Class 3 Flashcards by she ign

simplest index of water status

relative water content

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relative water content = – / (saturated mass - dry mass) x 100%

fresh mass - dry mass

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one weakness of RWC is that it is not very – for measuring drought responses

sensitive

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leaves can show strong responses to – change in RWC

less than 2 percent

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one weakness of RWC is that it tells us nothing about the – for water movement

forces

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– is another index of water status, that is correlated with RWC but lacks RWC’s weaknesses

water potential

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an overall, average water potential of the whole leaf, as the collection of all the leaf cells

leaf water potential

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leaf water potential can be measured with the –

pressure bomb

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for leaves of well watered plants, leaf water potential ranges from –

-0.2 MPa to -2 MPa

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plants of arid climates of saline environments can function at much lower leaf water potential down to below – due to accumulating solutes in the cells, producing a very negative solute potential

-5 MPa

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plant growth requires that cells have – turgor pressure

positive (pressure potential > 0)

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as cells lose water, pressure potential – quickly until turgor is lost (solute potential declines linearly)

drops

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T/F: as water potential declines further, different functions cease, and eventually plants die

true

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at zero turgor, unlignified tissues collapse and plants –

wilt

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plot of leaf water potential versus RWC

(or sometimes - 1/leaf water potential vs RWC, or vs 100%-RWC), and sometimes includes plots of leaf osmotic (solute) potential and pressure potential versus RWC

pressure-volume curve

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plotting the PV curve allows extraction of 4 main parameters: the –, determined from the intercept of the solute potential versus RWC

osmotic potential at full turgor

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osmotic potential at full turgor is an index of the – of cell sap in hydrated tissue

saltiness

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plotting the PV curve allows extraction of 4 main parameters: – which is the leaf water potential corresponding to the point at which the pressure potential = 0 or when the leaf water potential = solute potential

osmotic potential at turgor loss point

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osmotic potential at turgor loss point is also known as – or simply turgor loss point

water potential at turgor loss point

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because stomata close and cells may lose function at turgor loss, osmotic potential at turgor loss point is a – of cell, leaf and plant drought tolerance

predictor

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plotting the PV curve allows extraction of 4 main parameters: – determined as the slope of pressure potential versus RWC

modulus of elasticity

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modulus of elasticity is an index of the – of cell walls

rigidity

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some drought tolerant plants have – elastic modulus values, but not always

high

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plotting the PV curve allows extraction of 4 main parameters: – is the x-intercept of the -1/leaf water potential versus RWC curve

apoplastic function

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apoplastic function represents the -- in the apoplast in a hydrated leaf

% of water stored

of all the PV curve's parameters, -- is the strongest predictor of drought tolerance

osmotic potential at turgor loss point (water potential at turgor loss point, turgor loss point)

-- of cell sap is a strong predictor of drought tolerance across plant species

saltiness

water diffuses from the leaf due to a -- between leaf and air

water vapor concentration gradient (vapor pressure deficit)

the diffusion of water from the cell walls inside the leaf causes stretching of -- which generates a tension, pulling water from the xylem

air-water interfaces

the resulting tension, from the stretching of air-water interfaces, in the xylem pulls water by -- from the roots

bulk flow

water moves through soil by -- driven by pressure gradients, and dependent on soil hydraulic conductivity

bulk flow

soil hydraulic conductivity depends on -- and structure and how wet the soil is

soil type

clay = -- particles

small

sand = -- particles

large

water moves through channels between particles or as -- adhering to particles

film

soil saturated with water, with excess water drained away

field capacity

field capacity occurs when water stops dripping and water potential = --

soil solute potential is usually close to -- unless soil is very salty

for wet soils, pressure potential is close to --

as soil dries, air-water interfaces becomes stretched between soil particles generating a negative pressure because of -- so pressure potential becomes negative

surface tension

in drier soils, as the films around particles become thinner, smaller radii of curvature are generated = -- of the interface = stronger tension

greater distortion

when soils are -- soil water potential = pressure potential = -2MPa or lower

dry

as soil dries, soil hydraulic conductivity -- as channels in the soil empty of water

declines

water is more difficult to remove from drier soil both because the soil water potential is lower and because the -- is lower

soil hydraulic conductivity

water moves into the root principally through --

root hairs

root hairs constitute -- of root surface area and principally near the root apex

> 60%

roots need in contact with -- to absorb water and nutrients

soil

disturbance of root's contact with soil (new root hairs needed)

transplant shock

T/F: roots also need contact with air

true

during flooding, airspaces are filled with water --> roots can't respire and lose function --> plants --

wilt

water moves in the root via the apoplast, transmembrane and symplast pathways until reaching the --

endodermis

at the endodermis, the -- has suberized radial cell walls, and the apoplastic path is blocked; water enters the symplast

Casparian strip

after entering the symplast, the water moves to the --

xylem

water enters cells mainly through protein channels called --

aquaporins

aquaporins can be open or -- in response to environmental factors

gated

water pulled through xylem conduits: tracheids and vessels

tension-driven flow

-- are universal in vascular plants but vessels are found only in angiosperms, a gymnosperm called Gnetum and some ferns

tracheids

xylem conduits are --, hollowed out cells (tubes with lignified cell walls)

dead

xylem conduits make up a series connected by --

pits

pits may be simple or in conifers, with a --

margo/torus

xylem tubes allow a high --

hydraulic conductance

because xylem acts as a tube system, flow are -- times faster than if water had to move cell-to-cell to the top of tall tress

10 billion

hydraulic conductance is related to the -- power of the radii of the conduit so vessels are MUCH more conductive than tracheids and allow much more rapid flows of water to the leaf

4th

water drawn up to the top of trees by tensions in the xylem

cohesion-tension theory

challenge to the plant: cavitation by --

air-seeding

air is drawn into xylem conduits through -- from surrounding airspaces

pits

Or during --, air may come out of solution

cooling/freezing

when air bubbles enter the xylem, they -- in the water under tension, and fill the xylem conduit, rendering it useless

expand

when air bubbles enter the xylem, they expand in the water under tension, and fill the xylem conduit --> xylem conduit must be -- or it loses function forever

refilled

T/F: water can move in conduits around the air-filled conduit

true

one way refilling takes place is by -- the stomata

closing

one way refilling takes place is by --

root pressure

root pressure is found in some, but not all plants, sometimes only --

seasonally

roots transport solutes into the xylem, which draws in water, which -- the pressure in the xylem

increases

the pressurized water in the xylem dissolves air bubbles, and when air is moist, and transpiration is low, water may eventually -- from hydathodes in the leaves

guttate

the tension in the xylem is produced by the -- of water from cells and surface tension

evaporation

the -- the radii of curvature the greater the deformation of the interface and the stronger the tension

smaller

water from the cell walls evaporates into -- and diffuses through the leaf and out of stomata

airspaces

only -- of water evaporates through the cuticle

less than 5 percent

leaf is full of airspace (up to 50% of leaf volume) to allow rapid diffusion of -- into the leaf and also allows rapid diffusion of water out of the leaf

CO2

the average water molecule evaporated in the leaf travels -- outside, which would take 0.04 s by diffusion calculation

1mm

the concentration gradient driving the diffusion of vapor out of the leaf is --

strong

leaves have large internal wet -- (up to 50 x external leaf area) so air inside the leaf is considered to be close to saturation (close to 100% relative humidity)

mesophyll surface

saturation water concentration increases exponentially with --

temperature

higher temperature -- leaf-to-air concentration gradient

higher

T/F: moist air is 'dry' enough to drive strong transpiration

true

at 20 degrees Celsius, air at RH = 95% is the equivalent of -- MPa

-7

when air is at RH = 50%, the driving force is equivalent of -- MPa

-94

transpiration occurs through the --

stomata

transpiration: the diffusion through pores depends on the concentration gradient (VPD), on the diffusion coefficient (D), and the --

diffusional resistance

diffusional resistance = -- + boundary layer resistance

stomatal resistance

stomatal resistance depends on the total area of --

stomatal pore

stomatal resistance -- as stomata close

increases

boundary layer resistance depends on leaf size and --

windspeed

a smaller leaf and higher windspeed lead to a thinner boundary layer with -- resistance

lower

leaf shape and -- can also influence boundary layer resistance

hairiness

at high windspeed, the boundary later is very thin and -- becomes the major influence on diffusional resistance and on transpiration

stomatal resistance

at low windspeed, the -- is the major influenceon diffusional resistance and on transpiration

boundary layer resistance

at low windspeed, transpiration is relatively -- stomatal resistance, except when this becomes very high because stomata are nearly closed

insensitive

T/F: stomata evolved once for all plants, in a distant ancestor

true

stomata are required for control of -- relative to CO2 gain

water loss

plants can thus open pores to fix carbon when water is abundant, but close pores to save water from the water supply is low, or when the leaf demand for CO2 is --

low

stomata are controlled via -- swelling

guard cell

guard cells are -- shaped in grasses and kidney-shaped in non-grasses

dumbbell

differential wall thickening and arrangement of -- dictates which parts of the guard cells will stay fixed

cellulose microfibrils

as the rest of the cell swells, pores open when guard cells are --

pressurized

guard cells are pressurized by increasing -- in the cell via ion uptake or creating new organic ions in the cells

solute potential

increasing solute potential in the guard cells, drives water uptake from the surrounding mesophyll, and pressure potential increases and the cells --

swell

guard cell turgor is sensitive to light, --, leaf water status, and CO2 concentration

temperature

the guard cells are kept isolated from surrounding cells (no plasmodesmata), so their aperture is -- dictated by the water status of surrounding cells

not directly

overall soil-plant-atmosphere continuum: water moves through soil and xylem by -- and out of leaves by diffusion

bulk flow

there is a water potential -- (1) across the entire plant, and (2) between any two tissues in the flow pathway, from the soil to the leaf airspaces

drop