unit 3 botany
List the five commonly recognized groups of plant hormones and describe their role in plants.
auxin - apical dominanc, soften cell wall phototropism, high concentrations stem growth, low concentrations root growth, extremely high amounts stop growth, helpsplants move towards sun, in all apical areas, blocks fruit drops, seedless fruits
cytokinins - tissue growth division, used in tobacco, slows death of leaves and fruits, with auxin is can be like stems cells for cell differentiation
ethylene - in air, fruit ripenining, one apple can spoil a batch because they give off etheleyne to other fruits, causes abscision, hydrocarbon, dormnacy in seed release, sex expression
abscisic acid - go dormant, stress hormone, extensiblity inhibits growth, inhibits seed germination - stimulates seed storage proteins, conserves water when stressed (close stomata) ABA → increase stomata close
gibberellines - growth promoting, found in young leaves, roots, seeds, and embyros, disease “foolish seedling disease” fungi makes plant grow, so that fungi survives not plant, growing in space without dirt, stem elongation, dwarf wheat → no givverellins short plant, stimulates mating → flowering, partheocarpic fruits → seedless
barssinosteroids - protects plants freezing/drought
salicyclic acid - activates disease, heat
Define tropism, and give examples of three common tropisms in plants.
how the plant detects mositure, gravity, sunlight, growth toward or away from stimuli, positive stimuli towards, negative stimuli away
auxin is a positive tropism
phototropism = controlled by auxin
photoreceptor = pigment conataining protein
gravitropism = shoots grow against roots toward
hydrotropism = directed root growth, sensesed in columnella
thigotropism = avoids solid objects, tendrils cells shorten and length to climb
heliotropism = oritentation of flowers toward light “solar tracking” sunflowers
Explain the role of tropisms in seed development and flowering in a plant.
guiding the direction of plant growth, ensuring that seedlings emerge from the soil towards light and that flowers are positioned optimally to receive sunlight for pollination, which is achieved through responses to environmental stimuli like light and gravity, primarily through phototropism and gravitropism; this allows plants to maximize their access to necessary resources for successful reproduction.Describe the macronutrients and micronutrients that plants require.
Describe some adaptations of roots for obtaining minerals from the soil.
Root hairs: These tiny, hair-like projections significantly increase the root's surface area, allowing for greater contact with the soil particles and maximizing water and mineral absorption.
Branching root systems: Extensive branching of lateral roots helps explore a larger volume of soil, reaching nutrients that might be sparsely distributed.
Taproots vs. fibrous roots: Some plants have a single, deep taproot to access water and nutrients in deeper soil layers, while others develop a dense network of fibrous roots closer to the soil surface.
Mycorrhizal associations: Symbiotic relationships with fungi (mycorrhizae) where the fungi extend their hyphae into the soil, reaching nutrients that the plant roots alone cannot access, while the plant provides carbohydrates to the fungusDefine transpiration, and explain the role of stomata in regulating this process.
Explain and recognize the function of secondary metabolites
defense against predators, attracting pollinators, or communication with other organisms, often acting as chemical deterrents or attractants depending on the context; they are essentially "extra" compounds that provide a competitive advantage to the producing organism, unlike primary metabolites which are necessary for basic life functions like respiration and photosynthesis.
alkaloids, terpenoids, phenolics
VOCAB
chapter 27
phytochemicals - bioactive compounds found in plants that may help prevent chronic diseases and protect against environemntal toxins, reduce inflammation
terpenoids, polyphenols, phenolic constituents, alkaloids, carotenoids, phytosterols, saponins, and fibers.
auxin - plant developments, controls cell growth, phototropism, root and shoot growth
cytokinin - issue growth division, used in tobacco, slows death of leaves and fruits, with auxin is can be like stems cells for cell differentiation
abscisic acid - go dormant, stress hormone, extensiblity inhibits growth, inhibits seed germination - stimulates seed storage proteins, conserves water when stressed (close stomata) ABA → increase stomata close
gibberellins - growth promoting, found in young leaves, roots, seeds, and embyros, disease “foolish seedling disease” fungi makes plant grow, so that fungi survives not plant, growing in space without dirt, stem elongation, dwarf wheat → no givverellins short plant, stimulates mating → flowering, partheocarpic fruits → seedless
ethylene - in air, fruit ripenining, one apple can spoil a batch because they give off etheleyne to other fruits, causes abscision, hydrocarbon, dormnacy in seed release, sex expression
photoperiod - certain seasons, leaes keep track of darkness, long day plants, short day plants
phytochrome - red light triggers, turn on and off growth, healing growth, shady growth
works by absorbing red pr and converts to pfr vise versa
circadian rhythm - universal among eukaryotes, how long days are → regular ryhthms of activity growth, endogenous - no stimuli from environment
tropism - how the plant is able to move or gain stimuli
gravitropism - shoots grow against stimuli, roots grow towards stimuli
statoliths - starch plastids gravity sensing cells, rolls around to tell whats up, amyoplasts settle to bottom of cell signalling gravity
hydrotropism - directed root growth to water, sensed in columnella
thigmotropism - avoids solid objects, tendrils cells shorten and lengthing to climb
florigen - initiates flowerings in plants
vernalization - cold flowering “winter flowers”
dormancy - avoid freezing damage
stratification - cold
scarification - sand paper on seed to grow, water, light exposure
seed bank -
nastic movement - venus fly trap triggered by hairs, plant moves in response to stimuli, nyctinastic movements → leaves close at night, pulvinis thickening of leave parenchyma cells contract
heliotropism - orientation of flowers toward lights “solar tracking”
ammonification - plants acquire nitrate from soil through roots and transorm into proteins, ilable for plants to absorb and utilize as a nutrient; essentially, it's the conversion of organic nitrogen back into a usable form for plants through the action of decomposers like bacteria and fungi
denitrification - process that occurs when soil bacteria remove oxygen from nitrate, producing nitrogen gas and nitrous oxide that escape into the atmosphere
cuticle - outermost layer of plants which covers leaves, fruits, flowers, and non-wood stems of higher plants; regulates the diffusion of water, gases, and solutes
evapotranspiration - process by which water moves from the land to the atmosphere through plants and the soil, a term used to describe the water consumed by plants over a period of time
cohesion-tension theory - explains how water is transported upwards in plants through the xylem, primarily driven by the negative pressure created by water evaporation from the leaves (transpiration), which pulls a continuous column of water upwards due to the cohesive properties of water molecules and their adhesion to the xylem walls; essentially, the "tension" created by transpiration pulls the water column up like a continuous string, allowing water to reach the top of even tall trees
active transport - the process where molecules move across a cell membrane against their concentration gradient, requires energy
passive transport - the movement of substances across a plant cell membrane without the need for energy expenditure, typically occurring down a concentration gradient, non energy
translocation - the process of moving organic nutrients, primarily sugars produced during photosynthesis in the leaves, to other parts of the plant through specialized tissue called phloem, allowing the plant to distribute food to areas where it is needed for growth and development; essentially, it's the "transport system" within a plant that moves food from "source" (leaves) to "sink" (roots, fruits, etc.). energy, active process.
pressure-flow hypothesis - the widely accepted theory explaining how organic molecules like sugars are transported through the phloem of plants, driven by a pressure gradient created by the concentration of solutes at the "source" (like leaves) which draws water in, generating pressure that pushes the sap towards "sink" areas (like roots) where the sugars are unloaded and used; essentially, the movement of sap occurs from high pressure areas to low pressure areas within the plant, passive
plant physiology : hormones
plant physiology - field of study that investigates the metabolism and growth of plants
phytohormones -
chemical signals that communicate information
active at small doses
act in concert
“context dependent”: same hormone elicits different response based on when/where
gene expression controls hormone levels
horomone levels control gene expression
hormones are often made in the meristems and trasnported elsewhere or made in every cell and used where made
generally - bind to protein receptors to initiate signal (biochemical) transduction changes structure of receptor, releasing regulator molecule + activates the transcriptial cascade = change in gene expression
mediated by secondary messengers
transfer information
amplify the signal, CA 2+ ion channels
plant hormones summary
plants usually respond to stimuli environmetal stimuli by altering their pattern of growth
most of these occur at the cellular level
mediated by hormones - small organic molecules produced by the plant that serve as chemical signals between cells and tissues
five commonly recognized groups: auxin, gibberellins, cytokinins, abscisic acid, and ethylene
auxin, induces apical dominance
cytokinin: stimulates shoot growth & production
abscisic acid: regulates stomata opening
ethylene: stimulates fruit ripenining
gibberellin : elongates stem
auxins
soften the cell wall so plants can grow
involved in phototropism
stems bend toward light source
auxin moves to shady side and causes cells to elongate
responsible for apical dominance
commericially used to stimulate root formation and promote growth of fruit
apical dominance due to auxin
auxin produced at apical meristem inhibits growth of lateral buds
lateral bud grwoth is inhibited when a plant retains its terminal bud
when terminal bud is removed, laterla branches develop and plant is bushier
also stimulates root formation
first identified
frits went, missouri botanical gardens
primary growth regualtor
high concentraitons promote stem growth
low concentrations promotes root growth
inhibits root growth at high concentrations
promotes growth by increasing extensibility (loosening cell walls causing cells to enlarge)
promotes pollen tube growth
helps plants move? - in shoot auxin stimulates growth on one side
auxin is shuttled to one side of the plant and turns on genes
helps vascular tissue differentiate in developing leaves
gradient caused by its basipetal polar transport
produced in meristem
moves from shoot trip down stem
established apical dominance: apical buds produce auxin, basipetal flower of auxin inhibits growth of lateral buds
promotes lateral and adventitious root formation
promotes expanison of vascular cambium after bud break
regulates leaf and flower development
blocks early fruit drop
treat carpel with auxin = parthenocarpic fruits
synthetic auxin was used as herbicide
regulates other plant hormones
infamous side of auxin, active ingredient in agent orange
chemicals with auxin activity sprayed together with kerosene on forests in vietnam to cause leaf drop and fire
chemical process used to make the auxins also made dioxin, an extremely toxic compound
dixosin is linked to miscarriages, birth defects, leukemia, and other types of cancer
cytokinins
influence plant growth by promoting cell division
found in plant meristems, young leaves, root tips, seeds, and fruits
also prevents senescence or aging (as cytokinin levels drop, plant organ growth slows or stops)
plant organ formation in tissue culture influenced by ratio of auxin to cytokinin
found primarily in dividing tissues → seeds, fruits, leaves, and root tips
promotes cell division for growth and seed germination
slow senescence (death) of leaves and fruit
signals chloroplast synthesis
GMO tobacco (right) over-produces cytokinin, delays leaf senescence
with auxin helps with cell differentiation
ethylene
gas that can move freely in air
causes fruit ripening
once the process of abscission has begun, ethylene stimulates enzyme causing the leaf, fruit or flower to drop
kerosene stoves used to ripen fruits
ethylene given off
one rotten apple spoils the whole barrel
ethylene given off
simple hydrocarbon
influences growth & development of most tissues
inhibits cell expansions by decreasing extensibility
triple response in pea seedlings → seedlings avoid obstacle
influences growth and development of most tissues
releases dormancy in seed stimulates fruit ripening
influences growth and development of most tissues
stimulates leaf abscission (auxin prevents it)
influences growth and development of most tissues
stimulates flower opening
contributes to sex expression
abscisic acid
stress hormone
imitates and maintains seed and bud dormancy and brings about closure of stomata
inhibits shoot growth by decreasing extensibility but may promote root length
inhibits seed germination stimulates seed storage proteins
water conservation when water stressed (caused by drought, salt, freezing
increase in ABA = stomata closure
water conservaton when water stressed
increase ABA = stomata closure
uptake solutes by guard cells changes osmotic potential of guard cells and opens the stoma
ABA signals the release of those solutes and water moves from cytosol to the cell wall
gibberellins
most common is gibberellic acid GA3
found in young leaves, roots, seeds, and embryos and fruits
growth promoting hormone brings about elongation of cells
most obvious effect is stem elongation betwee nodes
dormancy period plant does not grow even though conditions are favorable can be broken by gibberellines
involved in seed germination
discovered by E. Kurosawa of Japan foolish seedling disease
gibberellin produced by fungus
present in all parts of the plant & high in conc in immature seeds
stimulates stem elongation by increasing cell division and elongation increases extensiblity
mutant dwarfing genes interfere with gibberellin synthesis or resonse
led to green revolution inthe 1970s
gibberellins are named after the fungus gibberella fujikuroi which causes rice plants to grow abnormally tall
required for pollen tube growth in some species
break seed dormancy
stimulate seed germination
in some species stimulate aleurnone
protein rich cells of endosperm produce enzymes that break down starch
releasing sugars, amino acids
stimulates bolting (stem elongation) → flowering
produces parthenocarpix fruits (like auxin)
brassinosteroids
growth promoting polyhydroxylated steroid hormones
can occur in virtually all parts of a plant and mostly act locally
without it leaves have fewer, smaller cells
protects plants during drought or chilling/freezing stress
essential for maturation of tracheary elements
secondary wall formation
programmed cell death
others
salicyclic acid: activates disease resistance and regulates thermogeneis
jasmonic acid: activates plant defense against insect herbivores
systemin: interfers with protein digestion of attacking insect
forligen; stimulates flower in shoot apical meristems
chapter 28
external factors and plant growth
tropism
growth toward or away from a directional stimulus
positive toward
negative away
phototropism - lights
controlled by auxin went expirement
briggs figures out that auxin moves from light to the dark side
protoreceptors - pigment-containing protein absorbs light
blue light (400-500) induces lateral movement of auxin to shady side
auxin moves basipetally from trip to elongation zone
stimulates cell elongation on one side differential growth
gravitropism - gravity
shoots grow against, roots grow with gravity
positive gravitropism
grow toward gravity
remember auxin inhibits growth in roots
negative gravitropism
statocytes gravity sensing cells
statoliths amyloplasts (starch containing plastids)
often found in the starch sheat (inner most layer of cortical cells) surround vascular tissue
in roots, they are found in the columella
growth in response to earths gravity
shoots exhibit negative gravitropism growing against gravity
increased auxin concentration on lower side of young stem results in upward growth
roots exhibit positive gravitropsim growings with gravity
organelle in root cells called amyloplast settle to bottom of endodermal cells and signal downward growth
auxin involved in positive phototropism
migrates to shady side causing cells to elongate
hydrotropism
directed root growth in response to moisture gradient
again, sensed in the columella
not sure how it researchs = ripe for research
thimotropism
avoidance of solid objects
rocks other plants shoots
moves in a specific direction
tendrils wrap around anything they touch
rapid response less than an hour
touching cells shorten
nastic movements in respones to stimulus
non directional response
nyctinastic movements
night closures leaves close at night
common at legumes
pulvinus: thickening at base of leaf
parenchyma cells expand, contract on opposites sides of pulvins
chemical and electrical signals
thigmonastic movements example
trap is lobed balde with midrip hinge of leaf
each lobe has three trigger hairs
when touched trigger hairs produce an electrical signal
activaites atp hydrolysis and proton transport
moves water from upper to lower epidermis closing the trap
digestive enzymes released
heliotropism: oritentation of leaves and flowers relative to light (parallel or perpendicular)
aka solar tracking
usually involve pulvini at base of leaves/leaflets or flower stems
circadian rhythems
universal among eukaryotes
regular rhythms of activity/growth
occur 24 hours but varies!
enogenous - without stimulation from the environment
circadian clocks have parts
oscillator generates the rhythmic behavior
input pathways - synchronize the oscillator to environemtal info
output pathways - regulate the phsyiological/biochemcal process
environmntal syncrhonization allows changes with the seasons
entrainment:resetting of an internal clock to match an external signal light dark cycles temperatures
temperation compensations: clock oscillates with temperature→ physiological effects of temp
gating: stimuli of same intensity elecit different resoponse depending on when they happen
example of circadian clock arabidopsis chlorophyll a/b binding proteins
photoperiodism
effect of daylength on the timing of a biological event
photoperiodic plants only flower under certain light conditions → during certain seasons
can have variation within species - photoperiodic ecotypes
sometimes depending on temperature
plants leaves keep track of the darkness
if darkness interrupted flowering suppressed
good news for growers! can time flowering!
short day plants
flower in early spring and fall
light must be shorter than a critical length
long day plants
flower in summer
light must be longer than a critical length
day neutral plants
regulated by phytochrome
photoreceptor
has 2 states: one inactive, and on active
activated by red light
deactivated by lack of light or far red light
regulates seedling growth form
from etiolate (elongated, colorless, or yellow)
to normal plant growth
induces shade-avoidance syndrome in many plants
light depleted in red/blue
corresponds to absorption by chlorophyll and carotenoids
stimulates upward growth
phytochrome
plants must have some way to detect night length
proportion of red light to far red light dusk determines form of phytocrhome
red light converts phytocrhome to the form pfr which indcates sunlight is available and conditions favorable
photoperiodism
some plants, flowering occurs according to the photoperiod
ratio of length of day to length of night over 24 hour period
three groups
short day plant long night plants flower when the day length is shorter and the night is longer than a definiite length called the critical length
long day short night flower when the day length is longer and the night is shorter than a critical length
day neutral plans do not depend on day night length for flowering and instead rely on other environemntal stimuli
both long day and short day can ahve the same critical length
length of continous darkness (not light) controls flower in many plants
floral stimulus
leaves perceive daylength - need signal to induce flowering
florigen : hormone that promotes flowering
moves through live tissue only phloem
COprotein induces expression of FT gene which produces florigen
vernalization
cold inducing flowering
plant often also requires suitable day length - don’t just flower at any old cold snap
can often trick palnts using gibberellin
dormancy
condition of arrested suspended growth after which growing resumes
controlled by inhibitors that must be removed
reactivation often requires certain conditions to avoid environemntal miscues
stratifcation
cold temperatures required for germination
most temperate plants
abrasion by soil wears away the seed coat
inhibitors removed water/oxygen allowed in
scarification
mechnical abrasion required to break thick seed coat
sometimes stay viable for thousands of years but usually don’t last more than few years or decase
seed banks: conservation effort
help temperature plants avoid freeze damage
often iniitated well before winter
dormant buds: embryoic shoot with
apical meristem
nodes
internodes
rudimentary leaves
bud scales : prevent dessication, restrict movement of oxygen into the bud, insulte the bud from heat loss
often accumulate growth inhibitors
acclimation - induced by decrease in daylength, physical and phsyiological changes to prep for winter
dormancy can be broken by
cold temperatures
photoperiod
ethylene
gibberellins
chapter 29
essential elements
9 macronutrients: required in large amounts C,O,and H they get via photosynthesis
N, K, Ca, Mg, Ph, and S
8 micronutrients: required in smaller amounts
Cl, Fe, B, Mn, Zn, Cu, Ni, Mo
some plants require additional benefical elements
Al, Co, Na, Se, Si
deficiences in these elements cause symptoms
based on what they are used for in the plant
stunted growth of stems and leaves
necrosis: localized death of tissue
chlorosis: yellowing of leaves with loss or reduced chlorophyll production
lack of nitrogen- need to produce proteins
causes chlorosis (yellowing of leaves)
especially older leaves- plants move nutrients where are most needed
lack of sulfur needed to produce proteins but less mobile than N
chlorosis in upper leaves
lack of magnesium - needed to produce chlorphyll
chlorosis- between veins on lower leaves
sometimes necrotic spots
lack of phosphorus-needed to produce ATP
often accumulate anthocyanins becoming red/purple
lack of calcium - needed for cell wall stiffening
young leaves blacken and wither esp at tips
lack of potassium 0 needed for ion balance and to open'/stomata
chlorotic and necrotic tissue, weak stems
lack of boron
needed for cell wall integrety nucleic acid production
roots stop growing shoot dies back
how do they get them?
plants are sessile
have to work with what is around them
sometimes they pump them in themselves
proteins in cell membrane move nutrients in based on their chemistry
nutrient must first be in a biologically available state
sometimes the enlist the help of others
nitrogen cycle
2 types of nitrogen fixing bacteria
free living and symbiotic
symbiotic are the most effective
rhizobia and bradyrhizobia
mycorrhizal associations
carnivorous plants use animal proteins
parasitic plants steal them from other plants
cluster roots (phosphorus uptake)
how plants protect themselves
main enemy list
herbivores eat essential parts of plants
insects, mammals, birds
pathogens feed off a plant and promote their own growth
using toxins, cell wall degrading enzymes
bacteria - single celled prokaryotes
viruses- non living pathogens, replicate in side plant cells
fungi - eukaryotes single or multi celled
nematodes - eukaryotes multicelled
parastic plants mistletoe
two types of defenses
chemical and mechanical
mechanical
spines modified leaves
thorns modivied stems
prickles outgrowths of the epidermis
chemical
may kill or harm a threat
may just taste bad
secondary metabolites: not required for life
phytoalexins: antimicrobial compounds
produced when attached by fungi/bacteria
once induced, they stay around (a kind of plant memory)
alkaloids: nitrogenous compounds
caffiene: toxic to insects and fungi and allelopathic
nicotine: produced in roots and stored in leaf vacuoles, deters large and small herbivores
capsaicin - especially good in determining mammals
terpenoids - largest class of secondary metabolites
various combinations of isoprene units
essential oilds - deter herbivores, protect against fungi/bacteria, some allelopathic
various combinations of isprene units
latex including rubber
cardiac glycosides
bioaccumlated by some animals for their own protection
phenolics : broad groups of chemicals
tannins - very common in angiosperms, cause bitter taste
ligins - deposited in cell wall in response to fungal attacks
salicylic acid - systemic acquired resistence to bacteria, fungi, and viruses
chapter 30
active transport
requires energy
atp directly or indirectly to fuel active transport
moves substances from low to high
requires highly selective carrier proteins
sodium-potassium pump
direct use atp for active transport
uses a protein to move 3 Na out of the cell and 2 K into the cell
against their concentration gradient
atp energy is used to change conformation of carrier protein
affinitiy of the carrier protein for either na or k changes so ion can be carried across the membrane
passive transport
movement of molecules through the membrane in which
no energy is required
molecules move in response to a concentration gradient
diffusion
movement of molecules from high to low
continue until the concentration is same in all regions
free
rate of diffusion depends on pressure, temperature, and density of medium
facilitated diffusion
molecules cannot cross membrane easily may move through proteins
high to low conc
channel proteins
hydrophilic channel when open
carrier proteins
bind specfically to molecules they assist
osmosis
cytoplasm of the cell is an aqueous solution
water solvent
dissolved substances are solutes
osmosis net diffusion of water across membrane toward high solute concentration
free
definitions
solvent - liquid in which substances dissolve
semipermeable membranes - membranes in which different substances diffuse at different rates
all plant cell membarnes
osmosis - diffusion of water through a semipermeable membrane from a region where water is more concentrated to region where it is less concentrated
osmotic pressure - pressure required to prevent osmosis
osmotic potential balanced by resistance of cell wall
pressure potential pressure that develops as walls as a result of water entering cell - turgor pressure
water potential of cell - osmotic pressure + pressure potential
turgid cell - firm cell due to water gained by osmosis
osmosis
osmosis is primary way water enters plants from environment
pathway of water through plant:
enters from soil into cell walls and intercellular spaces of roots hairs and root hairs and roots
crosses differentially permeable membrane and cytoplasm of endodermis then into xylem
flower through xylem to leaves and diffuses out through stomata
plasmolysis - loss of water through osmosis
accompanied by shrinkage of protoplasm away from the cell wall
imbibition - large molecules such as cellulose and starch develop when electrical charges when wet, and thus attract water molecules
water molecules adhere to large molecules
results of swellin gtissues
imbibtion first step of germination in seed
transpiratio - water vapor loss from internal leaf atmosphere
more than 90% of the water entering a plant is transpired
water needed for : cell activities, cell turgor, evaporation for cooling - if more water is lost then taken in stomata closes
evapotranspiration - water and dissolved minerals travel great distances in xylem
some pushing comes from pressure of water entering roots
most of the force is pulling created by transpiration
evaporatoin from thin films of water in the stomata
occurs due to cohesion (water molecules stick to each other) and adhesion (stick to walls)
why isn’t xylem huge?
adheasion - water molecule stick to other jpolar molecules by hydrogen bodning
choesion - water molecules stick to other water molecules by hydrogen bonding
cohesion tension theory the pull - transpiration generates tension to pull water columns through plants from roots to leaves
water columns created when water molecules adhere to tracheids and vessels of xylem and cohere to each other
when watre evaportes from mesophyll cells they develop a lower water potential than adjacent cells
water moves into mesophyll cells from adjacent cells with higer water potential
process is continued until veins are reached
creates tension on water columns, drawing water all the way through entire span of xylem cells
water continues to enter root by osmosis
regulation of transpiration
stomatal apparatus regulates transpiration and gas exchange
stomatal apparatus = 2 guard cells + stoma (opening)
transpiration rates influenced by humidity, light, temperature, and carbon dixoide concentreation
when photosynthesis occurs stomata open
guard cells expend energy to acquire potassium ions from adjacent epidermal cells
causes lower water potential in guard cells via osmosis
guard cells become turgid and stomata opens
when photosyntehsis does not occur, stomata close
potassium ions leave guard cells
water leaves
less turgid and stomata close
rate of transpiration
transpiration rates increase with temperature and wind velocity because water molecules evaporte more quickly
several pathways regulate stomatal opening and closing
abscics acid (ABA) initiates a singallin gpathway to close stomata in drought
opens k cl and malate channels
water loss
stomata of most plants are opne during day and closed at night
water conservation in some plants:
stomata open only at night- desert plants
conserves water, but makes co 2 inaccessible during day
thus undergo CAM photosyntehsis
carbon dioxide covernted to oragnic acids and stored in vacuoles at night
organic acids converted to carbon dioxide during day
stomata recessed below surface of leaf or in chambers
desert plants, pines
tropics
guttation - loss of liquid water
if cool night follows warm humid day water droplets are produced through hydathodes at tips of veins
in absence of transpiratoin at night, pressure in xylem elements forces water out of hydathodes
phloem transport:
most carbohydrates produced in leaves are distributed through phloem to rest of plant
translocation - provides building blocks for actively growing regions of the plant
also transports hormones, mRNA and other molecules
variety of sugars amino acids, organic acids, proteins and ions
transport of oeganic solutes in solutions
pressure flow hypothesis - organic solutes flow from source, where water enters by osmosis, to sinks, where food is utlizied and water exits
organic solutes move along concentartion graidents between sources and sinks
moving carbohydrates pressure flow theory
sources
photosynthetics tissues
food storage tissue can be sources or sinks
sinks
growing root and stem as well as developing fruits
specifics of pressure flow hypothesis
phloem loading - sugar enters by active transport into sieve tubes
water potential of sieve tubes decreases and water enters by osmosis
turgor potential of sieve tubes decreases and water enters by osmosis
food substances actively removed at sink and water exits sieve tubes, lowering pressure in seive tubes
using aphids to obtain the critical samples and radioactive tracers to mark them, plant biologist have demonstarted that substances in phloem can move remarkably fast as much as 50 to 100 cm/h
mineral requipremnt for growth
essential elements - essential as building blocks for compounds synthesized by plants
C, H, O, P, K, N, S, Ca, Fe, Mg, Na, Cl, Cu, Mn, Co, Zn, Mo, B
macronutrients - used by plants in greater amounts
nitrogen, potassium, calcium, phospohrus, magnesium, and sulfur
micronutrients - needed by the plants in very small amounts
iron, sodium, chlorine, copper, mangenes, cobalt, zinc, molybdenum and boron
when any required elemtn is deficient in soil, plants exhibit characterisitcs symptoms