Transcript Slide 1
Lecture #5 – Plant Transport Image of waterfall 1 Key Concepts: • The importance of water • Water potential: Ψ = 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 2 WHY WATER??? • Required for metabolism and cytoplasm • Nutrients are taken up and transported in water-based solution • Metabolic products are transported in waterbased solution • Water movement through the plant affects gas exchange and leaf T Diagram – movement of water through a tree 3 Water Potential (Ψ): • 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 Ψ=P-s 4 Diagram – water moves from high water potential to low water potential, sometimes toward a negative value; same next 3 slides 5 6 minus 4 is MORE NEGATIVE than minus 1 7 High Low 8 Diagram – water potential is universal, including with waterfalls 9 Water Potential (Ψ): • 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 Ψ=P-s 10 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 11 Turgid P>0 Plasmolyzed P<0 Flaccid P=0 12 What are the little green things??? Micrograph – photosynthetic cells: turgid on left, plasmolyzed on right; same on next 3 slides 13 Turgid Plasmolyzed 14 Critical Thinking • How can you tell this tissue was artificially plasmolyzed? 15 Critical Thinking • How can you tell this tissue was artificially plasmolyzed? 16 Crispy means plasmolyzed beyond the permanent wilting point Image – turgid plant on left, plasmolyzed on right 17 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 s s s 18 Remember, Ψ=P–s Diagram – effect on water potential of adding salts to solutions separated by semi-permeable membrane 19 Ψ=P–s Pressure can be +, -, or 0 Solutes always have a negative effect Simplest way to calculate Ψ is by this equation 20 Flaccid cell in pure water – what happens??? …..what do you know??? ….what do you need to know??? 21 Flaccid cell in pure water – what happens??? Ψ=? 22 Flaccid cell in pure water – what happens??? 23 Flaccid cell in pure water – what happens??? 24 Flaccid cell in pure water – what happens??? 25 Flaccid cell in pure water – what happens??? …..what do you know??? ….what do you need to know??? 26 Flaccid cell in pure water – what happens??? 27 Flaccid cell in pure water – what happens??? 28 Flaccid cell in pure water – what happens??? 29 Flaccid cell in pure water – what happens??? 30 Flaccid cell in pure water – what happens??? 31 Then what happens??? 32 Then what happens??? 33 Then what happens??? 34 Hands On • Prepare a section of plump celery and stain with T-blue • Examine and describe • Introduce a drop of salt water • Any change??? • Examine the stalk of celery that was in salt water vs. one that was in fresh water • Explain your observations in your lab notes. 35 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 36 Osmosis Diagram – osmosis across a semi-permeable membrane; next slide also Critical Thinking: Where does water move by osmosis in plants??? 37 Osmosis Critical Thinking: Where does water move by osmosis in plants??? Cell membrane is semi-permeable 38 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 39 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 – 40 Critical Thinking • Where does water move by bulk flow in plants??? 41 Critical Thinking • Where does water move by bulk flow in plants??? 42 Routes of water transport soil root stem leaf atmosphere Cell Wall Cell Membrane Diagram – apoplast, symplast and transmembrane pathways; same on next slide Cytoplasm 43 Routes of water transport soil root stem leaf atmosphere Cell Wall Cell Membrane Cytoplasm 44 Diagram – Casparian strip; same on next 2 slides 45 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 46 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 47 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??? 48 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??? 49 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??? 50 Membrane Transport (review in text if necessary) Diagram – review of membrane transport proteins 51 Water is on the move 52 Transpiration Diagram – transpiration • Movement of water from soil plant atmosphere • Controlled by HUGE water potential gradient • Gradient controlled by P Very little s contribution Ψ=P-s 53 Stomates are the Valves: as long as the stomata are open, water will move through the plant Micrograph – stomata 54 Transpiration Diagram – transpiration • Movement of water from soil plant atmosphere • Controlled by HUGE water potential gradient • Gradient controlled by P Very little s contribution Ψ=P-s 55 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 Ψ of the atmosphere • Daytime gradient is commonly 30+ MPa 56 Critical Thinking • Why do we have life on this planet and not the others in our solar system??? 57 Critical Thinking • Why do we have life on this planet and not the others in our solar system??? • Why do we have liquid water??? 58 Critical Thinking • Why do we have life on this planet and not the others in our solar system??? • Why do we have liquid water??? 59 Life is Random Model – our solar system 60 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 Ψ of the atmosphere • Daytime gradient is commonly 30+ MPa 61 - 200 asymptotic Atmospheric water potential (MPa) - 30 0 0 80 100 Relative Humidity (%) 62 Critical Thinking • Under what conditions does atmospheric water potential approach zero??? - 200 asymptotic Atmospheric water potential (MPa) - 30 0 0 80 100 63 Relative Humidity (%) Critical Thinking • Under what conditions does atmospheric water potential approach zero??? - 200 asymptotic Atmospheric water potential (MPa) - 30 0 0 80 100 64 Relative Humidity (%) Gradient is HUGE • Pressure plumbing ~ 0.25 MPa • Fully inflated car tire ~ 0.2 MPa • Only in the pouring rain does atmospheric Ψ approach zero • Soil Ψ is ~ zero under most conditions • Remember – gradient is NEGATIVE • Water is pulled into plant under TENSION 65 Gradient is HUGE • Pressure plumbing ~ 0.25 MPa • Fully inflated car tire ~ 0.2 MPa • Only in the pouring rain does atmospheric Ψ approach zero • Soil Ψ is ~ zero under most conditions • Remember – gradient is NEGATIVE • Water is pulled into plant under TENSION 66 - 200 asymptotic Atmospheric water potential (MPa) - 30 0 0 80 100 Relative Humidity (%) 67 Gradient is HUGE • Pressure plumbing ~ 0.25 MPa • Fully inflated car tire ~ 0.2 MPa • Only in the pouring rain does atmospheric Ψ approach zero • Soil Ψ is ~ zero under most conditions • Remember – gradient is NEGATIVE • Water is pulled into plant under TENSION 68 The tension gradient is extreme, especially during the day Diagram – transpiration gradient from soil to atmosphere 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 69 - 200 asymptotic Atmospheric water potential (MPa) - 30 0 0 80 100 Relative Humidity (%) 70 Critical Thinking • Tension is a strong force! • Why doesn’t the water stream break??? • Adhesion and cohesion • Why doesn’t the xylem collapse??? • Lignin! 71 Critical Thinking • Tension is a strong force! • Why doesn’t the water stream break??? • Why doesn’t the xylem collapse??? 72 Critical Thinking • Tension is a strong force! • Why doesn’t the water stream break??? • Why doesn’t the xylem collapse??? 73 Diagram – transpiration gradient plus pathways 74 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… 75 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!!! 76 Tropical deforestation is leading to ecological and social disaster • Poverty, famine and forced migration • 250 million victims of ecological destruction – that’s about how many people live in the US! ….and just a tiny fraction of the world’s impoverished people You can help change this!!! Image – deforestation snaps water cycle and also results in erosion 77 Panama Guatemala Tropical deforestation is leading to ecological and social disaster • Poverty, famine and forced migration • 250 million victims of ecological destruction – that’s about how many people live in the US! ….and just a tiny fraction of the world’s impoverished people You MUST help change this!!! 78 Panama Guatemala Social Justice I’m not angry with you …… 79 Social Justice But I do expect you to DO something !!! 80 Hands On • Examine variegated plant Water with dye solution What do you expect??? • Set up experiments with white carnations Vary conditions of light, temperature and air flow Re-cut stems and place in dye solution – why? • Be sure to develop hypotheses • Discuss findings with team and be prepared to share conclusions with the class 81 Hands On • Work with team to develop hypotheses about how different species might vary in water transport – rely on locally available plant species, and vary species only (not environmental conditions) • As a class, develop several hypotheses • Collect plant samples • Set up potometers, record data • Summarize results and discussions in lab 82 notes 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 83 Critical Thinking • What happens when soil moisture becomes limited??? 84 Critical Thinking • What happens when soil moisture becomes limited??? • What then??? 85 Critical Thinking • What happens when soil moisture becomes limited??? • What then??? 86 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 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+] does what to Ψ??? Micrograph – turgid guard cells; same next 4 slides 88 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 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 90 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 91 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 92 Diagram – open and closed stomata 93 Abscissic acid is the hormone that mediates this response Diagram – hormone mediated stomatal opening and closing 94 Cellulose orientation determines shape of turgid cells Diagram – spoke-like orientation of cellulose microfibrils 95 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 96 Micrograph – location of stomatal gradient This is the gradient that counts 97 Images – structural adaptations to dry environments 98 Images and diagrams – metabolic adaptations to dry environments Spatial separation helps C4 plants be more efficient in hot climates Temporal separation does the same for CAM plants Both use an enzyme that can’t fix O2 to first capture CO2 Both adaptations allow photosynthesis to proceed with stomata largely closed during the 99 day Hands On • Work with your team to make hypotheses about stomata number and placement on various types of leaves • Use nail polish to make impressions of stomata Put a tab of paper under the polish Make a dry mount of the impression • Count stomata in the field of view and estimate the number of stomata per mm2 • Be prepared to discuss your findings 100 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 101 The Pressure Flow Model For Phloem Transport • Xylem transport is uni-directional, driven by solar heating Diagram – pressure flow model of phloem flow; this diagram is repeated throughout this section • Phloem flow is multi-directional, driven by active transport – source to sink 102 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) 103 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 104 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 105 The Pressure Flow Model For Phloem Transport • High [solute] at source end does what to Ψ??? 106 Critical Thinking • Remember the water potential equation Ψ=P-s • What happens to Ψ as s increases??? 107 Critical Thinking • Remember the water potential equation • What happens to Ψ as s increases??? 108 The Pressure Flow Model For Phloem Transport 109 Critical Thinking • Remember the water potential equation • What does water do when Ψ decreases??? 110 Critical Thinking • Remember the water potential equation • What does water do when Ψ decreases??? 111 Critical Thinking • Remember the water potential equation • What does water do when Ψ decreases??? • Where does the water come from??? 112 The Pressure Flow Model For Phloem Transport • High [solute] at source end decreases Ψ • Water moves into the source end of the phloem • What does this do to P at the source end? 113 Critical Thinking • What will happen to water pressure in any plant cell as water moves in??? 114 Critical Thinking • What will happen to water pressure in any plant cell as water moves in??? • Why??? 115 Critical Thinking • What will happen to water pressure in any plant cell as water moves in??? • Why??? 116 The Pressure Flow Model For Phloem Transport • High [solute] at source end decreases Ψ • Water moves into the source end of the phloem This increases the pressure 117 The Pressure Flow Model For Phloem Transport • Increased pressure at source end causes phloem sap to move to any area of lower Ψ = sinks 118 The Pressure Flow Model For Phloem Transport • At sink end, the sugars are removed by metabolism, by conversion to starch, or by active transport 119 The Pressure Flow Model For Phloem Transport • What then happens to the Ψ at the sink end of the phloem??? 120 Critical Thinking • Remember the water potential equation • What happens to Ψ as s decreases??? 121 Critical Thinking • Remember the water potential equation • What happens to Ψ as s decreases??? 122 The Pressure Flow Model For Phloem Transport 123 Critical Thinking • Remember the water potential equation 124 Critical Thinking • Remember the water potential equation 125 Critical Thinking • Remember the water potential equation 126 The Pressure Flow Model For Phloem Transport 127 The Pressure Flow Model For Phloem Transport 128 The Pressure Flow Model For Phloem Transport • Active transport is always involved at the source end, but only sometimes at the sink end 129 Critical Thinking • What about the structure of the sieve cells facilitates the movement of phloem Micrograph – sieve cells; sap??? same next slide 130 Critical Thinking • What about the structure of the sieve cells facilitates the movement of phloem sap??? 131 The Pressure Flow Model For Phloem Transport Questions??? 132 Key Concepts: Questions??? • The importance of water • Water potential: Ψ = 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 133 Hands On • For tomorrow – bring some soil from your yard and/or garden • Put it in a clear, water-tight container (glass jar is easiest) 134