Studied by 9 people
need to find the nutrients and things they need to survive
need to avoid the things that will hurt them—predation, parasitism, harmful environmental conditions
need to be able to physically interact with their environment
need to find partners for sexual reproduction
sensory cells receive an external signal and change it to an intracellular signal
sensory cells send a signal to target cells in other parts of the body that can respond to the information
target cells receive the signal and change their activity in a way that produces an appropriate response
specialized proteins that change shape in response to an environmental stimulus (such as being struct by a particular wavelength of light, having pressure applied, or binding to a particular type of molecule)
shape change converts an external signal to an intracellular signal which primes the sensory cell for action
most are located in the plasma membrane, but may be located in the cytosol as well
the process activated when a receptor in the plasma membrane binds a signal
2 fundamental components, which may interact to modify cell response
signal transduction pathway triggered when the change in the receptor protein’s shape leads to the transfer of a phosphate group from ATP to the receptor or one of its associated proteins
activates proteins involved in chains of phosphorylated proteins
are produced when receptor proteins trigger the production of intracellular signals or their release from storage areas
includes calcium ions (Ca2+) which are stored in the vacuole, smooth ER, or cell wall
organic compounds produced in small amounts in one part of the plant and transported to the target cells, where they cause a physiological response
usually are small molecules in plants present in very low concentrations
may be transmitted by specialized membrane transport proteins (e.g. auxin), in xylem/phloem sap, or by simple diffusion from the originating cell
it is common for different types of hormones to interact with each other and modulate the cell’s response
a modified leaf that forms a sheath protecting the emerging shoots of young grasses
used in the first experiments on plants’ response to light
plants exposed to light excluding blue light (filtered through potassium dichromate solution) did not bend toward the light, suggesting that bending only occurs toward light including blue wavelengths
noted no photosynthetic response without the presence of blue wavelengths as well
the directed movement of plants in response to light
plants bend due to elongation of cells on the shaded side of the plant
membrane protein in the tips of emerging shoots
gains a phosphate group in response to blue light ( is a blue light receptor) and subsequently triggers the phototropic response
coded for by PHOT1, which was discovered by analyzing mutant Arabidopsis individuals that lack phototropic response
photoreceptors that detect blue light and initiate phototropic response
trigger signal transduction cascades that result in at least two other responses
shoot bending
chloroplast movements inside leaf cells
opening of stomata (and consequently photosynthesis)
put chloroplasts in positions to optimize light absorption
in high light, the chloroplasts move to the sides of cells to shade each other
in low light, they spread out to absorb more light
removal or covering of coleoptile tips resulted in no phototropism
covering below the tips in the area where bending occurs did not affect phototropism
suggests that sensory cells respond to blue light by releasing a hormone produced in the tips of the shoot and transported to site of bending
cut off oat tips and replacing them with porous agar or nonporous mica slabs under the tip
only plants with agar tips showed normal phototropism
suggests that the phototropic signal was a chemical that could diffuse and that the chemical was water-soluble (because the agar is water based)
first plant hormone ever discovered
promotes cell elongation in the shoot
most common naturally occurring hormone of the auxin class
was difficult to identify because it is present in such low concentrations
proposed that phototropism results from an asymmetric distribution of auxin
predicts that auxin produced in the tip of coleoptiles is transported at higher concentrations down the shaded side compared to the illuminated side
also predicts that the asymmetrical distribution of auxin causes cells on the shaded side to elongate more than cells on the illuminated side, causing the shoot to bend toward the light
TIR1 (intracellular receptor) and ABP1 (binding protein that is part of a receptor complex in the plasma membrane)
auxin binding to these receptors in stem cells triggers a signaling pathway that ultimately increases the activity of membrane proton pumps
the idea that proton pumps (acidification of cell wall) are responsible for cell elongation
as protons are pumped out of the cell, an electrochemical gradient is established
the gradient (negative inside, positive outside cell) favors the entry of cations such as K+ into the cell
as cation solute concentrations increase inside the cell, water follows via osmosis
when cell walls on one side of a stem are acidified in response to auxin, bending results through asymmetrical elongation
cell wall must loosen to allow for an increase in cell size
water must enter the cell and generate turgor pressure on the cell wall to trigger an increase in cell volume
cell wall proteins which “unzip” the hydrogen bonds that form between cellulose microfibrils and other polymers in the cell wall, loosening the structure
activated when proton pumping lowers the pH of the cell wall to 4.5
far-red wavelengths are not absorbed strongly by photosynthetic pigments, so they tend to pass through leaves
far-red wavelengths are therefore prominent in light that is filtered through leaves before reaching the forest flower, and are indicative of shade to a plant
since red indicates light and far-red indicates shade, the light sensed can act as a “switch” for cellular processes
e.g. red light promotes seed germination, while far-red light inhibits it
proposes that one pigment exhibits switching behavior and has two conformations, one of which can absorb red and the other of which can absorb far-red
hypothesized to occur because light absorption makes the photoreceptor pigment change shape
specialized light receptor which is hypothesized to exhibit photoreversibility in response to different wavelengths
has been shown to play a role in plant growth responses controlled by light, including seed germination, etiolation, and circadian rhythms
phytochrome conformation induced by red light
active conformation
phytochrome conformation induced by far red light
inactive conformation
phenomenon in which shaded plants develop a pale yellow color, lengthen their stems, and grow long, thin, and spindly
plants growing in shade decide to invest more energy in growing taller and less energy in leaf development as they try to reach the light
the leaves of some species open and close in slow but regular fashion that is determined by changes in light levels
closely tied to the plant’s molecular clock, which is reset each morning
develops from modified shoots
begins when an apical meristem stops making energy-harvesting stems and leaves and begins to produce the modified stems and leaves that make up flowers
plant commits to investing energy in sexual reproduction
switch that triggers flowering in response to changes in day length also shows red/far-red photoreversibility
any response by an organism that is based on photoperiod
important in plants because it allows individuals to respond to seasonal changes in climate
bloom midsummer, when days are longest and nights are shortest
flower only when days are longer than a species-specific length, usually between 10-16 hours
radishes, lettuce, spinach, corn, irises, etc
bloom in spring, late summer, or fall when days are shortest and nights are longest
flower only if days are shorter than a species-specific length
asters, chrysanthemums, poinsettias
flower without regard to photoperiod
roses, snapdragons, tomatoes, cucumbers, many weeds
interrupting the night period with a flash of light changed the flowering response, which allowed researchers to link the phytochrome switch to flowering
noted that clock protein levels rise during the day and trigger the expression of the gene CONSTANS (CO)
transcription factor that affects the production of a flowering hormone
stabilized by phytochrome when it is activated by light, allowing it to accumulate in cells
stimulates the production of the flowering hormone in long-day plants and inhibits the production of the flowering hormone in short-day plants
exposing just one leaf on the plant to flowering conditions led to the whole plant flowering—suggests that the signal to flower comes from the leaves and travels to the apical meristem
grafting leaves from plants exposed to flowering conditions resulted in plants which had not been exposed flowering—suggests that some product created in the transplanted leaf must travel to the recipient plant meristem, which would then trigger a developmental switch
gene known to promote flowering when activated
expressed in the leaf vascular tissue
research indicates that its protein product may be the flowering hormone
if removed, roots stop responding to gravity—suggests that gravity-sensing occurs somewhere inside the root cap
cells in the center contain starch granules which are critical for regulating gravitropic response
starch-storing organelles (amyloplasts) are pulled to the bottom of root cap cells by the force of gravity, since starch is denser than water
the position of the amyloplasts activates sensory proteins in the plasma membrane which initiate the gravitropic response
normal conditions: auxin flows down the middle of the root, toward the perimeter, then away from the root cap
tipped root: sensory receptors trigger changes in the position of auxin transport proteins that redistribute auxin
auxin is redistributed so that the lower part of the root receives increased concentrations and the upper portion receives lower concentrations
high auxin concentrations inhibit growth root, so the differences in auxin concentrations trigger differential growth that results in root bending downward
receptor cells transduce mechanical force into an internal signal
signal results in transcription of a large suite of genes being turned up or down in response to touch or mechanical stimuli such as wind
results in altered growth which is NOT directional, only resulting in sturdier plants
phenomenon in which some of proteins transcribed in response to wind/touch stiffen cell walls
results in shorter and stockier plants
a plant’s response to touch moving in a specific direction
can be moderately fast (e.g. climbing tendrils)
rapid, nondirectional movements such as a venus flytrap snapping shut
occur when a touch receptor cell transduces the mechanical signal into an electrical signal by allowing ion flow across the membrane, resulting in a change in membrane potential
the characteristic propagation of electrical signals that travels between a sensory receptor and a “motor cell” (cells which change shape by swelling and pushing venus flytrap shut)
generated by sensory hairs inside venus flytrap leaves
moves across plant tissues via plasmodesmata
growth is restricted to the main stems and lateral buds remain dormant
is broken if apical buds die or are removed, but can be experimentally maintained by applying auxin to the shoot’s cut surface after bud is removed—confirms role of auxin and suggests that the tip cells send a constant stream of information down to other organs and tissues
polar/unidirectional (only hormone to be so)
occurs down the stem and through the root via parenchyma cells in the ground and vascular tissue
enters apical end of cells via specialized membrane proteins, diffuses to other end of the cell, then transported out by proteins located only in the basal part of the cell
creates a strong auxin gradient down the long axis of the plant
control growth via apical dominance, phototropism, and gravitropism
promote fruit development when produced by seeds
involved in abscission when concentrations fall
essential for proper differentiation of xylem and phloem cells in the vascular tissue and development of the vascular cambium
stimulates development and growth of adventitious roots
hypothesized to signal where cells are located relative to the root-shoot axis and response to conditions affecting the root-shoot axis (gradient)
the group of plant hormones that promote cell division (strong evidence that it does so by activating genes that keep the cell cycle going)
mostly synthesized in root apical meristems and transported up into the shoot system via xylem
can also be synthesized in young fruits/seeds/buds and other developing organs
derived from adenine
cytokinin found in most species
naturally occurring adenine derivative
group of closely related proteins located primarily in the endoplasmic reticulum
activate genes that regulate cell division when cytokinins bind
large family of closely related compounds which stimulate growth in plants
discovered and isolated from quickly-growing rice seedlings with “foolish seedling disease” caused by Gibberella fungal infection
most species produce several different gibberellins
molecule which inhibits growth
involved in stomatal closing
digestive enzyme that breaks the bonds between the sugar subunits of starch
released during germination from the aleurone layer and diffuses into the endosperm—digestion of starch released sugars that can be used by the growing embryo
production and release is increased by gibberellic acid (GA) and decreased by ABA
did not water half of the experiment plant
stomata began to close even when the measured water potential in the un-watered leaves remained the same as fully watered plants
suggests that roots from the dry side of the pot were signaling drought stress even though the leaves were not actually experiencing a water shortage yet
ABA levels in roots of dry side of plant were measured to be very high relative to watered side and relative to control plants, suggesting ABA is produced in roots and transported to leaves to serve as early warning for drought stress
based on activity of proton pumps and ion transporters in the plasma membrane
creation of osmotic gradients result in the movement of water; guard cells open when turgid and close when flaccid
photoreceptors are stimulated by blue light
large numbers of protons are pumped out of each cell, resulting in strong electrochemical gradient
gradient favors entry of K+ and Cl- into the cell
water follows by osmosis
guard cells swell and stomata open
ABA inhibits guard cell proton pumps
chloride and other anion channels are opened, resulting in change in membrane potential
change in membrane potential causes potassium ion channels to open
large amounts of K+ leave cells
water follows by osmosis
loss of turgor, closing of the pore
sugars in these molecules trigger growth spurts
similar to testosterone and estradiol
promote growth; key regulator of overall plant body size
animal: often lipid soluble (bind to receptors in cytosol)
brassinosteroids: often hydrophilic (bind to membrane receptors)
a regulated process of aging and eventual death of an entire organism or organs such as fruits or leaves
regulated by complex interactions between several hormones in response to light, temperature, and other factors
hormone most strongly associated with senescence
gas at normal temperatures
synthesized from the amino acid methionine
involved in fruit ripening, flowers fading, and leaf abscission
influences plant growth
stress hormone induced by drought and other conditions
induces an increase in cellular respiration
characterized by a conversion of stored starch to sugar, removal or destruction of protective toxins, degradation of cell walls (softening the fruit) and chlorophyll, and production of pigments and aromas that signal ripeness
thought to be an adaptation that enhances the fruit’s attractiveness to animals that disperse seeds
auxin is produced in healthy leaves and transported through the petiole—when leaves produce less auxin (in response to environmental conditions or age), cells in a region of the petiole called the abscission zone become more sensitive to ethylene in the tissue
increased ethylene sensitivity activates enzymes that weaken the walls of cells in the abscission zone
chlorophyll in the leaf is broken down, and nutrients are withdrawn and stored in parenchyma in the stem
eventually, cell walls break down enough that the leaf falls
the interaction between the signal pathways triggered by different hormones
molecular mechanism responsible for integrating information from many sensory cells and signals
disease-causing agents
bacteria, viruses, fungi, etc
cuticle—good barrier to pathogens
thorns, spines, trichomes, etc help protect from damage by herbivores
lace tissues with secondary metabolites
this type of defense is effective but expensive in terms of ATP and materials invested
mostly inducible
molecules closely related to compounds in key synthetic pathways but not found in all plants
poison herbivores
insect-repellents—lemon, peppermint, basil, sage oils
insecticides—pine pitch, chrysanthemum pyrethroids
disrupt nervous systems—tannins, opium, caffeine, cocaine, nicotine, THC, etc
responses to attacks and infections that are triggered by the presence of a threat (not present all the time)
found in both plants and animals
tend to infect only one or a few host species (coevolution)
enter mostly through stomata or wounds
receptor proteins that can bind to residues left by pathogenic cells
signal to the plant that a pathogen is present, triggering HR and SAR through signal cascades
stomatal closure (prevent more pathogens from entering the plant)
production of toxin molecules targeted to the pathogen
reinforcement of neighboring plant cell walls to limit movement of the pathogen
rapid suicide of cells in the infected region within hours of the start of an infection; results in brown spots in leaves that accumulate over the growing season
small compound used by Pseudomonas pathogens to force stomatal re-opening after shutting during HR
allows more bacteria to enter the leaf
slower, more widespread of events triggered by a hormone produced at the infection site
primes cells throughout the root or shoot system over several days for resistance to assault by a pathogen
acts globally (throughout plant) as well as locally (point of infection)
results in the expression of a large suite of genes called the pathogenesis-related (PR) genes, which produce proteins that help prevent an infection from spreading
hypothesized to be the SAR hormone
derived from salicylic acid
levels increase dramatically after infection, particularly in the phloem sap leaving infection sites
reduction correlates with reduction or abolishment in SAR response
addition in lower leaves of tobacco plants leads to SAR in upper untreated leaves
found in many seeds and some storage organs such as potato tubers
block enzymes responsible for digesting proteins—ingestion causes herbivores to become sick and avoid them
allowed herbivorous beetles to attack one leaf on several potato plants
concentrations of inhibitor in non-attacked leaves on the attacked plants averaged over three times the concentrations in control plants
hormone produced in tomato plants and closely related species which induces the production of proteinase inhibitors
peptide hormone (18 amino acids long)
systemin is released from damaged cells
systemin travels through the phloem and binds to membrane receptors on target cells
activation of receptors triggers series of chemical reactions that synthesize another hormone (jasmonic acid)
Jasmonic acid activates a cytosolic signal pathway that induces the production of at least 15 new gene products (including proteinase inhibitors)
when an insect starts eating a plant, volatile compounds evaporate from a leaf’s surface and travel through the air
nearby plants sense the chemicals and respond by increasing their own defenses, even if the chemicals come from a totally different species
organism that is free-living as an adult but parasitic as a larva
tend to be similar in size to their hosts and therefore must consume and kill their hosts to complete development
particularly common when insect outbreaks occur in croplands
insect-damaged leaves produced 11 molecules that were not produced by undamaged leaves OR leaves mechanically damaged by scissors/tools
female wasps preferred to fly toward insect-damaged leaves over mechanically damaged leaves
supports the hypothesis that plants produce pheromones that recruit wasps in response to attack by caterpillars
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