Plant physiology

What are 5 characters that might define a good model plant for understanding genetics and physiology

1. Economic value - are cheaper

2. small size - easier to store

3. short generation time - can see results quicker

4. high fecundity - ability to produce a lot of offspring

5. easy to manipulate

extras : resilience, change in morphology

What are 3 features of cells that are distinctive and typical of plants

1. two cells walls

2. chloroplast

3. Vacuole

4. Plasmodesmata

What is Apoplast

this pathway involves the movement of water outside of the protoplast cell walls from cell to cell via spaces in the cellulose cell walls

Symplast

this pathway involves the movement of molecules through the cytoplasm from cell to cell via plasma membrane and plasmodesmata

Which is a better system to conduct water

Apoplast

Which is a better system to conduct large bodies of water

Symplast

it is more tightly regulated and specific, in apoplast they spread everywhere and waste energy

What are the three major kinds of plant tissues

1. Dermal tissue

2. ground tissue

3. vascular tissue

What is the function of the dermal tissue

provides protection through epidermis, cuticle, guard cells and root hairs

What is the function of ground tissue

structural and mechanical support and metabolic processes

What is the function of vascular tissue

functions in conduction of water and nutrients (xylem) and in conduction of sugars and signal molecules (phloem)

How many species of angiosperms are there

400,000

How many species of gymnosperms

1100

What kind of diversity in growth forms

Trees, shrubs, herbs, climbers

What kind of diversity in physiology

1. exhibit different metabolism such as C3, C4, CAM photosynthesis

2. in nutrient and pigment concentrations, hormones sensitivity

3. in all aspects of structure: wide variation in cell sizes in each tissue, leaf size and colors

What kind of diversity in adaptation to different habitats

1. Irrance habitats: plants thriving from <1% to 100% full daylight

2. moisture supplies: plants exist on chronically dry soil, on ever-wet soil or submerged in water

3. Temperature range: plants can exist where temp reaches < -40 C and greater than 40C

Three reasons plants need water

1. Transpiration

2. plant growth

3. photosynthesis

Transpiration

this accounts for the bulk of water being used. It cools the plants by dissipating heat energy via evaporation of water. Opens stomata to access CO2, but loss of water as a side effect (side effect of photosynthesis.

Plant growth

tissue expansion via turgor pressure, structural support

Photosynthesis

Insufficient water will close stomata and prevent photosynthesis. Water is also important to crop yields and cools the leaf

Why is transpiration cooling effective

The evaporation of water utilizes a high heat vaporization and a high specific heat. thus it takes alot of energy to increase the temperature of water. This allows the plants to stay under bright sunlight and be a few degrees cooler than air.

Capillary rise = (14.9 ×10^-6 m²)/ radius

1. how high can water rise in cell wall pore capillaries (radius = 100nm)

2. How high in xylem vessels (radius = 25 um)

Water is a supersolvent

due to small size of molecules and to its polar nature. H- bonds between water molecules and ions stabilize the ions and increase their solubility. great solvent for sugar and proteins with polar groups in plants

water has a high specific heat

because of hydrogen bonding, water has high specific heat. we do not want the plant to burn (will denature proteins, DNA, etc)

Water has high tensile strength

cohesion gives water a high tensile strength, pull a continuous column of water can withstand before breaking allowing water to be pulled like a rope. is responsible for transpiration pulling water from the roots to the leaves.

Water has high surface tension

because of hydrogen bonding water molecules are strongly attracted to each other (cohesion). high surface tension leads to a minimizing air-water interface which minimizes water surface area and pulls the rest of the water upward.

what are the three forms of water transport

1. Diffusion

2. Bulk flow

3. Osmosis

Diffusion

Ficks law: Flow = -Dx (𝚫C/𝚫x) → driving force is concentration gradient (𝚫C/𝚫x).

diffusion is important for transpiration from leaves to air, movement of solutes within cells, and movement of signal molecules across plasmodesmata, etc

• occurs in leaves and stomata

Bulk Flow

Darcy’s Law: Flow = Khx (𝚫⍦_{p ^/} 𝚫x)

poiseuilles law defines Kh = (pi r^4)/ 8n

The driving force is pressure gradient (𝚫⍦_{p ^/} 𝚫x). Bulk flow is important for movement of sap in xylem and phloem, through roots, stems and leaves, and for movement of water in the soil

• occurs in xylem conduits and soil

Osmosis

Flow = Lp x 𝚫⍦

the driving force is water potential gradient (𝚫⍦). Cell membrane are selectively permeable water crosses membranes by diffusion through the lipid bilayer.

For a tree in the garden, there are five times as many xylem conduits in a branch than in a petiole, and the conduits in the branch are twice as wide as those in the petiole. About how many times higher is the hydraulic conductance in the branch?

poiseuilles law defines Kh = (pi r^4)/ 8n

80 times higher because the branch as 5x the conduits (which are 2x wide) so 5 x (2r)^4

= 5 x (16r) = 80r

Which direction does the water flow? and what are s and p for the cell at equilibrium

Water flows into the cell. Solute potential became less negative, and pressure potential increased because water flowed in, putting more pressure on the cell

In which direction does water flow?

Water flows from cell B → A, because water flows to the more negative pressure

What are two concepts/ approaches to measure plants water statues?

1. Relative water content:

2. Water potential

What is an advantage of Relative water content

RWC = (fresh mass - dry mass)/ (saturated mass - dry mass) * 100%

• advantage is that it is an easy and simple technology requiring minimal equipment, and is easy to understand

What is an advantage of Water potential

an index of cell and tissue water status

• very scalable and can measure directly, many ways of measuring, gives you driving forces for water movement.

What are the leaf pressure volume curve parameters

1. Osmotic potential at full turgor: intercept of ⍦’s versus RWC. It is an index of the saltiness of cell sap in hydrated tissue

2. Osmotic potential at turgor loss point. Is the leaf water potential corresponding to ⍦p = 0, or when ⍦leaf = ⍦s. This predicts cell, leaf and plant drought tolerance

3. Modulus of elasticity: the slope of ⍦p versus RWC and index of rigidity of leaf cell walls. Some drought-tolerant plants have high elastic modulus values

4. Apoplastic fraction (af): the x-intercept of -1/leaf water potential vs RWC curve, and represents the % of water stores in the apoplast in a hydrated leaf

Which is thought to be the most directly related to a species drought tolerance

TLP: turgor loss point

Why is it difficult for plants to withdraw water from dry soil

Air water menisci in sand particles is larger and are dried out with larger distortions; hence, there is less tension compared to smaller clay particles

• more dry soil = the more negative pressure gets = the lower the soil water potential = the harder it gets for plants to get to the water

Dry soil:

what is the type of water transport, driving force and transport coefficient

driving force is the negative water potential, water transport is the bulk flow, transport coefficient is hydraulic conductivity

Dry soil:

How does the driving force depend on the soil moisture

driving force depends on the soil moisture because drying the soil makes the driving force decline - soil becomes more negative and water potential goes down

Dry soil:

How does the transport coefficient depend on the soil moisture

transport coefficient depends on soil moisture because soil hydraulic conductivity declines as soil dries

• the pathway that the soil can move are declining( sediments dry faster than clay)

What is the role of the Casparian strip in water uptake and ion uptake in the root

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What is the name of this tissue involved

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How does water cross this tissue? why do plants invest in such a tissue

Casparian strip is waterproofed with lignin and suberin in order to stop water transport at the inner core of the root to only tolerate what the plant needs

• stops wrong liquids from going to the xylem where it can spread everywhere

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Endodermis, water crosses it through aquaporins (must also have special ion transport channels) - through osmosis

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As an extreme filter to control what gets in the plant because until the endodermis, anything can get through

How does water move from the soil to the root xylem

1. water moves through soil by bulk flow, driven by pressure gradients and dependent on the soil hydraulic conductivity (depends on soil type and structure and how wet the soil is)

2. Water moves from soil into the root by 3 pathways

   1. symplast pathway

   2. Apoplastic pathway

   3. Transmembrane pathway

symplast pathway

water enters root via cell wall (no boundary). Water goes into one cell and then can move through plasmodesmata to the endodermis

Apoplastic pathway

water moves into the cell wall and through the endodermis

Transmembrane pathway

water moves across cell wall, across cell membrane, through the cell, out of the cell, back to cell wall, into next cell and so forth

*symplast and transmembrane involve water entering with no boundary, once water enters the xylem, it moves by bulk flow

Suppose that a pine tree has tracheids of 10um diameter and a sunflower has vessels of 50 um diameter

Kh is higher for the sunflower by up to how many times? (assuming everything but conduit diameter is the same)

5/10 = 5

(5)^4 = 625

> 600 times

Tracheid

a type of conduit of the xylem that is seen in vascular plants

vessel

made up of stacked up vessel elements that are only found in angiosperms (ex. flowering plants have vessels in addition to tracheids)

pits

where the water moves out of the vessels; in vascular plants, pits have primary and secondary walls while conifers only have primary cell walls

Poiseuille’s law

used for finding the Kh (the transport coefficient in bulk flow)

Kh = pi * r^4/ 8n

hydraulic conductance

a measure of the efficiency of bulk flow

conduit radius

the measure of how much water is in contact with the sides, depends on the pipe size

cohesion tension theory

water is pulled up because of cohesion and water is pulled through tension because of negative pressure

cavitation

the moment the air gets in before air spreads to block the xylem

influence transpiration rate

:larger stomatal aperture

increases and stomata resistance decreases

wider stomata → lower stomatal resistance → higher conductance (g)

influence transpiration rate

: Higher temp

Increases (VPD increases b/c saturation vapor pressure goes up)

influence transpiration rate

: Lower relative humidity

increases (VPD and RH are inverse)

influence transpiration rate:

Slower windspeed

decreases b/c boundary layer resistance goes up → g goes down

influence transpiration rate

large leaf

decreases b/c boundary layer thicker (higher resistance) → lower g