Chapter 36

1. Transport in Vascular Plants Chapter 36

2. http://bcs.whfreeman.com/thelifewire/content/chp00/00020.htmlhttp://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/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 H2O & minerals) & shoots (absorb light and CO2)

6. Transport sometimes over long distances Xylem transports H2O & 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. 2 4 1 Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon for photosynthesis. Some O2produced by photosynthesis is used in cellular respiration. 3 Sugars are produced by photosynthesis in the leaves. Transpiration, the loss of water from leaves (mostly through stomata), creates a force within leaves that pulls xylem sap upward. 7 6 5 Water and minerals are transported upward from roots to shoots as xylem sap. Roots exchange gases with the air spaces of soil, taking in O2 and discharging CO2. In cellular respiration, O2 supports the breakdown of sugars. Roots absorb water and dissolved minerals from the soil. A variety of physical processes are involved in the different levels of transport CO2 O2 Light Sugar H2O Sugars are transported as phloem sap to roots and other parts of the plant. O2 H2O O2 CO2 Minerals

10. H2O H2O Minerals 1. Roots absorb H2O & minerals from soil2. Transported up to shoots as xylem sap

11. CO2 O2 H2O H2O Minerals 3. Transpiration (loss H2O) through stomata creates force in leaves that pulls xylem sap up

12. 4. Through stomata, leaves take in CO2 & expel O2 (CO2 for photosynth, O2 from cell resp) CO2 O2 Light H2O 5. Sugar made by photosynth in leaves Sugar 6. Sugar transported as phloem sap to roots & other parts where needed H2O Minerals

13. CO2 O2 Light H2O Sugar O2 H2O CO2 Minerals 7. Roots exchange gases with air spaces of soil (O2 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. 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. Passive transport. Substances diffuse spontaneously down their concentration gradients, crossing a membrane with no expenditure of energy by the cell. No energy is required. ATP Facilitated diffusion. Many hydrophilic substances diffuse through membranes with the assistance of transport proteins, Review: passive and active transport compared Gated channel Diffusion. Hydrophobic molecules and (at a slow rate) very small uncharged polar molecules can diffuse through the lipid bilayer. Most solutes cannot cx memb without help of transport proteins

16. EXTRACELLULAR FLUID CYTOPLASM – + H+ + – ATP H+ – + H+ Proton pump generates membrane potential and H+ gradient. H+ H+ H+ – H+ + H+ – + B. Central Role of Proton Pumps Most impt active transport prot in plants is the proton pump in plant cells • - 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. 1. Uptake of K+ + – CYTOPLASM EXTRACELLULAR FLUID + – Cations ( , for example) are driven into the cell by themembrane potential. K+ K+ + – K+ K+ K+ K+ K+ – + K+ Transport protein – +

18. 2. Cotransport couples downhill passage of (H+) with concommitant uphill passage of (NO3) this = active transport + – H+ H+ NO3 – + – NO3– + – Cell accumulates anions (, for example) by coupling their transport to theinward diffusion H+ H+ H+ NO3– H+ H+ H+ H+ of through a cotransporter. NO3– – NO3 – + NO3 – – + H+ NO3– – H+ + H+ H+

19. + – H+ H+ H+ S + – Plant cells can also accumulate a neutral solute, such as sucrose ( ), by cotransporting down the steep proton gradient. H+ – + H+ H+ S H+ S H+ H+ H+ S S S – H+ + – + H+ S H+ + – – 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 H2O 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 H2O 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. (a) 0.1 M solution Pure water H2O P= 0 S= 0.23 = 0.23 MPa = 0 MPa • Addition of solutes reduces Ψ

24. (b) (c) H2O H2O P= 0.23 S= 0.23 = 0 MPa P= 0.30 S= 0.23 = 0.07 MPa = 0 MPa = 0 MPa • Application of physical pressure increasesΨ

25. (d) H2O P= 0.30 S= 0 = 0.30 MPa P= 0 S= 0.23 = 0.23 MPa • Negative pressure decreases Ψ

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 Hypertonic solution Hypotonic 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. E. 3 Major Compartments Vacuolated Cells Transport also regulated by compartmental structure of plant cells Cell wall Ke Cytosol Symplast Vacuole Apoplast Plasmodesma Vacuolar membrane (tonoplast) • 1. cell wall (maintain cell shape) edge of space • 2. plasma membrane (controls H2O in/out) & edge of protoplast (contents of cell less wall) • 3. vacuole Plasma membrane

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

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

33. F. Short lateral transport via one of 3 ways: Key 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) Symplast Apoplast Transmembrane route Apoplast Symplast Symplastic route Symplast= continuous cytosol, cell to cell via plasmodesmata Apoplast = continuum cell walls & extracellular spaces Apoplastic route These 3 ways from root hairs to vascular cylinder Substances may transfer from one route to another.

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 Sieve tube member = cell with sieve plate Companion Cell = nonconducting cntd via plasmodesmata ALIVE DEAD

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. 2.5 mm 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

41. Casparian strip Endodermal cell Pathway through symplast 1 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. Casparian strip 2 Plasma membrane 1 Minerals and water that cross the plasma membranes of root hairs enter the symplast. Apoplastic route 2 Vessels (xylem) 3 Root hair 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. Symplastic route Cortex Endodermis Epidermis 5 Vascular cylinder 4 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. Lateral transport of minerals and water in roots

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

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