Class 3 Flashcards
simplest index of water status
relative water content
relative water content = – / (saturated mass - dry mass) x 100%
fresh mass - dry mass
one weakness of RWC is that it is not very – for measuring drought responses
sensitive
leaves can show strong responses to – change in RWC
less than 2 percent
one weakness of RWC is that it tells us nothing about the – for water movement
forces
– is another index of water status, that is correlated with RWC but lacks RWC’s weaknesses
water potential
an overall, average water potential of the whole leaf, as the collection of all the leaf cells
leaf water potential
leaf water potential can be measured with the –
pressure bomb
for leaves of well watered plants, leaf water potential ranges from –
-0.2 MPa to -2 MPa
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
plant growth requires that cells have – turgor pressure
positive (pressure potential > 0)
as cells lose water, pressure potential – quickly until turgor is lost (solute potential declines linearly)
drops
T/F: as water potential declines further, different functions cease, and eventually plants die
true
at zero turgor, unlignified tissues collapse and plants –
wilt
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
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
osmotic potential at full turgor is an index of the – of cell sap in hydrated tissue
saltiness
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
osmotic potential at turgor loss point is also known as – or simply turgor loss point
water potential at turgor loss point
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
plotting the PV curve allows extraction of 4 main parameters: – determined as the slope of pressure potential versus RWC
modulus of elasticity
modulus of elasticity is an index of the – of cell walls
rigidity
some drought tolerant plants have – elastic modulus values, but not always
high
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
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 = –
0
soil solute potential is usually close to – unless soil is very salty
0
for wet soils, pressure potential is close to –
0
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
