Resource Acquisition and Transport in Vascular Plants

1. Resource Acquisition and Transport in Vascular Plants

2. Green algae (ancestors of land plants) live in water.

3. Mosses (early plants) live in very moist environments, very low – non vascular

5. CO2 O2 Light H2O Sugar • Land plants acquire resources: • Above ground – carbon dioxide and sunlight • Below ground – water and minerals H2O Minerals

6. Land plants compete for these resources.

7. CO2 O2 Light H2O Sugar • Natural selection favored the plants with efficient systems for long-distance transportation of • Water • Minerals • Products of photosynthesis H2O Minerals

8. Plants have to balance • Acquisition of light and CO2 • Evaporative loss of water

9. Various arrangement of leaves make it possible to maximize light and CO2 uptake and minimize water loss. • Leaves that are self shaded undergo programmed cell death and fall off because their photosynthetic output is less than their metabolic needs.

10. Roots undergo modifications to increase intake of water and minerals. • Roots associate with fungi to increase surface area (mycorrhizae) • Early association with land plants made colonization of land plants possible.

11. Transport occurs: • Short distance: passive and active transport • Long distance: bulk flow

12. Cell membranes are fluid mosaic model made of • phospholipid bilayer • proteins

13. Most nutrients cannot diffuse across phospholipid bilayer • Active transport: cell must expend ATP (energy) • Transport proteins are involved in active transport of nutrients

14. Proton pump: • energy from ATP pump protons, H+ out of the cells • inside of the membrane had –ve charge, outside has +ve charge: membrane potential EXTRACELLULAR FLUID CYTOPLASM ATP Proton pump generates mem- brane potential and gradient.

15. Proton pump facilitates cation uptake EXTRACELLULAR FLUID CYTOPLASM Cations ( , for example) are driven into the cell by the membrane potential. Transport protein Membrane potential and cation uptake

16. Proton pump facilitates cotransport of anions with H+ Cell accumulates anions ( , for example) by coupling their transport to; the inward diffusion of through a cotransporter. Cotransport of anions

17. Proton pump facilitates transport of neutral solutes with H+ Plant cells can also accumulate a neutral solute, such as sucrose ( ), by cotransporting down the steep proton gradient. Cotransport of a neutral solute

18. Osmosis (diffusion of water) across semipermeable membrane. • Concentration of water determines direction of water flow • Water flow is affected by rigid cell walls which exerts pressure on plasma membrane.

19. Water potential (y): The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure; units megapascals (MPa). • Water potential refers to water’s potential energy – water’s capacity to perform work when it moves region of high water potential to a region of low water potential.

20. y = ys + yp Where: y = water potential ys = solute potential/ osmotic potential yp = pressure potential

21. Free water has highest water potential. When bound to solutes water potential goes down.

22. Pressure potential can be positive or negative. • Usually cells are under positive water potential. Usually cell contents press against cell wall and cell wall presses against protoplast – turgor pressure.

23. Addition of solutes 0.1 M solution • Water potential and water movement in an artificial model. • a) In absence of pressure ys determines net movement’ Pure water H2O P = 0 S = –0.23  = 0 MPa P = –0.23 MPa

24. Applying physical pressure • b) Positive pressure can raise y by increasing yp. H2O P = 0 S = –0.23  = 0 MPa P = –0 MPa

25. Applying physical pressure • c) Raising y on the right causes movement to the left. H2O P = 0.30 S = –0.23  = 0 MPa P = –0.07 MPa

26. Negative pressure • d) –ve pressure reduces yp, causes net movement to the left by reducing y . H2O P = –0.30 P = 0.30 S = –0.23 S = –0.23 P = –0.30 MPa P = –0.23 MPa

27. Initial flaccid cell undergoes plasmolysis when placed in an environment with high solute concentration. • It becomes turgid when placed in pure water. Initial flaccid cell:  P = 0 S = –0.7  0.4 M sucrose solution: Distilled water: P = –0.7 MPa   P = 0 P = 0  S = –0.9  S = 0  P = 0 MPa   P = –0.9 MPa

28. What happens when you forget to water a plant? What happens when you water it?

29. Water transport is aided by transport proteins – aquaporins.

30. Three major pathways of transport: • Apoplastic route • Symplastic route • Transmembrane route Key Symplast Apoplast Transmembrane route Apoplast Symplast Symplastic route Apoplastic route Transport routes between cells

31. Bulk flow requires more efficient transport than diffusion and active transport.

32. Transport of water and minerals into the xylem: pushing and pulling

33. Casparian strip Endodermal cell Pathway along apoplast Pathway through symplast • Pushing up the xylem sap: root pressure Casparian strip Plasma membrane Apoplastic route Vessels (xylem) Symplastic route Root hair Epidermis Endodermis Vascular cylinder Cortex

34. When too much enters plants give out excess water through leaves – guttation

35. Transpiration: loss of water vapor through leaves and other aerial parts of plants. A single corn plant transpires 60L of water in the growing season.

36. LE 36-12 Y = –10.00 MPa Y = –0.15 MPa Cell wall • Transpiration pull Air-water interface Airspace Low rate of transpiration High rate of transpiration Cuticle Upper epidermis Cytoplasm Evaporation Airspace Mesophyll Air space Cell wall Evaporation Lower epidermis Water film Vacuole Stoma Cuticle O2 O2 CO2 CO2 Xylem

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

38. Stomata regulates rate of transpiration: opening and closing of stomata are regulated by transport of K+. Cells turgid/Stoma open Cells flaccid/Stoma closed H2O H2O H2O H2O K+ H2O H2O H2O H2O H2O H2O Role of potassium in stomatal opening and closing

39. Cells turgid/Stoma open Cells flaccid/Stoma closed

40. Adpatations in desert plants • Reduced life cycle • Reduced period of leaf production • Thicker cuticle • Bristles to reflect the heat • Reduced leaves, photosynthetic stems • Growing underground • Taking carbon dioxide at night

41. Upper epidermal tissue Cuticle Lower epidermal tissue Trichomes (“hairs”) Stomata 100 µm

42. Reduced leaves, photosynthetic stems

43. Movement of sugars from source to sink • Translocation: transport of photosynthetic products for use and storage by phloem tissue. • Sugar source: plant organ that is the net producer of sugar (leaves) • Sugar sink: net consumer of depository sugar (growing tips, roots, buds, stems, fruits)

44. Sieve tube (phloem) Vessel (xylem) Source cell (leaf) H2O Sucrose H2O • Positive pressure bulk flow in sieve tubes (phloem). flow stream Pressure Transpiration Sink cell (storage root) Sucrose H2O

45. Thinning helps prevent excess demand on sugar source (pruning in agriculture)