Lecture

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Lecture 5 Plant Transport
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Key Concepts

• The importance of water
• Water potential ? P - s
• How water moves gradients, mechanisms and
  pathways
• Transpiration water movement from soil to plant
  to atmosphere
• The pressure flow model of phloem transport

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WHY WATER???

• Required for metabolism and cytoplasm
• Nutrients are taken up and transported in
  water-based solution
• Metabolic products are transported in water-based
  solution
• Water movement through the plant affects gas
  exchange and leaf T

Diagram movement of water through a tree
4
Water Potential (?)

• Controls the movement of water
• A measure of potential energy
• Water always moves from an area of HIGH water
  potential to an area of LOW water potential
• Controlled by physical pressure, solute
  concentration, adhesion of water to cell
  structures and to soil particles, temperature,
  and gravity

? P - s
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Diagram water moves from high water potential
to low water potential, sometimes toward a
negative value same next 3 slides
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minus 4 is MORE NEGATIVE than minus 1
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High
Low
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Diagram water potential is universal, including
with waterfalls
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Water Potential (?)

• Controls the movement of water
• A measure of potential energy
• Water always moves from an area of HIGH water
  potential to an area of LOW water potential
• Controlled by physical pressure, solute
  concentration, adhesion of water to cell
  structures and to soil particles, temperature,
  and gravity

? P - s
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P Pressure Potential

• By convention, set to zero in an open container
  of water (atmospheric pressure only)
• In the plant cell, P can be positive, negative or
  zero
• A cell with positive pressure is turgid
• A cell with negative pressure is plasmolyzed
• A cell with zero pressure is flaccid

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Turgid P gt 0 Plasmolyzed P lt 0 Flaccid
P 0
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What are the little green things???
Micrograph photosynthetic cells turgid on
left, plasmolyzed on right same on next 3 slides
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Turgid Plasmolyzed
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Critical Thinking

• How can you tell this tissue was artificially
  plasmolyzed?

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Critical Thinking

• How can you tell this tissue was artificially
  plasmolyzed?
• Observe the cell on the far right it is still
  turgid ?

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Crispy means plasmolyzed beyond the permanent
wilting point ?
Image turgid plant on left, plasmolyzed on right
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s Solute Potential

• s zero for pure water
• Pure H2O nothing else, not a solution
• Adding solutes ALWAYS decreases the potential
  energy of water
• Some water molecules now carry a load there is
  less free water

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Remember, ? P s
Diagram effect on water potential of adding
salts to solutions separated by semi-permeable
membrane
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? P s

• Pressure can be , -, or 0
• Solutes always have a negative effect
• Simplest way to calculate ? is by this equation

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Flaccid cell in pure water what
happens??? ..what do you know???
.what do you need to know???
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Flaccid cell in pure water what happens???
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Flaccid cell in pure water what happens???
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Flaccid cell in pure water what happens???
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Flaccid cell in pure water what happens???
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Flaccid cell in pure water what
happens??? ..what do you know???
.what do you need to know???
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Flaccid cell in pure water what happens???
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Flaccid cell in pure water what happens???
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Flaccid cell in pure water what happens???
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Flaccid cell in pure water what happens???
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Flaccid cell in pure water what happens???
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Then what happens???
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Then what happens???
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Then what happens???
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Water Movement

• Osmosis the diffusion of water one molecule at
  a time across a semi-permeable membrane
• Controlled by both P and s
• Bulk Flow the movement of water in bulk as a
  liquid
• Controlled primarily by P

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Osmosis
Diagram osmosis across a semi-permeable
membrane next slide also
Critical Thinking Where does water move by
osmosis in plants???
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Osmosis
Critical Thinking Where does water move by
osmosis in plants??? Cell membrane is
semi-permeable
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Water Movement

• Osmosis the diffusion of water one molecule at
  a time across a semi-permeable membrane
• Controlled by both P and s
• Bulk Flow the movement of water in bulk as a
  liquid
• Controlled primarily by P

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Water Movement

• Osmosis the diffusion of water one molecule at
  a time across a semi-permeable membrane
• Controlled by both P and s
• Bulk Flow the movement of water in bulk as a
  liquid
• Controlled primarily by P no membrane, no
  solute gradient!

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Critical Thinking

• Where does water move by bulk flow in plants???

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Critical Thinking

• Where does water move by bulk flow in plants???
• Primarily in the xylem, also in phloem and in the
  cell walls

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Routes of water transportsoil ? root ? stem ?
leaf ? atmosphere
Cell Wall Cell Membrane Cytoplasm
Diagram apoplast, symplast and transmembrane
pathways same on next slide
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Routes of water transportsoil ? root ? stem ?
leaf ? atmosphere
Cell Wall Cell Membrane Cytoplasm
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Diagram Casparian strip same on next 2 slides
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The Casparian Strip is a band of suberin in the
transverse and radial (but not the tangential)
walls of the endodermis cells Water CANNOT PASS
THROUGH the Casparian Strip Water must GO AROUND
the Casparian Strip through the tangential face
of the endodermis
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The Casparian Strip is a band of suberin in the
transverse and radial (but not the tangential)
walls of the endodermis cells Water CANNOT PASS
THROUGH the Casparian Strip Water must GO AROUND
the Casparian Strip through the tangential face
of the endodermis
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Critical Thinking

• Apoplast water is forced into the symplast at the
  Casparian Strip
• What does this mean for the water???
• What is the function of the Casparian Strip???

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Critical Thinking

• Apoplast water is forced into the symplast at the
  Casparian Strip
• What does this mean for the water???
• It has to cross a cell membrane (easy for water!)
• What is the function of the Casparian Strip???

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Critical Thinking

• Apoplast water is forced into the symplast at the
  Casparian Strip
• What does this mean for the water???
• It has to cross a cell membrane (easy for water!)
• What is the function of the Casparian Strip???
• Solute uptake is regulated at the membrane!!!

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Membrane Transport(review in text if necessary)
Diagram review of membrane transport proteins
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Water is on the move
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Transpiration
Diagram transpiration

• Movement of water from soil ? plant ? atmosphere
• Controlled by HUGE water potential gradient
• Gradient controlled by P
• Very little s contribution

? P - s
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Stomates are the Valvesas long as the stomata
are open, water will move through the plant
Micrograph stomata
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Transpiration
Diagram transpiration

• Movement of water from soil ? plant ? atmosphere
• Controlled by HUGE water potential gradient
• Gradient controlled by P
• Very little s contribution

? P - s
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Solar Heating Drives the Process

• Air is dry because of solar heating
• The air molecules bounce around more which causes
  air masses to expand
• Warm air has tremendous capacity to hold water
  vapor
• Warm, dry air dramatically reduces the ? of the
  atmosphere
• Daytime gradient is commonly 30 MPa

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Critical Thinking

• Why do we have life on this planet and not the
  others in our solar system???

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Critical Thinking

• Why do we have life on this planet and not the
  others in our solar system???
• Liquid water!
• Why do we have liquid water???

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Critical Thinking

• Why do we have life on this planet and not the
  others in our solar system???
• Liquid water!
• Why do we have liquid water???
• 3rd rock from the sun!
• The Goldilocks Zone not too hot, not too cold
• Plus, we have enough gravity to hold our
  atmosphere in place
• Its our atmosphere that holds the warmth

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Life is Random
Model our solar system
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Solar Heating Drives the Process

• Air is dry because of solar heating
• The air molecules bounce around more which causes
  air masses to expand
• Warm air has tremendous capacity to hold water
  vapor
• Warm, dry air dramatically reduces the ? of the
  atmosphere
• Daytime gradient is commonly 30 MPa

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Critical Thinking

• Under what conditions does atmospheric water
  potential approach zero???

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Critical Thinking

• Under what conditions does atmospheric water
  potential approach zero???
• Only in the pouring rain

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Gradient is HUGE

• Pressure plumbing 0.25 MPa
• Fully inflated car tire 0.2 MPa
• Only in the pouring rain does atmospheric ?
  approach zero
• Soil ? is zero under most conditions
• Remember gradient is NEGATIVE
• Water is pulled into plant under TENSION

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Gradient is HUGE

• Pressure plumbing 0.25 MPa
• Fully inflated car tire 0.2 MPa
• Only in the pouring rain does atmospheric ?
  approach zero
• Soil ? is zero under most conditions
• Remember gradient is NEGATIVE
• Water is pulled into plant under TENSION

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Gradient is HUGE

• Pressure plumbing 0.25 MPa
• Fully inflated car tire 0.2 MPa
• Only in the pouring rain does atmospheric ?
  approach zero
• Soil ? is zero under most conditions
• Remember gradient is NEGATIVE
• Water is pulled into plant under TENSION

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The tension gradient is extreme, especially
during the day Sunday, 1 October 2006 8 am
RH 86 Noon RH 53 4 pm RH 36 8 pm
RH 62 5am, 23 September 94 in light rain
Diagram transpiration gradient from soil to
atmosphere
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Critical Thinking

• Tension is a strong force!
• Why doesnt the water stream break???
• Adhesion and cohesion
• Why doesnt the xylem collapse???
• Lignin!

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Critical Thinking

• Tension is a strong force!
• Why doesnt the water stream break???
• Adhesion and cohesion
• Why doesnt the xylem collapse???

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Critical Thinking

• Tension is a strong force!
• Why doesnt the water stream break???
• Adhesion and cohesion
• Why doesnt the xylem collapse???
• Lignin!!!

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Diagram transpiration gradient plus pathways
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Table water use by various crops
One hectare (2 football fields) of corn
transpires about 6 million liters of water per
growing season the equivalent of 2 of water
over the entire hectare
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Transpiration is a powerful force!

• A single broadleaf tree can move 4000 liters of
  water per day!!! (about 1000 gallons)
• If humans had to drink that much water we would
  drink about 10 gallons per day!
• Transpiration accounts for 90 of
  evapotranspiration over most terrestrial surfaces
• Plants are the most important component of the
  hydrological cycle over land!!!

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Tropical deforestation is leading to ecological
and social disaster

• Poverty, famine and forced migration
• 250 million victims of ecological destruction
  thats about how many people live in the US!
• .and just a tiny fraction of the worlds
  impoverished people

Image deforestation snaps water cycle and also
results in erosion
You can help change this!!!
Panama
Guatemala
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Tropical deforestation is leading to ecological
and social disaster

• Poverty, famine and forced migration
• 250 million victims of ecological destruction
  thats about how many people live in the US!
• .and just a tiny fraction of the worlds
  impoverished people

You MUST help change this!!!
Panama
Guatemala
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Social Justice
Im not angry with you
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Social Justice
But I do expect you to DO something!!!
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Transpiration is a Natural Process

• It is a physical process that occurs as long as
  the gradient exists and the pathway is open
• Under adequate soil moisture conditions the
  enormous water loss is not a problem for the plant

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Critical Thinking

• What happens when soil moisture becomes limited???

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Critical Thinking

• What happens when soil moisture becomes
  limited???
• Water stress causes stomata to close
• What then???

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Critical Thinking

• What happens when soil moisture becomes
  limited???
• Water stress causes stomata to close
• What then???
• Gas exchange ceases no CO2 no photosynthesis

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What happens when soil moisture becomes limited???

• Water stress causes stomata to close
• Closed stomata halt gas exchange
• P/T conflict ? P/T compromise
• Stomata are generally open during the day, closed
  at night
• Abscissic acid promotes stomata closure daily,
  and under water stress conditions
• Other structural adaptations limit water loss
  when stomata are open
• Other metabolic pathways (C4, CAM) limit water
  loss

85
Normally, stomata open during the day and close
at night in response to changes in K
concentration in stomata guard cells

• K accumulation is triggered by increased light,
  low carbon dioxide, circadian rhythms

• High K does what to ????

Micrograph turgid guard cells same next 4
slides
86
Normally, stomata open during the day and close
at night in response to changes in K
concentration in stomata guard cells

• K accumulation is triggered by increased light,
  low carbon dioxide, circadian rhythms

• High K lowers water potential in guard cells
• What does water do???

87
Normally, stomata open during the day and close
at night in response to changes in K
concentration in stomata guard cells

• K accumulation is triggered by increased light,
  low carbon dioxide, circadian rhythms

• High K lowers water potential in guard cells
• Water enters, cells swell and buckle

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Normally, stomata open during the day and close
at night in response to changes in K
concentration in stomata guard cells

• K accumulation is triggered by increased light,
  low carbon dioxide, circadian rhythms

• High K lowers water potential in guard cells
• Water enters, cells swell and buckle
• Pore opens

89
Normally, stomata open during the day and close
at night in response to changes in K
concentration in stomata guard cells

• K accumulation is triggered by increased light,
  low carbon dioxide, circadian rhythms

• High K lowers water potential in guard cells
• Water enters, cells swell and buckle
• Pore opens
• Reverse at night closes the pores

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Diagram open and closed stomata
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Abscissic acid is the hormone that mediates this
response
Diagram hormone mediated stomatal opening and
closing
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Cellulose orientation determines shape of turgid
cells
Diagram spoke-like orientation of cellulose
microfibrils
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What happens when soil moisture becomes limited???

• Water stress causes stomata to close
• Closed stomata halt gas exchange
• P/T conflict ? P/T compromise
• Stomata are generally open during the day, closed
  at night
• Abscissic acid promotes stomata closure daily,
  and under water stress conditions
• Other structural adaptations limit water loss
  when stomata are open
• Other metabolic pathways (C4, CAM) limit water
  loss

94
Micrograph location of stomatal gradient
This is the gradient that counts
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Images structural adaptations to dry
environments
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Spatial separation helps C4 plants be more
efficient in hot climates Temporal separation
does the same for CAM plants Both use an enzyme
that cant fix O2 to first capture CO2 Both
adaptations allow photosynthesis to proceed with
stomata largely closed during the day
Images and diagrams metabolic adaptations to
dry environments
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Phloem Transport

• Most of phloem sap is water (70 )
• Solutes in phloem sap are mostly carbohydrates,
  mostly sucrose for most plant species
• Other solutes (ATP, mineral nutrients, amino
  acids, hormones, secondary metabolites, etc) can
  also be translocated in the phloem
• Phloem transport driven by water potential
  gradients, but the gradients develop due to
  active transport both P and s are important

98
The Pressure Flow Model For Phloem Transport
Diagram pressure flow model of phloem flow
this diagram is repeated throughout this section

• Xylem transport is uni-directional, driven by
  solar heating
• Phloem flow is multi-directional, driven by
  active transport source to sink

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The Pressure Flow Model For Phloem Transport

• Sources can be leaves, stems or roots
• Sinks can be leaves, stems, roots or reproductive
  parts (especially seeds and fruits)

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The Pressure Flow Model For Phloem Transport

• Sources and sinks vary depending on metabolic
  activity, which varies daily and seasonally
• Most sources supply the nearest sinks, but some
  take priority

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Active transport (uses ATP) builds high sugar
concentration in sieve cells adjacent to source
Diagram the transport proteins that actively
transport sucrose into the phloem cells from the
leaf cells
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The Pressure Flow Model For Phloem Transport

• High solute at source end does what to ????

103
Critical Thinking

• Remember the water potential equation
• ? P - s
• What happens to ? as s increases???

104
Critical Thinking

• Remember the water potential equation
• ? P - s
• What happens to ? as s increases???
• Water potential is reduced
• This is what happens at the source end of the
  phloem

105
The Pressure Flow Model For Phloem Transport

• High solute at source end decreases ?
• What does water do???

106
Critical Thinking

• Remember the water potential equation
• ? P - s
• What does water do when ? decreases???

107
Critical Thinking

• Remember the water potential equation
• ? P - s
• What does water do when ? decreases???
• Water moves toward the area of lower water
  potential
• This is what happens at the source end of the
  phloem
• Where does the water come from???

108
Critical Thinking

• Remember the water potential equation
• ? P - s
• What does water do when ? decreases???
• Water moves toward the area of lower water
  potential
• This is what happens at the source end of the
  phloem
• Where does the water come from???
• The adjacent xylem remember structure and
  function are related!

109
The Pressure Flow Model For Phloem Transport

• High solute at source end decreases ?
• Water moves into the source end of the phloem
• What does this do to P at the source end?

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Critical Thinking

• What will happen to water pressure in any plant
  cell as water moves in???

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Critical Thinking

• What will happen to water pressure in any plant
  cell as water moves in???
• It increases
• Why???

112
Critical Thinking

• What will happen to water pressure in any plant
  cell as water moves in???
• It increases
• Why???
• The cell wall limits expansion it pushes back

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The Pressure Flow Model For Phloem Transport

• High solute at source end decreases ?
• Water moves into the source end of the phloem
• This increases the pressure

114
The Pressure Flow Model For Phloem Transport

• Increased pressure at source end causes phloem
  sap to move to any area of lower ? sinks

115
The Pressure Flow Model For Phloem Transport

• At sink end, the sugars are removed by
  metabolism, by conversion to starch, or by active
  transport

116
The Pressure Flow Model For Phloem Transport

• What then happens to the ? at the sink end of the
  phloem???

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Critical Thinking

• Remember the water potential equation
• ? P - s
• What happens to ? as s decreases???

118
Critical Thinking

• Remember the water potential equation
• ? P - s
• What happens to ? as s decreases???
• Water potential is increased
• This is what happens at the sink end of the phloem

119
The Pressure Flow Model For Phloem Transport

• ? goes up at the sink end of the phloem
• What does water do???

120
Critical Thinking

• Remember the water potential equation
• ? P - s
• What does water do when ? increases???

121
Critical Thinking

• Remember the water potential equation
• ? P - s
• What does water do when ? increases???
• Water moves away from the area of higher water
  potential
• This is what happens at the sink end of the
  phloem
• Where does the water go???

122
Critical Thinking

• Remember the water potential equation
• ? P - s
• What does water do when ? increases???
• Water moves away from the area of higher water
  potential
• This is what happens at the sink end of the
  phloem
• Where does the water go???
• The adjacent xylem remember structure and
  function are related!

123
The Pressure Flow Model For Phloem Transport

• ? goes up at the sink end of the phloem
• Water leaves the phloem at the sink end, thus
  reducing ?
• Adjacent xylem provides and accepts the water

124
The Pressure Flow Model For Phloem Transport

• Thus the phloem sap moves from source to sink
• Some xylem water is cycled into and out of the
  phloem in the process

125
The Pressure Flow Model For Phloem Transport

• Active transport is always involved at the source
  end, but only sometimes at the sink end

126
Critical Thinking

• What about the structure of the sieve cells
  facilitates the movement of phloem sap???

Micrograph sieve cells same next slide
127
Critical Thinking

• What about the structure of the sieve cells
  facilitates the movement of phloem sap???
• The open sieve plate
• The lack of major organelles

128
The Pressure Flow Model For Phloem
TransportQuestions???
129
Key Concepts Questions???

• The importance of water
• Water potential ? P - s
• How water moves gradients, mechanisms and
  pathways
• Transpiration water movement from soil to plant
  to atmosphere
• The pressure flow model of phloem transport