Ch. 36 Transport in Vascular

Feb 4­1:32 PM 1 Essential Question:

How does a tall get the from its to the top of the tree?

Feb 4­1:38 PM 2 architecture and Capture:

Phyllotaxy ­ arrangement of on a stem to maximize light capture, reduce self shading ­ determined by shoot apical and specific to each ­alternate = one per node ­opposite = two leaves per node ­whorled = more than two leaves per node

Norway ­ 1 is youngest leaf

Apr 14­7:00 AM 3 leaf area index = ratio of total upper leaf surface of a single divided by surface area of land, normal value ~ 7 if above 7 ­ leaves,branches undergo self pruning ­ programmed death

Mar 28­2:46 PM 4 Leaf orientations: horizontal leaf orientation ­ for low­light, capture more effectively vertical leaf orientation ­ for high light, grasses, light rays coming in parallel to leaf so not too much light

Apr 14­7:05 AM 5 architecture: mychorrhizae ­ mutualistic relationship between fungi and roots ­80% of land plants have this ­increases surface area for water and absorption

Mar 28­2:49 PM 6 Overview of transport in

Feb 6­9:37 AM 7 Three types of transport in vascular plants:

1. transport of water and solutes by individual cells a. passive transport () through aquaporins ­ transport

­ combined effects of solute concentration and physical pressure (esp. in plants due to ) ­determines direction of movement of water ­free water moves high to low [ ] ­measured in megapascals (MPa) ­water potential = "0" in an open container (at sea level and rm. temp.)

Feb 4­1:39 PM 8 = water potential

= solute potential ­ proportional to # of dissolved solute molecules (adding solutes lowers the water potential, so is always negative)

= pressure potential ­physical pressure on a solution ( can be + or ­ relative to atmospheric pressure)

= force against the cell wall after cell swells with water

Feb 4­2:05 PM 9 Water potential and water movement in an artificial model (keep in mind water goes from high to low water potential)

Feb 4­2:12 PM 10 Water relations in plant cells

Feb 4­2:14 PM 11 Feb 6­9:43 AM 12 b. active transport a. proton pump ­ uses ATP to pump Hydrogen ions out of cell ­makes proton gradient, membrane potential (voltage) outside cell = positive, inside = negative

Feb 4­1:58 PM 13 proton pumps can help:

1. get potassium (K+) inside cell


Feb 4­1:46 PM 14 2. cotransport of anions ­ transport couples H+ downhill with uphill ­ of nitrate (NO )3

Mar 28­2:53 PM 15 3. Cotransport of neutral solute (ex. )

Mar 28­2:53 PM 16 Three compartments of that regulate transport:

1. Cell wall ­ barrier between extracellular contents and plasma membrane

2. plasma membrane ­ barrier between cell wall and cytosol

3. tonoplast (wall of ) ­ barrier between cytosol and vacuole (holds cell )

Feb 4­1:51 PM 17 between cells plasmodesmata link the cytosol so molecules can pass easily ­ called the continuous cell walls and extracellular spaces is called are not shared between cells

Feb 4­2:25 PM 18 2. short distance transport cell to cell also known as lateral transport three ways: a. transmembrane­ crossing of cell wall and plasma membrane from cell to cell b. via the symplast­ via plasmodesmata c. along the apoplast ­ pathway of cell walls and extracellular spaces

Feb 4­2:27 PM 19 happens in root tips/root (increase surface area) particles coated with water and dissolved adhere to root hairs ­can then go by apoplastic or symplastic routes

Feb 4­2:46 PM 20 ­water and minerals then have to pass endodermis (innermost layer of root cortex) ­minerals already in symplast can go right through ­if via apoplast ­ reach dead end [ made of (waxy material)] ­to get past Casparian strip ­ need to pass through plasma \ membrane and enter via symplast ­end of pathway is back through the apoplast by and active transport ­ then can go into and vessels and go up plant

Feb 4­2:53 PM 21 Casparin strip

Feb 6­9:50 AM 22 3. long distance transport ­ Bulk Flow

movement of fluid driven by pressure ­through tracheids in and sieve tubes in

­transpiration ( of water from a leaf) reduces pressure in leaf xylem, creates tension that pulls xylem sap up from the roots

Feb 4­2:34 PM 23 Factors affecting ascent of xylem sap:

1. pushing xylem sap water flows in from root cortex ­generates to push sap upward ­if more water enters leaves than transpired = water droplets that can be seen on tips of leaves ­minor mechanism

Feb 4­3:07 PM 24 2. Pulling xylem sap (pulled by negative pressure)­transpirational pull ­normally air outside leaf is drier than inside leaf so water potential is higher inside leaf than outside so water leaves the leaf via stomata

­also involved­ water adhesion to microfibrils and cohesion of the water molecules to each other

­negative water potential of leaves provides the "pull"

­only works if there is an unbroken chain of water molecules

Feb 4­3:08 PM 25 in winter when sap freezes = can get (formation of pocket) so breaks chain ­ causes clicking noises in tree due to rapid expansion of bubbles when tree warms ­water can find an alternate route to go ­youngest, outermost secondary transports water

Mar 25­3:08 PM 26 Ascent of xylem sap

Feb 4­3:19 PM 27 Stomata regulate the rate of a leaf has high surface to volume ratio and large surface areas for ­due to this ­ has a large area to lose water stomata help reduce the water loss transpiration is high on sunny, warm, dry and windy days because these increase evaporation ­stomata close to decrease water loss ­prolonged drought = ­lose turgor pressure

Feb 4­3:20 PM 28 transpiration also causes evaporative cooling of the leaf, prevents enzymes from denaturing cacti can survive low rates of transpiration and high leaf

Mar 25­3:08 PM 29 typical stomata

Feb 4­3:28 PM 30 mechanism of stomatal opening and closing

Transport of potassium across the plasma membrane and vacuolar membrane causes the turgor changes in guard cells.

Feb 4­3:29 PM 31 stomata open in day and close at triggers for opening: 1. light ­ blue­light receptors in guard cells trigger accumulation of potassium ions and become turgid 2. low due to photosynthesis 3. "internal clock" of guard cells

triggers for closure in daylight: 1. low water ­ guard cells lose turgor 2. ­ signals closure of guard cells

Feb 4­3:35 PM 32 ­ plants adapted to arid environments have leaf modifications­ small, thick leaves, thick ­stomata on lower side of leaf, located in depressions ­some plants shed leaves during dry months ­have fleshy stems that store water

Feb 4­3:36 PM 33 phloem transport = translocation (transport of organic nutrients)

use sieve tube members ­phloem sap movement is variable, but always from a sugar source to a sugar sink sugar source = plant this produces sugar by photosynthesis or breakdown of ex. mature leaves sugar sink = an organ that consumes or stores sugar ex growing roots, , stems or tubers or may be source or sink depending on season ­sugar sink receives sugar from nearest source ex. upper leaves provide stem with sugar lower leaves provide roots with sugar ­neighboring sieve tubes may flow in opposite directions

Feb 4­3:40 PM 34 loading of into phloem

Feb 4­3:48 PM 35 ­sap flows through sieve tube by bulk flow moved by positive pressure

­pressure at source end and low pressure at sink end cause water to flow from source to sink, carries sugar along with it

­xylem recycles the water

Feb 4­3:49 PM 36 tapping phloem sap with the help of an

Feb 6­9:56 AM 37 Apr 14­8:03 AM 38