Plant Structure & Transport Systems Chapter 28 & 29

I. Plant Structures  A. Roots : anchor, absorb minerals and water, store carbs  1. Root hairs: individual cells: absorption  2. Tap roots: Main vertical root: anchor  3. Lateral roots: Branch to sides: absorb  4. fibrous roots: mat of shallow roots

 B. Shoots: leaves and stems  1. Stems & Branches: transport & elevation  a. veins in stem transport  i. xylem cell : water up  ii. phloem cells : sugars down  b. Elevation advantage..  i. light  ii. pollen dispersal

 2. Leaves: photosynthesis/Gas exchange  a. mesophyll cells do Photosynthesis  i. fill interior of leaf  ii. Chloroplasts  b. stoma  i. opening  ii. Allow gas  in/out of  air spaces  inside leaf

II. Gas Exchange  A. Guard Cells: open and close stomata  1.Open stomata let CO 2 in but..  also let water out by transpiration  2. Transpiration in leaf  i. water evaporates from mesophyll cells into air space (High ψ to low ψ)  ii. Water vapor moves from air space through stomata into air  (High ψ to low ψ)

C. Stomata number & location  Drier climate : fewer stomata  Aquatic plants : many stoma always open  Most stomata on bottom of leaf  Stomata open & close in response to stimuli

D. Guard Cells Open  Blue light stimulus received by photoreceptors on guard cells  Signal transduction causes active transport of K + into guard cell  water flows into cell  Increasing turgor pressure  Bending guard cells apart= response

E. Guard Cells Close Stoma  ABA hormone = signal molecule produced by plant cells lacking water  ABA binds guard cell receptors  Signal transduction opens Ca+ and K+ channels reducing solute conc in cell  H2O leaves cell. Low turgor pressure due  to shrinking vacuole makes cell flaccid  Stoma closes

III. Water Transport  A. Into Root  1. hydrophilic cell walls of root tips/root hairs  2. water & minerals flow into cortex extracellular spaces  3. cortex & epidermal  cells selectively absorb  minerals (high SA)  4. Active transport increases mineral conc.

Apoplast –extracellular Symplast-cytoplasm

B. Into Vascular cylinder  1. Endodermis cells regulate what enters  vascular cylinder  2. Casparian strip of wax (suberin) forms tight junctions around endodermal cells  3. only what crosses endodermal cell membranes can enter Xylem  4. active transport moves ions increasing osmotic pressure as H 2 O follows

 4. Root pressure pushes xylem sap (water/minerals) up root by bulk flow  (fluid movement by pressure)

C. Up Stem & to veins in leaves (p588)  1. Cohesion-tension hypothesis  a. Pulls sap up stem & into leaf veins  b. Water evaporates from cell wall of mesophyll cells into air spaces  c. Lost water creates tension on water in the rest of the leaf (negative pressure)  d. tension and negative pressure potential result in low water potential  e. cohesion pulls water toward air space  f. adhesion keeps them from falling

Transpiration

IV Sugar Transport =Translocation  A. From sources to sinks  1. summer  a. source: mature leaves  b. sink: growing structures & root cortex (storage)  2. Spring  a. source: root  b. sink: growing leaves

B. Phloem  1. Phloem sap  a. high sucrose content  (glucose + fructose: easy transport)  b. hormones  c. maple syrup  2. Phloem cells  a. sieve tube cells = pipeline  b. companion cells = load sugars

Plasmodesmata Connect Sieve tube Cells at Sieve plate

C. Bulk Flow in Phloem: POSITIVE pressure  a. pressure built at source by active transport  b. pressure reduced at sink by removal of sucrose for storage in cortex cells  D. Sugar loading  a. companion cells use active transport to move sucrose into sieve tube  b. water follows by osmosis  c. pressure potential is high: bulk flow

 E. Sugar Storage/Use at sink  1. sugar diffuse out of phloem  2. sugars used for growth  3. sugars converted to starch/stored

 Translocation

p  Phloem loading  /student_view0/chapter38/ani mation_-_phloem_loading.html /student_view0/chapter38/ani mation_-_phloem_loading.html

V. Plant Growth  A. Meristem tissue  1. undifferentiated cells doing mitosis to grow  2. apical meristem in root/shoot tips  B. Tropism : growing toward or away  1. Positive = toward, Negative = away  2. phototropism  3. Thigmotropism – touch (vines curl)  4. geotropism

C. Auxin Mechanism  1. Auxin = plant growth hormone  2. Auxin concentrations control transcription  3. controls genes to regulate differentiation  4. Auxin only made in apical meristem  5. Auxin transported down shoot by  Polar transport (faster than diffusion)

 a. Polar bcs Auxin transport proteins only located at base of cells.  (at one pole)  b. Unidirectional movement

D. Acid Growth Hypothesis  1. High Auxin concentration = elongation of apical cells (growth)  2. Called Acid Growth bcs high Auxin conc. causes protein pumps to actively transport H + out of the cell (making the cell wall low pH)

3. Effects of high H+ conc. in cell wall  a. Membrane potential created.  (voltage across memb.)  Memb. Pot. Causes ion uptake by cell  Cell becomes hypertonic  Osmosis increases turgor pressure  b. Low pH.  Activates expansins  Enzymes that break crosslinks (H-bonds) btwn cellulose fibers  Allows cell wall to expand

4. Result = cell elongates (grows)  a.Under uniform light cells grow equally  b. Directional light causes dark side cells to elongate more  ml ml  ml ml

Hormones = signaling molecules carry info from cell to cell  1) Gibberellins – Lengthen stem/root  seed germination  2) Auxins – lengthen shoots & apical dominance  - decrease abscission (leaf dropping)  - fruit formation  3) Cytokinins – cell division  - slow aging  - decrease apical dominance

 4) Ethylene – directional growth  - ripen fruit (is a gass)  - promotes senescence (aging)  - promotes abscission  5) ABA = Abscisic Acid – induce dormancy  - drought tolerance by  - closing stomata

Seed Dormancy  A) mature seed produces ABA  1. induces production of proteins to resist dehydration  2. induce seed dormancy  B) To germinate ABA levels must come down  1. heavy rain washes ABA out of seed  2. light and cold exposure may also be needed