Chapter 39: Flowering Plants - Transport

What are the four systems of plant transport?

Root systems, shoot systems, photosynthetic cells, and conducting tissues

Passive Transport

Movement of materials down a concentration gradient. Doesn’t require ATP

Simple Diffusion vs. Facilitated Diffusion

Movement of molecules through the phospholipid bilayer vs, using membrane transport proteins

What are the two types of transport proteins?

Channels (membrane pores) and Transporters (selectively bind to molecules on one side and change their conformation to release it on the other side)

What is the purpose of aquaporins?

They are membrane transport proteins used to move water across the membrane based on solute concentration (osmosis). This enables osmosis to occur more rapidly than it would with just the lipid bilayer

How does the ATPase proton pump work?

It uses ATP hydrolysis to move a proton against the gradient (active transport). This creates an electric charge difference across the lipid bilayer that is relieved when a proton moves back down the gradient, which powers the transport of other molecules.

Symporter

Moves two molecules in teh same direction. Used for sugar, protein, and nucleotide base uptake.

How does ion tranpsort work in the epidermis of the root hair?

Protons are pumped out, allowing for the intake of moelcules such as NH4+, K+, HPO42- into the root hair.

What directs osmosis?

• Turgos pressure (osmotic pressure) - hydrostatic pressure (equal pressures from two fluids) result in the stop of water flowing

• Solute content

What are the three types of water content states?

Turgid (more water inside), Plasmolyzed (less water inside), Flaccid (same)

What is water potential?

The potential energy of water, water wants to move from high potential to low potential

What is the equation for water potential?

W = S + P

• S = solute potential (negative for water with solutes)

• P = pressure potential (turgid is positive, flaccid and plasmolyzed is zero)

What does the sign of water pressure indicate?

• A positive water potentail indicates water moving out (turgid, low solute)

• A negative water potential indicates water moving in (high solute)

What is Relative Water Content?

RWC = (fresh-dry weight)/(turgid-dry weight) * 100%

• Fresh Weight: weight of plant as is

• Turgid Weight: weight of plant full with water

• Dry Weight: weight ot plant dehydrated

How far is this plant off from its healthy state? If >50%, it can recover from wilted back to turgid, otherwise it will die.

What type of platns must adapt to osmotic stress?

Plants in cold, dry, or high salt environments

How do plants adapt to osmotic stress?

• Increase solute concentration in cell to keep water in. Also lowers the freezing point

• Stabilize their cell membrane with sugars

• Increased aquaporins

What are the three types of tissue level transport?

Transmembrane (moving material via membrane proteins), Symplastic (moving cytosol to another cell), and Apoplastic (through cell walls and intercellular spaces)

How does transport work in roots?

Through symplastic and apoplastic transport

What is the limitation on apoplastic transport in roots?

The intercellular transport stops at the endodermis, which keeps it from moving into the roots vascular tissues. This is prevented by Casparian strips (barriers in between cells)

What is the role of the endodermis?

It is a molecular filter that keeps harmful solutes from getting to the shoot and has selective transport membranes that only allow mineral nutrients.

What mechanism allows water to flow into the vascular tissue?

Solutes get transported into the apoplast of the vascular tissue by the endodermal cells, increasing solute concentration. Water then moves into the vascular tissue.

What is long distance transport?

This moves water/dissolved minerals from roots to shoorts via the xylem and phloem in the vascular tissue.

What is bulk/mass flow?

Mass movement of liquid facilitated by gravity and/or pressure (ex. leaching - loss of nutrients from the leaves due to rain)

Transpiration

Water evaporates from the shoot system through the stomatas

What is the process of bulk flow in the xylem?

When water evaporates, the intercellular surface tension increases (due to less water present, there is a high cohesive force between the remaining water molecuels), causing water from the roots to move upward.

What limits plant growth height?

Gravity which pulls water downwards

How does sugar solute concentration affect bulk flow in the phloem?

Photosynthesis increases the sugar concentration in the sap of leaves, causing water to enter and pressure to rise.

What are the components fo flowering plant xylems?

• Alive cells: Parenchyma

• Dead Cells: Tracheary elements that conduct water because they have no cytosol

• Alive/Dead: Supportive Fibers

What is the structure of tracheids?

They are long tubes that contain a lignin-containing second wall and pits (like veins) that water runs through

Vessels or vessel elements?

• More abundant in flowering plants

• They are larger and longer than tracheids with sometime perforated side walls, allowing for bulk flow

• Vulnerable to embolisms

How do embolisms affect plants?

Embolisms, or air bubbles, occur in vessels and can lead to damage through thawing and freezing cycles. They may become completely blocked by air, resulting in the plant needing to develop new growth. These do not affect tracheids because air bubbles don’t form.

How does guttation help remove embolisms?

Solutes build up in the xylem, causing water to flow up from the leaves and leave as droplets, pushing out the air bubble

Cohesion-Tension theory

Transpiration causes water to be loss from the plant leaves, increasing cohesion and creating a negative tension that draws up water from the roots. This is a continuous upward stream of water, and transpiration helps cool plants

How do guard cells control stomata opening and closing?

Guard cells surround the stomata opening. In high water, stomata opens because the guard cells expand outward, widening the pore. In low water, it closes because the guard cells “deflate” closing the pore.

What was the conclusion of the Park Study?

They investigated the effects of chemical treatment to the ABA receptor which is responsible for drought response. They engineered the gene to respond to an agrochemical, resulting in the plant closing its stomata - helping it survive drought.

How does leaf abscission help plants prevent water loss?

• Drop their leaves to reduce low water potential in the leaves and prevent embolisms from occuring (low water in the soil = more likely for air to be pushed into leaves from the roots)

• Reduces the need for a lot of root mass to maintain leaves.

How have confiers adapted to lower water loss at their leaves?

Their needles have a lower surface area for evaportation

What are the two layers involved in leaf abscission?

• Separation Layer - thin cells

• Protective Layer - thick cells near the branch

Process of Leaf Abscission

• Ethylene forms abscission zone

• Water supply cut

• Chlorophyll breaks down

• Enzymes degrade cell-walls at the separation layer and the leaf breaks off

• Protective layer froms leaf scar

What are the two types of phloem?

• Primary: in the vascular bundles of herbaceous plants

• Secondary: In the inner bark of woody plants

Phloem structure

fibers, parenchyma cells, sieve tube elements, companion cells

Sieve tube elements

Lack a nuceluous and some cytoplasm elemnts to allow the transport of sap. The companion cells supply mRNA and proteins via the plasmodesmata

How does the sieve element help when the phloem is damaged?

Its cytoplasm elements sruge towards teh sieve plate and deposit P protein which prevents nutrient loss and prevents infection.

What are the two types of phloem loading?

Symplastic: sugar from sugar-producing cells move to companion cells and to sieve tubes via plasmodesmata (woody, no ATP)

Apoplastic/Transmembrane: load from intercellular membrane (herbaceous, ATP)

How is the transport of phloem sap described?

Movement from sugar source (leaves) to sinks (roots and developing leaves/fruits) via turgor pressure differences

sieve tubes can be located near source or sink tissues. Source → xylem, phloem → sink