
Review structure presented earlier
PPP pathway
Light Saturation Point Curve see graph below
Plot light intensity against photosynthetic rate
Examine Handouts From Class
Light compensation point. See graph below:
Examine Handouts From Class FIG. 9.8
Blackmans Curves
Examine Handouts From Class FIG. 7.8
These curves demonstrate there are two sets of reactions:
light reactions (Hill reactions, light dependent) and
dark
reactions (Calvin Cycle, light independent).
Absorption and Action
Spectrum (describe differences)
Examine Handouts From Class FIG. 7.8
Far Red Drop-off
Examine Handouts From Class FIG. 7.13
1957 Emerson Enhancement Effect - Demonstrates
two Photosystems PS I and
PS II
Exlplain why?
Photosystem I:
11 polypeptides (6 formed by nucleus/ 5 formed by chloroplast genome)
Pigments - 2 chlorophyll "a"
(P700) to 130 chlorophyll "a"
16 beta carotenes
-
(core antenna + reaction center)
Quinones
-
(carriers)
Associated with:
Ferredoxin (FE/S protein carrier)
FAD, NADP
Ferredoxin - NADP oxido - reductase
Light Harvesting Center I - accessory light gathering
Protein Kinase -
maintain light balance between PS I and PS II
80 - 120 chlorophyll molecules (3 chlorophyll "a" / 1 chlorophyll "b"
Spans the entire membrane and permanently attached to PS I
Photosystem II:
20 polypeptides
Pigments -
2 chlorophyll Aa@ 680 to 50 chlorophyll Aa@
Smaller number
of carotenes
(Core antenna)
Z (electron carrier forms water)
Quinones Q-A
(primary electron acceptor)
Pheophytin
Associated with:
Q-B carrier
________
Plastoquinone
!
Cytochrome b6
! Electron transport
system
Fe/S carriers
! Linking PS
I , PS II
Cytochome f
!
Plastocyanine (Cu+ )
________!
Water spliting complex --------
O2 split from water
Consisting of 3 polypeptide + Mn H2O
-----> 2H + 2 O2
Light Harvesting complex - II -
antenna
8 chlorophyll "a"/ 7 chlorophyll "b", carotenoids
50% of chlorophyll "a" and 75% of chlorophyll "b" located in LH II
Spans the entire membrane but not permanently attached
CF - 1 particle Photophosphorylation
Polypeptide with CF - 1 head (ATP ase_, CF tail (channel through membrane)
Protons moving through channel will drive force to synthesis of ATP
Photophosphorylation is
different from substrate and oxidative phosphorylation
Light Dependent Reactions include:
PSI, PS II, Photophosphorylation (ATP synthase)
ATP formed by chemiosmotic mechanism
These reactions are located in the membranes of the thylakoid membranes
Chloroplast consist of stroma, grana lamellae, stroma lamellae
Examine Handouts From Class or Figure in Text FIG.
7.15, 7.16
Z scheme (PS II linked to PSI via cytochrome system)
Examine Handouts From Class or Figure in Text FIG.
7.14
This system of electron transfer will pump protons from stroma side
the membrane to the lumen side of the membrane.
Water is oxidized to oxygen to conserve the flow of electrons.
This proton gradient will allow the ATP synthase to form ATP
Examine Handouts From Class or Figure in Text FIG.
7.33
Light absorbing antenna funnels energy to reaction center.
Light Harvesting complex proteins LHC II associated with PS II
Light harvesting complex proteins LHC I associated with PS I
resonance transfer -mechanism for light energy absorbed by chlorophylls
a and b; carotenoids to be conveyed to reaction center
Examine Handouts From Class or Figure in Text FIG.
7.19
Both red and blue light may be absorbed by chlorophyll but the energy
level must be reduced to that of 700 or 680 to drive electrons through
the series of electron carriers (Z scheme).
Summarize:
Red and blue light may be absorbed by both chlorophylls or other pigments (carotenoids) by LHC II or LHC I.
The energy levels are funneled down to either the P680 or P700 reaction centers by resonance transsfer.
Photosystem II oxidizes water to oxygen in the thylakoid lumen and in the process releases protons into the lumen.
Cytochrome b6f receives electrons from PSII and delivers them to PSI. It also transports additional protons into the lumen from the stroma.
Photosystem I reduces NADP to NADPH in the stroma by the action of ferredoxin (Fd) and the flavoprotein ferredoxin NADP reductase.
ATP synthase produces ATP as proton diffuse back through it from
the lumen into the stroma.
Review Z scheme Electrons flow through PSII, Cytochrome, PSI utilizing red light to eject electrons into higher state, eventually forming reduced coenzyme (NADPH) and ATP
This represents a noncyclic electron flow.
PSII is predominately in stacked regions of thylakoid membrane
PSI and ATP synthase is predominately located in unstacked regions (stroma)
Cytochrome b6f dimer is evenly dispersed through all membranes
The ratio of PSII : PSI is about 1.5:1
See Figure in Text FIG. 7.18
In the stroma region of the membrane where PSI and cytochromes complexes
are found, the electron flow may flow from PSI back to cytochrome forming
only ATP and no NADP.
This represents the cyclic electron flow. This will function
in cells which require higher levels of ATP . Bundle sheath
cells.
Some herbicides block this electron flow of electrons:
DCMU -blocking electron flow at cytochrome
Paraquat hydrogen acceptor
LHCII antenna complex
See Figure in Text FIG. 7.20
Carotenoids serve as photoprotective agents
These molecules can quench (dissipate extra electron
exicitation energy)
Thylakoid stacking allows a balance between PSI and PSII
by protein kinases that phosphorylating threonine residues on LHCII.
Control of Light Reactions which in turn control the rate of the Dark Reactions
Organization of protein complexes of thylakoid membranes
(Refer to Handout From Class)
PS II located in stacked region
PS I and ATPase located in unstacked
Cytochrome are evenly distributed
PS II activated results in reduced plastoquinone activates a protein kinase which phosphorylates PSII LHC
Electrostatic repulsion into unstacked region
PS I activated results in oxidized plastoquinone phosphatase is activated which remove phosphates from LHCII
migrate back
Refer to Handout from Class
Where is oxygen produced?
Where is NADP reduced?
Which light is used to drive reaction centers?
Main product of light dependent reactions: ATP, NADPH + H,
Oxygen gas is byproduct.
6 CO2 + 6 H2O + 62 ATP + 36 NAHPH + H - --------> 62P + 36 NADP + 72H + 62 ADP + 62 Pi + C6H12O6 + 6 O2
6 CO2 + 6 H2O
+ 18 ATP + 12 NAHPH + H
- --------> 62P + 36 NADP +
18 ADP + C6H12O6 + 6
O2
(chlorophylls a and b)
Light - 9 to 10 photons
Labeling Studies using C14 bicarbonate
Chromatogram and Radioautograph
Refer to Handout from Class
C14 bicarbonate labeling studies indicated that PGA as the first
product formed.
Refer to Handout from Class
Look for a two carbon compound
Percent Radioactivity in Each of Three Carbons of PGA at Various Times
Carbon atom of PGA 1 minute 10 minutes 20 minutes 60 minutes
1
82
70
50
33
2
9
15
25
33
3
9
13
24
33
Light - Dark changes in concentration of PGA and RuBP
(chart)
Refer to Handout from Class
Test tube containing chloroplast, C14 bicarbonate, NADPH, ATP
exposed to light
C14 fixed into glucose
Test tube containing chloroplast, C14 bicarbonate, NADPH, ATP
placed in dark
C14 fixed into glucose
Test tube containing chloroplast, C14 bicarbonate, NADP, ATP
placed in dark
C14 not fixed into glucose
Test tube containing chloroplast, C14 bicarbonate, NADP, ATP
exposed to light
C14 fixed into glucose
Since PGA (3 carbon organic acid) was formed this is known as the
C-3 pathway.
SUMMARY OF THESE EXPERIMENTS
PGA and Ribulose Bisphosphate were heavily labeled.
The carbon in PGA is recycled.
NADP is reduced during the light reactions.
Carboxylation of Ribulose Biphosphate is catalyzed by Rubisco.
Three stages: Carboxylation Rubisco used
Reduction - triose phosphates are formed
ATP and NADPH from light reactions are utilized
reactions occur in stroma
Regeneration - regenerates Ribulose-1,5-Bisphosphate
reductive pentose phosphate pathway
(review oxidative PPP)
Refer to Handout from Class FIG.
8.3
Light-dependent enzyme activation regulates the Calvin Cycle.
Refer to Handout from Text FIG. 8.5
Light dependent ion movement (Mg) regulates Calvin Cycle
Refer to Handout from Text FIG.
8.6
Light dependent membrane transport regulates the Calvin Cycle
Trioses are transported into cytosol and converted
to sucrose (via glucose), transporter are activated by light
Hatch, Slack and Kortschack working with corn and sugar cane discovered
that the main product of photosynthesis in these plants was malate and
aspartate.
Refer to Handout from Class FIG.
8.10
The enzyme utilized is PEP carboxylase:
Phosphoenolpyruvate + Carbon Dioxide -------> OAA
OAA + NADPH + H --------> malate + NADP
This pathway became known as the C-4 pathway
Refer to Handout from Class
Kranz anatomy of Bundle Sheath Cells in these plants
Refer to Handout from Text FIG.
8.9
PEP Carboxylase - has a high affinity for water
found in mesophyll cells/ not in bundle sheath cells
Rubisco - found in bundle sheath cells only
Need a lot of carbon dioxide to perform optimally
Not only found in tropical grasses but found in monocots and dicots.
This system probably evolved in the region near the equator.
Crassulacean Acid Metabolism Succulent Species - Opuntia, Agave, Aloe, Crassula
CAM
Stomata of CAM Plants open at night and close during the day.
Diurnal Cycle
Refer to Handout from Class FIG.
8.12
(Chart)
Adaption to conserve water
C-3 and C-4 are temporally separated
Refer to Handout from Class FIG.
8.11
Photorespiration -
Refer to Handout from Class FIG.
8.7
(chart) light dark cycle and carbon dioxide compensation point
Involves cooperative interaction between three organelles - chloroplasts,
peroxisomes, and mitochondria
Competition for enzyme Rubisco and Ribulose 1, 5 - biphosphate
Found only in C-3 plants
Refer to Handout from Class FIG.
8.8
(chart) pathway
PHOTOSYNTHETIC CHARACTERISTICS OF THREE PLANT GROUPS
C-3
C-4
CAM
Leaf Anatomy
No Bu Sh. Bundle Sheath
No Bu. Sh.
Rubisco PEP carboxylase
PEP carboxylase
Carboxylating Enzyme
Rubisco in Bu. Sh. Rubisco
Transpiration Ratio (H2O/dry wt 450-950
250-350
18-125
increase)
CO2 Compensation Point
30-70
0-10
0-5 (dark)
umol/CO2
inhibition by 21% O2 Yes No Yes
Photorespiration Detection
Yes
Only Bu. Sh. Late
after-
noon
Dry Wt Increase (tons/
22
39
1
hectare/year
CONVERSION OF TRIOSES INTO SUGARS AND STARCH IN THE
CHLOROPLAST
Triose phosphates are converted into starch in
chloroplast
Starch synthase, phosphorylase
Triose phosphates are converted into sucrose in
cytoplasm
to be transported out.
Sucrose synthase
REFER TO FIGURES IN TEXT FIG.
8.14, 8.15
High cytoplasmic phosphate will favor chloroplast to release triose
phosphate -
sucrose is synthesized
Low cytoplasmic phosphate will prevent chloroplast from releasing
triose phosphate -
and starch is synthesized
Control of Sucrose Synthesis
Stroma - pH, Mg, NADPH conc., ATO
conc.
FIG. 8.14
PHYSIOLOGICAL AND ECOLOGICAL CONSIDERATIONS
5% of incident energy is converted into carbohydrates
REFER TO FIGURES IN TEXT FIG.
9.2, 9.4
Chloroplast movement and leaf movement can control light absorption
REFER TO FIGURES IN TEXTFIG. 9.5
Plants adapt to sun and shade
Shade Plants and Leaf location on plant
Shade leaves have more chlorophyll per reaction center and a higher chlorophyll b to a ratio.
REFER TO FIGURES IN TEXT FIG. 9.8
Sun Leaves have more rubisco and larger pools of xanthophyll
REFER TO FIGURES IN TEXT FIG. 9.9
Response of photosynthesis to light intensity
REFER TO FIGURES IN TEXT FIG. 9.8
C-3 plant Light Compensation Point, Saturation
point
Light limited, Carbon Dioxide limited
REFER TO FIGURES IN TEXT FIG. 9.20
Sun Plant
Shade Plant
REFER TO FIGURES IN TEXT FIG. 9.11
Sun Plant grown under sun or shade conditions
Xanthophyll cycle
REFER TO FIGURES IN TEXT FIG. 9.13
Carbon Dioxide Compensation point
REFER TO FIGURES IN TEXT FIG. 9.8
CAM plants Aphotosynthetic carbon assimilation, evaporation and stomatal
conductance@
REFER TO FIGURES IN TEXT FIG. 9.21
Carbon isotope discrimination in C-3 and C- 4 plants
Atmosphere contains 12C .98 : 13C .011 : 14C 10-8
Compare 13C/12C ratio to limestone located at various sites
Both plants discriminate against : 13C
C- 4 plants have less 13C than C-3 plants
Look at ratios of 13C/12C you can determine if it has come from a C-3 plant or C-4 plant.
Sugar Cane is a C-4; Sugar Beet is C-3
REFER TO FIGURES IN TEXT pp. 188
Nitrogen Metabolism -
N2, NO2, NO3, NH4, organic nitrogen (urea)
Nitrogen cycle - nitrogen fixation, nitrification, denitrification,
assimilaton, ammonification
REFER TO HANDOUT GIVEN OUT IN CLASS
Nitrogen fixation
Abiotic or Biotic
Haber Process forms ammonia - Abiotic
Free Living nitrogen fixers: Biotic
Cyanobacteria, Anabeana (heterocysts), Nostoc
Clostridium nonautotrophic
Symbiotic nitrogen fixers: Biotic
Rhizobia with legumes
Anabaena with Azolla (water fern)
Anaerobic
Nodule formation - leghemoglobin - bacteroids
Nitrogenase - reaction
N2 + 6e- + 12 ATP + 8 H+ -----> 2 NH4
+ 12 ADP + 12 Pi
REFER TO FIGURES IN TEXT FIG. 12.11 AND 12.12
Ammonia is toxic - export nitrogen
in the form of amides
(Asparagine and Glutamine)
Nitrification - conversion of ammonia into nitrates
Denitrification - conversion of nitrates into nitrogen gas
Ammoniafication - conversion of organic nitrogen into ammonia
Assimilation - conversion of ammonia and nitrates into organic nitrogen
Nitrate Assimilation- roots and shoots
Nitrate Reductase
REFER TO FIGURES IN TEXT FIG. 12.04 AND 12.05
Light enhances
Nitrite Reductase
REFER TO FIGURES IN TEXT FIG. 12.04 AND 12.05
Ammonium can be assimilated into organic amides
enzyme: glutamine synthatase
aspartate aminotransferase
glutamate synthatase
aspargine synthase
glutamate dehydrogenase
Transamination reactions - example
organic acid(1) + amino acid(1) transfer ketone group
for amine group to form
organic acid(2) + amino acid(2)
Glutamate + OAA --------> aspartate + oxoglutarate
aspartate aminotranferase
REFER TO FIGURES IN TEXT FIG. 12.6 AND 12.7
Lipid Metabolism - Oils in plants
Most lipids are in the form of Triacylglycerol
248
Fatty Acids and Glycerol
Common Fatty Acids (12 18 carbons)
REFER TO FIGURES IN TEXT FIG. 11.4 AND 1tABLES 11.3
AND 11.4
Stored in Oleosomes of seeds (cotyledons)
Used for membrane structure; chlorophylls,
carotenoids, etc
Fatty Acid Synthesis occurs in plastids
Cycle of two carbon additions
(Condensing enzyme)
Glycerol comes from PGAL from glycolysis or photosynthesis
REFER TO FIGURES IN TEXT FIG. 11.15 AND 11.16
Storage Lipids are Converted into Carbohydrates in Germinating Seeds
Three organelles - oleosome, glyoxysome and mitochondrion
Lipase hydrolyzes lipids into glycerol and fatty acids
Fatty acids are broken down into acetyl CoA molecules by Beta Oxidation
Acetyl Co A molecules are converted into succinate in
the glyoxysomes
(glyoxylate cycle)
Mitochondrion - succinate converted into malate
Cytoplasm - malate converted into sucrose
REFER TO FIGURES IN TEXT FIG. 11.18
SUMMARY
SYSNTHES OF GLYCERIDES
GLYCEROL IS SYNTHESIZED IN CYTOSOL FROM PGAL (GLYCOLYSIS)
FATTY ACIDS ARE SYNTHESIZED IN PLASTIDS
ACEYL CoA ENTER CYCLES OF TWO-CARBON
ADDITION
FATTY ACIDS + GLYCEROL UNDERGO CONDENSATION TO FORM TRIACYLGLYCEROL WATER IS LOST
LIPIDS ARE STORED IN OLEOSOME FOR LATER USE
OR FORMS MEMBRANE PHOSPHATE LIPID BILAYER
IF STORED (USUALLY SEEDS) IN OLEOSOMES, LIPIDS ARE CONVERTED INTO SUCROSE TO BE MOVED OUT
OLEOSOMES LIPIDS ARE HYDROLYZED WATER IS INSERTED AND MONOMERS OF FATTY ACIDS AND GLYCEROL ARE FORMED - LIPASE
GLYCEROL MAY BE FURTHER BROKEN DOWN BY BEING CONVERTED BACK INTO PGAL AND MOVING BACK INTO GLYCOLYSIS
FATTY ACIDS ARE CONVERTED INTO SUCROSE VIA :
BETA OXIDATION FORMING ACETYL CoA
GLYOXYLATE CYCLE FORMING SUCCINATE
KREB CYCLE FORING MALATE
GLYCOLYSIS IN REVERSE FORMING GLUCOSE
AND FRUCTOSE
SUCROSE SYNTHESIS
PHENOLIC COMPOUDS
PHENOLS
PHENYLALANINE IS THE MAIN INTERMEDATE IN BIOSYNTHESIS OF PLANT PHENOLICS
SHIKIMIC ACID PATHWAY CONVETS SIMPLE CARBOHYDRATES WHICH COME FROM GLYCOLYSIS AND PPP PATHWAY INTO PHENYLALANINE H
ERYTHROSE
4- PHOSPHATE FROM PPP
PEP
PHOSPHOENOLPYRUVATE FROM GLYCOLYSIS
Translocation (movement of photosynthates) in Phloem Tissue
( sieve tube elements)
Table 10.1
Companion cells aid the sieve elements alive, numerous plasmodesmata
ordinary companion cells, transfer companion cells and intermediary
companion cell
Phloem Sap is collected and analyzed
Table 10.2
Sugars are translocated in nonreducing form sucrose
Nitrogen in the form of glutamic acid and glutamine; aspartic acid
and asparagine
Photosynthates move from a source to sink (may be up or down, bidirectional)
Bulk Flow (Pressure Flow Model )
Figures
Source to Sink (involves active and passive transport mechanisms)
Apoplast nonliving part of cell - diffusion
Symplast living part of cell - plasmodesmata
ordinary companion cells contains plasmodesmata towards its
own sieve cell
sucrose moves from apoplast of mesophyll
into synmplast of companion
sucrose moves from symplast of companion
to symplast of sieve tube
transfer companion cells have fingerlike wall ingrowths increase
surface area of cell membrane;
these cells contain plasmodesmata towards its own sieve cell
sucrose moves from apoplast of mesophyll
into synmplast of companion
sucrose moves from symplast of companion
to symplast of sieve tube
intermediary companion cells have many plasmdesmata towards the mesophyll
cells
sucrose can move by symplast movement from mesophyll
source into sieve tube
Rates of movement exceeds rate of diffusion - 1 m/hr-1
Bidirectional movement of molecules is due to separate set of sieve
tubes
not individual cells
Low temperature have slight effect on translocation which indicate
energy requirement is small
Phloem Loading - from Chloroplasts to Sieve Elements
Triose from chloroplast to cytosol converted to sucrose
Sucrose moves to vicinity of sieve tube cell in smallest veins (short
distance transport)
Sieve element loading sugars move into sieve elements and companion
cells
Fig. 10.13
Movement from mesophyll to sieve elements via apoplast or symplast
Fig 10.14
Sieve Element Loading use a Sucrose Symport System
Fig. 10.16
Phloem Loading Specific and Selective
Polymer Trapping Model
sucrose combines with galactose forming raffinose
in intermediary cell, raffinose selectively moves into sieve element
Fig. 10.17
Symplastic uses plasmadesmata
Apoplastic uses sucrose - H Symporter
Movement though vascular tissue to sink is long-distance trasnport
Phloem unloading symplastic or apoplastic
Fig. 10.18
Transition of a Leaf from Sink to Source is gradual
Sink Strength is a Function of Sink Size and Sink Activity
Water and Plant Cells/ Water Balance of a Plant
Terms - Diffusion, Osmosis, Facilitative Diffusion, Active
Transport
Adhesion, Cohesion, Transpiration
pp 36 - 45
Fig. 3.6
Review the Mineral Nutrition Laboratory - nitrates, nitrites, and
ammonia in relation to moving out of the soil into the plant.
Uptake of water occurs at tips of roots - root hairs
Examine Figures 4.1, 4.2, 4.3 in text
Apoplast and Symplast (review definition)
Epidermis, Cortex
Endodermis with Casparian Strips (selective absorption) forces ions to move into symplast via active transport which is selective.
When water moves from apoplast to symplast passive
When minerals move from apoplast to symplast - active
Two types of tracheary elements in xylem: Tracheids
and Vessel Elements
Pits
Examine Figures 4.3,4.6 in text
Root Pressure -
Transpirational Pull - Adhesive and Cohesive Forces
Two factors effect transpirational pull - difference in water vapor concentration and diffusional resistance
See Figures Handed Out In Class
Examine Figures 4.10 in text
Roll of Stomatal Control
Two types of guard cells - kidney bean shaped and bulbous
ends - grass
Examine Figures 4.13, 4.15 in text
Transpiration ratio = moles of water transpired/ moles of carbon dioxide fixed
C-3 Plants = 500 (500 water lost/ 1 carbon dioxide fixed)
C-4 Plants = 250/1
fewer stoma
CAM plants 50/1
fewer stoma and sunken
Cavitation air bubble form in tracheary elements
Hollow trees, active xylem
Solute transport - Via of channels, carriers, proton
pumps
Examine Figures 6.14, 6.17 in text
Secondary Active Transport uses electrochemical potential gradients.
Examine Figures 6.9, 6.7 in text
Plants use Hydrogen ions or Calcium ions
Hydrogen ion pumping ATPase and Calcium pumping ATPases
Call these symports
Hormones - chemical mediators for intercellular communication
Synthesized at one location and mode of action occurs at a different location.
Small amounts required to stimulate a mode of action
Plant Hormones five classes (auxins, cytokinins, gibberelins,
abscisic acids, ethylene
Auxins - stimulates cell elongation place on one side of
stem and the stem bends
towards this direction
Natural Auxin is IAA Indol-3-Acetic Acid
Chart
Examine Figures in text
Quantified by : bioassay - coleoptile straight-growth test (detect small amounts)
Radioimmunoassay labeled antigen, antibody, precipitates
chart
Examine Figures in text
Biosynthesis occurs in leaf primodia, developing leaves and
developing seeds
Largest amount is at the shoot apex (stem tips)
Synthesized from the amino acid tryptophan
Examine Figures in text Chart 19.5, 19.6
Hydathodes auxin synthesis
GUS reporter gene with auxin-sensitive promoter
GUS stain blue - moves
towards sink and stimulates differentiation of xylem tissue
IAA is the biologically active form.
Conjugated IAA is inactive; stored in this form
(conjugated with glucose, inositol, amides, glycoprotein)
IAA is degraded to control development
(oxidative degradation)
Two subcellular pools of IAA: Cytosol and Chloroplast (.33)
IAA- does not cross membrane
IAA conjugates located in cytosol
Examine Figures in text
Auxin is transported polarly from shoots to roots
(requires energy, and is gravity independent)
Auxins move basipetally to the tissue below
Chemiosmotic Model explains polar auxin transport anionic
form of IAA move through auxin transport carriers concentrated
on basal end
Active and Passive movement
Chart
Examine Figures in text
PIN protein are carriers specifically transports IAA at basal ends of cells
These pin proteins are rapidly cycled to membrane.
Parenchyma cells of embryonic tissue meristiematic
region, region of elongation
IAA moves nonpolarly through sieve tube cells
of phloem
Levels of IAA in different regions of plants
Optimum concentration is 10-5, 10-6 M for stem tissue
Optimum concentration is 10-10, 10-12 for root tissue
Higher than this causes inhibition
Physiological Effects of Auxins
Cell Elongation
Auxin promote growth in stems but inhibit growth in roots
Auxin rapidly
increases the extensibility of the cell wall 5 to 10 fold in 10
minutes
Wall
loosening (protein) expansins breaks cellulose cross linkages
under acidic conditions.
Read pages 331 - 335
Acid Growth
Hypothesis - Auxin rapidly increases the extensibility of the
cell wall
and increases cell extension.
Activates H ion ATPases
Synthesizes H ion ATPases
Protein inhibitors such as cyclohexamide inhibits the cell wall
loosening.
Model for IAA induced H+ extrusion
Cessation of wall expansions is irreversible.
Secreted matrix polysaccharides are altered to form tighter complexes
De-esterfication of pectins leads to more rigid pectin gels
Cross linking of phenolic
groups in the wall makes for a more rigid cell wall
PHOTOTROPISM- Cholodny-Went Model
May be mediated by the lateral redistribution of auxin
19.26
Examine Figures in text
Production of auxin
Perception of unilateral light stimulus
(action spectrum indicates blue light,
flavoprotein is light receptor, kinase
activity)
Lateral transport
19.27
Examine Figures in text
GRAVITROPISM- Cholodny-Went Model
Involves lateral redistribution
of IAA
Gravity Perception Involves Amyloplasts
in Cells of the Starch Sheath and Root
Cap (statoliths)
19.30
Stems auxin stimulates cell elongation
Roots - more sensitive to auxin
Root Cap may play a role in the lateral redistribution of auxin
19.33
Auxin regulates Apical Dominance
Cytokinin and ABA also play a role in apical dominance
19.36
Auxin promotes formation of lateral roots and adventitious
roots
19.38
Auxin delays the onset of leaf abscission
Auxin moving from leaf blade prevent abscission
layer from forming
Auxin regulates floral bud development
Auxin promotes fruit development
Fruit set, Parthenocarpy
Auxin induce vascular differentiation
High auxin concentration stimulates xylem and phloem tissue to develop
Low auxin concentration stimulates phloem differentiation
GIBBERELLINS - GA3, GA1
Structure:
Bioassay: several, dwarf rice sheath
Synthesis controlled by genes since dwarf plants
are affected and
normal size plants are not affected by
GA
Gibberellins are synthesized via the Terpenoid
Pathway
GA synthesized in developing seeds (highest concentration)
and leaves (young)
GA may be conjugated to other organic molecules
glucose
Processes controlled by GA:
Photperiodism Day length effects flowering in some plants
GA is synthesized during long days
Bolting - Cabbage plants, rosette forms under short day, undergo
stem elongation and flowering only under long days.
Application of GA induces bolting.
20.9
GA stimulates stem growth in dwarf and rosette plants
(cell division and cell wall extensibility in internode
region) Compare to auxins: not polar, not at tips.
Stratification-
cold temperature required for germination of certain seeds
GA (exongenous) can replace this process in some seeds
Vernalization
- cold temperature required for flowering (vernalization)
GA (exongenous) can replace this process in some seeds
Winter wheat is a biennial, requires cold temperature to
flower. GA (exogenous) can overcome this process.
Gibberellins
regulate transition from juvenile to adult phases
woody species have different leaves, GA (exogenous) can induce Ivy to
revert from mature to juvenile forms.
Sex determination monoecious plants (corn) and dioecious plants spinach
GA (exogenous or endogenous 100 time more GA in tassel) causes male
flowers short days and cooler night induce tassels; spinach is
opposite
- staminate flower are produced when GA is added
Promote Fruit Set Parthenocarpic Fruit
Grapes Thompsons seedless grapes two treatmets 1st to induce
fruit
formation and 2nd to increase size
Malting Mechanism of Gibberellin Action: Mobilizing Endosperm Reserves
GA formed in embryo of cereal grains; induces alpha production
occurs in
aleurone layers; moves to endosperm where it breaks down
starch into sugar
which is mobilized out stimulating growth (germination)
GA stimulates transcription of alpha amylase mRNA
20.17
Cytokinins
Kinetin synthetic ; Zeatin natural
Purines
Fig. 21.3
Assays: Bioassay - radish seed cotyledon expansion bioassay performed in the laboratory
Immunological methods -
Synthesized in the root apical meristems, small amounts in young
leaves and shoot meristems
Transported through the xylem tissue
Main function - stimulates cell division in meristematic regions
and cambiums
Tumor induction by Agrobacterium tumefaciens
Crown Gall Disease
21.6
Ratio of auxin to cytokinin regulates morphogenesis in cultured plant tissue
low kinetin/ high auxin favor root differentiation, higher
kinetin/ lower auxin favor shoot differentiation
21.12 or table
Ti Plasmid and Plant Genetic Engineering
Page 631
Cytokinin Regulated Processes
Modify Apical Dominance and Promote Lateral Bud Growth
Cytokinins Delay Leaf Senescence
Cytokinins Promote Nutrient Mobilization
21.15
Cytokinins Promote Chloroplasts Maturation
21.16
Seeds germinated in the dark produce pale, spindly seedlings. etiolated
Expose a dim light to seedlings and chloroplasts will form. photomorphogenesis
Absorption/action spectrum indicates that red and far-red light is responsible.
Pigment responsible is phytochrome, a protein blue pigment common in etiolated parts of a plant.
Ethylene C2H4
Produced throughout the life cycle of the plant.
Abundant in young leaves and senescing organs
Ripening bananas
Synthesis starts with the amino acid methionine
Yang Cycle
Aminocyclopropane (ACC)
ACC may be conjugated
Stress and age induced
Auxin and cytokinin induced
Inhibited by Ag and carbon dioxide
Fruit Ripening Senescence (death) of fruit; breakdown of cells releasing organic acids
Classify fruits as: Climacteric Fruits banana and apples
Nonclimacteric Fruits grape cherry
Leaf epinasty
Stimulates flower senescence
Stimulates root hair formtion
Break seed dormancy
Induces Flower formation in pineapple
Enhances leaf abscission
Abscisic Acid Dormin
ABA
Biosynthesis occurs in plastids from
carotenoid intermediates
Inactivated by oxidation or conjugation.
Translocated through xylem and phloem (mostly phloem).
Physiological Effects of ABA
Maintains seed and bud dormancy, functions during
water stress (maintain desiccation tolerance).
Seed Dormancy controlled by ABA and GA.
Vivipary-
Immature embryos removed
from seeds develop right
away(precociously)
Accumulates in dormant seeds and buds
ABA closes stomata during water stress
1. Prevents stomatal opening by inhibiting inward
K ion channels and plasma membrane proton pumps
2. Promotes stomatal closing by activating outward
anion channels, thus leading to activation of potassium ionse
efflux channels.
Phytochrome Pigments
Seeds germinated in the dark produce pale, spindly seedlings. etiolated
Expose a dim light to seedlings and chloroplasts will form. photomorphogenesis
Absorption/action spectrum indicates that red and far-red light is
responsible.
Pigment responsible is phytochrome, a protein blue pigment common
in etiolated parts of a plant.
Lewis Flint demonstrated that the effects of red light (650 to 680)
is reversed by far-red light 710-740) in lettuce seed germination.
17.2
Several activities are controlled by photoreversible response.
17.1
Pr/Pfr model
17.3
Structure of Pr and Pfr
Pfr is the physiologically active form
Phytochrome synthesis involves phytochromobilin formed in plastids and a phytochrome apoprotein synthesized in the cytoplasm.
17.6
Distribution of phytochrome
Phytochrome responses can be distinguished by the amount of light required
VLFRs very low fluence responses are nonphotoreversible
LFRs low fluence responses are photoreversible
HIRs high fluence responses are propotional to irradiance
Table 17.2 and 17.3
Photoperiodism ability of an organism to detect
day length
Short Day Plants example Chrysanthem morifolium,
Xanthium strumarium
Long Day Plants example Spinach
Plants Monitor Day Length by measuring the length of the Night
Leaf is the Site of Perception of the Photoperiodic Stimulus
Phytochrome is the main Photoreceptor
Phytochrome regulates certain daily rhythms
circadian rhythms (nyctinasty in leaves pulvinus of legumes)