Transport and Translocation of Water and Solutes

Plasma Membrane

Separates plant cells from the environment

Turgor Pressure

Regulates pressure within plant cells

Phospholipid Bilayer

Structure of cell membranes composed of hydrophilic heads and fatty acid tails

Membrane Potential

Charge gradient maintained by electrogenic pumps

Electrogenic Pumps

ATPases that create charge gradients by pumping out protons

Ion Homeostasis

Balancing ion concentrations within plant cells

Passive Transport

Movement down an electrochemical gradient

Active Transport

Movement against an electrochemical gradient

Electrochemical Potential

Dictates passive and active transport based on concentration and charge

Channels

Transmembrane proteins for fast, unidirectional ion transport

Carriers

Proteins that bind and transport specific organic compounds

Pumps

Active transporters that move molecules against gradients

Aquaporins

Integral membrane proteins facilitating water movement

Facilitated Diffusion

Passive transport aided by carrier proteins

Primary Active Transport

Energy-requiring transport against gradients

Secondary Active Transport

Coupling uphill transport with downhill transport

Symport

Transport where substances move in the same direction

Antiport

Transport where substances move in opposite directions

ABC Transporters

Superfamily using ATP to transport molecules across membranes

Facilitated diffusion

Passive transport through carriers specialized for specific organic compounds

Active transport

Primary: Uphill transport coupled with energy release; Secondary: Uphill molecule with downhill another

ABC transporters

Superfamily with ATP binding domains driving conformational changes for molecule transport

Vacuole

Plant cell organelle maintaining turgor pressure, storing substances, and supporting structures

Tonoplast

Vacuolar membrane containing water, ions, and enzymes

Turgor pressure

Pressure from vacuoles providing structural rigidity to plants

Ion homeostasis

Maintenance of ion balance in plant cells through transporters and channels

Plasmodesmata

Channels connecting plant cells for intercellular transport

Casparian strip

Forcing ions from root apoplast to symplast in root cells

Xylem loading

Active transport of ions into xylem for long-distance transport

Translocation

Movement of molecules and ions within plants controlled by cellular membranes

Phloem transport

Specialized process redistributing photosynthesis products and organic compounds

Sources and sinks

Regions in plants producing and utilizing photosynthates for growth and metabolism

Vascular tissue

System in plants for transporting sugars and nutrients to growing parts

Sink

Organs that do not produce enough photoassimilate to meet their own needs, e.g., roots, tubers.

Source

Organs that produce photoassimilate for transport, e.g., developing apex.

Beta maritima

Wild beet root acts as a sink in the first growing season and as a source in the second season.

Sucrose

Most common sugar transported in phloem, made up of glucose and fructose.

D-Mannitol

Mobile sugar in phloem, containing sucrose bound to varying numbers of galactose units.

Osmotic Effect

Tied to the number of particles in solution, influencing energy transport in plants.

Invertase

Enzyme breaking down sucrose, unlikely present in phloem sieve tubes.

Companion Cells

Provide energy for sieve elements, involved in transport of photosynthesis products.

Symplastic Transport

Movement of sugars via cytoplasmic connections between cells.

Callose

Long-term protective mechanism in phloem, sealing off damaged sieve elements.

Pressure-Flow Model

Theory explaining phloem transport driven by osmotically generated pressure gradient.

Bulk Flow

Movement of water in phloem driven by pressure gradient, transporting solutes.

Triose Phosphate

Compound formed from photosynthesis, crucial for phloem loading.

Sieve Element Loading

Process where sugars are transported into sieve elements and companion cells.

Phloem Unloading

Process of sugars leaving sieve elements, transported to sink cells for storage or metabolism.

Apoplastic Pathway

Phloem loading requiring active transport against chemical potential gradient.

Symplastic Phloem Loading

Dependent on open plasmodesmata between cells, facilitating sugar transport.

P Proteins

Short-term protective mechanism in phloem, sealing damaged sieve elements.

Phloem Velocity

Rapid movement of materials in phloem, averaging 1 meter per hour.

Phloem Structure

Comprised of sieve elements and companion cells, conducting sugars and amino acids.

Phloem Transport Cells

Living cells specialized for phloem transport, forming continuous tubes.

Phloem Transport Pathway

Conducting sugars and organic materials throughout the plant in the phloem.

Phloem Loading Process

Involves active loading of sugars into sieve elements and companion cells.

Phloem Unloading Process

Involves sugars leaving sieve elements and being transported to sink cells for storage or metabolism.

Phloem Protective Mechanisms

Include P proteins and callose, sealing off damaged sieve elements.

Phloem Transport Mechanism

Driven by pressure gradient, allowing for rapid movement of materials.

Phloem Transport Rate

Movement in the phloem is rapid, well exceeding rates of diffusion.