Chapter 36: Transport in Vascular Plants 1. Where does transport occur in plants? Start with water….

Figure 36.2 An overview of transport in a vascular plant Minerals H2O

Figure 36.2 An overview of transport in a vascular plant Minerals H2O CO2 O2

Figure 36.2 An overview of transport in a vascular plant CO2 O2 Light H2O Sugar H2O Minerals

Figure 36.2 An overview of transport in a vascular plant Minerals H2O CO2 O2 Sugar Light

Chapter 36: Transport in Vascular Plants Where does transport occur in plants? Start with water…. How are solutes transported between cells?

Figure 36.3 Proton pumps provide energy for solute transport CYTOPLASM EXTRACELLULAR FLUID ATP H+ Proton pump generates membrane potential and H+ gradient. – +

Figure 36.4 Solute transport in plant cells + CYTOPLASM EXTRACELLULAR FLUID Cations ( for example) are driven into the cell by the membrane potential. Transport protein K+ – (a) Membrane potential and cation uptake H+ NO3– NO3 – (b) Cotransport of anions Plant cells can also accumulate a neutral solute, such as sucrose ( ), by cotransporting down the steep proton gradient. S (c) Cotransport of a neutral solute Cell accumulates anions (NO3 –, for example) by coupling their transport to the inward diffusion of H+ through a cotransporter.

Chapter 36: Transport in Vascular Plants Where does transport occur in plants? Start with water…. How are solutes transported between cells? What influences the movement of water? Ψ = Ψs + Ψp Water moves from HIGH  low (more  less)

Fig. 36.5 Water potential and water movement: an artificial model Ψ = Ψs + Ψp Y = –0.23 MPa (a) 0.1 M solution (d) (c) (b) YP = 0 H2O YS = –0.23 Y= –0.23 MPa YS = –0.23 Y = 0 MPa YP = 0.23 Y = 0.07 MPa YP = 0.30 YS = 0 Y = –0.30 MPa YP = –0.30 YP = 0 Y = 0 MPa Pure water + solute decreases Ψs Water goes from high  low + pressure counteracts Ψs More pressure forces water across membrane (-) pressure also moves water

Chapter 36: Transport in Vascular Plants Where does transport occur in plants? Start with water…. How are solutes transported between cells? What influences the movement of water? What does this mean for plant cells?

Figure 36.6 Water relations in plant cells 0.4 M sucrose solution: p = 0 s = –0.9  = –0.9 MPa p = 0 s = –0.7  = –0.7 MPa Initial flaccid cell: p = 0 s = 0  = 0 MPa Distilled water: Plasmolyzed cell at osmotic equilibrium with its surroundings p = 0  = –0.9 MPa p = 0.7 s = –0.7  = 0 MPa Turgid cell at osmotic Initial conditions: cellular  > environmental . The cell loses water and plasmolyzes. After plasmolysis is complete, the water potentials of the cell and its surroundings are the same. Initial conditions: cellular  < environmental . There is a net uptake of water by osmosis, causing the cell to become turgid. When this tendency for water to enter is offset by the back pressure of the elastic wall, water potentials are equal for the cell and its surroundings. (The volume change of the cell is exaggerated in this diagram.) (b) Plasmolysis – shrinking of a plant cell away from its cell wall due to water loss Turgid – plant cell full of water due to its high solute concentration (turgor pressure) Aquaporins allow water to move quickly across a membrane

Chapter 36: Transport in Vascular Plants Where does transport occur in plants? Start with water…. How are solutes transported between cells? What influences the movement of water? What does this mean for plant cells? What are the transport routes dissolved substances can take between cells?

Fig 36.8 Cell compartments and routes for short-distance transport Transport proteins in the plasma membrane regulate traffic of molecules between the cytosol and the cell wall. the vacuolar membrane regulate traffic of molecules between the cytosol and the vacuole. Plasmodesma Vacuolar membrane (tonoplast) Plasma membrane Cell compartments. The cell wall, cytosol, and vacuole are the three main compartments of most mature plant cells. Key Symplast Apoplast The symplast is the continuum of cytosol connected by plasmodesmata. The apoplast is the continuum of cell walls and extracellular spaces. Transmembrane route Symplastic route Apoplastic route Transport routes between cells. At the tissue level, there are three passages: the transmembrane, symplastic, and apoplastic routes. Substances may transfer from one route to another. Cell wall Cytosol Vacuole (a) (b) How does water get into the plant?

Figure 36.9 Lateral transport of minerals and water in roots 1 2 3 Uptake of soil solution by the hydrophilic walls of root hairs provides access to the apoplast. Water and minerals can then soak into the cortex along this matrix of walls. Minerals and water that cross the plasma membranes of root hairs enter the symplast. As soil solution moves along the apoplast, some water and minerals are transported into the protoplasts of cells of the epidermis and cortex and then move inward via the symplast. Within the transverse and radial walls of each endodermal cell is the Casparian strip, a belt of waxy material (purple band) that blocks the passage of water and dissolved minerals. Only minerals already in the symplast or entering that pathway by crossing the plasma membrane of an endodermal cell can detour around the Casparian strip and pass into the vascular cylinder. Endodermal cells and also parenchyma cells within the vascular cylinder discharge water and minerals into their walls (apoplast). The xylem vessels transport the water and minerals upward into the shoot system. Casparian strip Pathway along apoplast Pathway through symplast Plasma membrane Apoplastic route Symplastic Root hair Epidermis Cortex Endodermis Vascular cylinder Vessels (xylem) 4 5 Why is the Casparian strip so important? forces dissolved substances across a selectively permeable membrane Keeps unwanted & unrecognized substances OUT of the plant

Chapter 36: Transport in Vascular Plants Where does transport occur in plants? Start with water…. How are solutes transported between cells? What influences the movement of water? What does this mean for plant cells? What are the transport routes dissolved substances can take between cells? What is the mutualistic relationship between plant roots and another biological organism?

Figure 36.10 Mycorrhizae, symbiotic associations of fungi and roots 2.5 mm

Chapter 36: Transport in Vascular Plants Where does transport occur in plants? Start with water…. How are solutes transported between cells? What influences the movement of water? What does this mean for plant cells? What are the transport routes dissolved substances can take between cells? What is the mutualistic relationship we discussed between plant roots another biological organism? How is xylem sap transported? (How can it defy gravity?) Cohesion – water’s ability to stick to itself via hydrogen bonds Adhesion – water’s ability to stick to other polar substances via H-bonds WHY?? electronegative oxygen creates polar covalent bond in water

Figure 36.13 Ascent of xylem sap Outside air Y = –100.0 MPa Leaf Y (air spaces) = –7.0MPa Leaf Y (cell walls) = –1.0 MPa Trunk xylem Y = – 0.8 MPa Water potential gradient Root xylem Y = – 0.6 MPa Soil Y = – 0.3 MPa Mesophyll cells Stoma Water molecule Atmosphere Transpiration Adhesion Cell wall Cohesion, by hydrogen bonding Root hair Soil particle Cohesion and adhesion in the xylem Water uptake from soil Transpiration – loss of water vapor through leaves that pulls water up from roots What controls the loss of water? Stomata

Fig. 36.14 Open stomata (left) and closed stomata (colorized SEM) What controls the opening & closing of the stomata? - K+ in the guard cells

Figure 36.15 The mechanism of stomatal opening and closing Cells turgid/Stoma open H2O Radially oriented cellulose microfibrils Cell wall Vacuole Guard cell K+ Changes in guard cell shape and stomatal opening and closing (surface view). Guard cells of a typical angiosperm are illustrated in their turgid (stoma open) and flaccid (stoma closed) states. The pair of guard cells buckle outward when turgid. Cellulose microfibrils in the walls resist stretching and compression in the direction parallel to the microfibrils. Thus, the radial orientation of the microfibrils causes the cells to increase in length more than width when turgor increases. The two guard cells are attached at their tips, so the increase in length causes buckling. (a) Role of potassium in stomatal opening and closing. The transport of K+ (potassium ions, symbolized here as red dots) across the plasma membrane and vacuolar membrane causes the turgor changes of guard cells. (b) Cells flaccid/Stoma closed

Chapter 36: Transport in Vascular Plants Where does transport occur in plants? Start with water…. How are solutes transported between cells? What influences the movement of water? What does this mean for plant cells? What are the transport routes dissolved substances can take between cells? What is the mutualistic relationship we discussed between plant roots another biological organism? How is xylem sap transported? (How can it defy gravity?) How is phloem sap transported?

Figure 36.17 Loading of sucrose into phloem Sucrose manufactured in mesophyll cells can travel via the symplast (blue arrows) to sieve-tube members. In some species, sucrose exits the symplast (red arrow) near sieve tubes and is actively accumulated from the apoplast by sieve-tube members and their companion cells. (a) Mesophyll cell Cell walls (apoplast) Plasma membrane Plasmodesmata Companion (transfer) cell Sieve-tube member Phloem parenchyma cell Bundle- sheath cell High H+ concentration Cotransporter Proton pump ATP Key Sucrose Apoplast Symplast H+ A chemiosmotic mechanism is responsible for the active transport of sucrose into companion cells and sieve-tube members. Proton pumps generate an H+ gradient, which drives sucrose accumulation with the help of a cotransport protein that couples sucrose transport to the diffusion of H+ back into the cell. (b) Low H+ concentration S

Figure 36.18 Pressure flow in a sieve tube Vessel (xylem) H2O Sieve tube (phloem) Source cell (leaf) Sucrose Sink cell (storage Root) 1 Loading of sugar (green dots) into the sieve tube at the source reduces water potential inside the sieve-tube members. This causes the tube to take up water by osmosis. 2 4 3 This uptake of water generates a positive pressure that forces the sap to flow along the tube. The pressure is relieved by the unloading of sugar and the consequent loss of water from the tube at the sink. In the case of leaf-to-root translocation, xylem recycles water from sink to source. Transpiration stream Pressure flow

Please put your Ch. 29 & 10 Learning Logs in the blue bin. Take a Ch. 36 Notes Packet AND the Plant Unit Potential FRQs. FYI: Animal Unit FRQs are graded…we’ll review them tomorrow in class.