plant hormones lecture 14 12/4/2012 9:56:00...
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Plant Hormones – Lecture 14 12/4/2012 9:56:00 AM
Gibberellins (GA)
Gibberellins make up a large family of STUCTURALLY RELATED
COMPOUNDS, found in fungi and plants
Gibberellic acid (GA3)
o Giberellin that appears to promote CELL ELONGATION,
INCREASE RATES OF CELL DIVISION IN ROOTS
Cytokinins (CK)
Cytokinins are a group of plant hormones that promote cell division
Cytokinins are synthesized in ROOT TIPS, YOUNG FRUITS, SEEDS,
GROWING BUDS and other developing organs
Cytokinins regulate growth by activating genes that keep the cell
cycle going
When lacking CKs, cells arrest at G1
o Cell cycle stops, stop growing
EX. Kinetin, Zeatin
Brassinosteroids (BR)
Involved with elongation in the dark (ETOLIATION)
Auxins (mainly IAA)
Produced in the apical meristems and young leaves (apical dom.)
The transport is polar
o Produced in the ap. Meris. and travels top to bottom to the
root were it will then move slightly upwards
o Apical to Basal end in cells
o Cotransporters at top of cells bring auxin in
Carrier proteins at bottom of cell send auxin out
Some auxin is destroyed in the process
Within the cells,
The pH between cytosol and cell wall is
different
pH within cell is lowered by pumping
protons out using ATP
the auxin itself has negative charge but is
neutralized by protons, so that it may enter
the cell easily
Once auxin has entered the cell, it releases the proton and ATP pumps
the proton out
Auxins stimulate ELONGATION
Remember auxin brings in protons and those protons are pumped
out of the cell by pumps
The protons that are pumped out activate EXPANSINS
The cellulose will loosen, cell elongates
ALLOWS FOR NATURAL ENLARGEMENT OF CELL BY MEANS OF
WATER PRESSURE
Promotes cell divions and leaf expansion
Induces ethylene production
Cytokinins and Auxins are used together to promote the growth and
differentiation of cells in culture
CKs promote cell division in the prescence of auxin
Ethylene
Involved in fruit ripening
Induces senescence in fruits, flowers and leaves
Produced when plants are under stress
Ethylene causes a decrease in growth and elongation
o High Auxin
Cells in abscission zone are insensitive to ethylene
o Low auxin:
Cells in abscission zone are more sensitive to ethylene,
leaf senescence occurs
Leaf detaches from abscission zone
Abiscisic acid (ABA)
Inhibits bud growth and seed germination
Induces closure of stomata in response to water stress
o Water Control
ABA binds to receptors on guard cells
Stop the pumping out of H, opens outward
directed Cl channels
Open outward directed K channels
H2O follows ions via osmosis
Stomata guard cells close
Salicylic Acid (SA)
Occurs during HYPERSENSTIVE RESPONSE to pathogens
SA is produced at the infection site
o Triggers a slower, more widespread set of events
SYSTEMIC ACQUIRED RESISTANCE (SAR)
Primes cells throughout the root and shoot
systems for resistance to pathogen attack
How Do Plants Sense and Respond to
Herbivore Attack? Many plant seeds and storage organs contain proteinase
inhibitors
o proteins that block the enzymes found in the mouths and
stomachs of animals that digest proteins
If herbivore ingests a large amount of protinease inhibitor it will get
sick, herbivores will then learn to detect and avoid plants that
contain these proteins
Systemin
o Hormone produced in response to wounds caused by
herbivores
o Initiates a protective response
Synthesis of Jasmonic Acid
Activates the production of proteinase inhibitors
Hypersensitive Response (HR)
Causes the rapid and localized death of cells surrounding the
site of infection, starving pathogen
Pathogen
Disease causing agents
Induced defenses
Responses to attacks that are induced by the presence of a
threat
Parasitoid
Organism that is free living as an adult but parasitic as a
larva
Parasitoid attacks limit the amount of damage done to plants
by herbivores, they kill their host
Pheremones
Chemical messengers made by an individual that are
released to elicit a response in a different individual
Intro to Gas Physiology/Respiratory Structures – Lecture 15 + Lecture 16 12/4/2012 9:56:00 AM
Introduction to Oxygen Physiology
Animals do not actively transport Oxygen across respiratory
surfaces
Movement of O2 must depend on diffusion
All living cells must be bathed in fluid
o Respiratory surfaces are moist
O2 must dissolve in fluid
o Then must diffuse across liquid barrier
Respiratory surface supplies gas exchange for the entire
body of the animal
o Size dependent
Larger body will have larger resp. system
o Water or land
o Will vary dependent on metabolic demands ie.
Endotherms vs ectotherms
Terrestrial organisms have an invagination of the respiratory system
Allows for the retention of moisture
John Dalton
Articulated the LAW OF PARTIAL PRESSURES
o Pressure
o Pressure differences determine direction when materials flow
and affect the rate of flow, whether the flow is in blood
circulation, breathing or filtration of water
o Force per unit of area, standard unit of pressure is pascal
Each gas in a mix exerts pressure
Partial pressure is the amount of pressure that the gas
exerts
Px=FxPtot
o Px = partial pressure o Fx = fractional concentration of gas (moles or by
volume) o Ptot = Total pressure of the gas mixture
As you increase in height, the pressure decreases
Gases dissolve in liquids
Pliquid is proportional to Pair
Amount of gas in solution depends on:
o Temperature
Molecules will be moving at a greater rate at
higher temps
o Salinity
o Gas
*Gases that have reacted chemically do not contribute to partial pressure in
solution
Henry’s Law
The partial pressure and concentration of a gas in an aqueous
solution are proportional to each other
Cx =APx
o Cx = Concentration in solution
o A = solubility of the gas in the liquid, (absorption
coefficient)
o Px = Partial Pressure (in liquid)
Diffusion of Gases (Derived from Fick equation)
J=K∙(P1‐ P2)
X
J = rate of net movement of the gas (per unit area)
K = Diffusion coefficient
(P1-P2) = Concentration gradient, movement of over time in
relation to area
X = Distance to be diffused
Diffusion Coefficient
Depends on gas, temperature and medium
Also depends on the permeability of any barriers,
o eg. Cell membranes, cuticle, epidermis
What can an organism do to improve gas exchange?
Make the diffusion distance as small as possible (decrease the
distance of a membrane)
o Ex. capillary walls are responsible for diffusion of oxygen
across particular membranes
It is made up of a single, eplithelial cell layer, very thin
Maximize the area
o Increase the surface area by for example, many folds.
Maximize the concentration gradient to maximize the rate of
diffusion
Convection can minimize the dependence of diffusion
Convection can move gases such as oxygen much farther than just
diffusion alone
Utilize convection through
o Active pumping of water
Eg. Choanocytes
o Passive Pumping of water
Created by current
Created by propulsion mechanisms (jellyfish)
Ex. The Sponge Pump
o Sponge pumps a volume of water equal to its body volume
once every 5 seconds
o 1 litre sponge pumps about 720 of water in an hour
o The engine of the pump is the CHOANOCYTES which is its
active pumping mechanism, it brings in water through
currents in the ocean which is its passive pumping mechanism
o Convection can be used to get rid of CO2 and bring in O2 to
replace it
This example was used for the tunnel system used by
groundhogs
The same system applies for jellyfish using propulsion
to move fluid and remove oxygen depleted water for
oxygen rich water
Breathing water
Getting rid of CO2 isnt a problem
o CO2 has a high diffusivity and absorption in water
Getting O2 is
o It has a low solubility in water
o It has a low partial pressure
How to breath water?
Fast ventilation
o More water across respiratory surface means more oxygen
will come in contact to absorb
Efficient Absorption
o Via countercurrent exchange
Highly vascularised system with a large surface area
Ventilatory structures
o Gas exchange surfaces
o Usually highly vascularised
o Open to the ‘outside world’
o Actively ventilated using a convective flow of medium
These structures would be
o Skin
o Gills (evaginations)
o Lungs (invaginations)
o Or combination of the three
Gas Exchange in Plants – Lecture 17 12/4/2012 9:56:00 AM
Gas exchange in PhotoSynthesis
Plants get CO2 out of air and into the leaf through FICKIAN
diffusion through stomata
o Relies on a concentration gradient that allows for the diffusion
to occur, resistance affects this diffusion
The diffusion of CO2 also allows for the diffusion of water vapour as
well
When oxygen diffuses in and carbon dioxide moves
out, photorespiration takes place
When carbon dioxide is taken in and oxygen is
released, photosynthesis takes place
How do gases get in and out of a plant?
This occurs through the stomata
o These are pores in the leafs surface that allow for access from
the outside air to air spaces within the leaf
Here >90% of all gas exchange takes place
Vast majority of water loss occur through these
pores
These pores open and close
When they are open it is good for CO2 uptake but
bad for WATER loss
Structure of Stomata
Stomata are located:
o On top – floating aquatic plants
o Underside - most angiosperms
o Rows on needles – conifer
o Top and Bottom – Grasses
Two Types of Stomata
o Ellipsoid
Graminceous
dumbell shape, the cytosolic and vasculature are at the
ends, the pore is very small
How do plants open and close their stomata?
When water enters the guard cells, these cells will swell, the swelling
will be limited by cellulose microfibrils that act as ‘bands’
Think of strength bands or tightened rope
These guard cells swell by water uptake? But How?
The water uptake is driven by POTASSIUM INFLUX
Lower cell water potential within the cell caused by osmotic (solute)
potential, causes water to flow into the cell which will increase
turgor pressure
When guard cells are open, the potassium levels are
higher than when they are closed
A guard cell with its vacuole. When you have
a trigger such as light, an ATPase proton pump will use
ATP energy to pump out protons into the apoplast, this
will generate an electron proton gradient. Voltage gated
potassium channels will bring in K in and chloride will
follow.
Water will then follow as the water
potential in guard cell declines
How is stomatal opening and closing regulated?
If you shut the stomata completely the pressure inside the cell will
build up and when it opens up finally, more water will leave as a
result
The stomata will respond to internal PCO2
Close in response to water stress
Respond to light
Have endogenous, diel rhythms
Photorespiration
Dominates when there is high levels of Oxygen
o Oxygen competes for Rubisco which also acts as an
oxygenase
o If you want to use photosynthesis, you would need to
increase the amount of CO2 coming into contact with rubisco
In stomata
o There is a trade off
You wlll obtain CO2 but lose water in the process
Atmospheric CO2 conc. have been lower in the past
Soil moisture can very low, and atmospheric demand
for water can be very high
Plants may use 2 different ways to sequester CO2 while retaining
water for use -> -> -> ->
C4 photosynthesis
o SPATIAL separation of CO2 influx and Calvin Cycle
o (Light Rxns)
Mesophyll cells contain low conc. of CO2
Carboxylation of PEP to C4 acid occurs and acid is
transported to bundle sheath cells
o (Dark Rxns)
Bundle Sheath Cells have high conc. of CO2
Decarboxylation of C4 acid
Allows for CO2 to be available for CC (rubsico)
o C4 plants are ANGIOSPERMS
Ex maize and sugarcane
CAM photosynthesis (CAM – Crassulacean Acid Metabolism)
TEMPORAL separation of CO2 influx and photosynthesis
o Open stomata during the night, store CO2
o Use stored CO2 during the day and photosynthesize with
stomata closed
o Used in very dry places eg deserts as well as tropical
rainforests eg: epiphytes
o Requires Succulence
They tend to be thick and fleshy, they require vaculous
to buffer the acid that builds up over the day
How does it work?
o Relies on PEPCase to carboxylate PEP
o OAA converted to MALATE and stored as Malic Acid in vacuole
o Malic Acid converted back to pyruvate during the day
This process releases CO2 to the CC
o This all happens within the SAME cell, this is temporal
separation!
Gas exchange in Aquatic Plants?
Water have low O2 concentrations
Aquatic plants will have all of its cells photosynthesize
Rely on diffusion
How?
Aerenchyma
o These allow oxygen to get from the leaves to the roots
Also are able to bring in CO2 from anoxic and high
PCO2 sediments to photosynthetic tissues
o Develop in regular plant roots in waterlogged conditions
water and water logged conditions
Lecture 18 – Respiratory Pigments 12/4/2012 9:56:00 AM
BLOOD MUST BE THICKER THAN WATER
The solubility of O2 in water is not enough to provide adequate
amounts of O2 to active tissues
Many organisms use RESPIRATORY PIGMENTS to bind O2 and
transport it to tissues
Respiratory pigments
Can be in solution or enclosed in blood cells
o Find Hematocrit
Centrifuge whole blood and measure proportion of
solids (i.e. cells)
It is a pretty good measure of blood oxygen carrying
capacity in vertebrates
What does it mean to have a respiratory pigment?
Without hemoglobin the heart would need to pump 50 litres of
blood for every single litre it pumps right now
o The blood, containing Hemoglobin, picks up oxygen from the
lungs
o Holds about 200 ml of O2 per litre of blood in chemical
combination
Compared to, 4 ml of O2 in solution
o This represents a 50 fold increase in oxygen!
Respiratory Pigment
Substance that combines reversibly with oxygen
o Many animals contain these pigments
Metalloproteins
Protein that contains a metal atom
This metal gives them color
o Can take a lot of O2 out of water, but transport a lot of O2
per unit of volume as well
Hemoglobin
4 subunits (2 alpha and 2 beta)
Metal containing ‘Heme’ group – site of oxygen bonding
hemoglobin is found thoughout the animal kingdom
Chlorocruorins
Found in four polychaete families
o Serpullidae
o Sabellidae
o Chlorhaemidae
o Ampharedtidae
Hemerythrins
o Spinuculida
o Priapulida
o Brachiopoda
Hemocyanins
o Some arthropods
o Many Molluscs
Pigment Structure O2 binding
Hemoglobin
Bright red/
purple
Protein +
Heme +
Fe2+
1/Fe2+
Chlorocruorin
Green
Protein +
Porphyrin
+ Fe2+
1/Fe2+
Hemerythrin
Violet/
Colourless
Protein +
Fe2+
1/2Fe2+
Hemocyanin
Blue/
Colourless
Protein +
Cu2+
1/2Cu2+
Hb Oxygen Association curve (SIGMOID CURVE)
o Cooperativity
Cumululative increase in affinity as O2 binds to the
heme groups
Subunit changes conformation slightly, INCREASING the
AFFINITY of other Heme groups in the tetramer
Subunit interaction
At first, without an abundance of oxygen, the
molecule is referred to as tense, give it a little bit
of oxygen, it binds to the iron and slowly starts to
relax, oxygen then can start to bind to other
heme groups more rapidly AFTER
o Affinity can change however
Higher affinity : needs a bigger drop in PO2 to release
O2
Lower affinity : O2 is released much more easily
The Bohr Effect
The ‘flex’ in an oxygen affinity curve
o Exercising tissues produce CO2
As Pco2 increases and pH decreases, affinity of Hb
decreases
Allows for more O2 to be unloaded when needed
Affinity is still high at the blood gas barrier for initial O2
uptake
Lecture 19 – Principles of Water 12/4/2012 9:56:00 AM
Water concentration gradients drive transportation
The capacity of air to hold water molecules increases exponentially
as air temperature increases linearly
The amount of water needed to saturate a volume of cool air is less
than the amount of water required to saturate the same volume of
warm air
As air warms over the day, rel. humidity will drop
Leaves lose less water through TRANSPIRATION at night than at
Noon
Osmoregulation:
Balancing water and ions in the cells and the body to allow
physiological function
Osmolarity/Osmolality
The amount of stuff in a solution
1 mole of solutes = 1 osmole
Osmolality – per Kg of Solvent
Osmolarity – per litre of Solvent
Water, Water, Water
Highly polar
o Hydrogen bonding
o High heat of fusion and vaporization
o Large thermal capacity
o Cohesion and adhesion
! Creates a ‘shell’ of bound water around many macromolecules (ex
proteins), it can also keep ions dissociated !
Water in Cells
Determines cell volume in animals
o Cell volume is often the bottom level of regulation of water and
ion balance
Determines cell turgor in plants
Animal and Plant cells at high and low concentration
Animal Cells
o In hyperosmotic solution, water leaves the cell, making it flaccid
and turgid
o In isosmotic solution, the cell has a proper amount of water
within it
o In hypoosmotic solution, water flows into the cell, causing the
cell to expand and finally burst
Plant Cells
o Plant cells are different from animal cells because they have cell
walls
o Because of rigid cell walls, they will behave slightly differently
from animal cells
In a solution with just water, water will flow into the
vacuole of the cell, expanding itself, but only pushing
against the cell wall, not expanding the size of the cell
In as isomotic system, the cell is not as bloated as in an
hypoosmotic system
Within a salty solution (hyperosmotic), water is drawn out
of the vacuole of the cell, and the cell collapses within,
however the cell wall remains intact
Moving of Water in and out of the Cell
Water is not moved actively throughout the cell
o Aquaporins are used to transport water, NOT active transport,
NO ATP being used
In order to move water, a gradient must be created
o This can be achieved through ACTIVE transport of IONS, inside
and outside the cell
o Maintaining these gradients require ENERGY
Plant cell have a variety of pumps that move ions in one direction
o Symporters: bring multiple ions in at once
o Channels: open and shut when needed
o Antiporters: bring some ions in, bring some out
o Proton pumps/H pumps: pump protons out (DUH)/ move H out,
uses ENERGY
Cell/Solution conditions
Hypotonic -> Isotonic
- Low concentrations of solute within the cell
- High concentration of solute outside cell
- Net Efflux of water OUTSIDE cell
o To regulate this and return to isotonicity…
Use active transport of ions into the cell, pump them
into the cell
No net osmotic pressure
Does NOT require the same solutes to maintain
isotonicity
- an increase in concentration will lead to an net water influx
Moving of Solutes and Water
Through the cell (TRANSCELLULAR transport)
Around the cell (PARACELLULAR transport)
Ψw = Ψp + Ψs
Equation defines how water will move
Ψp
o Pressure Potential
Refers to the hydrostatic pressure of the solution, and it
can be positive or negative. Positive pressure raises the
water potential, negative pressures reduce it.
Ψs
o Osmotic (solute) potential
The potential of the water component of a solution
containing solutes
Where do Cells get water?
Plants – Roots
Animals - Drinking
-Metabolic Water
o Water that is the result of the metabolism breaking down
sugar and oxygen through oxidation
-Bound water
o Some fuel molecules have large amounts of water hydrogen-
bound to them
Eg. Glycogen
o When you metabolise Fuel,
A small amount of metabolic water is release
A Large amount of bound water is released!
Osmoregulation in Animals
Osmoregulator Osmoconformer
Osmoregulators
- Bony (teleost) fishes
- Reptiles
- Mammals, birds and terrestrial animals
Osmoconformers
- Hagfish
- Bivalve molluscs
- Coelacanth
- Some marine arthropods
Osmoregulatory strategies
o Stenohaline:
Survive across a narrow range of salinities
Narrow tolerance ranges for different salinities
o Euryhaline:
Survive across a broad range of salinites
Changes on an almost 1:1 basis between external
osmolarity and internal osmolarity
-> These strategies do not have anything to do with whether the
organism is an osmoconformer or regulator
Osmoregulatory Strategy in Plants
Cells utilize a cell wall to maintain tonicity
- The use of a cell wall means that you cannot have too much water
within the cell
- Vacuole is used to maintain turgor pressure
Osmoregulation in Extreme conditions:
- Anhydrobiosis
o Toleration of the loss of >99% percent of body water
Ex. Fly larva (Polypedilum vanderplanki)
- Resurrection plants
o Plants survive total dehydration
o Recover within hours when they obtain water
o During dry periods, the plant will completely fold up and dry
out
o Ex. Ferns, lichens, mosses, and many higher plants
Lecture 20 – Water and ion balance in plants 12/4/2012 9:56:00 AM
Water Balance
Water is obtained by pulling it up from the soil into roots and up into
leaves
o Cohesion-tension theory
Water diffuses out of leaves and evaporates
Negative water potential in leaves is created
Cohesion of water molecules (via Hbonding)
Tension is propagated down the xylem
Water is pulled up, via Hbonds, to the site of evaporation
Water balance within the LEAF
Stomata: CO2 comes in, Water leaves
Leaf: Resistance
Boundary Layer
o A layer of unstirred air on the outside of a
leaf
Eddies of turbulence formed by
aberrations on the leaf surface
Contains a high amount of water vapour
o Therefore less water vapour is lost
from the leaf when the stomata is
open
Boundary Layer
Affected by wind
o Higher winds decrease the thickness of the boundary layer
This leads to MORE transpiration
How does water enter the plant?
……Through the roots!
This is what a root looks like!
Root cap:
protective layer, as root is pushing
its way through soil,
it could easily be damaged, so theres a
root cap which protects
mucigel - carb gel like substance that
helps act as a lubricant to move
thorugh the soil and prevent damage to tip
quiescent center –
- dont have a lot of cell division here, will divide
later in the life but its a constant base of cells
have an area of rapid cell divison which is
where roots starts growing and they rapidly divide
lay themselves out in a very organized manner
Then get epidermis (outside of root)
then cortex
then endodermis (area that also has a casparian strip)
Area inside the endodermis is the vascular tissue, where xylem and phloem are located
Above that you have the area where you start getting root hairs
Meristematic Zone
Elongation Zone
Maturation Zone
Above maturation, root is pretty impermeable
start off fine at the bottom, then grow woodier and more impermeable
Root Hairs
Single cells that extend between soil grains into films of water
They increase the SA and absorption area to help absorb extra water
and nutrients
Routes of Water Absorption
1. Symplastic
a. Moves through plasmodesmata via water gradient
2. Transmembrane
a. Moves through aquaporins or transporters between cells
3. Apoplastic
a. Movind in cell walls, intracellular spaces and through the xylem
(dead cells)
Casparian band/strip
Ensures what the plant can control what goes in or out
The barrier where plants start to have control over what moves into
the plant
Laid down in apoplast, blocks it so that there cant be continous
apoplastic transport
Water and solutes will have to move through these cells rather than
around or through cell walls
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