1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 36 Transport in Vascular Plants

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

3. Concept 36.1: Physical forces drive the transport of materials in plants over a range of distances Transport in vascular plants occurs on three scales: – Transport of water and solutes by individual cells, such as root hairs – Short-distance transport of substances from cell to cell at the levels of tissues and organs – Long-distance transport within xylem and phloem at the level of the whole plant

4. LE 36-2_4 Minerals H2OH2O H2OH2O CO 2 O2O2 Sugar Light CO 2 O2O2

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Selective Permeability of Membranes: A Review The selective permeability of the plasma membrane controls movement of solutes into and out of the cell Specific transport proteins enable plant cells to maintain an internal environment different from their surroundings

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Central Role of Proton Pumps Proton pumps in plant cells create a hydrogen ion gradient that is a form of potential energy that can be harnessed to do work They contribute to a voltage known as a membrane potential CYTOPLASM ATP EXTRACELLULAR FLUID Proton pump generates mem- brane potential and gradient.

7. LE 36-4a CYTOPLASM EXTRACELLULAR FLUID Cations (, for example) are driven into the cell by the membrane potential. Transport protein Membrane potential and cation uptake

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In the mechanism called cotransport, a transport protein couples the passage of one solute to the passage of another Cell accumulates anions (, for example) by coupling their transport to; the inward diffusion of through a cotransporter. Cotransport of anions

9. LE 36-4c Plant cells can also accumulate a neutral solute, such as sucrose ( ), by cotransporting down the steep proton gradient. Cotransport of a neutral solute

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Effects of Differences in Water Potential Water potential is a measurement that combines the effects of solute concentration and pressure Water flows from regions of higher water potential to regions of lower water potential

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Quantitative Analysis of Water Potential The addition of solutes reduces water potential Addition of solutes 0.1 M solution Pure water H2OH2O  = 0 MPa  P = –0.23 MPa  P = 0  S = –0.23

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Physical pressure increases water potential Applying physical pressure H2OH2O  = 0 MPa  P = 0 MPa  P = 0  S = –0.23 Applying physical pressure H2OH2O  = 0 MPa  P = 0.07 MPa  P = 0.30  S = –0.23

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water potential affects uptake and loss of water by plant cells If a flaccid cell is placed in an environment with a higher solute concentration, the cell will lose water and become plasmolyzed Video: Plasmolysis Video: Plasmolysis P = –0.9 MPa P = 0 S = –0.9    P = –0.9 MPa P = 0 S = –0.9  conditions: cellular  > environmental Plasmolyzed cell at osmotic equilibrium  0.4 M sucrose solution: P = –0.7 MPa P = 0 S = –0.7 Initial flaccid cell: P = 0 MPa P = 0 S = 0 Distilled water: P = 0 MPa P = 0.7 S = –0.7 Turgid cell at osmotic equilibrium   u dings              

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If the same flaccid cell is placed in a solution with a lower solute concentration, the cell will gain water and become turgid Video: Turgid Elodea Video: Turgid Elodea

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Aquaporin Proteins and Water Transport Aquaporins are transport proteins in the cell membrane that allow the passage of water Aquaporins do not affect water potential

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The cytoplasmic continuum is called the symplast The apoplast is the continuum of cell walls and extracellular spaces Transmembrane route Key Symplast Apoplast Symplastic route Transport routes between cells Apoplastic route Apoplast Symplast

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 36.2: Roots absorb water and minerals from the soil Water and mineral salts from the soil enter the plant through the epidermis of roots and ultimately flow to the shoot system Animation: Transport in Roots Animation: Transport in Roots Casparian strip Endodermal cell Pathway along apoplast Pathway through symplast Casparian strip Plasma membrane Apoplastic route Symplastic route Root hair Vessels (xylem) Cortex EndodermisEpidermisVascular cylinder

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water can cross the cortex via the symplast or apoplast The waxy Casparian strip of the endodermal wall blocks apoplastic transfer of minerals from the cortex to the vascular cylinder Casparian strip Endodermal cell Pathway along apoplast Pathway through symplast Casparian strip Plasma membrane Apoplastic route Symplastic route Root hair Vessels (xylem) Cortex EndodermisEpidermisVascular cylinder

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 36.3: Water and minerals ascend from roots to shoots through the xylem Plants lose an enormous amount of water through transpiration, the loss of water vapor from leaves and other aerial parts of the plant The transpired water must be replaced by water transported up from the roots

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Transpiration Transpiration Cohesion Tension Theory – Transpiration – water loss through leaves – Cohesion – attraction of like molecules Adhesion – attraction of unlike molecules – Tension – negative pressure

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Factors Affecting the Ascent of Xylem Sap Xylem sap rises to heights of more than 100 m in the tallest plants Is the sap pushed upward from the roots, or is it pulled upward by the leaves?

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Root pressure sometimes results in guttation, the exudation of water droplets on tips of grass blades or the leaf margins of some small, herbaceous eudicots

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cohesion and Adhesion in the Ascent of Xylem Sap The transpirational pull on xylem sap is transmitted all the way from the leaves to the root tips and even into the soil solution Transpirational pull is facilitated by cohesion and adhesion Animation: Transpiration Animation: Transpiration Xylem sap Mesophyll cells Stoma Water molecule Atmosphere Transpiration Xylem cells Adhesion Cell wall Cohesion, by hydrogen bonding Cohesion and adhesion in the xylem Water molecule Water potential gradient Root hair Soil particle Water Water uptake from soil Trunk xylem = –0.8 Mpa Root xylem = –0.6 MPa Leaf (air spaces) = –7.0 MPa Outside air  = –100.0 MPa Leaf (cell walls) = –1.0 MPa Soil = –0.3 MPa      

24. LE 36-14 20 µm

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Effects of Transpiration on Wilting and Leaf Temperature Plants lose a large amount of water by transpiration If the lost water is not replaced by absorption through the roots, the plant will lose water and wilt

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Transpiration also results in evaporative cooling, which can lower the temperature of a leaf and prevent denaturation of various enzymes involved in photosynthesis and other metabolic processes

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stomata: Major Pathways for Water Loss About 90% of the water a plant loses escapes through stomata Cells turgid/Stoma open Changes in guard cell shape and stomatal opening and closing (surface view) Radially oriented cellulose microfibrils Vacuole Cell wall Guard cell Cells flaccid/Stoma closed

28. LE 36-15b Cells turgid/Stoma open Role of potassium in stomatal opening and closing Cells flaccid/Stoma closed H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O K+K+

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Movement from Sugar Sources to Sugar Sinks Phloem sap is an aqueous solution that is mostly sucrose It travels from a sugar source to a sugar sink A sugar source is an organ that is a net producer of sugar, such as mature leaves A sugar sink is an organ that is a net consumer or storer of sugar, such as a tuber or bulb

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pressure Flow: The Mechanism of Translocation in Angiosperms In studying angiosperms, researchers have concluded that sap moves through a sieve tube by bulk flow driven by positive pressure Animation: Translocation of Phloem Sap in Summer Animation: Translocation of Phloem Sap in Summer Animation: Translocation of Phloem Sap in Spring Animation: Translocation of Phloem Sap in Spring Vessel (xylem) Sieve tube (phloem) Sucrose Source cell (leaf) H2OH2O H2OH2O Sucrose Sink cell (storage root) H2OH2O Pressure flow Transpiration stream

31. LE 36-19 Sap droplet Aphid feeding Stylet in sieve-tube member (LM) Stylet Severed stylet exuding sap Sap droplet Sieve- tube member 25 µm