2. Question ? u How do plants move materials from one organ to the other ?

3. Levels of Plant Transport 1. Cellular 2. Short Distance 3. Long Distance

4. Cellular Transport u The transport of solutes and water across cell membranes. Types of transport: 1. Passive Transport 2. Active Transport 3. Water Transport

5. 1. Passive Transport u Diffusion and Osmosis. u Requires no cellular energy. u Materials diffuse down concentration gradients.

6. Problems u Usually very slow. u How can diffusion be assisted? u Transport Proteins u Ex. K+ channel

7. Potassium Channel u Found in most plant cell membranes. u Allow K + but not Na + to pass. u Often “gated” to respond to environmental stimuli (see cell signaling)

8. 2. Active Transport u Requires cell energy. u Moves solutes against a concentration gradient. u Ex: Proton Pumps

9. Proton Pump u Uses ATP to move H + out of cells. u H + creates a membrane potential. u H + allows cotransport.

10. Membrane Potentials u Allow cations to moved into the cell. u Ex: Ca +2, Mg +2 u Allow anions to move by co- transport. u Ex: NO 3

11. Summary

12. 3. Water Transport u Osmosis - water moves from high concentration to low concentration.

13. Water Potential u The potential energy of water to move from one location to another.  Abbreviated as 

14. Problem u Cell wall creates a pressure in the cells. u Water potential must account for this pressure. u Pressure counteracts the tendency for water to move into plant cells.

15. Water Potential u Has two components:  Pressure potential:    Solute potential:      

16. Comment u See the Ts lab handout for more on water potential.

18. Bulk Flow u The movement of water between two locations due to pressure or tension.

19. Bulk Flow u Much faster than osmosis. u Tension (negative pressure) pulls water from place to place. u May cause bulk flow against the diffusion gradient.

20. Plant Vacuoles u Create Turgor Pressure against the cell wall. u Affect water potential by controlling water concentrations inside cells.

21. Tonoplast u Name for the vacuole membrane. u Has proton pumps. u Comment – genetic modification of these pumps gives plants salt tolerance.

22. Proton Pumps u Drives solutes inside the vacuole.  Lowers water potential (    ) inside the vacuole.

23. Result u Water moves into the vacuole. u Vacuole swells. u Turgor pressure increases.

25. Turgor Pressure u Important for non-woody plant support. u Wilting: u Loss of turgor pressure. u Loss of water from cells.

26. Flaccid Turgid

27. Aquaporins u Water specific facilitated diffusion transport channels. u Help water move more rapidly through lipid bilayers.

28. Aquaporins with GFP

29. Short Distance Transport 1. Transmembrane route 2. Symplast route 3. Apoplast route

30. 1. Transmembrane u Materials cross from cell to cell by crossing each cell's membranes and cell walls.

31. 2. Symplast u The continuum of cytoplasm by plasmodesmata bridges between cells.

32. 3. Apoplast u Extracellular pathway around and between cell walls.

34. Long Distance Transport u Problem: diffusion is too slow for long distances. u Answer: tension and bulk flow methods.

35. Root Hairs u Main site of absorption of water and minerals. u Comment - older roots have cork and are not very permeable to water.

36. Root Cortex u Very spongy. u Apoplast route very common.

37. Problem u Can't control uptake of materials if the apoplast route is used.

38. Solution u Endodermis with its Casparian Strip.

39. Casparian Strip u Waxy layer of suberin. u Creates a barrier between the cortex and the stele. u Forces materials from apoplast into endodermis symplast.

40. Endodermis Casparian Strip

41. Result u Plant can now control movement of materials into the stele.

42. Mycorrhizae u Symbiotic association of fungi with roots of plants. u Help with water and mineral absorption (replaces root hairs in some plants). u May also prevent toxins from entering the plant.

43. Mycorrhizae

44. Xylem Sap u Solution of water and minerals loaded into the xylem by the endodermis. u Endodermis - also prevents back flow of water and minerals out of the stele.

45. Xylem Sap Transport Methods 1. Root Pressure 2. Transpiration (Ts)

46. Root Pressure u Root cells load minerals into xylem.  Water potential (   ) is lowered. u Water flows into xylem.

47. Result u Volume of water in xylem increases u Xylem sap is pushed up the xylem tissues creating root pressure.

48. Comments u Root Pressure: limited way to move xylem sap. u Most apparent at night. u Excess water may leave plant through Guttation.

49. Transpiration (Ts) u Evaporation of water from aerial plant parts. u Major force to pull xylem sap up tall trees.

50. TCTM Theory u Transpiration u Cohesion u Tension u Mechanism

51. How does TCTM work? u Water evaporates from leaves, especially from the cell walls of the spongy mesophyll. u Reason: water potential of the air is usually much less than that of the cells.

53. As water evaporates: u Cohesion: water molecules sticking together by H bonds. u Adhesion: water molecules sticking to other materials (cell walls etc.).

54. Result u The loss of water from the leaves creates “tension” or negative pressure between the air and the water in the plant.

55. Tension causes: u Xylem sap to move to replace the water lost from the mesophyll cells.

56. Xylem Sap u Is “pulled” by the resulting tension all the way down the plant to the roots and soil.

57. Ts Summary u Xylem sap moves along a continual chain of water potential from: air  leaf  stem  roots  soil

59. Comments u Tension is a negative pressure which causes a decreased in the size of xylem cells. u Xylem cells would collapse without secondary cell walls.

60. Factors that Affect Transpiration Rate 1. Environmental 2. Plant Structures Multiple Layer Epidermis Stomatal Crypt

61. Homework u Read – Chapter 36, 39 u Chapter 36 – Mon. 4/16 u Test 2 – next week – Chapters 29, 30, 35, 36. A few questions may come from 37, 38 and possible 39.

62. Environmental Factors 1. Humidity 2. Temperature 3. Light 4. Soil Water Content 5. Wind

63. Plant Structure Factors 1. Cuticle 2. Stomate Number 3. Hairs

64. Stomates u Openings in the epidermis that allow water and gas exchange. u Controlled by Guard Cells. u Control rate of Ts and Ps.

65. Guard Cells u Turgid: Swell - open stomata. u Flaccid: Shrink - close stomata. u Size of the cells is a result of turgor pressure changes.

66. Turgid - Open Flaccid - Closed

67. Turgor Pressure of Guard cells u Controlled by K + concentrations.

68. To Open Stomata: 1. K + enters the guard cells. 2. Water potential lowered. 3. Water enters guard cells. 4. Turgor pressure increases. 5. Guard cells swell and Stomata opens.

69. To Close Stomata: 1. K + leaves guard cells. 2. Water leaves guard cells. 3. Turgor pressure decreases. 4. Guard cells shrink and Stomata close.

70. K + Movement u Regulated by proton pumps and K + channels. u Controlled by: u Light (Blue) u CO 2 concentrations u Abscisic Acid (water stress)

71. Comment u Plant must balance loss of water by transpiration with CO 2 uptake for Ps.

72. Adaptations for Balance u C4 Ps u CAM Ps

73. Phloem Transport u Moves sugars (food). u Transported in live cells. u Ex: Sieve & Companion Cells

74. Source - Sink Transport u Model for movement of phloem sap from a Source to a Sink.

75. Source u Sugar production site u Ex: Ps Starch breakdown in a storage area.

76. Sink u Sugar uptake site. u Ex: Growing areas Storage areas Fruits and seeds

77. Comment u The same organ can serve as a source or a sink depending on the season.

78. Result u Phloem transport can go in two directions even in the same vascular bundle.

79. Xylem Transport: In Contrast to Phloem u Usually unidirectional. u Endodermis prevents back flow. u Dead cells.

80. Phloem Loading at the Source: 1. Diffusion 2. Transfer Cells 3. Active Transport

81. Phloem Loading

82. Transfer Cells u Modified cell with ingrowths of cell wall to provide more surface area for sugar diffusion.

83. Result u Sugar loaded into phloem.  Water potential (   ) decreases. u Bulk flow is created.

84. Bulk Flow u Movement of water into phloem. u Pressure forces phloem sap to move toward the sink.

85. At the Sink: u Sugar is removed. u Water potential is raised. u Water moves out of phloem over to xylem.

87. Phloem: summary u Source - builds pressure. u Sink - reduces pressure. u Pressure caused by: u Sugar content changes u Water potential changes

88. Comment u Plants move materials without "moving" parts, unlike animals.

89. Summary u Know various ways plants use to move materials. u Know how Ts works and the factors that affect Ts. u Know how phloem transport works.