Transport in Plants I
If you're not part of the solution, you're part of the precipitate.
- Steven Wright
Business
• Quiz: mean = last term, ~6/9 (not good enough),
?
– didn’t study enough,
– studied, did well, with tinkering will master,
– studied, but didn’t do too well,
• probably memorized terms, without grounding the words in reality.
• Midterm I: one week from Friday,
– Essay questions due Tuesday afternoon, 3 pm.
• email to young@biol.wwu.edu,
– Subject Line must say 206 Question,
– Include your name, if your email address is esoteric,
• 2 extra credit point (maximum) if you provide at least one GOOD question,
and email it, on time, and with correct subject line.
Rote
Not so Good
Concept/Process oriented Question
Good
Integrated question, i.e spanning chapters
Excellent
Today
• Introduction to Transport,
• Mechanisms of Transport,
– passive,
– active,
• Questions, Extra Credit?
Transport
…molecular and ionic movement from one location
to another,
– H2O,
– Sugars,
– Minerals,
– Gases,
– Other Macromolecules: proteins, RNA, hormones, etc.
Plant Transport
(What’s Transported)
Xylem
• H2O,
– uptake by roots, transport via
xylem, loss to the atmosphere
and metabolic process,
• Minerals (in solution),
– Uptake by roots, loss to
senescence, herbivory, etc.
Plant Transport
(What’s Transported)
Stomates
• Gases,
– CO2, O2, H2O.
– N2, ethylene, etc.
Plant Transport
(What’s Transported)
Phloem
bydirecional
• Sugars,
• other organics,
– hormones,
– amino acids,
– etc.
Plant Transport
(What’s Transported)
Gas Exchange/Respiration
• Roots,
»
– uptake O2,
– discharge CO2.
Plant Transport
Across Membrane(s)
Everything
First
Symplastic and Apoplastic
Then
What Drives Transport?
Gravity,
Pressure,
Electrical fields,
(for charged substances),
Concentration gradients,
(entropy-driven diffusion).
Mechanisms of Transport
in organisms
• Diffusion, by molecular motion,
– good only at short distances,
• Pump, Channel and Carrier mediated transport,
– small molecules across membranes,
• Osmosis (water across membranes),
• Bulk Flow,
– efficient large-scale, mass movement.
Fick’s First Law
“Uber Diffusion” (1855) Adolf Fick
concentration gradient
flux density
Dcs
flow rate
Js = Ds
Dx
change in distance
diffusion constant
Adolf Fick: Contributions
• Ophtalmotonometer – Intraocular pressure
• Aneroid manometer – Vascular grad (BP)
• Pneumograph – Peripheral thorax variation link
• Plethysmography – I/O of blood, air in lungs, etc.
• Dynamometer – Muscle output
• Laws of diffusion 1855
• Contact lens
Fick’s Law and Organisms
(tc = 1/2) for a molecule to move (p = 0.5) a set distance (L)...
tc = 1/2 =
L2
Ds
… is equal to the distance (L) squared divided by the
diffusion coefficient (Ds).
• Ds for sucrose is ~10-9 m2 s-1,
– 50 mm:
– 1 m:
tc = 1/2 = 2.5 seconds,
tc = 1/2 = 32 years.
Fick’s Law and Organisms
50mm
Chlamydomonas reinhardii
Bryophytes
Choleochaete orbicularis
Trees ?
Mechanisms of Transport
in organisms
• Diffusion, by molecular motion,
– good only at short distances,
• Pump, Channel and Carrier mediated transport,
– small molecules across membranes,
• Osmosis (water across membranes),
• Bulk Flow,
– efficient large-scale, mass movement.
Membranes
Plasma Membrane (1x),
Plastids (2x),
Mitochondria (2x),
Vacuole (1x),
Golgi, ER (1x),
Peroxisomes, etc. ( 1x).
Coordinated
Transport
Arabidopsis
Genome
H+ (protons)
ATP synthase
Transporters
- carriers,
- channels.
ATP hydrolase (ATPase)
Adapted from Biochemistry and Molecular Biology of Plants, pp. 115
ATP Pumps
all organisms
vacuolar
organelles
P-Type ATPases
Phylogentic Family
Tree
P-Type ATPases
plasma membrane
…ATP driven cation pumps (typical),
10
transporters
NA+ K+
H+ K+
H+
2+
Ca
Cd2+
Hg2+
Cu2+
animals
plants, animals, fungus, yeast
animals, plants, fungus, yeast
bacteria, animals, plants, etc.
+
Plasma Membrane H -ATPases
H+
Plasma
Membrane
H+
H+
H+
+
H+
H+ H
Proton Pump
H+ symport
(ATPase)
ATP
ADP + Pi
X
2 H+
H+ antiport
H+
2 H+
X
D 300 mV
ions
Transport channels
Mechanisms of Transport
• Diffusion, by molecular motion,
– good only at short distances,
• Channel and Carrier mediated transport
– small molecules across membranes,
• Osmosis (water across membranes),
• Bulk Flow,
– efficient large-scale, mass movement.
Osmosis
…the diffusion of water across a selectively permeable membrane,
– water (free) moves from a region of higher H2O concentration, to a region of
lower H2O concentration, until in equilibrium,
…the concentration of water is lowered by the addition of solutes.
Mechanisms of Transport
• Diffusion, by molecular motion,
– good only at short distances,
• Channel and Carrier mediated transport
– small molecules across membranes,
• Osmosis (water across membranes),
• Bulk Flow,
– efficient large-scale, mass movement.
Bulk Flow
Jean Louis Marie Poiseuille (Poiseuille’s Law, ~1838)
…the concentrated movement of groups of molecules,
– in response to gravity, i.e. rain, rivers, etc.,
– in biological systems, most often in response to pressure.
Volume flow rate =
in a cylinder
pr4
DYp
8h
Dx
viscosity (h)
viscous: tendency to resist flow
pressure gradient
distance
Increase Flow?
Increase radius.
Lower Viscosity.
Increase Pressure.
Shorten Distance.
Volume flow rate =
viscosity (h)
pr4
DYp
8h
Dx
pressure gradient
distance
Friday
• Water and Water Potential,
• Cell Water Relations,
• Water Transport in Plants.
Catch up in the readings, review materials from
204 and 205 if necessary.