Chapter 6 - Plant Phys

Chemical Potential

Free energy available to do work in transport.

Nernst Equation

Calculates equilibrium potential for ions across membranes.

Membrane Potential

Voltage difference across a cell membrane.

Transport Proteins

Proteins facilitating movement of solutes across membranes.

Channels

Proteins allowing passive movement of ions.

Carriers

Proteins that transport solutes via conformational change.

Pumps

Proteins using energy to move solutes against gradient.

Secondary Active Transport

Transport driven by ion gradients, not ATP directly.

Passive Transport

Movement of solutes down a chemical potential gradient.

Active Transport

Movement of solutes against a gradient, requires energy.

Translocation

Larger scale movement of substances, e.g., sugars.

Free Energy Gradient

Difference in chemical potential driving solute movement.

Hydrostatic Pressure Component

Pressure affecting solute transport, important for osmosis.

Diffusion Potential

Electric potential due to charge separation across membranes.

Nernst Potential

Equilibrium potential calculated using ion concentrations.

Concentration Gradient

Difference in solute concentration across a membrane.

Goldman Equation

Predicts membrane potential considering multiple ions.

Ion Distribution

Concentration of ions inside vs. outside the cell.

Microelectrodes

Tools used to measure membrane potential.

K+ Transport

Potassium ions transported passively across membranes.

Na+ Transport

Sodium ions actively pumped out of cytosol.

H+ Transport

Protons actively pumped out of cytosol.

Anion Transport

Anions actively transported into the cytosol.

Ca2+ Transport

Calcium ions actively pumped out of cytosol.

Driving Force

Magnitude of concentration gradient influencing solute movement.

Membrane Permeability

Ability of membrane to allow ion passage.

Electrogenic pump

Pumps one ion, does not balance charge.

H+-ATPase pump

Pumps H+ across cell membrane.

Membrane permeability

Biological membranes differ due to transport proteins.

Transport proteins

Integral proteins facilitating solute transport.

Channel proteins

Mediate passive transport through selective pores.

Carrier proteins

Bind solute, causing conformational shift.

Pumps

Active transport coupled to energy source.

Passive transport

Movement of solutes without energy input.

Potassium channels

Allow K+ flux based on membrane potential.

Nernst potential (EK)

Equilibrium potential for K+ across membrane.

Inward K+ channels

Open when potential is more negative than EK.

Outward K+ channels

Open when potential is more positive than EK.

Stomatal opening

Regulated by inward and outward K+ channels.

Facilitated diffusion

Slower transport via carrier proteins.

Primary active transport

Transport using ATP hydrolysis or redox reactions.

Electrogenic transport

Net charge movement, often H+ in plants.

Electroneutral transport

No net charge movement during transport.

Secondary active transport

Uphill transport of one solute coupled to another.

Proton motive force (pmf)

Energy stored from H+ gradient.

Symport

Substances move together into the cell.

Antiport

Substances move in opposite directions.

Michaelis-Menten equation

Describes transport rate based on solute concentration.

Vmax

Maximum transport rate for carriers or channels.

Km

Substrate concentration at half Vmax.

Binding affinity

Strength of solute binding to carrier.

Active uptake of sucrose

Carriers transport sucrose below 10 mM.

Simple diffusion

Occurs at concentrations above 10 mM.

Electrochemical gradient

Generated by ATP-driven H+ pump.

Antiporter

Transports Na+ in secondary active transport.

Symporters

Transport Cl-, NO3-, H2PO4-, sucrose, amino acids.

K+ Transport

Follows electrochemical gradient via H+-ATPase.

Nitrogen Compound Transporters

Transport NO3- using symporters and affinity components.

High-affinity Transporters

Low KM, effective at low substrate concentrations.

Low-affinity Transporters

High KM, effective at high substrate concentrations.

Peptide Transport

Some utilize H+ gradient; ABC transporters use ATP.

Amino Acid Transport

Utilizes symporters; varies by tissue affinity.

Cation Transport Channels

Six types identified in Arabidopsis, including K+ channels.

HAK Family

High-affinity K+ transporters for low-K soils.

CPA Family

Cation-H+ antiporters for electroneutral exchange.

HRK Family

K+-H+ or K+-Na+ symporters for ion transport.

Na+ Transport

Na+-H+ antiporters in plasma membrane and vacuole.

Ca2+ Regulation

Low cytosolic levels; efflux via Ca2+-ATPases.

Anion Transporters

Transport NO3-, Cl-, SO42- via electrochemical gradients.

Anion Efflux

Driven by electrochemical gradient through channels.

Metal Transporters

High-affinity transporters for metals in roots.

ZIP Family

Transporters for Fe, Mn, Zn in low concentration.

Vacuole Transport

Metals often sequestered in vacuoles due to toxicity.

Metalloid Transporters

Transport boron and silicon via aquaporin channels.

Aquaporins

Facilitate water flux; may sense osmotic pressure.

H+-ATPases

P-type ATPases generating H+ gradient for transport.

V-ATPase

Pumps protons into vacuole; uses ATP indirectly.

Stomatal Opening

Blue light causes guard cells to swell.

K+ Channel Activation

H+ gradient opens K+ channels, increasing concentration.

Ion Transport in Roots

Ions move through apoplast and symplast.

Casparian Strip

Blocks apoplastic ion movement at endodermis.

Xylem Loading

Regulated exit of ions from xylem parenchyma.

Cell Membrane Components

Includes H+-ATPases, aquaporins, ion channels, carriers.