Midterm l 1+2 Flashcards
6 plant life processes
primary producers; growth > motility to obtain resources; structurally reinforced; transport systems; mechanisms to avoid dessication; plants develop from embryos
what is the meristem
localized regions of ongoing cell division. enable growth
difference between primary and secondary plasmodesmata?
primary = ER membrane maintained thru CW as cell splits secondary = metabolism digests CW to get ER thru to other cell.
3 major tissue systems
dermal; ground; vascular
tissue type within dermal tissue system?
epidermis
tissue type within ground tissue system
cortex, pith, mesophyll
tissue type within vascular tissue system
xylem + phloem
typical cell types in epidermis?
epidermal; guard, gland; root haris; trichomes
typical cell types in cortex/pith/ mesophyll
parencyma, collenchyma, sclerenchyma
typical cell types in xylem?
vessel elements, tracheids. parenchyma, fibers
typical cell types in phloem
sieve tube elements, companion cells, parenchyma, fibers + sclereids
function of epidermal cell?
protection
function of guard cell?
air +water exchange
function of gland cell
air +water exchange
function of root hairs/trichomes
uptake, protection
function of parenchyma
matrix, metabolism, storage, secretion, photosynthesis, transport
function of collenchyma
support of growing tissue
function of sclerenchyma
support of non-growing tissue
function of vessel elements +tracheids
water conduction
function of parenchyma
matrix, metabolism, storage, secretion, photosynthesis, transport
function of fibers
support
function of sieve tube elements
carbohydrate transport
function of companion cells
work in tandem with sieve tube elements
function of fibers, sclereids
support
function of waterprood outer cuticel?
physical barrier for penetration of viruses/predators
what are stomatal apertures controlled by?
guard cells
pattern of pavement cells? what tissue system do they belong to?
jigsaw puzzle - tight pack.
dermal tissue
what is foudn on lower epidermis
guard cell, stomata, pavement cells + cuticle.
functino of guard cells?
regulate gas exchange by changing their shape, depending on whether they are turgid or not
guard cells are symplastically isolated - why?
because if they were connected to plasmodesmata + symplast they would have very easy access to water + water would be very easily lost
function of trichomes?
protect against pests + water loss. synthesize metabolites + may deposit molecules
gland cells function?
secrete products onto leaf
root hairs functin? what tissue system?
major site of absorption of water + nutrients
–> dermal tissue
parenchyma cells - make up ?
make up bulk of plant. metabolic workhorse.
capacity to continue cell division + differentiate into other ground + vascular tissues
collenchyma primary cell walls
thickened. involved in reinforcement - important in herbacious not woody plants. can continue to elongate thru maturity.
sclerenchyma 2-ary cw
hardened with lignin. dead @ maturity. derive from parenchyma + develop in response to enviro stress
fibers - function + tension?
support structure in ground tissue + vascular tissue. high tensile strength
why are xylem vessel elements important + better than tracheids?
can bypass xylem vessel in case of rupture or embolism.
phloem conduction
sieve cell (gymnosperm) sieve tube element ( angiosperm) --> living at maturity therefore needs metabolic activity.
photosynthetic compounds to roots + flowers/seeds.
sieve elements in angiosperms
- organelles? metabolic activity?
lost organelles, dont have mechanisms to maintain metabolic activity, connected by plasmodesmata btw companion and sieve tube
function of companion cell, parenchyma cell + connection via plasmodesmata and sieve tubes?
help load/unload photosynthates. metabolically dependent on companion cells (angio)
organization of vascular tissue?
phloem outside, xylem inside.
function of vascular cambium in stem?
allows for secondary growth
stem organization - eudicot vs monocot
eudicot = arranged in bundles, vascular cambium separates phloem from xylem. monocot = vascular bundles scattered throughout
root vascular tissue organization?
single central vascular cylinder. cross of cylem, 4 pockets of primary phloem. vascular cmabium separates, parenchyma pericycle surrounds - may differentiate to 2-ary root development.
vascular organization of leaf
vascular bundles in spongy mesophyll - xylem is upper, phloem lower. protected by parenchyma.
9 functions of cell wall?
mechanical strength; adhere cells together; control cell shape + expansion; that resists collapse; sensory proteins; diffusion resistance; armour; cuticle
how does cw provide mechanical strength?
pectin = tensile strength, still needs flexibility tho. also ensures xylem doesnt collapse - facilitates water transport.
how does cw control cell shape + expansion
dictates plant development + morphogenesis = determines growth + polarity.
limits max volume of cell + allows high cell turgor pressure to develop.
sensory proteins in cw?
protrude into cell wall space, enable perception of internal + external cues
diffusion resistance as cw function?
governs movement thru apoplast - regulates water
armour function os cw?
structural + chemical barrier
cuticle function of cell wall?
hydrophobic barrier - barrier to water loss, pests, pathogens.
varied architecture in CW - parenchyma vs epidermal cells?
asymmetrical?
p = thin, epi = thick. thick i xylem, phloem fibers, sclerenchyma too.
may be asymmetrical thickened like in guard cells or have structural features like pits.
primary cell wall classification
young, growing cells. outside = middle lamella = thin pectin-rich layer that cements cells together.
thin + architecturally simple
secondary cell wall classification
non-growing mature cells. formed between PM and 1-ary cw after cell enlargement.
- cellulose+lignin. less water, maybe waterproof. very strong. may be highly specialized.
composition of 1-ary cell wall
cellulose mf embedded in polysaccharide matrix
where is there highler density of pectin?
middle lamella - adhesion btw cell walls
name cw polysaccharides
cellulose mf, hemicellulose, pectin matrix, callose, non-enzymatic protein, lignin (mostly 2-ary)
what is callose?
forms agregates in phloem to repair or seal hole.
cellulose in 1-ary cw
network, crosslinked with matrix polysacch.
mf = ribbones. insoluble in water, high tensile strength + resistant to enzymatic degradation
cellulose chain made of?
b (1,4)-d-glucan chain
what is cellulose repeating unit?
cellobiose, a b-(1-4)-linked -d- glucose disaccharide
cellulose similar to starch how? different how?
glucose polymer. bonds are different = diff properties. every 2nd glucose moleculee flipped to make blink= linear molecule
microfibrils composed how?
overlapping b(1-4)-d-glucan chains. arranged in parallel. h-bonds btw neighbouring chains. = v strong - prevent degradation.
biosynthesis of cellulose – in membrane
hexameric (6 subunit( rosette - complex contains cellulose synthase - uses MT of skeletal system to deposit cellulose on the outside. cellulose deposited in mf form - not alone bc alone is not rigid.
mutation in rosette - higher temp sensitive or
more heat = mutated rosettes. blow up like balloon rather than proper structure. affect cellulose synthase + affect ability of cell expansion
discuss CESA - cellulose synthase
membrane- spanning.
cytosolic catalytic domain transfers glucose from donor to glucan chain.
CESA is multigene. many diff forms of the complex.
microfibril orientation influences growth directionality of cells
cellulose mf perpendicular to axis of cell expansion in growing tissue. - facilitates directional growth = high tensile strength of mf, but can pull mf apart and deposit cw in between = growth.
how is cellulose mf deposition regulated?
cellulose synthase commplex moves across membrane + leaves trail of cellolose parallel to Cw.
== anisotopic cell expansion
difference btw isotropic and anisotropic cell expansion
iso = randomly oriented mf = expand in all directions = circle
aniso - transverse mf. = expand at right angles to mf orientation.
alignment hypothesis of cellulose deposition
assoc with underlying cortical MT. MT guide CSC as they synthesize cellulose
what would occur if cell synthase didnt have MT?
lose ability to track + place cellulose. lose directionality/pattern of deposition
2 components of matrix polysaccharides
hemicellulose + pectin
- nonlinear, branched polysacch
matrix polysacch synthesized whered?
golgi + secreted into apoplast via vesicles
structure of hemicellulose?
long, linear polusacch with short side branch. ex: xyloglucan. b(1-4)-d-glucose chain w xylose branches
consequence of hemicellulose branches?
can’t do tight packing.
what kind of plants have high density of xyloglucans?
dicots = angiosperms.
two models of hemiceullulose binding to cellulose
tethered network model
+ biomechanical junction
what is the tethered network model?
hemicellulose binding to cellulose == early model suggests xyloglucans coated cellulose = cross bridge = tether mf together.
what did tethered network model miss?
- that mf not coated with xyloglucans. 2. mutatants that don’t synthesize xyloglucans show normal growth pattern.
what is the biomechanical junction model?
hemicellulose bind to cellulose == better model suggest there are regions of close association btw mfs. hemicellulose mediates this region = double sided sticky tape
what are pectins?
highly branched, heterogeneous polysacch. = galatouronic acid backbone.
what are pectins important for?
cell adhesion.
hold 40% of the mass in cell wall, and 60% of the water in the cell wall.
where are pectins found?
middle lamella - cell adhesion.
how does pectin gel form?
charged - so highly hydrophilic. creates gel = no flow to water, enables flex but prevents flow.
what does the amount of pectin determine?
the amount of flow/porosity of the gel
function of pectin?
prevent aggregation + prevent collapse of 3d structure
pectin - branches, bonding & effect on gel
less branching = more ordered gel = smaller pore size
how Ca2+ effects pectin gel formation
Ca2+ creates ionic bridges = increase methylation.
-> methylation of carboxyl groups on pectin = prevent bridges = lless rigid.
what is callose?
b(1,3)-glucan. not linear = can aggregate + plug holes. sticky properties.
where is callose synthesized?
PM, deposited btw PM and CW.
what is callose for?
pollen development, induced by wounding, deposited at Plasmodesmata to regulate cell-cell movement
callose function in plasmodesmal aperture
deposited in CW collar = control open/closure of PD. easily broken down/replaced
proteins in primary cw. functino?
2-10% non-enzymatic proteins. function? maybe cell-cell adhesion, cell differentiation
where are 2-ary cw deposited? functin?
around mature cells, between pm and 1-ary cw. add strength, compression resistance to stems.
- each layer has different macrofibril orientations
what are macrofibrils?
2-ary cw tightly packed into macrofibrils. coated w hemicellulose = less branched more rigid. bound by lignin = waterproof
1-ary vs 2-ary cw
1 : large variation, lots of pectin, highly hydrated, can be modified with cell growth
2: higher cellulose, hemicellulose has less branching, lignin = waterproof + mechanical support
lignin function
structurally rigid; transport (strength for xylem); hydrophobic walls (casparian strip - regulate water flow into pericycle); defense
what is zone of dehiscence? relates to seed dispersal?
on zone surface, lignin assoc with surface of valves. when dehydrated on top, lignin on bottom stays rigid= open valve = seeds spring out + disperse.
what are the building blocks of lignin + what are building blocks derived from?
monolignols - derived from phenylalanine
how is lignin synthesized?
monolignol secreted, random polymerization of monolignols by oxidative coupling. lignin displaces water
function of water in plants
participate in biochemical rxn, affect ion absorption, turgor, movement, role in phenotypic expression ( root morphology, leaf morphology, stomata
most limiting factor in agriculture?
water.
CO2 absorptio effect on water?
loss of water. transpiration = stomata open bc need CO2 at same time, water diffuses out.
what is chemical potential?
measure of the free energy per mole of a substance.more concentrated = more free energy.
diff values of mew (u) - chemical potential?
(-) = spontaneous. (+) = requires energy input. 0 = at equilibrium
chemical potential of water measures?
free energy per mole of water within system. . proportional to concentration of water.
if difference in water potential is (-)?
water will flow from higher chemical potential to lower chemical potential
what affects water movement?
physical + chemical properties; mode of water transprot - diffusion/mass flow
properties of water due to polarity
excellent solvent (reduce electrostatic interaction); liquid at “biological” temps; water has high specific heat + thermal conductivity (buffer temp fluctuation); high latent heat of vaporization (energy required to shift from liquid to gas phase); highly cohesive ( attraction btw water molecules. surface-tension = energy required to increase air around water molecule; highly adhesive to surfaces); high tensile strength (supports large (-) hydrostatic pressue; incompressible; allow internal hydrostatic pressure in plants); low viscosity; max density at 4C
water movement by bulk flow
move when external force is applied; long distance travel; independent of concentrations; sensitive to change in radius of transport conduit
water movement by diffusion
directional movement down free energy gradietn. high -> low.
diffusion affected by any factor that influences chemical potential.
ficks law
js = d + change in c / change in x -> js is flux density (rate of diffusion) d = diffusion coefficient c = concentration x = distance (-) = diffusion from high -> low
what does diffusion coefficient mean?
describes how easily substance (s) moves through a medium.
what 3 factors effect diffusion coefficient?
substance characteristics (larger molecule = slower); medium (thru air faster than water); temperature (diffuse faster at higher temp)
rate of diffusion inversely proportional to?
distance over which movement occurs. only important over sort distances.
define osmosis
movement of water across a selectively-permeable membrane. other solutes restricted.
factors + contributors to osmosis?
diffusion, bulk flow + pressure (counteracts movement of water)
how is water potential related to chemical potential?
chemical potential of water = specific, can predict outcome of processes
how do plants control water movement?
indirectly. move ions/solutes to alter the free energy of water.
2 major components of water potential
osmotic potential + pressure potential.
what is water potential of pure water?
factors that effect water do what to its value?
0 ; make more negative, lower water potential
first law of thermodynamics?
conservation of energy - energy cannot be created or destroyed.
second law of thermodynamics?
total entropy always increases, no outside input = spontaneous = increase entropy
how does entropy relate to thermal energy?
amount of isothermically unavailable energy in system = TS ( T is absolute temp; S - entropy.
related to energy of molecular motion. when temp is 0, entropy is 0. more free = more chaotic - greater entropy. hotter temp - increase entropy
what doe gibbs free energy measure?
max energy available for conversion to work.
change in free energy - when (-); when (+)
- : spontaneous
+: endergonic. requires energy input
value of change in free energy depends on 2 factors
standard free energy change for reaction; concentration of reactants + products
at equilibrium no work can be accomplished, why?
free energy at minimum and entropy at maximum.
further the mass-action ratio is displaced form equilibrium (Keq), what happens to reactan?
greater free energy for given change in reactant to product.
further a rxn from equilibrium, greater capactiry to do work
as reactant reaches equlibrium what happens to deltaG
deltaG is negative and free energy is available to do work.
when [products]/[reactants] is greater than less than Keq
greater than = positive; less than = negative = spontaneous
many factors that affect water potential
solute potential; pressure potential; temperature, concentration, gravity, water adsorption to solid surface
solutes in water affect water potential (+/-)
mole fraction of water is reduced when solutes are added. (-)
what is pressure potential due to?
hydrostatic pressure on free energy of water. measured relative to ambient pressure for pure water in an open state, which is set to zero.
pressure potential + effect on water potential
+ = raise Y; ex: water influx - positive pressure on cw - turgor.
- = lower Y; ex: xylem conduits when water column under tension
what is matric potential?
from adsorption of water to solid surfaces of cell, soil etc.
- > greatest effect on dry states.
- > matric potential = negligible
temperature potential
driving force in diffusion. but effect is quite small overall
concentration potential
contributor to chemical potential gradients in most systems.
changes in water concentration are negligible. concentration potential is negigible in plants
gravitational potential
causes water to move downward - depends on height of water + density of water + acceleration due to gravity.
-> negligible at cell level
why is measuring water potential useful?
measured experimentally; relevant to soil-plant-atmosphere system; gradients in water potential describe passive flow of water; measure physiological status (water stress - lose turgor - decrease water potential)
vacuole + water potential
hold dissolved solutes + 50-80% of cellular water = major contributor to water potential.
plants gain water = ? pressure
turgor. equal + opposite wall pressure/water pressure
cell loses water called?
flaccid
hypotonic solution vs hypertonic
hypo = cell gain water bc water potential in cell more negative than outside.
hyper = cell lose water = plasmolysis bc cell more + than solution
vacuole + water potentiall
greatest contribution to water potential bc occupies majority of cell volume.
-> isolated from cytosol by tonoplast
why is movement of water through biological membranes greater than dissuion thru lipid bilayer?
water can diffuse thru phospholipid molecules, but ALSO transferred across membrane through Aquaporins.
aquaporins - water, energy, direction. gates? influence on conductivity
water-selective (prefers water but moves small neutral particles thru); no energy inputs. provide a channel for diffusion. bidirectional - based on water potential.
gated= can be selectively opened/closed (due to pH, cation concentration, protein phosphorylation); role in hydraulic conductance - measure of membrane permeability to water.
where are aquaporins found?
PM and tonoplast. water movement in out of membranes.
how does water move from soil to top of tree?
diffusion would not occur because rate is inverse to distance. greater distance = decreased rate of diffusion.
what is a “plant’s conundrum”
absorption of atmospheric CO2 thru stomata exposes plant to water loss while stomata are open.
describe water movement thru plants. rlies on ?
relies on continuous connection of water from soil -> roots -> stem -> leaves. high tensile strength + cohesiveess of water contribute.
how water is transpired?
water vapour concentration = plant —> atmosphere.
how soil particles act with water?
soil particle size determines characteristics of soil ie retention of water. large pores= more water fills = field capacity.
dry soil vs clay re: water
dry soil will drain water quicker, whereas clay will hold more water. dry - more suceptible to dehydration, clay takes a lot longer to let go of water
how surface tension works in soil?
surface tension is increased around curved surfaces. as more water exaporates, the tension between the soil particles and water increases and water potential decreases.
water potential in soil, how does water travel to roots?
water travels through bulk flow from soil, to root-soil.
gravitational potential plays an important role. solute potential is negligible because of dilute solutions. pressure potentials are usually negative; with greater surface tension as soil dries = decreases pressure potential
flow of water + soil-water content. what is soil-water content?
water moves from greater soil water content to lower soil water content.
greater = larger water-filled spaces, less surface tension, greater (less neg) water pressure potential.
-> plants tak eup water, deplete water from soil, keeps water pressure potential of soil near roots more negative = induces bulk flow
2 things that have greatest effect on water flow thru soil
- pressure potential.
2. hydraulic conductivity - larger interstitial space = higher hydraulic conductivity
what is permanent wilting percentage? how does this correspond to soil-water potential?
- plant cannot maintain turgor pressure even if water loss is minimized.
- -> due to water potential of soil. if lower hydraulic conductivity = more resistance, water cant get thru soil to roots. = decrease water potential of soil. but need greater water potential of soil compared to water potential of root cells to have flow of water into roots.
4 functions of roots
- anchoring plant; 2. store carbs + molecules; 3. synthesis of hormones + metabolites; 4. uptake + transport of water + minerals.
plant root exploration facilitates ?
where does water uptake mainly occur?
water uptake.
mainly occur at growing tips of roots, where root hairs are. non-growing regions are lignified to prevent water +nutrients to flow there. focus on “feeding” growing area. also helps establish water potential in plant
how does lignification of older roots help to establish water potential?
lignified = water-resistant. low water concentration higher up in root = lower water potential, pulls water up, as well xylem takes water away from older roots bc of pressure potential drives water uptake in young roots.
how do root hairs contribute to water uptake?
increase explored volume of soil + can penetrate small pores (access areas big roots couldnt)
3 ways of radial movement of water
apoplast: cell wall space, continuous with root’s outside enviro.
symplast: cytoplasmic connections via plasmodesmata
transmembrane: cell:cell, aquaporins/difusion thru membrane
what is Casparian strip? what’s its function?
casparian strip = lignified + suberized cell wall at epidermis. function: forces water to pass thru symplasm before entering xylem. requires aquaporins for water to flow from apoplast to symplast, thru casparian strip to vascular bundle.
xylem loading
concentration of ions in xylem ; get in thru selective transport through endodermis = greater solute concentration = lower solute potential inside xylem = lower water potential in xylem drives water in.
root pressure = positive pressure.
water flow into xylem. increase water in pushes water up.
what is guttation?
xylem sap/water exudes from plant when positive pressure pushes water up xylem due to high water potential of soil and low rates of transpiration. - water being pushed up bc high positive pressure &xylem solute loading. no transpiration, water not lost so xylem extrudes thru pores of plant.
what evidence shows that positive root pressure is not the main mechanism of xylem transport?
root pressure is rarely more than 0.1 MPa (raises only short distance) & transpiring plants show xylem is under negative pressure (tension)
evidence that shows atmospheric pressure/suction is not the mechanism for xylem transport?
under standard conditions, water could be raised 10 m, however, not standard conductions; water colum not subject to atmospheric pressure because they are in equilibrium
why capillarity is not the mechanism for xylem transport?
water under curved surface develops negative pressure potential however, radius of xylem wouldn’t contribute much to pulling water up
what is cohesion-tension theory?
water evaporation from cell walls of mesophyll cells is driving force. water evaporates = tension (closer to surface of cells), cohesive network of water pulled by this tension
fourcell types in tracheary elements
tracheids, vessel elements (angiosperms); fibers (sclerenchyma, elongated + lignified - dead at maturity); parenchyma (storage, living)
how tracheids + vessel elements contirbute to moving water
lower resistance to moving water. open tubes.
-> extensive 2-ary cell wall = compression strength = negative pressure = decreases pressure potential
function of lignin?
strength + increase hydrophobicity = less interaction btw cw and water = greater flow
tracheids pits - how do they work?
plasmodesmata connection between adjacent tracheids. thin filters.
embolism - how?
when pressure potential more negative than vapour pressure = water vapour bubbles + expands. low pressure potential and high water vapour pressure - water turns to water vapour instantly = bubble. embolism
vessel element - found where? assembled how?
in angiosperm (absent in most gymnosperm), shorter + wider. assembled end-to-end. separated by perforation plates (open hole or drain - low friction, high flow)
radius of conduit
-> slight increase in diameter = great increase in flow.
but, increased risk of cavitation (xylem break) - vessel elements in contact = easily spread embolism
resistance to water movement thru xylem; pressure required for xylem resistance. gravity pressure?
resistance thru xylem lowered bc vessel elements + tracheids. need 0.01MPa/m to overcome xylem resistance. but, water potential due to gravity is 1 MPa/100m ==> need 2Mpa to move water up
how transpiration is the driving force for water up the xylemm
water on surfaces of mesophyll cells; water vapour in intercell space higher than in air outside = diffuses + exits leaf. water liquid + vapour in equilibrium. as vapour diffuses out, liquid on surface of cell vapourizes. as it vapourizes, surface tension of water induces negative pressure&pulls water up xylem.
how is water loss reduced?
presence of waes + cuticl.
how much of water lost thru transpiration? how to regulate?
95%. regulate by open/closing stomata.
driving force for transpiration?
difference in [water vapour] inside + outside the leaf.
saturation water vapour content increases with leaf temp. = warmer air holds more water, pull water vapour from leaf even when v humid.
water vapour diffusion proportional to?
difference in [water vapour] inside vs outside. inversely proportional to length of diffusion path.
diffusion coefficient (Ds) influenced by?
- leaf stomatal resistance = stomatal pore diameter can be regulated
- boundary layer resistance = trapped air close to surface, increase distance of water movement thru stomata to decrease water loss.
what is the boundary layer resistance? what affects its thickness?
boundary layer resistance = trapped air close to surface, increase distance of water movement thru stomata to decrease water loss.
- > leaf shape (leaf curls in - increase boundary layer bc air trapped inside roll), size, stomatal architecture (pore, or sunken stomata -trapped layer of air = increase path)(stomata cluster - increase overlap = increase boundary layer, presence of leaf hairs (increase boundary layer bc trap air) + wind speed.
- > wind reduces boudnary layer = more water loss
stomata regulation + transpiration
- cant modify water vapour gradient dirctly. regulate stomatal aperture to regulate resistance.
what is stomatal aperture determined by?
changes in turgor pressure of guard cells.
-> open = turgor pressure increase
two main types of guard cells
dumb bell = grasses. pore is slit btw bulbous guard cells, flanked by subsidiary cells.
- kidney: pore forms in center. may/may not have subsidiary cells
dumb-bell guard cells = cw, cytosol?
cw is thicker in centre, like q-tips. cytosol restricted to bulbous ends.
kidney-shape guard cell
thicker inner + outer lateral cw. thin CW adjacent to epidermal cells == thicker on inner surface of pore
what determines cell shape changes during fluctuating cell turgor?
cellulose microfibril alignment. - expansion perpendicular to orientation of cellulose.
dumbbell: increase water in cytosol (q-tip ends) - long inner parts separate + slit widens
kidney= inner pore has thicker cellulose. as cell swells, thicker layer inside cant move, rather bends + opens pore.
stomata open when?
in response to light, or high [co2], leaf water status, stress signals.
light dominant = restricts water loss at night bc no CO2 fixing bc no light = no water lost.
2 main stimulations of stomatal opening
photosynthesis in guard cell chloroplast & blue light
how does blue light cause stomatal opening?
establishes PM H+ pump = inward elecrochemical gradient, K+ enters down gradient, cl- and malate follow due to charge. = solute loading in guard cell = water follows = increase turgor = open stomata.
what is hydropassive closure of stomata?
rapid water loss from guard cell = loss of trugor
what is hydroactive closure?
water stress stimulates synthesis of ABA => influx Ca2+, inhibits H+ pump & K+ influx. stimulate ion effluc = watter follows out to decrease turgor + close stomatal conductance
how does xylem not collapse even under extreme negative pressure
sufficiently lignified to prevent collapse
how water in xylem maintained in metastable state?
cohesion + adhesion properties of water = decrease water vapour; xylem structure minimizing nucleation sites (air bubbles)
define embolism
-> limited how?
gas-filled obstruction of the conduit that breaks the water column.
pits act to limit movement of bubbles, easier to move bubble thru vesssel element perforated plates. root endodermis limits bubble entry
how do plants minimize xylem cavitation? conifer
conifer pit membranes = central torus (plug) + flexible pit membrane (margo AKA strings)
when pressure differntials occur, torus lodges into side with lowest pressure = valve to prevent embolism
minimie xylem cavitation - angiosperm
lack tori, smaller pores in pit membrane. block movement of water. gas bubbles cant get thru readily - decrease cavitation
how adaptation helps w cavitation
adapted to dry enviro = less suceptible to cavitation. => minimize spread of embolism (outgrowths of xylem parenchyma seal xylem vessels) repair embolism
measure susceptibiility of cavitation
centrifuge attachment - induce large (-) pressure to simulate moist stress. cavitation occurs after xylem conduits blocked = measure hydraulic conductance of stem. more (-) pressure potential = more likely to develop embolism
how to restore water flow after cavitation
- those w 2-ary growth => generate new tracheary conduits ( replace, spring = new xylem growth)
- refill cavitated conduits: gass dissolve into liquid if pressure is sufficient (+ pressure potential) night = decrease difference in pressure potential. root pressure continues to load xylem = + pressure.
-> refill can also occur if xylem remains under tension (unsure how).
freezing + dehydration cause embolism, water thaws = positive hydrostatic pressure = dissolve embolism
most abundant chemical elements in plants?
O,C,H.
what is mineral nutrition?
study of how plants obtain + use mineral nutrients
3 main mineral nutrients, acquired how?
N, P, K : acquired as inorganic ions from soil
why is mineral nutrition important?
availability limits plant growth + primary productivity.
features of essential mineral nutrients?
absence = cannot complete normal life cycle
element is part of essential molecule or must be involved in biological process.
macronutrients vs micronutrients.
macro: relatively high concen. [ >10 mmol/kg)
micro: low concen. [<10 mmol/kg]
examples of macronutrients
N , K, P, Ca, Mg, S, Si
micronutrients
Cl, Fe, Mn, Na, Cu
how to determine mineral nutrient essentiality?
grow plants in solution = containing inorganic salts; simulate soil nutrient enviro.
what is deficiency zone?
range of [mineral nutrient] below critical, to where plant growth is just observed. no longer limiting.
what is adequate zone?
range of [mineral nutrients] beyond which addition of nutrient doesnt increase growth/yield.
what is critical concentration?
minimum concentration of mineral nutrient correlated with max growth/yield.
what is toxic zone?
range of [ mineral nutrient] in excess of adequate zone = growth/yield declines. toxic
deficiency in nutrient display 2 visual symptoms
chlorosis: loss of chlorophyll pigment.
necrosis: death of cell + tissue
describe phosphate deficiency
purple margins on young leaves
describe potassium deficiency
firing on margins of older leaves.
describe nitrogen deficiency
yellowing in center of older leaves
why is there a problem with visual symptoms?
may be multiple deficiencies; deficiency in 1 nutrient, toxicity in another; disease imitates mineral deficiency
mineral deficiency depend on 2 things
- nutrient function. 2. mobility of nutrient.
phloem-mobile: affect older.
phloem- immobile affect yougner.
mobile nutrients?
N, P, Mg, K, Cl, Na, Z
immobile nutrients
Ca, S, Fe, Cu
forms of N available?
requirement? role? deficiency symptom
ammonium, nitrate. require 1000 mmol/kg. most required. role = synthesis of macromolecules. (-): inhibit plant growth, chlorosis of old leaves, accumulation of anthocyanin
form of P available? requirement? role? deficiency symptom?
PO4(3-); require: 30mmol/kg. role: sugar-phosphates in metabolism, ATP. deficiency: dwarf, stunted dark green leaves, anthocyanin, malformation of leave. older first (bc mobile)
K form available? requirement? role? deficiency symptom?
K+; 250 mmol/kg. primary osmolyte, cofactor in enzymes.
chlorosis + mottling in old leaves. marginal leaf necrosis. older leaves first bc mobilized
why i P limiting at such a low requirement?
30 mmol/kg. closely assoc w soil. hard to acquire into plant therefore limiting
soil features:
heterogeneous, vertically stratified, biologically diverse.
when are nutrients available to plant in soil?
when in soil solution = solution phase.
what happens when ion assimilated by plant?
creates nutrient depletion zone around root.
what are soil colloids?
clay particles in soil solution, main reservoir for soil nutrients.
role of colloidal fraction depends upon?
specific surface area (capacity to hold ions); density of fixed negative charges (more neg charge = more cation attraction + hold)
*dont bind anions. cation binding is exchangable
Iyotropic series = ability of colloidal surfaces to bind soil cations follows this trend
al > H > Ca > Ca >K = NH4 > Na.
factors influencing mineral nutrient delivery to roots
- soil cation exchange capacity (exchangeable + bind to -. dynamic equilibrium + buffering capacity.
- soil pH (decomp of organic matter; ammonium, rain):
- water flow
- root architecture
- root-microbe interactions
what influence pH and cation exchange?
rhizosphere: immediate microenvironment surrounding the root.
how water flow influences mineral nutrient dlivery to roots
bulk flow important when soil moisture high + [nutrient] high. (pull soluble to roots by bulk flow)
rate of nutrient uptake exceeds rate of delivery via bulk flow = nutrition depletion zone.
mycorrhizal increase nutrient depletion soil.
two components of increased soil pH that relate to mineral nutrient delivery to roots
a. regulate solubility: phosphate precipitates by Fe + Al/pH
b. regulating cation exchange, soil acid release bound cations, lost thru leaching. + binds higher binding ability = less avail but more necessary.
how does root architecture affect nutrient delivery to roots?
- > what does root development depend on?
- -> 3 areas of root development
- –> influence on root proliferation
fibrous ( many branches) vs. taproot (one long branch)
-> responsive to environmental factors, differ in surface area covered. nutrient uptake greatest at root apical zone = most demand.
- -> depend on root apical meristem. meristematic zone: cells generate root cap + upper tissue.
- cells in elongation zone - vertical, phloem, xylem cortex produced.
- – root hairs formed by epidermal cells, in maturation zone first
—> nutrient concentration determines degree of proliferation. denser roots where more nutrients are.
how do root-microbes influence mineral delivery to root?
rhizosphere modified to enhance nutrient acquisition.
exude organic compounds into rhizosphere = growth of microorganisms, give + get (fixed nitrogen, solubilized nutrients)
what is mucigel?
mix of root exudates, living + dead microorganisms + soil colloids.
what is function of mucigel?
protect root cap, lubricate root cap, symbiotic enviro for fungi + N-fixing bacteria (symbiotic); diffusion bridge btw roots + soil, more efficient.
what does mycorrhizal symbiosis facilitate?
water + nutrient uptake by roots.
exhcnage nutrients for carbs provided by plant.
increase effective root surface area. increase nutrient depletion zone.
hyphae of ectomycorrhizal do what?
surround root cells, obtain nitrogen from decomposition of soil organic matter. close connection to plant CW = get’s nutrients there.
= endomycorrhizae = arbuscular mycorrhizae
highly branched, large surface area. vesicles for storage, fast-growing + short-lived. form invaginations in cell membrane.
PM function in ion transport?
metabolic control of ion uptake. selective; requires energy to move ion thru the root. = xylem loading.
-> larger molecule = hard to get across. same w charged. higher Ds = easier solubility
what is fick’s law:
rate molecules diffuse btw regions is function of the concentration difference.
ion charge interacitons - why is ion permeability hgiher in biological membranes than lipid bilayers.
ion charge + attract water = larger water-bound complex. insoluble thru membrane.
higher transport than diffusion = transporter facilitating.
two important characteristics of solute transport across membrane
accumulation ( concen.) and selectivtiy ( certain ion thru certail channel)
role of vacuole in electrochemical gradients
accumulates K+ when external conc. are low.
Na+ and Ca2+ pumped into apoplast + vacuole; same w H+. anions taken up too
2 components of membrane potentials
- diffusion potential ( potential due to diffusion)
2. electrogenic transport established by H+-ATPase. (1-ary active transport; generate gradient of H+ movement across PM)
effect of PM H+-ATPase
change in pH: accumulate H+ in vacuole and apoplast.
- > electrogenic: net change movement.
- -> establish proton motive force.
speed of transporters:
channels: 10^8 ions/sec.
carriers: 100-1000 molecules/sec
tissues often have complex kinetics for ion transport - indicates what?
indicates presence of more than one type of transport mechanism. = high (low KM - quickly saturable) + low-affinity ( high KM, linear portion) transporters.
time-dependent effect on ion transport?
saturable = diffusion into cell wall space.
biphasic: cation uptake due to accumulation in apoplasm (rapid, passive) & symplasm (linear, metabolism-dependent)
2 regulatory functions of PM H+-ATPase
regulates cell turgor of guard cells; regulates cell expansion (auxin needs to be acidified => loosend cw)
define energy
capacity to cause change
define work (mechanical)
diplacement against an opposing force
define kinetic energy
associated with motion and includes thermal energy associated with random motions of atoms or molecules
define heat
thermal energy in transfer from one object to another
define potential energy
stored energy that can be converted to other forms of energy to do work
work (biological)
displacement against forces that living things encounter or generate
- often involves changes in chemical potential energy
what is first law of thermodynamics
conservation of energy
- in all chemical and physical changes, energy cannot be created or destroyed, only transferred or transformed from one form to another
what is second law of thermodynamics
total entropy always increases in a closed system.
- spontaneous = no outside input of energy.
what is entropy?
amount of isothermically unavailable energy in a system. therefore, amount of energy in a system not available to do work.
- related to molecular motion + temperature.
at absolute zero, molecular motion ceases. more molecules are free to more when greater temp - more chaotic.
what is gibbs free energy?
measure of the maximum energy available for conversion to work.
enthalpy - total heat energy, including work.
different signs of change in free energy (+/-)
negative: spontaneous. exergonic
positive : non-spontaneous, required energy for reaction to occur. endergonic
value of gibbs free energy depends on what? (2)
standard free energychange of reaction
concentration of reactants + products
what happens to free energy and entropy when at equilibrium?
free energy at minimum
entropy at maximum
what is chemical potential?
partial molal Gibbs free energy
- free energy per mole of substance within a system
what are properies of water
- excellent solvent: reduces electrostatin interaction = solubility of ionin and polar molecules is high
- liquid at “biologial”temps
- high specific heat + thermal conductivity
- high latent heat of vaporization: required to move molecules form liquid to gas phase is high
- highly cohesive: mutual attraction. =surface tension and adhesion
- high tensile strength. supports large negative hydrostatic pressure, incompressible.
- low viscosity
- max density at 4C
function of ATP in cellular work
couples exergonic reactions to endergonic reactions.
- high stored energy. PO4 repel each other by nature. when unbind lots of energy released
-stores potential energy.
drives endergonic reaction by transfer of phosphate group to reactant - phosphorylated intermediate that is more reactive.
effect of phosphorylation of H+-ATPase
+ dephosphorylation?
changes proteins conformation, release of bound H+
-protein returns to original, low energy state. binds H+.
describe channels
charge-lined, water-filled.
passive but specific (pore size +charge)
rapid movement
-often gated in response to external signs.
describe carriers
no transport pore.
bind solute to be transporter - induces conformational change to shift solute across membrane.
highly selective, slow compared to channel
primary active transport?
carrier proteins directly use energy source to mediate transport. against electrchemical gradient + unidirectional
electrogenic vs electroneutral?
electrogenic: net movement of charge across the membrane
electroneutral no net movement of charge
secondary active transport?
against gradient
coupled to movement oof another solute down its electrochemical gradient.
-may be driven by electrogenic H+ATPase = proton motive force
define symport + antiport
symport: H+ and solute move in same direction
antiport: H+ and solute move in opposite directions
kinetics of solute transport - Vmax and Km
Vmax = maximum rate of transport. carriers full, channel at max
Km - 1/2Vmax - binding properties of binding-site (affinity)
why do tissues show complex kinetics for ion transport?
usually indicates more than one type of transport mechanism.
kinetics predict saturation - high affinity transporters do saturate, but low affinity (slow movement) continue to transport after high affinity maxed out.
how time affects complex kinetics
becomes saturated over time.. not immediate.
PM H+-ATPases
REALLY IMPORTANT
maintain electrochemical potentials across membranes, regulate cyosolic pH.
- affects cell turgor (guard cells)
and cell expansion (induced by auxin - initiate cell wall loosening)
-> energize cell nutrient transport across barriers separating symplast from apoplast
PM H+-ATPase in guard cells
blue light stimulates H+-ATPase activity.
PM hyperpolarized, generates driving force for ion (K+) uptake. decrease solute water potential (malate accumulation) of guard cells and increase guard cell turgor causing stomatal opening
how PM H+-ATPase functions
N-domain of protein binds nucleotide. = phosphorylation causes conformaitonal change.
- twist head, tension opens other side to extrude H+. no counter-ion movement
