Chapter 36 Transport in Vascular Plants

1. Chapter 36 Transport in Vascular Plants

2. A. Physical Forces CO2 O2 light sugar H2O O2 H2O CO2 minerals

3. A. Physical Forces • major substances transported are: • H2O and minerals • transport in xylem • moves water because of transpiration evaporation, cohesion and adhesion • sugars phloem • transport in • bulk flow • gas exchange

4. transport occurs on three scales • cellular • from environment into plant cells • transport of into root hairs H2O and solutes • short-distance transport • from cell to cell • loading of from photosynthetic leaves into phloem sieve tubes sugar • long-distance transport • transport in throughout whole plant xylem and phloem

5. membranes • selective permeability • diffusion, passive transport, active transport • phospholipid bilayer, protein channels

6. Cellular Transport • solutes are moved into plant cells by active transport • proton pumps • active transport protein • in cell membrane • mechanism that uses the energy stored in a concentration gradient to drive cellular work chemiosmosis – • use to pump against the concentration gradient the cell ATP H+ (hydrogen) ions out of • sets up a separation of across a membrane membrane potential – opposite charge

7. The Proton Pump

8. both the proton pump and membrane potential have which is used to drive the transport of many different solutes stored energy

10. Water Potential • water uptake and loss must be balanced osmosis • water moves by • add which affects osmosis cell walls physical pressure • water potential, , takes both and into account solute (dissolved substances) concentration Ψ physical pressure megapascals, MPa (or bars) • measured in

11. Ψ = ΨS + ΨP where: Ψ = water potential ΨS = solute potential (osmotic potential) ΨP = pressure potential • the ΨS of pure water is zero Pure water  = 0 MPa

12. H2O Addition of solutes • adding solute the water potential (because there is less free water molecules less capacity to do work) and ΨS is lowers 0.1 M solution negative Pure water P = 0 S = –0.23  = 0 MPa = –0.23 MPa

13. H2O • ΨP can be relative to atmospheric pressure positive or negative Applying physical pressure Applying physical pressure Pure water Pure water  H2O P = 0.30 P = 0.23 S = –0.23 S = –0.23  = 0 MPa  = 0 MPa  = 0.07 MPa  = 0 MPa

14. H2O • water under (pulling) gives pressure eg) water in xylem tension negative Negative pressure Pure water P = –0.30 P = 0 S = 0 S = –0.23  = –0.30 MPa  = –0.23 MPa

15. water gives pressure eg) turgor pressure pushing out positive • water always moves from areas of to areas of high Ψ low Ψ • water moves through the phospholipids bilayer and through transport proteins called aquaporins • cells will be or depending on the environment plasmolyzed turgid plasmolyzed turgid

16. loss of turgor causes wilting

17. Short-Distance Transport • plant cells are compartmentalized • cell wall • cell membrane – cytosol • vacuole Cell wall Cytosol Vacuole Vacuolar membrane (tonoplast) Plasmodesma Plasma membrane

18. transport routes for water and solutes • transmembrane route • repeated of plasma membrane crossing Transmembrane route

19. symplast route • movement within cytosol • plasmodesmata junctions connect cytosol of neighboring cells Key Symplast Transmembrane route Symplast Symplastic route

20. apoplast route • movement through the continuum of from cell to cell cell walls • no cell membranes are crossed Key Symplast Apoplast Transmembrane route Apoplast Symplast Symplastic route Apoplastic route

21. Long-Distance Transport • which is the movement of fluid driven by bulk flow pressure • flow in xylem tracheids and vessels • creates which xylem sap upwards from roots transpiration negative pressure pulls • loading of sugar from photosynthetic leaf cells generates high positive pressure which pushes phloem sap through sieve tubes • lack of some organelles in phloem cells and the complete lack of cytoplasm in xylem cells makes them very efficient tubes for transport

22. B. Roots • much of the absorption of takes place at the root tips water and minerals • root hairs • extensions of epidermal cells • walls are hydrophilic • huge amount of surface area

23. soil solution moves into apoplast • flows through walls into cortex • solution moves into of root cells symplast high • water moves from Ψ in soil to Ψ in root low • active transport concentrates certain molecules in the root cells eg) K+ ions

24. mycorrhizae • symbiotic structures • plant roots with fungus • greatly increases surface area for water and mineral absorption • greatly increases volume of soil reached by plant

25. endodermis • layer surrounding vascular cylinder of root • lined with impervious Casparian strip • forces solution through selective cell membrane and into symplast • also prevents leakage of xylem sap back into soil • solution in endodermis and parenchyma cells is discharged into cell walls (apoplast) by active and passive transport • this allows the solution to then move to the xylem cells

26. Casparian strip Pathway along apoplast Endodermal cell Pathway through symplast Casparian strip Plasma membrane Apoplastic route Vessels (xylem) Symplastic route Root hair Epidermis Endodermis Vascular cylinder Cortex

27. C. Ascent of Xylem Sap • root pressure • in xylem of roots the Ψ mineral ions lowers • water flowscausing in root pressure • pressure positive • of xylem sap upward push • accounts for of ascent of sap very small part

28. transpiration pull • generated by leaf • powered solar • Ψ in leaf is than Ψ in higher atmosphere • water vapour leaves the leaf through the stomata (transpiration) • water pulled up • Ψ is in roots andin leaves, moves water plant high low up • adhesion, cohesion, hydrogen bonding

29. Xylem sap Outside air Ψ = –100.0 MPa Mesophyll cells Stoma Leaf Ψ(air spaces) = –7.0 MPa Water molecule Transpiration Atmosphere Leaf Ψ(cell walls) = –1.0 MPa Adhesion Xylem cells Water potential gradient Cell wall Trunk xylem Ψ = –0.8 Mpa Cohesion, by hydrogen bonding Cohesion and adhesion in the xylem Water molecule Root xylem Ψ = –0.6 MPa Root hair Soil particle Soil Ψ = –0.3 MPa Water Water uptake from soil

30. D. Stomata • photosynthesis and transpiration • compromise • in and out but also out CO2 O2 H2O • leaf transpires more than its weight in a day • xylem sap can flow at 75 cm/min O2, H2O CO2

31. H2O evaporation takes place even with closed stomata • drought will cause wilting evaporative cooling • transpiration causes of the leaves

32. regulation of stomata • microfibril mechanism • guard cells attached at tips • contain microfibrils in cell walls • guard cells elongate and bow out when turgid • guard cells shorten and become less bowed when flaccid Cells turgid/Stoma open Cells flaccid/Stoma closed Radially oriented cellulose microfibrils Cell wall Vacuole Guard cell

33. Cells flaccid/Stoma closed Cells turgid/Stoma open H2O H2O H2O H2O H2O H2O K+ H2O H2O H2O H2O • ion mechanism • proton pumps are used to move into guard cells (stored in vacuoles) K+ ions • Ψ in cells than surrounding cells H2O moves lower in • guard cells become and turgid open • of K+ ions causes H2O to move of guard cells out loss close • become and flaccid

34. other cues • light • blue-light receptors in plasma membrane triggers ATP-powered proton pumps causing K+ uptake • stomata open • depletion of CO2 • CO2 in air spaces in mesophyll is used for photosynthesis • depletion causes stomata to open

35. circadian rhythm • automatic 24-hour cycle • stomata open in day, close at night

36. xerophytes • plants adapted for arid regions • adapted to water loss reduce • small, thick leaves • reflective leaves • hairy leaves • stomata in pores on underside of leaves • alternative photosynthetic pathway (CAM)

37. E. Organic Nutrients • is the transport of organic nutrients translocation • phloem contains: sap • water • sugar (sucrose) (30% by weight) • minerals • amino acids • hormones

38. sieve tubes carry sap from to sugar source (leaves) sugar sink (growing roots, buds, stems and fruit) variable direction of flow • sap flow rate can be as high as 1 m/hr • sugars are loaded into the phloem • flow through via symplast plasmodesmata • active of sucrose into phloem cells with H+ ions in proton pump cotransport

39. Key Apoplast Symplast Cotransporter High H+ concentration Mesophyll cell Companion (transfer) cell Sieve-tube member Proton pump Cell walls (apoplast) Plasma membrane Plasmodesmata Sucrose Phloem parenchyma cell Bundle- sheath cell Low H+ concentration Mesophyll cell

40. pressure flow • Ψ in is than in the xylem at because of the that takes place phloem lower sugar source sugar loading • H2O diffuses from xylem into phloem • is generated which causes the through phloem sieve tubes positive pressure sap to move • Ψ in is than in the xylem at because of the from the phloem phloem higher sugar sinks sugar being removed • H2O diffuses from phloem back into xylem

41. Vessel (xylem) Sieve tube (phloem) low Ψ high Ψ H2O Sucrose Source cell (leaf) H2O flow stream Pressure Transpiration Sink cell (storage root) Sucrose H2O low Ψ high Ψ