1. Transport in Vascular Plants

2. http://bcs.whfreeman.com/thelifewire/content/chp00/00020.html Chpt 35 : REVIEW SECONDARY GROWTH Chpt 36: TRANSPORT IN PLANTS

3. http://glencoe.mcgraw- hill.com/sites/9834092339/student_view0/chapter38/ Phloem loading Water intake Osmosis Etc.

4. Text Summary of Transport http://www.wou.edu/~bledsoek/103materials/chapter_notes/103Ch42b.pdf

5. Vascular land plants = plant body of roots (absorb H 2 O & minerals) & shoots (absorb light and CO 2 )

6. Transport sometimes over long distances Xylem transports H 2 O & minerals from roots to shoots Phloem transports sugars, etc. from where synth (source) to where needed (sink)

7. I. Physical forces drive the transport of materials in vascular plants

8. A. 3 levels of transport 1. Transport of water and solutes by individual cells, e.g., root hairs via plasmodesmata 2. Short-distance transport of substances from cell to cell at the levels of tissues and organs, e.g. loading sugar from photosynthetic leaf cells sieve tubes of phloem 3. Long-distance transport within xylem & phloem throughout whole plant

9. Minerals H2OH2O O2O2 O2O2 CO 2 O2O2 H2OH2O Sugar Light A variety of physical processes are involved in the different levels of transport Sugars are produced by photosynthesis in the leaves. 5 Sugars are transported as phloem sap to roots and other parts of the plant. 6 Through stomata, leaves take in CO 2 and expel O 2. The CO 2 provides carbon for photosynthesis. Some O 2 produced by photosynthesis is used in cellular respiration. 4 Transpiration, the loss of water from leaves (mostly through stomata), creates a force within leaves that pulls xylem sap upward. 3 Water and minerals are transported upward from roots to shoots as xylem sap. 2 Roots absorb water and dissolved minerals from the soil. 1 Roots exchange gases with the air spaces of soil, taking in O 2 and discharging CO 2. In cellular respiration, O 2 supports the breakdown of sugars. 7 CO 2

10. 1. Roots absorb H 2 O & minerals from soil 2. Transported up to shoots as xylem sap Minerals H2OH2O H2OH2O

11. 3. Transpiration (loss H 2 O) through stomata creates force in leaves that pulls xylem sap up Minerals H2OH2O CO 2 O2O2 H2OH2O

12. 4. Through stomata, leaves take in CO 2 & expel O 2 (CO 2 for photosynth, O 2 from cell resp) Minerals H2OH2O CO 2 O2O2 H2OH2O Sugar Light 5. Sugar made by photosynth in leaves 6. Sugar transported as phloem sap to roots & other parts where needed

13. Minerals H2OH2O CO 2 O2O2 O2O2 H2OH2O Sugar Light 7. Roots exchange gases with air spaces of soil (O 2 used in catabolism of sugars)

14. B. Selective Permeability of Membranes Selective permeability of plant cell’s plasma membrane controls movement of solutes into & out of cell Specific transport proteins enable plant cells to maintain internal environment different from their surroundings

15. Review: passive and active transport compared Passive transport. Substances diffuse spontaneously down their concentration gradients, crossing a membrane with no expenditure of energy by the cell. No energy is required. Active transport. Some transport proteins act as pumps, moving substances across a membrane against their concentration gradients. Energy for this work is usually supplied by ATP. ATP Facilitated diffusion. Many hydrophilic substances diffuse through membranes with the assistance of transport proteins, Diffusion. Hydrophobic molecules and (at a slow rate) very small uncharged polar molecules can diffuse through the lipid bilayer. Gated channel Most solutes cannot cx memb without help of transport proteins

16. B. Central Role of Proton Pumps Most impt active transport prot in plants is the proton pump in plant cells CYTOPLASM EXTRACELLULAR FLUID ATP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Proton pump generates membrane potential and H + gradient. – – – – – + + + + + - Creates a hydrogen ion gradient (a form of potential energy that can be harnessed to do work) - Contributes to a voltage known as a membrane potential (also potential energy) Plants use energy stored in proton gradient & memb potential to drive transport of different solutes

17. + CYTOPLASM EXTRACELLULAR FLUID Cations (, for example) are driven into the cell by the membrane potential. Transport protein K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ – – – + + 1. Uptake of K+ – – + +

18. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ NO 3 – – – – + + + – – – + + + 2. Cotransport couples downhill passage of (H+) with concommitant uphill passage of (NO 3 ) this = active transport H+H+ of through a cotransporter. Cell accumulates anions (, for example) by coupling their transport to the inward diffusion

19. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ S S S S S Plant cells can also accumulate a neutral solute, such as sucrose ( ), by cotransporting down the steep proton gradient. S H+H+ – – – + + + – – + + – H+H+ H+H+ S + – 3. Uptake of sucrose with contransport of H+ moving down its conc gradient in uptake of sucrose by plant cells

20. C. Water Potential To survive plants must balance water uptake & loss Osmosis (diffusion of H 2 O acx selectively permeable memb) responsible for net uptake or loss of water

21. Water potential (Ψ) is a measurement that combines effects of solute conc & pressure. to determine the direction of H 2 O movement Water flows from regions of high water potential to regions of low water potential

22. Solute contribution to water potential of a solution is proportional to the number of dissolved molecules Pressure contribution to water potential of a solution is the physical pressure on a solution (involves plant cell wall)

23. Addition of solutes reduces Ψ 0.1 M solution H2OH2O Pure water  P = 0  S =  0.23  =  0.23 MPa  = 0 MPa (a)

24. Application of physical pressure increases Ψ H2OH2O  P = 0.23  S =  0.23  = 0 MPa (b) H2OH2O  P = 0.30  S =  0.23  = 0.07 MPa  = 0 MPa (c)

25. Negative pressure decreases Ψ H2OH2O  P = 0  S =  0.23  =  0.23 MPa (d)  P =  0.30  S = 0  =  0.30 MPa

26. If a flaccid cell is placed in an environment with a higher solute conc (hypertonic soln), the cell will lose water & plasmolyze (memb will shrink away from its cell wall) Flaccid = limp. A walled cell is flaccid in surroundings where there is no tendency for water to enter Hypotonic solutionHypertonic solution

27. If the same flaccid cell is placed in a soln with a solute concentration lower than that in the protoplast, the cell will gain water and become turgid (very firm) as cell wall pushes back against enlarging memb. A walled cell becomes turgid if it has a greater solute conc than its surroundings, resulting in entry of water.

28. Loss of turgor (due to loss of water in environment) in plants causes wilting which can be reversed when the plant is watered. Healthy plants are turgid most of the time.

29. D. Aquaporin and Water Transport ● Aquaporins = transport prots in memb that allow the passage of water ● Do not affect water potential

30. Plasmodesma Plasma membrane Cell wall Cytosol Vacuole Ke Symplast Apoplast Vacuolar membrane (tonoplast) E. 3 Major Compartments Vacuolated Cells Transport also regulated by compartmental structure of plant cells 1. cell wall (maintain cell shape) edge of space 2. plasma membrane (controls H 2 O in/out) & edge of protoplast (contents of cell less wall) 3. vacuole

31. Plasma membrane - Directly controls the traffic of molecules in/out protoplast - Is a barrier between two major compartments, cell wall & cytosol

32. 3rd major compartment vacuole = a large organelle that can occupy as much as 90% of more of the protoplast’s volume Vacuolar membrane r egulates transport between the cytosol and the vacuole Transport proteins in the plasma membrane regulate traffic of molecules between the cytosol and the cell wall. Transport proteins in the vacuolar membrane regulate traffic of molecules between the cytosol and the vacuole. Plasmodesma Vacuolar membrane Plasma membrane Cell wall Cytosol Vacuole Cell compartments. The cell wall, cytosol, and vacuole are the three main compartments of most mature plant cells.

33. Key Symplast Apoplast Transmembrane route Symplastic route Symplast 1. transmembrane route (out of memb-ax cell wall-into another cell) 2. symplastic route (cell memb to cell directly vis dermatoplasmata) 3. apoplastic route (stay outside cells) F. Short lateral transport via one of 3 ways: Symplast = continuous cytosol, cell to cell via plasmodesmata Apoplast = continuum cell walls & extracellular spaces Substances may transfer from one route to another. Apoplastic route These 3 ways from root hairs to vascular cylinder

34. Water & minerals travel short distances from root hairs to vascular cylinder of root via 3 lateral (not up/down) routes 1. Transmemb: out of one cell, across a cell wall, & into another cell = repeated crossing plasma memb 2. Via symplast == continum of cytosol; only one crossing of plasma membrane & then cell-to-cell via plasmodermata 3. Along apoplast == continuem of cell wall; no entering protoplast Can change from one route to another route

35. G. Bulk Flow for Long-Distance Transport is movement of fluid in the xylem & phloem driven by pressure differences at opposite ends of the xylem vessels and sieve tubes Diffusion OK for short distances, but too slow for long distances …. need bulk flow

36. Water & fluids move through tracheids & vessels of xylem & sieve tubes of phloem Tracheids = tapered cells with pits Vessel elements = wider, long channels, end walls perforated for easy flow DEAD ALIVE Sieve tube member = cell with sieve plate Companion Cell = nonconducting cntd via plasmodesmata

37. Phloem: loading of sugar = high + pressure at opposite end of sieve tube = mvt fluid Xylem: negative pressure tension by transpiration from leaves pulls sap up from roots Cytoplasm of sieve-tube members almost devoid of internal organelles & porous sieve plates = easier flow Dead tracheids & vessel elements (porous end walls) have no cytoplasm to inhibit flow

38. Bulk flow due to pressure differences = way long-distance transport of phloem sap & active transport of sugar at cellular level maintains pressure difference

39. II. Roots absorb water & minerals from soil enter the plant through the epidermis of roots, cx root cortex, pass into vascular cylinder & ultimately bulk flow to shoot system

40. Root hairs account for much surface area of roots Most plants form mutually beneficial relationships with fungi, which facilitate the absorption of water and minerals from the soil Roots and fungi form mycorrhizae, symbiotic structures consisting of plant roots united with fungal hyphae = increase surface area of roots 2.5 mm

41. 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 & 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 & also parenchyma cells within the vascular cylinder discharge water and minerals into their walls (apoplast). The xylem vessels transport the water & minerals upward into shoot system. Pathway through symplast Plasma membrane Casparian strip Apoplastic route Symplastic route Root hair Epidermis CortexEndodermis Vascular cylinder Vessels (xylem) Casparian strip Endodermal cell 4 5 2 1

42. Root hairs (extensions of epidermal cells) absorb Passes freely apoplastic route into cortex Cells of epidermis & cortex take up = into symplast

43. Endodermis: innermost layer cells in root cortex, surrounds vascular cylinder & is last checkpoint for selective passage of minerals from cortex into vascular tissue Minerals/water from roots into symplast of epidermis or cortex, continue via plasmodesmata of endodermal cells into vascular cylinder Minerals/water from roots into apoplast meet Casparian strip (dead end & cannot enter vascular cylinder via apoplast) BUT can enter symplast and enter Waxy belt in walls endodermal cells; impervious to water/minerals

44. III. 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

45. Pulling Xylem Sap: The Transpiration- Cohesion-Tension Mechanism is the major pressure driving flow of xylem sap up to shoot system Water is pulled upward by negative pressure in the xylem produced by transpiration through stomata Cohesion of water (H bonding) transmits upward pull along length of sylem to roots

46. IV. Stomata help regulate rate of transpiration Leaves generally have broad surface areas & high surface-to-volume ratios that increase photosynthesis & increase water loss 20 µm

47. ● Plants lose a large amount of water by transpiration ● If lost water is not replaced by absorption through roots, plant will lose water & wilt ● Transpiration = evaporative cooling which lowers T of leaf to prevent denaturation of various enzs involved in photosynthesis & other metabolic processes

48. Each stoma is flanked by guard cells that control diameter by changing shape

49. V. Nutrients translocated through phloem Phloem sap (an aqueous solution, mostly sucrose) that translocated from source to sink A sugar source : a plant organ that is a net producer of sugar, such as mature leaves A sugar sink: an organ that is a net consumer or storer of sugar, such as a tuber or bulb

50. Sucrose manufactured in mesophyll cells can travel via the symplast (blue arrows) to sieve-tube members. In angiosperms sap moves through a sieve tube by bulk flow driven by positive pressure Phloem loading may be via active transport; proton pumping & cotransport of sucrose & H +

51. 1. Load sucrose (green) into sieve tube at source = ↓Ψ in sieve tube = causes sieve tube to take up water by osmosis 2. Uptake water = ↑ Ψ P to force sap to flow 3. At sink, sugar unloaded = ↓ Ψ P & water out via osmosis Phloem sap flows from source to sink via bulk flow mediated by pressure