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