PLANT TRANSPORTRemember Osmosis???

It results in the net uptake or loss of water by the plant cell and

depends on whether the cell or the extracellular fluid has a higher or

lower……

“WATER POTENTIAL”

So…. What exactly is WATER “POTENTIAL”?

Here is the “Helm Definition”: The potential to….. MOVE!!!!

In other words:

Water will always move across a membrane from an area of high to low potential.

Let’s see if you get it: More HYPERtonic = LESS Potential

More HYPOtonic = MORE Potential

More Pressure = More Potential

Less Pressure = LESS PotentialSo… Potential results from a combination of BOTH solute concentration AND pressure.

•Negative Pressure (or Tension) pulls in water•….and don’t forget about the role of the central vacuole!!

Lateral Transport:3 main routes:

1. Across the membrane/cell walls: (you know… through the cellulose & phospholipid bilayer)

2. The SYMPLAST- through the continuum of cytoplasm

formed by plasmodesmata. 3. The APOPLAST- between the actual plant cells

-never enters the cells, just worksits way through the matrix of cell walls

Campbell Animation

Long Distance Transport…

Xylem for Water

Phloem for “Phooood” (sap)

Transpiration “Plant Sweat”

Transpiration / Photosynthesis Ratio- g water lost / g CO2 assimilated

– The __________ the better??LOWER!

Example: 600:1 in C3 plants 300:1 in C4 plants

•Benefits of Transpiration:•Assists in mineral transfer from root to shoot•Evaporative cooling keeps enzymes from overheating

Drawbacks:if transpiration exceeds delivery of water…

Stomata close, photosynthesis ceases, plants wilt.

Stomata & Guard Cells When guard cells are turgid, they buckle

due to radially arranged microfibrils.

Turgid = Buckled = OPEN!!

Flaccid = Unbuckled = CLOSED!!!

•Caused by the reversible uptake & loss of K+ ions by Guard Cells.•More K+, higher [solute], lower p , water goes IN,

microfibrils buckle, STOMATA OPEN!(and vise- versa, of course)

K+ movement is triggered by H+ out by proton pumps.

Open or Closed??

OPEN:LIGHT: stimulates proton pumps by making ATP available

from photosynthesis.

DECREASE in CO2: from increased Photosynthesis.

CIRCADIAN RHYTHMS: internal clock (plants are often on a 24 hour cycle even in the dark)

Open or Closed?Closed:

WATER DEFICIENCY- makes guard cells flaccid

ABSCISIC ACID PRODUCTION- hormone that is activated in response to low water.

HIGH TEMPERATURES- increases CO2 due to increased respiration.

http://www.tvdsb.on.ca/westmin/science/sbioac/plants/stoma.htm

Translocation: food/phloem transport Sugar source: sugar production organ

(mature leaves) Sugar sink: sugar storage organ (growing

roots, tips, stems, fruit) 1- loading of sugar into sieve tube at

source reduces water potential inside; this causes tube to take up water from surroundings by osmosis

2- this absorption of water generates pressure that forces sap to flow along the tube

3- pressure gradient in tube is reinforced by unloading of sugar and consequent loss of water from tube at the sink

4- xylem then recycles water from sink to source

OK… so what about what’s goin’ on with the PHLOEM??

Campbell Animation