Final Flashcards
When does signal transduction occur
When an extracellular signalling molecule activates a specific receptor on the cell surface or inside of the cell
What does activation of a receptor in signal transduction cause?
A biochemical chain of events inside the cell, creating a response alters the cell’s metabolism, shape, gene expression, or ability to divide
The signal from signal molecules can be —— at any step
Amplified
Can one signal cause many reponses
Yes
What are the two types of signal transduction mutation
Signal hyposensitive mutations
Signal hypersensitive mutations
Signal hyposensitive (or insensitive) mutations
Signal but no response
Signal hypersensitive (or constitutive) mutations
No signal but response
How are forms and functions of multi-cellular organisms achieved?
By sophisticated communications among cells, tissues, and organs.
Chemical signals from one part of the body to another coordinate
Morphogenesis and physiology (interactions with environments) of plants.
Chemical messangers are _____
Hormones
Example of enviornmental or develepmental signal
Light, temperature, touch, hormone, nutrient
Example of receptor
Receptor kinase, G-protein-coupled receptor, F-box protein, ion channel
Example of signal transduction pathway
Repressor protein degration, protein phosphorylation, second messengers, (action potential/membrane voltage)
Example of signal transmission
Hormone transport, electrical signaling
Example of response
Transcriptional (gene expression), posttranslational (cytoskeletal, reorganization, enzyme de/activation)
What are the six major plant hormones?
Auxin
Cytokinin
Gibberellin
Ethylene
Abscisic acid
Brassinosteroid
What is Auxin (IAA) signal transduction
de-repression by protein degradation
What is cytokinin signal transduction
Prokaryote two-component system
What is gibberellin (GA) signal transduction
de-repression by protein degradation
What is ethylene signal transduction?
Prokaryote two-component system
What is abscisic acid (ABA) signal transduction
de-repression involving kinase and phosphotase
What is brassinosteroid signal transduction
de-repression involving kinase and phosphotase
What are the minor plant hormones
Strigolactone
Jasmonic acid
Salicylic acid
Plant hormone structures
Other than ethylene every hormone has at least one ring
What is a cotyledon?
An embryonic leaf of seed bearing plants
What is a hypocotyl?
The part of the stem of an embro plant beneath the cotyledon
What does the de-etiolation2 (DET2) mutation show?
A shortened hypocotyl and expanded cotyledons in dark.
What is the function of brassinosteroids?
Can stimulate stem elongation and cell division, was first isolated from the pollens of Brassica napus (rapeseed or CANOLA) in 1979 and thus named as brassinosteroid
What is etiolation?
A process in flowering plants grown in partial or complete absence of light
What does DET2 encode?
A reductase enzyme involved in the synthesis of brassinolide [human steroid (or isoprenoid) sex hormone-like molecule].
What do brassinolides play a pivotal role in?
Plant development, including cell elongation, skotomorphogenesis, germination, leaf senescence.
Where are brassinolides synthesized?
In the cytosol
The molecular cloning suggests that brassinolide is a ________
Necessary hormone for Etiolation
What is abscission?
The shedding of various parts of an organism, such as a plant dropping a leaf, fruit, flower, or seed
What does ABA negatively regulate
Seed germination
What hormone balance determines dormancy?
ABA:GA
What happens to ABA levels in drought conditions
Increase dramnatically to trigger signaling for stomata closure
What causes the stomata to close when ABA levels are increased?
Ca2+ which is used as a messenger to causes the physiological changes in stomata
Where is ABA synthesized?
Chloroplast
What molecule is ABA a breakdown product from?
C40 isoprenoid
How many of the 6 major hormones are isoprenoid?
Four
Where are C15, C30 synthesized?
Cytosol
Where are C10, C20, and C40 synthesized
Chloroplast
What did the first notion of auxin come from?
Darwin’s phototropism experiments
What does auxin mean?
To grow
What type of experiments proved the prensce of a chemical substance regulating cell growth
blue-light phototropism
What is the optimal concentrayion of auxin for cell elongation?
10^-6 to 10^-5
What is auxin consdiered in plants?
Morphogen
What is auxin?
Indole-3-acetic acid (IAA)
Several different bioactive auxins have been identified, but IAA is the most abundant and active auxin.
Where is auxin from?
Cytokinin
Cell division
Where are new cells supplied from?
Meristem cells (shoot and root)
What is plant tissue culture
Indefinite cultivation of plant cells in the medium containing sucrose, mineral salts, and vitamins, like we culture bacteria in the medium.
Plant tissue culture cannot be achieved by auxin alone because cells cannot divide, suggesting that cell-division promoting factor is required.
Two streams of research resulted in the identification of a chemical substance for cell division.
a) Screening various naturally occurring or synthetic compounds for cell-division activity.
- Bioassay-based screening, purification, structural elucidation, and chemical synthesis.
b) Studies of the crown gall forming bacteria - Agrobacterium tumefaciens.
- Molecular genetics and biochemistry
Chemical purification
Philip White discovered that coconut milk has a substance which supports the continued cell division of mature, differentiated cells. But the substance could not be purified.
In 1950s, Skoog identified that aged or autoclaved herring sperm DNA has a potent cell-division promoting activity. This substance was purified, and its structure was determined.
Adenine derivative. MS medium was named after his name (MS = Murashige and Skoog medium).
In 1973, Letham isolated a new cell-division promoting substance from the immature maize endosperm.
This is named Zeatin. Although several other zeatin derivatives were also found to be active in cell-division, zeatin is widely accepted as a dominant cytokinin in plant.
What is the dominant cytokinin in plants
Zeatin
Where is zeatin synthesized?
In chloroplast from ATP and DMAPP (dimethyl allyl diphosphate).
What is a key enzyme in zeatin biosynthesis?
IPT (Isopentenyl transferase)
What is fasciation?
An abnormal growth of plant tissues
What can an abnormal occurrence of apical meristems facilitate
The cell growth perpendicularly to the direction of main stem (or root) growth
Studies of Agrobacterium tumefaciens
A. tumefaciens can infect wounded tissues and alters plant cells to form tumor-like tissue (called a gall).
Infected plant cells continue to divide throughout the life-cycle of the plants, and form an entirely unorganized mass of tumor cells.
The gall was isolated and treated with 42 degree heat, which can kill A. tumefaciens but plant cells can survive this heat treatment. Then this bacteria-free gall could be cultured in hormone-free medium. -> undifferentiated callus tissue are growing forever, can it give a hint on cancer?
What does T-DNA encode genes for?
auxin, cytokinin, and octopine biosynthesis
Wht is suxin synthesized from?
tryptophan, and the modified cytokinin by bacterial enzyme.
What is octopine derrived from?
arginine and alanine, and no organism can utilize the octopine as a carbon source except A. tumefaciens.
What determines morphogenesis in cultured tissues?
Auxin:cytokinin
When auxin is high and cytokinin is low we see
only root growth
When auxin is low and cytokinin is high we see
Only stem/leaf growth
When auxin is intermediate and cytokinin is intermediate we see
no growth
_____, ______ and _______ play essential roles in plant genetic enegineering
Auxin, cytokinin and agrobacteria
Gibberellins (GA)
When purified GAs were applied to plants, a spectacular response in stem elongation was observed in dwarf and rosette plants.
Where is gibberellin synthesized?
In chloroplast, endoplasmic reticulum (ER) and cytosol.
At least ___ different GAs have been identified from different species
136
Seedless fruits can be made by either:
the fruit develops without fertilization (parthenocarpy), or pollination triggers fruit development, but the ovules or embryos abort without producing mature seeds (stenospermocarpy)
GA treatment can _______ the berry size and fruit stalk (pedicel) length,
increase
Synthetic ethylene and its analogs cause
Dramatic physiological changes in plants
Used to control the post-harvest ripening process of fruits.
coal gas resulted in _______ in trees around the street lamps.
defoliation
ripened fruit emits ________ to facilitate the ripening of the immature (unripen) fruit.
gaseous chemical
we can alleviate the post-harvesting problem if we ______
Can control either the endogenous ethylene biosynthesis or the ripening progress by an external ethylene treatment
What AA is precursor in ethylene formation
MET
Climacteric fruits
Show a steady respiration rise before the ripening, and then shows a spike of ethylene production immediately before the respiratory rise.
Sensitively responds to the externally applied ethylene. This is due to autocatalytic effect (or positive regulatory loop).
Non-climacteric fruits
Do not show the same pattern of respiration and ethylene production
Difficult to control
What is veraison
The onset of ripening in grapevine
Similarity between animal and
plant signal transduction
“Kinase” and “phosphatase” are important signal delivering components in both plant and animal.
What is the function of kinase
adds phosphates
What is the function of phosphotase
Removes phosphates
What does a kinase cascade do?
Amplifies signals
Difference 1 between plant and animal signal transduction
GPCRs are NOT playing any important role in plant signaling transduction.
What are G protein-coupled receptors (GPCRs) involved in?
Hormones, odors, flavors and light in animals
Difference 2 between plant and animal signal transduction
Plant signal transductions have evolved from both eukaryotic and prokaryotic ancestors.
What is one example of a prokaryotic signal transduction has been identified in plants
Crytochrome and two-component systems in plants
Difference 3 between plant and animal signal transduction
Signals can be sensed at many different subcellular sites in plants.
Where can signals be sensed in plants?
Brassinosteroid: Plasma-membrane.
Cytokinin: Plasma-membrane.
Red-light: cytosol.
Blue-light: Plasma-membrane (Phototropin).
Ethylene: Endoplasmic reticulum
Blue-light: Nucleus (Cryptochrome)
Blue-light: Chloroplast Thylakoid (Zeaxanthin)
Auxin: nucleus (SCFTIR1).
Difference 4 between plant and animal signal transduction
Inactivation of repressor protein (de-repression) is common in plant signal transductions.
What is ubiquitin
small regulatory protein (8.5 kDa), 4 genes in human
Role of Ubiquitin-activation enzyme (E1 enzyme):
Load (activate) an ubiquitin to E1 protein, 9 genes in human
Role of Ubiquitin-conjugation enzyme (E2 enzyme)
obtain an ubiquitin from E1, and transfer the ubiquitin to the substrate proteins specified by E3. 20-30 genes in human
Role of ubiquitin protein ligase (E3 enzyme):
Adapter proteins specifying substrate proteins. 500-1000 genes in human
What is the most common type of E3 enzyme?
SCF protein
What does SCF protein consist of?
SKP + Cullin + F-box subdomains.
What do these names mean? SCFTIR1 or SCFCOI1 or SCFSLY1
Transporter inhibitor response 1, coronation insensitive 1, sleep 1
What is Molecular Glue theory
A term coined to describe the mechanism of action of the plant hormone auxin and subsequently used to characterize synthetic small molecule protein degraders exemplified by immune-modulatory imide drugs (IMiDs)
What did chemical genetic screening identified Pyrabactin (PYR) as
An agonist
What does ABA signaling involve?
An interaction between phosphatase and kinase activity.
(This is also a de-repression-type regulation, involving kinase and phosphatase)
What does phosphorylation of the key regulator (SnRK2) lead to
Activation of ABA actions.
Brassinolide signaling
Also a de-repression –type regulation, involving kinase and phosphatase.
1. BSU1 = phosphatase
2. Bin2 = kinase
3. BZR1, BES1 = transcription factor
4. Phosphorylated BZR1/BSE1 will be removed from the nucleus
The signaling unit is repressed in brassinolide signaling when
There is no brassinolide but when brassinolide activates BUS1 (phosphatase), BUS1 in turn activates BIN2 by dephosphorylation.
What has been the major cause of crop loss in agriculture
Lodging
What is lodging
a bending of stems to the ground due to the weight of water collecting on the ripened heads. > harvesting becomes difficult.
What does a shorter inter-node do?
Reduces lodging
What has been done to combat lodging?
A number of chemical inhibitors that block the biosynthesis of GA have been developed and used for greenhouse (e.g., lilies, chrysanthemum) and for wheat.
The “Green Revolution” in 1960s are due to
the introduction of high yielding dwarf varieties of wheat and rice into Latin America and Southeast Asia, such as wheat GA-insensitive dwarf mutant, called Reduced height (Rht).
What is believed to allow human population growth?
the breeding research for dwarf mutants
Describe the mutation in wheat GA-insensitive dwarf mutant, called Reduced height (Rht).
This is a mutation in DELLA domain in DELLA protein.
Why does a mutation in DELLA domain cause dwarf phenotype?
Similar to auxin signal perception, but it has GA receptor and negative regulator.
GID1 (GA insensitive dwarf 1) is GA receptor.
FORMATION OF THE GA-GID1-DELLA COMPLEX
PROTEASOME-DEPENDENT DEGRADATION OF DELLAS
PROTEIN DEGRADATION
A mutation in DELLA domain (of DELLA) will make DELLA
resistant to degradation.
unable to block downstream transcription factors.
What is the action domain?
GRAS domain
Functional domain
DELLA (Asp-Glu-Leu-Leu-Ala) protein has
DELLA domain and GRAS domain.
The DELLA domain is the _____ domain
regulatory
The GRAS domain is the _____ domain
functional
When were distinct developmental variations observed
When plants were grown in dark and light.
Plant developmental process in dark is called
Skotomorphogenesis
Plant developmental process in light is called
photomorphogenesis
Development under like is characterized by:
Decrease in the rate of stem elongation.
Apical-hook straightening
Initiation of the synthesis of pigments
Blue light wavelengths
400-500
Red light wavelengths
650-680
Far red light wavelengths
710-740
Lettuce seed germination is a _______ response
photo-reversible
Two hypothetical models for light sensors and responses in plants
- Two light sensors are present in plants – one for red-light and the other for far-red light. They work antagonistically.
- One light sensor plays two distinct roles in two interconvertible forms – photoreversible molecule.
Which of the hypothetical models is correct?
The second
Two light sensors are present in plants – one for red-light and the other for far-red light. They work antagonistically.
What is a phytochrome
A superfamily of photosensory receptors
In dark seedling, phytochrome is present as
a red-light absorbing form (Pr), and it is converted to a far-red light absorbing form (Pfr) by red-light
What can far-red light do to Pfr
Convert it to Pr
What can red light do to Pfr
Convert it to Pr
IS Pfr or Pr the physiologically active form
Pfr
Is phytochrome pool ever fully converted to the Pfr or Pr form, following red or far-red irradiation
NO
How does phytochrome sense light and deliver signals?
Using Holoproteins =
Chromophore + Apoprotein
Chromophore is ______
phytochromobilin
What is phytochromobilin covalently bonded to?
A cysteine residue
Where is phytochromobilin synthesized
Chloroplast
Attachment of phytochromobilin to apoprotein is ________
autocatalytic
Molecular structure and proposed mechanism of phytochrome
Two domains : N-terminal sensing and C-terminal action domains.
WHat is PRD involved in
Dimerization
What does Red-light convert cis form to
Trans form which causes a conformational change of phytochrome.
Pfr protein relocates to ____ to induce gene expression resulting in photomorphogenesis
nucleaus
Phytochromes can phosphorylate other proteins, can be phosphorylated by other proteins, can degrade other proteins what are some examples of this?
Phytochrome Interacting Factors (PIF);
Phytochrome kinase substrate (PKS)
What does early signalling involve?
The rapid degradation of PIFs
What does lag time?
The time-gap between red-light reception and physiological response
What is escape from photoreversibility
After a certain time, red light-induced response cannot be reversed by far-red light
What is fluence
The amount of light measured in (µmol quanta m^-2)
What is irradiance or fluenece rate?
The amount of light in a given time measured in (µmol quanta m^-2 s^-1)
What are the three classes of responses that were found?
VLFR (Very low Fluence Response)
LFR (Low Fluence Response)
HIR (High irradiance response)
VLFR
Reciprocity applies, not FR-reversible
After treating seeds with some chemicals or stresses (e.g., ethanol and chilling), the sensitivity of seeds of some species to Pfr can be increased several orders of magnitude.
A flash of light for a second (0.001 – 0.1 µmol quanta m-2 ) is sufficient to induce Arabidopsis germination.
Germination of sensitized seeds can be triggered by light treatments that establish < 0.02 % Pfr.
Agricultural observation – Tillage in dark can markedly reduce the occurrence of weeds. It is likely that seeds of some plant species becomes sensitized when they are buried under deep soil for a long time.
LFR
Reciprocity applies, FR-reversible
LFR occurs between 1 and 1000 umol quanta m-2
Most of the red- and far-red light reversible responses
Total fluence [ = fluence rate (or irradiance) x time] determines whether LFR occurs or not.
Reciprocal relationship between irradiance and time -> Law of reciprocity
Both VLFR and LFR follow the law of reciprocity.
HIR
Fluenece rate dependent, long irradation required and not photo-reversible, reciprocity does not apply
HIR requires continuous exposure to light of relatively high irradiance.
Irradiance (fluence rate) determines whether HIR occurs or not (not fluence amount!).
HIR saturates at much higher level of fluence (>100 times).
HIR does not obey the law of reciprocity.
Not photo-reversible
Discovery of blue-light response
Some physiological events (e.g., phototropism) could not be perfectly explained by two major light-responses (photosynthesis and phytochrome).
These physiological actions appear to be responsive to blue-light (400- 500 nm) – action spectrum.
Therefore, it appears that some cryptic signaling mechanisms (distinguishable from the photosynthesis and phytochrome) operate in plants.
Some examples of blue-light responses are
Phototropism
Stomatal movement
Chloroplast relocation within cells
Inhibition of hypocotyl elongation
Characteristics of blue-light responses
Blue-light responses can be distinguished from the photosynthesis because any photosynthesis related response occurs both in blue- and red-light; however, blue-light response is not initiated by red-light.
Blue-light responses can be distinguished from the phytochrome because the blue-light responses do not show red/far-red reversibility.
Phototropism, stomatal movement, and chloroplast relocation do not show reversibility and do not respond to red-light.
Action spectra of blue-light responses show “three-finger” patterns.
Three major blue-light receptors are:
- Crytochrome
- Phototropin
- Zeaxanthin
Crytochrome
HY4 gene isolated from the hy4 mutant was not phytochrome. -> named as cryptochrome.
74-kDa protein which displays significant sequence homology to microbial DNA photolyase – an ancient protein on earth!
In bacteria, photolyase is activated by blue-light and repairs the UV-damaged DNA (pyrimidine dimer).
Both photolyase and crytochrome have two co-factors, flavin adenonucleotide (FAD) and pterin.
Cryptochrome does not show any DNA-repairing activity.
Cryptochrome is present in nucleus (no evidence for cytosol-nucleus shuttle like phytochome)
Cryptochrome has an extended domain at its C-terminus, which is absent in photolyase.
The C-terminal domain acts as a signal transducer.
Cryptochrome is involved in the regulation of anthocyanidin biosynthesis and inhibition of hypocotyl.
Phototropin
One Arabidopsis mutant lacks a phototropic response but sill has normal blue-light stimulated inhibition of hypocotyl. On the other hand, hy4 mutant (a known Arabidopsis cryptochrome mutant) has the converse phenotype under blue-light.
Molecular cloning of the mutated gene showed that it encodes a new gene, which was named as “Phototropin”.
N-terminal half has a Flavin mononucleotide (FMN)-binding site. Experiments showed that FMN is covalently bound to a specific cysteine residue by blue-light (see Figure).
N-terminus has light-oxygen-voltage (LOV) domain and C-terminus has a serine/threonine kinase domain.
Phototropin regulates “phototropic response” and “chloroplast movement”.
It localizes on plasma membrane!.
LOV2 domain is responsible for kinase activation, and the phosphorylation status of phototropin determines its activity (Uncaged Model).
Arabidopsis has Phototropin 1 and 2 (Phot1 and Phot2).
phot1/pho2 double-mutant lack both the avoidance and accumulation responses.
Chloroplast Unusual Positioning 1 (CHUP1) mutant failed proper chloroplast movement.
CHUP1 has F-actin-binding activities.
Zeaxanthin
Photosynthesis, phytochrome, cryptochrome, and phototropin showed “no or partial” influence on stomata movement.
One Arabidopsis mutant (npq1) that has a lesion in the enzyme converting violaxanthin to zeaxanthin in chloroplast, and stomata cells from this mutant lacked the blue-light response! -> Serendipitous discovery.
Very close correlation between stomata opening and zeaxanthin amount (A).
Absorption spectra of zeaxanthin = action spectra of blue-light response (C).
In detached stomata cells, blue-light sensitive is proportional to zeaxanthin amount (A + B).
Inhibitor (DTT, dithiothreitol) for zeaxanthin-forming enzyme can abolish stomata opening by blue-light.
Blue-Green reversibility of stomata opening was observed!
Action spectra for blue light-stimulated stomatal opening and for its reversal by green-light are similar.
Three-finger pattern but ~90 nm shift.
Similar absorption shifts have been observed upon isomerization of various carotenoids in protein environments
Zeaxanthin is also known to be isomerized by light.
A specific zeaxanthin/protein complex for blue/green photo-reversibility has not been identified.
However, orange-carotenoid protein (OCP) provides a hint on blue-light receptor.
OCP is a 35-kDa protein that has a non-covalently bound carotenoid, 3’-hydroxyechinenone.
The blue-light converts the dark-form of OCP to light-form of OCP.
Zeaxanthin-bound protein is likely to be converted by blue-light to a physiologically active form (green-light absorbing form). Green-light will convert the active form to inactive blue-light absorbing form. What is this protein?
What may inform plants of unfavorable conditions for photosynthesis
Green light
H+-ATPase pump regulation after recieving signals from zeaxanthin-protein
Default status of the H+-ATPase pump is “locked” condition by its C-terminal domain (auto-inhibitory).
Removal of C-terminus by protease makes the pump “constitutively active”.
Upon blue-light irradiation, the pump’s C-terminus is phosphorylated.
Upon phosphorylation, the pump shows low Km value and high Kcat (turnover) value.
Phosphorylated domain is recognized (bound) by 14-3-3- protein. 14-3-3 protein is a ubiquitous regulatory protein.
What is an essential co-factor of blue-light sesing protein which reguklates stomata opening and closing
zeaxanthin
Quick facts about cryptochrome
in nucleus, hypocotyl inhibition (hy4 mutant) and anthocyanin biosynthesis.
Quick facts about phototropin
on the plasma-membrane, phototropic response, chloroplast movement
Quick facts about Zeaxanthin (carotenoids)
in the chloroplast, stomata movement (opening and closure).
It is believed that zeaxanthin and meso-xanthin in the macula function to
block blue light from reaching the underlying structures in the retina, thereby reducing the risk of light-induced oxidative damage that could lead to macular degeneration (AMD).”
What are Nitogen firtilizers made from?
Ammonia (NH3)
How is the ammonia for nitrogen fertilizers produced?
Haber-Bosch process
WHat is the Haber-Bosch process
an artificial nitrogen fixation process and is the main industrial procedure for the production of ammonia today.
Reaction equation: N2 + 3H2 → 2NH3
What is the source of nitrogen in the Haber-Bosch process
Atmospheric nitrogen
What is the source of hydrogen in the Haber-Bosch process
Methabe from natural gas
The most popular phosphate-containing minerals are referred to collectively as
Phosphate rock
How are the minerals in phosphate rock converted to water soluble phosphate salts
By treatment with sulphuric acid
Is phosphate rock finite
Yes
What used to be used for phosphate fertilizer in US, 1870
Bison skulls
What is used to manufacture phosphate fertilizers
Phosphate rock
What country is #1 for phosphate rock reserve
Morocco
WHat was potassium traditionally prepared from?
Pot ash
Potash became the term widely applied to naturally occurring potassium _________ and the commercial product derived from them.
Mineral salts
Potash Corporation of Saskatchewan Inc.
World’s largest potash producer, started by Sask. provincial government and privatized in 1989-1990 with mines in Patience Lake, Cory, Allan, Lanigan and Rocanville Sask. and Sussex, N.B.
Mechanism of stomatal opening observation 1
Blue-light influences stomatal opening
Photosynthesis can be saturated by illumination of red-light
A rapid stomatal opening was observed, and its action spectrum showed a three-finger pattern, which are different from photosynthesis action spectrum.
Mechanism of stomatal opening observation 2
Stomata protoplasts swell by blue-light
Irradiation of blue-light on stomata protoplasts causes swelling of the protoplasts by gaining a high osmatic pressure.
pH values of the medium containing the stomata protoplasts markedly decrease when protoplasts were irradiated by blue-light. -> Blue-light induces acidification.
A proplast is
A plant cell without a cell wall
What. isthe degree of acidifcation proportional to
the amount of photons
What kind of treatment abolishes cell swellings
Orthovanadate (H+-ATPase inhibitor)
How can electric current be measured?
Patch-clamp methods
What activates H+-ATPase and CCCP
Fusicoccin
What chemivals can be used to modulate proton gradients in stomata cells
H+-ATPase and CCCP (cyanide m-chlorophenylhydrazone)
What is a primary response by blue-light
Proton gradient
___ and ___ are taken up by ion channels
K+ and Cl-
A series of subsequent secondary reactions help increase osmotic pressure of stomata cells.
Potassium (K+) and counter ion (Cl-) are taken up by ion channels (step 1).
Malate (counter ion) is also produced by the hydrolysis of starch in chloroplast (step 1).
Accumulation of sucrose by starch hydrolysis (step 2).
De novo synthesis of sucrose by photosynthesis (step 3).
What else is also produced by the hydrolysis of starch in chloroplast
Malate (counter ion)
Accumulation of ____ by starch hydrolysis
Sucrose
De novo synthesis of ______ by photosynthesis
Sucrose
How are the stomata closed upon drought stress?
The stress hormone, ABA, concentration increases under drought conditions. (we learned the role of ABA).
ABA binds to the receptor, and derepression occurs (we learned that PP2C is a major negative regulator).
Ca2+ is a key signaling messenger.
Ion efflux is promoted ; Ion influx is inhibited. These are essentially the physiological response, reversal to those in stomata opening.
Stomata closure.
Summary of stomatal biology
Blue-light relays a signal, which is distinct from photosynthetic and red/far-red signaling.
An action spectrum of stomata movement (opening/closure) is unique- three-finger pattern.
Blue-light activates “H+-ATPase” proton pumps on the plasma-membrane of stomata cells.
A number of secondary responses occur to build solutes and ions inside stomata cells.
Increase osmotic pressure, followed by water uptake and stomata opening.
Entirely reversal responses occur by drought stress, mediated by ABA and Ca2+ signaling, to close stomata.
Whaty is a unique feature among angiosperms
Double fertilization
What is doubl fertilization
Along with the fusion of a sperm with the egg to create a zygote (chromosome = 2n), a second male gamete fuses with the polar nuclei in the embryo sac to generate the endosperm tissue
Pattern Formation during Arabidopsis embryogenesis
Straight-forward observation of cell differentiation starting from zygote using microscope
What are marker proteins useful for?
Tracing gene expression and protein localization.
What is the only hormone displaying a concentration gradient in plant = morphogen
Auxin
Auxin in 2-cell stage
Maximum auxin at top
Auxin in globular embryo
Maximum axin at the base
Auxin in early heart stage
Maximum at base and in top L/R corners
Does Auxin have polarity
Yes
What does not control the direction of auxin flow
gravity
What is a morphogen
Signaling molecules (proteins or otherwise) that act over long distances to induce responses in cells based on the concentration
WHat property is an important criterterion for auxin being a morphogen
polarity
How can plants achieve the “polar transport of auxin”?
Chemiosmotic model of polar auxin transport
Chemiosmotic model of polar auxin transport
IAA enters the cell
Cell wall has an acidic pH maintained by H+ ATPase
Cytosol has neutral pH (the anionic form IAA- dominates
The anions exit the cell via auxin anion efflux carriers
What is Aux1
influx pump (more specifically 2H+-IAA- permease that co-transporting two protons and one IAA).
What is phyllotaxy
The pattern of leaf formation from the shoot in plants, and scientists were interested in the leaf pattern formations – Use Arabidopsis as a model to study phyllotaxy.
What happens to the stem and organs in Arabidopsis pin1 mutant
The stem grows normally but no lateral organs are formed.
What is the The PIN family of proteins
auxin efflux pump. The name PIN was derived from the pin-shaped influorescence formed by pin1 mutation.
How many PIN genes have ben identified
Five PIN genes have been identified in Arabidopsis (PIN1,2,3,4, and 7), but PIN1 is the most important one.
What does auxin transport induce?
Auxin transport induces floral and leaf bud (primordial) development (directly influencing phyllotaxy)
An additional family of efflux pump help PINs desrcibe some of their features
These are ATP-binding Cassette (ABC) integral membrane protein – ABC transporter.
“B-subfamily” of ABC transporter is responsible for this efflux, and thus called as ABCB.
They are sometime called “P-glycoproteins”.
Energy-requiring and consumes ATP.
Independent pump and synergistic pump functions.
Do humans have these ATP-binding Cassette (ABC) integral membrane protein – ABC transporters?
Yes
DRug efflux transporters
Role in tissue protection and detoxification
Multidrug resistance in Cancer
Testable hypothesis: Auxin concentration gradient is generated by dynamic and sophisticated distributions of transporters.
- Influx - Proton:Auxin co-transporter & passive diffusion
- Efflux – PIN protein (Auxin transporter) + ABC transporter (B-family)
The most dramatic evidence for this hypothesis comes from the studies of PIN protein localization.
Remarkable plasticity of plant development is attributed to specialized tissues called
Mesistem
Meristem is a group of cells that
Retain the capacity to proliferate and maintain “cells whose fates were undetermined”.
Two major meristem cells are
root meristem (RAM) and shoot meristem (SAM).
What are initials
a group of slowly dividing and undetermined cells in RAM and SAM. Their descendants are displaced away by polarized pattern of cell division and take on various differentiated cell fates.
Quiescent center is chracterized by
no cell division and elongation
Central cylinder of the root cap
Columella
“Initials” in Shoot Meristem cells by zone
CZ (central zone) - equivalent to QC in RAM
PZ (peripheral zone) – leaf primordial
RZ (rib zone) – stem tissue
“Initials” in Shoot Meristem cells by layer
L1 (Layer 1) – epidermis
L2 and L3 (Layer 2 and 3) – internal tissue
Subcellular localizations of PIN protein in Arabidopsis
Central region of RAM where cells divide more slowly than surrounding cells, or do not divide at all
QC
The Quiescent Center (QC) has the highest level of
Auxin
T/F Different PIN family protein mediate auxin efflux in different tissues.
T
They regulate distinct cell patterning genes in different tissues.
Cell-type specific presence of PIN and ABCB proteins specify the
directional auxin flow in plants.
seeds are grouped into two classes:
endospermic or non-endospermic (absence and presence of endosperm at seed maturity).
Sources for germinations:
endosperm vs. perisperm & cotyledons
WHat are some of the major nutrients in seeds, stored for germination
Starch, oil, and proteins
What are some of the major factors that promote germination
Water, oxygen, and temperature
Seeds may not germinate even though favorable conditions are given. This is called
Seed dormancy
Seed coats can cause dormancy by limiting water permeability (mechanical scarification), physically constraining the redicle growth, interfering with gas exchange, or providing germination inhibitors. This is chracteristic of?
Coat imposed dormancy
Inherent nature of plants (is not caused by seed coats). e.g. small undifferentiated embryo of parasitic plants.
Embryo dormancy
Release from dormancy is dependent on
Hormonal balance between ABA and GA
Light signal (e.g. Red/Far-red ratio) is sometime a critical decision-maker for ______. Often small seeds are far more sensitive to light condition.
Breaking dormancy
What is stratification
chilling seeds to break dormancy. It is a common agricultural practic
Various chemicals can break dormancy
(e.g., chemicals in smoke or 1M HCl)
Seeed gernination phase 1: imbibition
a process of water uptake by seeds (water potential)
What stage of seed germination do metabolic changes occur in
2
What stage of seeds germination do developmental progresses occur in
3
Phase 2 of seed germination
Metabolic changes (Mobilization of stored reserves) are mediated by hormone signaling. GA is the most important hormone in germination
Phase 3 of germination
Seed growth and establishment
Various tropisms and hormone actions are involved
Two hypotheses for whether phototropism occurs by auxin break-down or redistribution
Auxin may be light sensitive and light could mediate decomposition of auxin on the lighted side.
Auxin could be redistributed to the shaded side. Auxin produced at the tip is transported laterally toward the shaded side.
> Cholodny-Went Model
Classical experiments supporting auxin redistribution in phototropism
Cholodny-Went hypothesis: lateral movement (asymmetric distribution) of auxin causes tropisms.
What does asymmetric distribution of auxin control?
Phototropism
Graviation
What is gravitropism
A coordinated process of differential growth by a plant in response to gravity pulling on it.
Physiology of gravitropism and balance
The auxin (growth hormone) redistribution occurs by coordinated work of statolith, columella cells (statocytes), and auxin efflux and influx pumps.
Auxin acts as an growth inhibitor in root by an unknown reason.
What is a statolith
Specialized starch filled plastid
What is a columella cell (statocyte)
A specialized cell in the root cap
Rapid cytosolic alkalization (or apoplast acidification) occurs by
Gravi-stimulation
Starch-statolith hypothesis
How do statocytes sense the sedimenting bodies (statolith)?
The Great Famine (or Irish Potato famine) between 1845 and 1852.
Potato was introduced to the Ireland in early 1600 from South America, and it became main food for the poor in Ireland in the first decade of 1800
Lack of genetic variability by monoculture – one potato cultivar was grown!
Potato blight was introduced from USA - Phytophthora infestans (Oomycete)
Don’t know the exact number of death, but it is estimated that 1 million (mostly the poor farmers and their families) died during the Great Famine
Dutch elm disease
eliminated elm trees in America and Europe.
Caused by pathogenic fungi (Ascomycota), which is spread by elm bark beetles.
To prevent the spread of the fungi, elm tree reacts to plug its own xylem tissue with the development of new tissues – eventually it leads to the failure of xylem function.
Sources for the plant disease are :
virus (mediated by feeding insects), fungi (Ascomycetes and Basidomycetes), Oomycete (it forms a very unique clade, closer to water mold), and bacteria. Although bacteria are common causes for human disease, fungi are major causes of plant disease.
Constitutive defense
- Mechanical barriers
Surface structures, mineral crystal, thiagmonastic (touch-induced) leaf movement
What kind of crystals are present in the vacuoles of many species
Calcium oxalate
What is the purpose of Calcium oxalate crystals
form needle-like structures, called “Raphide”
Harmful to larger herbivores as it can penetrate the soft tissues (throat and gut) in insects.
Secondary (or specialized) metabolites
Are not the essential metabolic products for “plant growth and development”, but they significantly increase the fitness of plants in real eco-systems, filled with hostile pathogens and insects.
Three major classes are phenolics, terpenoids, and alkaloids
Are often toxic to plants themselves and thus are stored in specialized storage organs – resin duct, trichome, or laticifer
Example 1. glucosinolate
Plants store toxic secondary metabolite as non-toxic sugar conjugates in vacuoles
In the order of Brassicales, soluble, non-toxic glucosinolate is stored in S-cell (sulfur-rich cells) and myrosinase (a thioglucosidase) is stored in different cells than its substrate (glucosinolate).
When leaves are chewed by insects, enzymes (myrosinase) and substrates (glucosinolate) meet each other, and highly toxic isothiocyanate is produced – mustard bomb!
Isothiocyanate is responsible for the flavors in Mustard, wasabi, radish, brussels sprout
Cyanogenic glycosides in sorghum and cassava
Upon tissue damage, the sugar group is removed from the cyanogenic glycosides and hydrogen cyanide (HCN) is generated. Cyanide ion inhibits electron transport chain in mitochondria (more specifically block cytochrome c oxidase).
Problems of constitutive defense responses:
Constitutive defenses always use valuable resources, whether insects are present or not. In a wild eco-system, many different plant species compete to dominate restricted niches, and they have to allocate resources to growth and reproduction too. Constitutive defenses are expensive!
Insects (or other pathogens) can acquire resistance against the defensive chemicals, if they are constitutively exposed to the toxic chemicals (as pathogenic bacteria gain anti-biotic resistance when anti-biotics are inappropriately or unnecessarily used).
Different types of insect attacks – Phloem feeders (aphids and while flies); Cell-content feeders (mites and thrips); Chewing insects (caterpillars).
Plants need sophisticated inducible defense mechanisms for different types of attacks, and at the first place plants need to sense the insect attacks.
What are elicitors
chemicals (from insects) which trigger defense responses in plants to a wide variety of herbivores and pathogens.
Fatty acid amide (fatty acid and amino acid conjugate) in the saliva of larvae of the beet armyworm. Fatty acid backbone [linolenic acid (18:3) and linoleic acid (18:2)] is from plant!
Volicitin
Sulfated fatty acids isolated only from grasshopper (suborder: Caelifera). Unlike the Volicitin, the fatty acid backbone is unusual structure (irregular number carbon number and trans-configuration double-bond).
Caeliferins
Insect elicitors (Volicitin and Caeliferin) induce
The Ca2+ -mediated signaling and jasmonic acid (JA) biosynthesis in plants
First, cytosolic calcium concentration rapidly increases upon treating plants with elicitors. Calcium is used as a secondary massager to activate calmodulin proteins, calcium-binding proteins, and calcium-binding kinase.
Second, octadecanoid pathway is activated to synthesize jasmomic acid (JA), which in turn activates a wide array of defense responses. JA can also be considered as a hormone in plant-insect interactions
SImilar to prostaglandin
Biosynthesis and physiological roles of prostaglandin in humans
Constriction and dilation in vascular smooth muscle.
Aggregation of platelets.
Induce labor.
Regulate inflammation.
Act on the thermoregulatory center in brain.
What induces anti-digestive proteins in plants
JA
JA initiates the synthesis of defense-related proteins that inhibit
Herbivore digestions
“α-amylase inhibitor” proteins are synthesized when
plants are treated with JA. This enzyme inhibitor from plants inactivate “α-amylase” in insect digestive tracks.
“Lectin” proteins are synthesized in response to
JA
This protein interfere with nutrient absorption in insect digestive track.
“Proteinase inhibitor” proteins are synthesized in response to
JA
This protein tightly binds to key protein-hydrolyzing enzymes, trypsin and chymotrypsin.
Gene-for–Gene (hypothesis) model by Dr. Flor in 1940s
Defense against virus, fungi, oomycetes, and bacteria
Resistant gene in plant
R
Avirurence gene in pathogens (bacteria, fungi, and virus)
AVR
Where do microbial pathogens invade plants through?
Natural openings, such as stomata and hydathode
T/F wounding sites can be infected by microbial pathogens
T
Fungi and oomycetes can release cell-wall degrading enzymes to actively penetrate into the plant tissues (using unique structures, such as:
Appressorium, infection peg, haustorium, see next slide)
Necrotrophic pathogens:
kill plants by releasing cell wall-degrading enzymes, toxins. Then they use the dead plant tissues as a food source.
Biotrophic pathogens:
causes minimal cell damages on plants and use nutrients provided by the infected plant tissues
Hemibiotropic pathogens:
Keep the plants alive initially but they kill plants at the later stage of infections.
What are effectors?
Molecules (produced from the pathogens) that change the plant’s structure, metabolism, or hormone regulation to the advantage of the pathogens. They can be enzymes, toxin, and growth regulator
Types of effectors from pathogens
Enzymes: cell wall-degrading enzymes such as cutinase, cellulase, xylanase, pectinase, polygalacturonase.
Toxins: HC toxin from Cochliobolus carbonum inhibit the histone deacetylation in plants; Fucicoccin from Fusicoccum amygdali binds to H+-ATPase and irreversibly activate this transporter on the membrane.
Hormone: Gibberella fujikuroi synthesizes gibberellic acid to cause foolish seedling disease in rice.
Pkants deploy two layers of immune systems :
MAMP (microbe associated molecular patterns)-triggered immunity and effector-triggered immunity.
Pattern recognition receptors (PRR) on the cell surface play important roles.
Two types of PRRs are “MAMP” released from pathogens and “DAMP” (damage-associated molecular patterns) released from plants.
Examples of MAMPs
chitin from fungi and flagella from bacteria
Example of DAMP
is systemin in tomato or cell wall-components
MAMP and DAMP are recognized by
receptor-like kinase (RLK) or receptor-like protein (RLP)
Pathogenic bacteria can bypass the surface-deployed detection systems by
Directly injecting various effectors into the cytoplasm of plant cells.
Plants have a secondary immune system to detect those effectors in cytoplasm using
soluble nucleotide binding site-leucine rich repeat (NBS-LRR) receptors – or R (resistant) genes
Specificity of disease resistant in plant is determined by a specific ______ in pathogen and a specific ________ in plant.
Effector and R gene
Guard hypothesis for R gene signaling during plant defense against pathogens
Scientists had difficulties in finding evidence for direct interaction of R (e.g., NBS-LRR receptor) and Avr (effector). What is the target of effector then?
It is proposed that plant uses the target protein as a decoy to recognize the presence of effector. There are some experimental data to support this hypothesis.
Once virulence protein bound on target protein in plant to weaken defense, but now plants use the target protein as a decoy to sense the attack of pathogen.
What’s the result of Avr-R interaction?
Hypersensitive responses in plant
Essential components for hypersensitive response
“Nitric oxide (NO)” and “reactive oxygen species (ROS)”
Disease resistant mutants for Gene-for–Gene (hypothesis) are:
R/R or R/r and AVR/avr and AVR/AVR
All the other mutants are susceptible to disease
Plant pathology and disease monitoring system
- University or government laboratories
- Database for pathogens (Molecular ID)
- Genetic resources (thousands of cultivars of each crop)
In primary cell walls, _________ microfibrils are embedded in a hydrated matrix of non-cellulosic polysaccharides (sugars) and a small amount of structural protein.
cellulose
Primary cell walls are formed by
growing cells
Secondary cell walls are formed
after cell growth stops between the primary cell walls and the plasma membrane.
What is the most important component in the secondary cell walls
Lignin
Components of primary cell walls
Cell wall polysaccharides are classified into three groups.
Cellulose
Hemicellulose
Pectin
Additional non-carbohydrate components
Lignin
Structural proteins
Main components of cell walls are
Sugars
Cellulose
The most abundant bio-polymers on earth (the second most abundant one is lignin).
1.5×1012tons of the total annual biomass production. Cellulose is considered an almost inexhaustible source of raw material. 1x109 tons of celluloses = 1/3 of transportation fuel in USA.
A linear chain of several thousands of β(1→4) linked β-D-glucose. Cellobiose is the repeating units in cellulose.
Tightly packed to form a microfibril by hydrogen bonds.
Micrometer (µm) length and 1-10 nanometer (nm) width.
Each cellulose chain in microfibrils is composed of thousands of monomers (2,000 – 25,000).
Scanning Electron Microscopic (SEM) data
Focused electron beams are used to examine surface topology of the samples at nm resolution.
Biosynthetic model for cellulose synthesis on the plasma membrane
Cellulose synthases span the plasma membrane with their catalytic site on the cytoplasmic side.
Abundant carbon source, sucrose, is cleaved to glucose and fructose by sucrose synthase.
Glucose is activated to uridine diphosphate D-glucose (UDP-glucose)
Hemicellulose
Hemicelluloses are primarily made of five carbon sugars.
Different from cellulose, they have side-chains which interfere the crystalline formation of hemicellulose molecules.
Xyloglucan and glucuronoarabinoxylan are two common hemicelluloses. Examine these structures!
Hemicelluloses are usually longer than cellulose microfibrils, and they cross-link cellulose microfibrils on cell walls.
Pectin
Hydrophilic gel-forming components.
Pectin is also composed of heterogeneous polysaccharides but it is different from hemicellulose in that..…
Galacturonic acids form the main backbone of pectin (galacturonan)
Pectins are hydrophilic gel-forming components of the matrix.
Ca2+ ions help pectin form a network by ionic bonds.
Matrix polymers are synthesized in the _____and secreted via _____
Golgi apparatus, vesicles
Cell wall assembly
Synthesis -> deposition -> assembly -> modification
Self-assembly model:
Isolated celluloses can be dissolved in strong solvents, and stable fiber can be formed spontaneously - Manufacturing of Rayon (cellulose fiber)
Enzyme-mediated assembly model:
XET enzyme can cut xyloglucan and add a new xyloglucan molecules in vitro
Lignin is more abundant in
Secondary cell walls
Overall, three major constituents of all cell walls (primary + secondary) are:
cellulose, hemicellulose, and lignin
Plant cells sometimes continue to synthesize a ______ after wall expansion ceases.
Secondary wall
The secondary cell walls have all cell wall components, but it becomes more strengthened by
Lignin
Two important considerations for cell wall expandability are:
How can directional growth of plant cells occur?
How can rigid cell walls expand?
Microtubules dictate the orientation of newly deposited cellulose microfibrils.
Tubulin is a subunit of cytoskeletal structure microtubules, and oryzalin depolymerize microtubules.
Treatment of oryzalin on root tip cells causes non-directional enlargement.
Immunofluorescent signals of CesA overlaps with microtubule subcellular locations.
Microtubules guide the deposition of CesA inside the cells.
Does the lignin biosynthesis randomly occur in plants?
Casparian strip model
CASP1 protein organizes membrane proteins at the Casparian strip.
Acid growth hypothesis
To change shape, plant cells must control the direction and rate of cell wall expansion.
Plants need to deposit cellulose in a biased orientation and selectively loosen the bonding between cell wall polymers.
“Creep” refers to an irreversible extension of cell walls, which occurs by slippage of cell wall polymers relative to one another.
Two important observations relevant to cell wall expansion are 1) cell wall loosening is enhanced at acidic pH and 2) drug fusicoccin treatment on plants enhanced cell wall loosening. Fusicoccin is known to activate H+-ATPase on plasma membrane (e.g., H+-ATPase agonist).
An “extensometer” can be used experimentally to measure cell wall expandability.
Expansin proteins play an important role in cell wall expansion.
Applications of acid growth hypothesis
Cotton (fibre is pure cellulose)
Lignocellulosic biofuel
