Transport in PlantsTransport in Plants

K. Foster K. Foster MScMSc. L.M.S.N. L.M.S.N

ObjectiveObjective

��Students should be able to Students should be able to demonstrate an understanding of the demonstrate an understanding of the mechanism by which plants absorb mechanism by which plants absorb minerals and water through the roots minerals and water through the roots minerals and water through the roots minerals and water through the roots and transport them through the and transport them through the xylem.xylem.

��Students should be able to:Students should be able to:

��describe using diagrams the three describe using diagrams the three mechanisms that water travels across the mechanisms that water travels across the roots.roots.roots.roots.

��State the purpose of the endodermisState the purpose of the endodermis

��Relate the structure of the xylem to its Relate the structure of the xylem to its purpose in transport and support.purpose in transport and support.

��Describe using the diagrams the Describe using the diagrams the transpiration stream.transpiration stream.

Before we do that…..Before we do that…..

��Definitions of what you should know:Definitions of what you should know:

��DiffusionDiffusion-- movement of particles from an area of high movement of particles from an area of high

concentration to an area of low concentrationconcentration to an area of low concentration..

��OsmosisOsmosis-- movement of water particles from an area of movement of water particles from an area of ��OsmosisOsmosis-- movement of water particles from an area of movement of water particles from an area of

high concentration to an area of low concentration through a high concentration to an area of low concentration through a selectively permeable membraneselectively permeable membrane

��Active transportActive transport-- movement of particles from an movement of particles from an

area of low concentration to an area of high concentration through area of low concentration to an area of high concentration through a selectively permeable membrane ( against the a selectively permeable membrane ( against the concconc gradient). gradient).

��Cytoplasmic StreamingCytoplasmic Streaming

��PinocytosisPinocytosis-- Introduction of fluids into a cell by Introduction of fluids into a cell by

invagination of the cell membrane, followed by formation invagination of the cell membrane, followed by formation of vesicles within the cells.of vesicles within the cells.

Exocytosis Exocytosis --��Exocytosis Exocytosis -- A process of cellular secretion or excretion A process of cellular secretion or excretion

in which substances contained in vesicles are discharged from the in which substances contained in vesicles are discharged from the cell by fusion of the vesicular membrane with the outer cell cell by fusion of the vesicular membrane with the outer cell

membranemembrane..

��EndocytosisEndocytosis-- A process of cellular ingestion by A process of cellular ingestion by

which the plasma membrane folds inward to bring which the plasma membrane folds inward to bring substances into the cell.substances into the cell.

Cytoplasmic streaming:Cytoplasmic streaming:

�� is the flowing of is the flowing of cytoplasmcytoplasm in in eukaryotic cellseukaryotic cells. .

�� Occurs in both Occurs in both plantplant and and animalanimal cells. cells.

�� Creates cytoplasmic reorganization during cell reproduction.Creates cytoplasmic reorganization during cell reproduction.

�� In unicellular In unicellular eukaryoteseukaryotes such as like such as like amoebaamoeba, it provides the , it provides the mechanism for cell locomotion. mechanism for cell locomotion.

It aids in the delivery of nutrients, metabolites, and genetic It aids in the delivery of nutrients, metabolites, and genetic �� It aids in the delivery of nutrients, metabolites, and genetic It aids in the delivery of nutrients, metabolites, and genetic information to all parts of larger information to all parts of larger plantplant cellscells. It vigorously . It vigorously "stirs" these components about the cytoplasm, allowing them "stirs" these components about the cytoplasm, allowing them to flow to all parts of the cell. As membraneto flow to all parts of the cell. As membrane--bound bound organellesorganellescrawl along the inner crawl along the inner cell wallcell wall they set the cytoplasm into they set the cytoplasm into motion. This streaming allows other motion. This streaming allows other organellesorganelles and nutrients and nutrients to flow in the stream created. Actin filaments play a role in to flow in the stream created. Actin filaments play a role in streaming.streaming.

HW#1HW#1

��YoutubeYoutube--look for look for cytoplasmiccytoplasmicstreaming streaming

Water Potential Water Potential ΨΨ

�� Thermodynamic term given to the energy Thermodynamic term given to the energy that water possesses.that water possesses.

�� Pure water has the highest water Pure water has the highest water potential.potential.0 Pa (Nm0 Pa (Nm--22))potential.potential.0 Pa (Nm0 Pa (Nm ))

�� Water molecules always move from high Water molecules always move from high water potential to low water potential until water potential to low water potential until [water] is equal in both systems.[water] is equal in both systems.

�� All solutions have a lower All solutions have a lower ΨΨ than pure than pure water, i.e. they are water, i.e. they are ––veve))

Solute potential Solute potential ΨΨss

��Change in water potential of a Change in water potential of a system due to the presence of solute system due to the presence of solute molecules.molecules.

��ΨΨs s is alwaysis always ––ve.ve.

Pressure Potential Pressure Potential ΨΨpp

�� if pressure is applied to pure water if pressure is applied to pure water its pressure potential increasesits pressure potential increases

�� thus if water moves inside a cell and thus if water moves inside a cell and causes turgidity then its pressure causes turgidity then its pressure ΨΨsscauses turgidity then its pressure causes turgidity then its pressure potential increasespotential increases

��ΨΨp p is usually +is usually +veve except for in the xylem when except for in the xylem when water is under tensionwater is under tension

��Ψ Ψ = = ΨΨp + p + ΨΨs s

ΨΨss

Concept checkConcept check

��Why is the Why is the ΨΨp p of water in the xylem of water in the xylem ––veve? ?

��Why is the Why is the ΨΨ of pure water?of pure water?

What happens when you add sugar What happens when you add sugar ��What happens when you add sugar What happens when you add sugar to pure water ?to pure water ?

Transport in Plants.Transport in Plants.

1.1. Transport from soil to rootTransport from soil to root

2.2. From root to xylem tissueFrom root to xylem tissue

3.3. From xylem in up into xylem in From xylem in up into xylem in stemstemstemstem

4.4. From stem into leaves.From stem into leaves.

Root AnatomyRoot Anatomy

��DicotyledonDicotyledon Microscopic view of the root of a buttercup (Ranunculus) showing the central stele and 4-pronged xylem.

Transport from Soil to Root.Transport from Soil to Root.

�� Root hairs Root hairs (extensions of the epidermis)(extensions of the epidermis) are specialized are specialized to reach into small spaces into soil to reach into small spaces into soil (many of them=large (many of them=large surface area).surface area).

�� Which has a higher water potential? Soil water or Which has a higher water potential? Soil water or root hair cells?root hair cells?

�� Soil water has some inorganic ions but it is a relatively Soil water has some inorganic ions but it is a relatively �� Soil water has some inorganic ions but it is a relatively Soil water has some inorganic ions but it is a relatively dilute solution when compared to the cell solutiondilute solution when compared to the cell solution (which has (which has inorganic substances as well as organics like sugars and proteins some inorganic substances as well as organics like sugars and proteins some wastes).wastes).

�� Root hairs also function to absorb inorganic Root hairs also function to absorb inorganic ions e.g. nitrates.ions e.g. nitrates.

�� Some roots have mutualistic mycorrhizae which Some roots have mutualistic mycorrhizae which functions like root hairs to absorb water and functions like root hairs to absorb water and nutrients e.g. Phosphates.nutrients e.g. Phosphates.

From Root hair to XylemFrom Root hair to Xylem

�� Water crosses the cortex and enters the Water crosses the cortex and enters the xylem in the centre of the root.xylem in the centre of the root.

�� Since the Since the ΨΨ xylemxylem < < ΨΨ rootroot

�� Water gets to the xylem via 3 means:Water gets to the xylem via 3 means:

Apoplastic pathwayApoplastic pathway�� Apoplastic pathwayApoplastic pathway (cell wall to cell wall)(cell wall to cell wall)

�� Symplastic pathway (Symplastic pathway (through cytoplasm and through cytoplasm and plasmodesmata)plasmodesmata)

�� Vacuolar pathway (Vacuolar pathway ( through cell membrane through cell membrane cytoplasm and tonoplast of the cytoplasm and tonoplast of the vacuole)vacuole)--little water moves little water moves

through this pthrough this p--wayway

Transport of Minerals and Water in Transport of Minerals and Water in

RootsRoots

HW2HW2

��Why did the Lord place the Why did the Lord place the endodermis there?endodermis there?

From Root hair to XylemFrom Root hair to Xylem

�� Once the water reaches the stele Once the water reaches the stele apoplastic p’way is barred except in apoplastic p’way is barred except in passage cells.passage cells.

�� Presence of waxy, watery suberin in Presence of waxy, watery suberin in Presence of waxy, watery suberin in Presence of waxy, watery suberin in endodermisendodermis-- Casparian strip.Casparian strip.

�� As the endodermal cells get older suberin As the endodermal cells get older suberin deposits are more extensivedeposits are more extensive

�� Once across the endodermis the water Once across the endodermis the water continues to move down continues to move down ΨΨ gradient.gradient.

Up the Xylem… Up the Xylem…

��CapillarityCapillarity

��TranspirationTranspiration

��Root pressure (not as much)Root pressure (not as much)

XylemXylem

Functions

1. support

2. transport

Support:Support:

Has sclerenchyma cells with thickened walls not involved in transport.

These have lignin laid down within them.

Where no lignin is laid down=pits/not open pores(crossed by cellulose walls-permeable).

Structure of the XylemStructure of the Xylem

XylemXylem

�� The end walls of The end walls of neighbouring neighbouring vessel elements vessel elements break down break down =continuous =continuous =continuous =continuous drainpipedrainpipe

�� Tube is long and Tube is long and nonnon--living.living.

�� What causes What causes water to move up water to move up the plant?the plant?

CapillarityCapillarity

TranspirationTranspiration

��Air spaces in mesophyll layer are Air spaces in mesophyll layer are looseloose--filled with airfilled with air

��Cell walls are wet.Cell walls are wet.

If there is a If there is a ΨΨ gradient b/w leaf and gradient b/w leaf and �� If there is a If there is a ΨΨ gradient b/w leaf and gradient b/w leaf and external env. Then water diffuses external env. Then water diffuses from the leaf.from the leaf.

TranspirationTranspiration

The Transpiration StreamThe Transpiration Stream

1.1. Water moves up the xylem Water moves up the xylem vesselsvessels

2.2. Water leaves a xylem vessel through Water leaves a xylem vessel through a pit. It may enter the cytoplasm or a pit. It may enter the cytoplasm or a pit. It may enter the cytoplasm or a pit. It may enter the cytoplasm or cell wall of a mesophyll cell.cell wall of a mesophyll cell.

3.3. Water from the mesophyll Water from the mesophyll cytoplasm enters the cell wall.cytoplasm enters the cell wall.

Transpiration cont’dTranspiration cont’d

1.1. Water evaporates form the cell Water evaporates form the cell wall into the air space through wall into the air space through an open stoma.an open stoma.

2.2. Water vapour diffuses from the Water vapour diffuses from the 2.2. Water vapour diffuses from the Water vapour diffuses from the air space through an open air space through an open stomastoma

3.3. Water vapour is carried away Water vapour is carried away from the leaf surface by air from the leaf surface by air movements.movements.

Functions of transpirationFunctions of transpiration

��Cools leafCools leaf

��Transport of mineral saltsTransport of mineral salts

��What about water stress?What about water stress?��What about water stress?What about water stress?

��ABA (abcisic acid)ABA (abcisic acid)--plant growth plant growth regulator produced by the root regulator produced by the root secreted into xylemsecreted into xylem--causes rapid causes rapid closure of stomata when there is no closure of stomata when there is no water in soil.water in soil.

Factors that Affect Transpiration Factors that Affect Transpiration

RateRate

�� Describe the effect of Describe the effect of

�� Wind speed,Wind speed,

�� TemperatureTemperature

�� LightLight�� LightLight

�� Humidity and Humidity and VapourVapour pressure on pressure on transpiration rate.transpiration rate.

–– There are some There are some xeromorphicxeromorphic adaptations that adaptations that some plants have to counteract the effects of some plants have to counteract the effects of Transpiration Discuss… HW 3Transpiration Discuss… HW 3

Root PressureRoot Pressure

��There is active secretion of solutes There is active secretion of solutes (mineral ions) into the water in the (mineral ions) into the water in the xylem vessels in the root.xylem vessels in the root.

��The presence of solutes lowers the The presence of solutes lowers the ΨΨ��The presence of solutes lowers the The presence of solutes lowers the ΨΨin the xylem = influx of waterin the xylem = influx of water

�� Nb water can continue to move up the plant even if it is Nb water can continue to move up the plant even if it is deaddead--once there is transpiration pull.once there is transpiration pull.

What about the uptake of ionsWhat about the uptake of ions

��Occurs by active transportOccurs by active transport

��Observations:Observations:

Affected by: metabolic poisonsAffected by: metabolic poisons

presence of oxygenpresence of oxygenpresence of oxygenpresence of oxygen

raising the temperature raising the temperature

PhloemPhloem

�� Consist of sieve elements and Companion Consist of sieve elements and Companion cells….cells….

�� Sieve tubes are made up of sieve elongated Sieve tubes are made up of sieve elongated elements joined end to end vertically to form a elements joined end to end vertically to form a continuous columncontinuous column--where they meet =sieve where they meet =sieve continuous columncontinuous column--where they meet =sieve where they meet =sieve plate.plate.

�� Each sieve element is living….Each sieve element is living….

�� It has everything like a normal plant cell except It has everything like a normal plant cell except nucleus or ribosomes…nucleus or ribosomes…

�� Thin layer of cytoplasmThin layer of cytoplasm

Companion CellsCompanion Cells

�� Each sieve element has at least one sieve Each sieve element has at least one sieve element beside it.element beside it.

�� Have the structure of a normal plant cell.Have the structure of a normal plant cell.

�� However the number of mitochondria and However the number of mitochondria and �� However the number of mitochondria and However the number of mitochondria and ribosomesribosomes are larger than a normal cell.are larger than a normal cell.

�� Numerous Numerous plasmodesmataplasmodesmata pass through pass through their walls.their walls.

�� Why do u think?Why do u think?

�� To make direct contact b/w sieve elementTo make direct contact b/w sieve element

Structure of the PhloemStructure of the Phloem

Contents of the PhloemContents of the PhloemSolute Solute Concentration Concentration

(mol/dm(mol/dm33))

SucroseSucrose 250250

K+K+ 8080

Amino acidsAmino acids 4040

ClCl-- 1515ClCl-- 1515

PO4PO4 1010

Mg2+Mg2+ 55

Na+Na+ 22

ATPATP 0.50.5

NO3NO3-- 00

Plant growth Plant growth substances eg auxin, substances eg auxin, cytokininscytokinins

Small tracesSmall traces

Which of the previous substances have Which of the previous substances have

been synthesized by the plant?been synthesized by the plant?

�� If you answered:If you answered:

1.1. SucroseSucrose

2.2. Amino acidsAmino acids

ATPATP3.3. ATPATP

4.4. AuxinsAuxins

5.5. CytokininsCytokinins

Then you are correct!!!Then you are correct!!!

How did they sample the phloem How did they sample the phloem

contents?contents?

Translocation?Translocation?

�� Phloem sap moves by mass flow Phloem sap moves by mass flow (just like the (just like the

xylem)xylem)--

�� however unlike the xylem energy is used to however unlike the xylem energy is used to create the pressure differencecreate the pressure difference--(Active )(Active )create the pressure differencecreate the pressure difference--(Active )(Active )

�� Active loading of the sucrose into the sieve Active loading of the sucrose into the sieve elements from elements from point of transportpoint of transport (source)(source) to to sinksink(where the sucrose is going to be removed)(where the sucrose is going to be removed)

�� How does this happen?How does this happen?

Munch’s Mass Flow HypothesisMunch’s Mass Flow Hypothesis

Your time…..Your time…..

1.1. Explain the pressure flow hypothesis that Explain the pressure flow hypothesis that transports the sucrose from the source transports the sucrose from the source to sink to sink against the concentration against the concentration gradientgradient

2.2. Compare the structures of the sieve Compare the structures of the sieve element and the xylem vessel.element and the xylem vessel.

3.3. Construct a table to compare and Construct a table to compare and contrast the mechanisms of transport in contrast the mechanisms of transport in the xylems and the xylems and phloemsphloems

1.1. Plants which live in environments Plants which live in environments where the soil is very salty, such as where the soil is very salty, such as estuaries are called halophytes.estuaries are called halophytes.

a)a) What problems might halophytes What problems might halophytes a)a) What problems might halophytes What problems might halophytes have to overcome with regards to have to overcome with regards to taking up water and maintaining a taking up water and maintaining a suitable salt and water suitable salt and water concentration in their cells?concentration in their cells?

b) Suggest how each of the following b) Suggest how each of the following adaptations might help a halophyte adaptations might help a halophyte to overcome these problems:to overcome these problems:

i.i. Rapid active uptake of ions, such as Rapid active uptake of ions, such as i.i. Rapid active uptake of ions, such as Rapid active uptake of ions, such as NaNa++ and Cland Cl--, by the roots., by the roots.

ii.ii. Ability to tolerate low water Ability to tolerate low water potentials in cell sap and potentials in cell sap and cytoplasm.cytoplasm.

i.i. Ability to maintain higher salt Ability to maintain higher salt concentrations in cell vacuoles than concentrations in cell vacuoles than in cytoplasm, by active transport of in cytoplasm, by active transport of sodium and chlorine ions across the sodium and chlorine ions across the sodium and chlorine ions across the sodium and chlorine ions across the tonoplast.tonoplast.

ii.ii. Salt glands in leaves, which actively Salt glands in leaves, which actively excrete salt onto the surface of the excrete salt onto the surface of the leaf.leaf.