1. Chpt 36: Transport In Plants

2. Transport Overview 81- uptake and loss of water and solutes by individual cells (root cells) 82- short-distance transport from cell to cell (sugar loading from leaves to phloem) 83- long-distance transport of sap within xylem and phloem in whole plant

3. Whole Plant Transport 81- Roots absorb water and dissolved minerals from soil 82- Water and minerals are transported upward from roots to shoots as xylem sap 83- Transpiration, the loss of water from leaves, creates a force that pulls xylem sap upwards

4. 84- Leaves exchange CO2 and O2 through stomata 85- Sugar is produced by photosynthesis in leaves 86- Sugar is transported as phloem sap to roots and other parts of plant 87- Roots exchange gases with air spaces of soil (supports cellular respiration in roots)

5. Proton pumps (chpt 8) 8Passive transport--Solutes diffuse down their gradients – requires no E (proteins in plants that passively transport water = aquaporins) 8Cross slowly unless they can pass through transport proteins 8Active transport – pumping solids across membrane against gradient – requires E— 8Carried out by special proteins

6. Proton pump -most impt active transporter in plants p.150 8Membrane proteins store E by generating voltage across (separating charges) membranes. 8Uses ATP for power 8Moves pos charges (H + ) so creating a voltage difference & a chemical difference that can be used to drive other processes 8You expend a little E & get more in return

7. Water potential (ψ) differences drive water transport 8Plant survival depends on balancing water uptake with water loss! 8Hypotonic –lower solute concentration 8Hypertonic – higher solute concentration 8Water will move from hypo to hyper 8Since plant cells have a cell wall, pressure must also be taken into consideration 8Water potential includes concentration & pressure

8. Water potential & concentration 8Water moves from higher water potential to lower water potential 8This moving water can do work so it has the potential to do work! 8Measured in megapascals (Mpa) 1MPa = 10 atm 8Adding solutes lowers water potential so, if [↑] then ψ↓

9. Water potential & pressure 8If pressure goes ↑ then ψ↑ 8So, ψ = ψ pressure + ψ [solute] Look at p.751

10. Cellular Transport 8Water transport √ Osmosis; hyper-more solute; hypo-less solute; iso- same solute 8Cell wall creates physical pressure to go along with [solute]

11. 8Water moves from high to low water potential 8Flaccid (limp, isotonic –plants need to be in hypotonic envr.); 8Plasmolysis (cell loses water in a hypertonic environment; plasma membrane pulls away); 8Turgor pressure (influx of water due to osmosis; hypotonic environment) 8 flaccid

12. Cells with vacuoles (vacuolated) have 3 compartments 8Cell wall 8Cytosol 8Vacuole –membrane around vac. called tonoplast

13. Transport within tissues/organs 8Tonoplast - vacuole membrane– controls traffic between vacuole & cytosol 8Plasmodesmata – connections between dif. Cells - cytosolic connection 8Symplast route (lateral) – all of the plant cells are connected & this is called a cytoplasmic continuum or symplast route –materials move from inside 1 cell to inside the next cell

14. 8Apoplast route (lateral) – walls of adjacent cells are also in contact = continuum of cell walls – water etc… travel across tissue via cell walls & extracellular spaces 8Diffusion process is fine for cell to cell, but to slow for long distances 8Bulk flow (long distance) -movement of a fluid drive by pressure (in xylem)

16. Transport of xylem 8Capillary action (rise of liquids in a narrow tube) –due to adhesion (water sticks to walls) is minimal 8Osmosis creates Root pressure: at night (low transpiration), roots cells continue to pump minerals into xylem; this generates pressure, pushing sap upwards; usually doesn’t create a great amt of pressure

17. Root pressure causes guttation – exuding water droplets on tips of grass blades in morn.

18. Transport of Xylem Sap – cohesion-tension theory 8Transpiration: loss of water vapor from leaves pulls water from roots (transpirational pull or tension); 8cohesion (water sticks to water) produces a single polymer- like column of water from roots to leaves 8Bulk Flow occurs when water evaps from leaves– as molecule evaps it pulls up a column behind it (sun causes transpiration so sun provides E for the process!)

19. Remember – water moves from greater water potential to lesser!

20. Transpiration control – balance between opening for CO 2 & closing to maintain water 8Stomata close when Temp is high- reduces H2O loss, but stops photosyn 8Stomata open when CO 2 levels low – CO 2 required for photosyn. 8Stomata close at night ([CO2] high due to respiration so no need to open….) 8Guard cells control the size of the stomata

21. Scanning electron micrograph of Equisetum (horsetail or scouring rush) epidermis. Note the oval stomatal apparatuses in the center of the stem.

22. Pea Leaf Stoma, Vicea sp.

23. Transpirational Control 8Stomata opening- ↑K+ ions create a gradient that’s used to move H2O into guard cells causing g-cells to enlarge & open stomata (K+ charge gradient in dif plant species balanced by H+ out or Cl- ions in) 8Photosynthesis-Transpiration compromise… 8Xerophytes (plants adapted to arid environments)~ thick cuticle; small spines for leaves

24. Translocation of Phloem Sap 8Translocation: movement of food through phloem to a sink 8Sugar source: sugar production organ (mature leaves) 8Sugar sink: sugar storage organ (growing roots, tips, stems, fruit)

25. 81-sugar enters sieve-tube members via active transport – this creates a concentration gradient between source (higher) & sink (lower) 82-water enters sieve-tube members by diffusion – passive transport 83- pressure gradient in tube moves water & sugars to sieve-tube members at sink (bulk flow due to pressure) Pressure-flow hypothesis

26. 84 – pressure at sink reduced as sugars are removed to by used –removing sugars decreases conc of solutes which lowers water pressure at sink & helps keep process going 85- in plants the sugar can also be “removed” by changing it to starch – it doesn’t have to be immediately used 86- xylem then recycles water from sink to source

27. 8Driving force for water movement in plants is transpiration & cohesion! 8Driving force for sugar movement in plants is a concentration gradient!