- Plant Growth Wrap-up - Thinking About Transport Today: - Plant Growth Wrap-up - Thinking About...

Today: - Plant Growth Wrap-up- Plant Growth Wrap-up - Thinking About Transport - Thinking About Transport

Reminder: Turn in a draft of your Intro and Methods

Thursday!

Quick Review:Quick Review:

Where Does Primary Where Does Primary Growth Happen?Growth Happen?

What Tissues Are What Tissues Are Responsible?Responsible?

How does this compare How does this compare to secondary growth?to secondary growth?

Using Using Yesterday’s Yesterday’s

Stem Diagram Stem Diagram to Be Obnoxious to Be Obnoxious on a Road Trip…on a Road Trip…

What order would What order would you encounter the you encounter the tissues in as you tissues in as you drove through?drove through?

One Last Application: What One Last Application: What would girdling do to a tree?would girdling do to a tree?

These trees are These trees are being used being used as “trap as “trap trees” in trees” in Oregon to Oregon to test for the test for the presence of presence of the recently the recently introduced introduced emerald ash emerald ash borer.borer.

A Few Big Ideas in Plant A Few Big Ideas in Plant DevelopmentDevelopment

How can we determine the

importance or role of things like

asymmetrical cell division?

Make or find

mutants!

Cell Shape is Determined by Cell Shape is Determined by Position of Microfibrils in Cell Position of Microfibrils in Cell

WallWall

How do How do you you

know?know?

Homeotic Genes and Positional Homeotic Genes and Positional Effects are Powerful During Plant Effects are Powerful During Plant

DevelopmentDevelopment

Meristem Identity Genes Meristem Identity Genes Trigger the Production of a Trigger the Production of a

FlowerFlower

Next Up: Next Up: TransportTransport

What does this tree need to transport?

What sorts of forces are

available to do this transport?

Transport Transport in Plants: in Plants:

An An OverviewOverview

Let’s Get Our Bearings…Let’s Get Our Bearings…

Strasburger’s Strasburger’s ExperimentsExperiments

Root FunctionRoot FunctionTransport occurs on 3 levels:Transport occurs on 3 levels:

1. Uptake and loss of 1. Uptake and loss of water/solutes by water/solutes by individual cellsindividual cells

2. Transport from 2. Transport from cell to cell to cellcell (tissues and organs) (tissues and organs)

3.3. Long-distance Long-distance transporttransport at plant level at plant level

Cellular Level TransportCellular Level Transport

Remember…Remember…

Plasma membranes are Plasma membranes are selectively selectively permeablepermeable!!

Solutes will spontaneously diffuse Solutes will spontaneously diffuse down down their concentration gradientstheir concentration gradients

Transport proteinsTransport proteins in in the membrane can speed the membrane can speed the rate at which solutes the rate at which solutes

cross a membranecross a membraneTransport proteins may Transport proteins may directly bind the solute, directly bind the solute, or may act as or may act as selective selective channelschannels (passageways (passageways across the membrane)across the membrane)

Many such channels are Many such channels are gatedgated..


Proton PumpsProton Pumps are are activeactive transporters in transporters in the plasma membranesthe plasma membranes

Proton pumps consume (hydrolyze) ATP to Proton pumps consume (hydrolyze) ATP to pump hydrogen ions out of the cellpump hydrogen ions out of the cell

What happens

to the charge

inside the cell?


Separation of opposite charges across a Separation of opposite charges across a membrane = membrane = Membrane PotentialMembrane Potential

Stored Potential Energy! Used to drive Stored Potential Energy! Used to drive the transport of other solutesthe transport of other solutes


““Downhill” passage of one solute may Downhill” passage of one solute may also be coupled with the “uphill” also be coupled with the “uphill”

passage of anotherpassage of another

= = CotransportCotransport


Using the stored energy of a proton Using the stored energy of a proton gradient to perform work is called gradient to perform work is called

chemiosmosischemiosmosis

Hmm… Where else have I seen

this Chemiosmosis??


An Aside: An Aside: Proton Proton

pumps also pumps also make make critical critical

nutrients nutrients available available via via Cation Cation ExchangeExchange

Cellular Level Transport: Cellular Level Transport: OsmosisOsmosis

The effects of osmosis are different in The effects of osmosis are different in plant and animal cells. plant and animal cells.

WHY?WHY?


The effects of osmosis are different in plant and The effects of osmosis are different in plant and animal cells. animal cells.

The cell wall creates The cell wall creates turgor pressureturgor pressure..

The combined effects of solute concentration The combined effects of solute concentration and pressure are called and pressure are called water potential.water potential.

Water will move across a membrane Water will move across a membrane from an area of high water from an area of high water

potential to the solution with lower potential to the solution with lower water potentialwater potential


Water Potential (psi) is often Water Potential (psi) is often measured in measured in megapascalsmegapascals (MPa) (MPa)


1 MPa = ~ 10 1 MPa = ~ 10 atmospheres of atmospheres of

pressurepressure

The presence of The presence of solutes solutes lowerslowers the the

water potential water potential

Water diffuses Water diffuses across the across the membrane membrane towards the towards the

solution with lower solution with lower water potentialwater potential


But must also But must also consider the consider the influence of influence of pressure…pressure…

Increasing pressure Increasing pressure increasesincreases the the water potential water potential

(directly (directly proportional)proportional)


External pressure or negative pressure (External pressure or negative pressure (tensiontension) ) can force water across the membrane against can force water across the membrane against

its concentration gradient.its concentration gradient.


Combined effects of pressure and Combined effects of pressure and solute concentration:solute concentration:

= +P S


Calculating Water Potential in Calculating Water Potential in CellsCells

Where is water potential greatest? So which way will

water move? What will the cell’s water potential be after

soaking in this solution?

Where is water potential greatest? So which way will

water move? What will the cell’s water potential be after

soaking in this solution?

Calculating Water Potential in Calculating Water Potential in CellsCells

Cellular Transport: AquaporinsCellular Transport: AquaporinsWater can cross the membrane, but not very Water can cross the membrane, but not very

rapidly!rapidly!

Cells have specific channels for traffic of water, Cells have specific channels for traffic of water, called called aquaporins aquaporins (Gated?)(Gated?)

Cellular Level Transport in Cellular Level Transport in Cells!Cells!

Cellular Level Transport in Cellular Level Transport in CellsCells

a: Longitudinal section. Plasmodesma at a young cell wall between haustorial cells of dodder (Cuscuta odorata). The endoplasmatic reticulum of the two cells forms a continuous system through the plasmodesmata. Both cells are rich in rough ER. (Ch. GLOCKENMANN, R. KOLLMANN, 1975) b: Cross-section (top view). Plasmodesmata with callose cylinders in a wall between phloem parenchyma cells in the shoot of Metasequoia glyptostroboides. (Ch. GLOCKMANN, R. KOLLMANN, 1979).

Plasmodesmata in Real Life…

Tissue Level TransportTissue Level Transport

Water and minerals are absorbed by the outer cells of Water and minerals are absorbed by the outer cells of the root, and transported to inner cells the root, and transported to inner cells (Lateral (Lateral

Transport)Transport)

Long Distance Transport: Bulk FlowLong Distance Transport: Bulk Flow

Diffusion is too slow!Diffusion is too slow!

Water and solutes Water and solutes move through move through

xylem vessels and xylem vessels and sieve tubes by sieve tubes by bulk bulk

flowflow (driven by (driven by pressure)pressure)

Lateral Transport in

Roots

Endodermis = Gatekeeper!Endodermis = Gatekeeper!

Presence of the Presence of the Casparian Casparian

StripStrip assures assures that water and that water and minerals will minerals will

have to cross a have to cross a plasma plasma

membrane of membrane of an endodermal an endodermal cell to enter the cell to enter the

stele!stele!

Transport in StemsTransport in Stems

Why do some plants have these little

water droplets hanging off them in the morning??

Transport in StemsTransport in Stems

Xylem sapXylem sap ascends ascends (bulk transport) due (bulk transport) due

to to

root pressureroot pressure and and transpirational pulltranspirational pull

Root Pressure can result in guttation

Transport in Stems: Transpirational Transport in Stems: Transpirational PullPull

Our Current Model:Our Current Model:

Regulating Transpiration:Regulating Transpiration:Photosynthesis Creates a DilemmaPhotosynthesis Creates a Dilemma

Stomata must be open Stomata must be open to allow entry of COto allow entry of CO22 and clearance of Oand clearance of O22, , but open stomata but open stomata

allow for water loss!allow for water loss!

~90% of a plant’s ~90% of a plant’s water loss is through water loss is through

the stomata!the stomata!

Source: www.microscopy-uk.org.uk

Measuring EfficiencyMeasuring EfficiencyEfficiency of water Efficiency of water

use can be use can be measured by the measured by the

transpiration-to-transpiration-to-photosynthesis photosynthesis

ratioratio

For many plants (C3) the ratio is ~ 600:1 (600 g of water for each gram of CO2 incorporated)

How do you expect C4 plants to compare?

CAM plants?

Regulating Stomata is KeyRegulating Stomata is Key

Each stoma flanked by a Each stoma flanked by a pair of pair of guard cellsguard cells

Guard cells change shape, Guard cells change shape, narrowing or widening narrowing or widening the gap between themthe gap between them

How can a plant cell change its shape?!?

Osmosis is regulated by the transport of potassium Osmosis is regulated by the transport of potassium ions across the plasma membrane and tonoplastions across the plasma membrane and tonoplast


Stomata are Stomata are generally open generally open during the day, during the day, and closed at and closed at

night!night!

How do the How do the guard cells tell guard cells tell

time??time??


Regulating StomataRegulating Stomata

1.1. Light Light (Blue-light receptors in the (Blue-light receptors in the cell)- stimulates proton pumps, cell)- stimulates proton pumps, promoting the uptake of Kpromoting the uptake of K++

2.2. Depletion of CODepletion of CO22

3.3. Circadian RhythmsCircadian Rhythms

4.4. Hormonal ControlsHormonal Controls

5.5. High TemperatureHigh Temperature

The Effect:The Effect:

Onto Stems: TranslocationOnto Stems: Translocation

The Phloem sap is The Phloem sap is primarily sucrose, primarily sucrose,

and may also and may also contain minerals, contain minerals,

amino acids, amino acids, hormones, etc.hormones, etc.

Travels in variable Travels in variable directions!directions!

A A sugar sourcesugar source is a region in is a region in

which sugar is which sugar is being produced being produced

A A sugar sinksugar sink is a is a region that region that

consumes or consumes or stores sugarsstores sugars

Transport in Stems: Transport in Stems: TranslocationTranslocation

Am I a source or a sink??

Speed of Speed of phloem phloem sap flow sap flow requires requires

bulk flowbulk flow, , driven by driven by pressurepressure

- Plant Growth Wrap-up - Thinking About Transport Today: - Plant Growth Wrap-up - Thinking About...

Documents

Transcript of - Plant Growth Wrap-up - Thinking About Transport Today: - Plant Growth Wrap-up - Thinking About...