Chapter 39 Flashcards
etiolation
morphological adaptions for growing in darkness
de-etiolation
when plants that were growing in darkness now are exposed to light and their shoots and roots grow normally
what are the steps to signal-transduction pathways
- reception
- transduction
- response
what happens in the reception part of transduction pathways
Internal and external signals are detected by receptors, proteins that change in response to specific stimuli
• In de-etiolation, the receptor is a phytochrome capable of detecting light
second messengers
molecules that transfer and amplify signals from receptors to proteins that cause responses
what are the two types of second messengers in plants?
- Ca2+ ions
2. cGMP
how does the phytochrome receptor work?
– Opening Ca2+ channels, which increases Ca2+
levels in the cytosol – Activating an enzyme that produces cGMP
what happens in transduction
second messengers send a message to kinases to do something
what happens in “resonse” section of transduction pathway?
-regulation of one or more cellular activities
-activate transcription factors
-activate enzymes in cytosol
-
what is post-translational modification?
modification of existing proteins in the signal response
- often involves phosphorylation of specific amino acids
- cGMP and Ca2+ activate protein kinases directly
De- etiolation activates enzymes that do what?
- function in photosynthesis directly
- supply the chemical precursors for chlorophyll production
- affect the levels of plant hormones that regulate growth
hormones
chemical signals that modify or control one or more specific physiological processes within a plant
tropism
any response resulting in curvature of organs toward or away from a stimulus
phototropism
- a plant’s response to light
- They observed that a grass seedling could bend toward light only if the tip of the coleoptile was present
- They postulated that a signal was transmitted from the tip to the elongating region
auxin hormone
-a chemical that promotes elongation of the pointed protective sheath covering the emerging shoot
- produced in the shoot tips and is transported down the stem
-• According to the acid growth hypothesis, auxin stimulates proton pumps in the plasma membrane
• The proton pumps lower the pH in the cell wall, activating expansins (that loosen the wall’s fabric)
• With the cellulose loosened, the cell can elongate
-also alters gene expression and stimulates a sustained growth response
expansins
enzymes that loosen the wall’s fabric
if auxin is reduced in the shoot what happens?
the lower branches begin to show growth
the activity of the vascular cambium is under the control of what?
auxin transport
cytokinins
- stimulate cytokinesis (cell division)
- produced in actively growing tissues such as roots, embryos, and fruites
- cytokinins work together with auxin to control cell division and differentiation
- if auxin is not present cytokinin can take control and help lower branches grow
- slow aging of some plant organs by inhibiting protein breakdown, stimulation RNA and protein synthesis, and mobilizing nutrients from surrounding tissues
gibberellins
- stem elongation, fruit growth, and seed germination
- produced in young roots and leaves
- stimulate growth of leaves and stems
- stimulate cell elongation and cell division
brassinosteroids
- similar to sex hormones of animals
- induce cell elongation and division in stem segments
- slow leaf abscission and promote xylem differentiation
abscisic acid
- slows growth
- seed dormancy ; ensures that the seed will germinate only in optimal conditions
- dormancy is broken when ABA is removed by heavy rain, light or prolonged cold
- early germination can be caused by inactive or low levels of ABA
- drought tolerance; the primary internal signal that enables plants to withstand drought
- ABA accumulation causes stomata to close rapidly
strigolactones
- stimulate seed germination
- help est. mychorrhizal associations
- help control apical dominance
- striga seeds germinate when host plants exude strigolactones through their roots
ethylene
a response to stresses such as drought, flooding, mechanical pressure injury, and infection
-effects of ethylene include response to mechanical stress, senescence, leaf abscission, and fruit ripening
what is the triple response?
- something that allows a growing shoot to avoid obstacles
- it consists of a slowing of stem elongation, a thickening of the stem, and horizontal growth
senescence
the programmed death of cells of organs
- the process of aging in plants
leaf abscission
- a change in the balance of auxin and ethylene controls leaf abscission, the process that occurs in autumn when a leaf falls
- when plants drop their leaves
what triggers the rippening process in a fruit?
a burst of ethylene
-then ripening triggers release of more ethylene
photomorphogenesis
effects of light on plant morphology
action spectrum
a graph that depicts relative response of a process to different wavelengths
what are the two major classes of light receptors?
- blue-light photoreceptors
2. phytochromes
blue light photoreceptors
• Various blue-light photoreceptors control hypocotyl elongation, stomatal opening, and phototropism
phytochromes
• Phytochromes are pigments that regulate many
of a plant’s responses to light throughout its life
• These responses include seed germination and shade avoidance
many seeds remain dormant until what?
light conditions change
what type of light increases germination?
red light
what type of light inhibits germination?
far - red light
germination
the process by which a plant grows from a seed.
the photoreceptor responsible for the opposing effects of red and far-red light is a _____
phytochrome
phytochromes exist in what two states?
P “r” and P “fr”
- P “r” is the phytochrome shape that accepts red light
- P “fr” is the phytochrome shape that accepts far red light
- P “r” that gets red light changes to a P “fr” shape
- P “fr” that gets far red light changes to a P “r” shape
if the cytochrome is hit with red light then what happens?
the cytochrome changes shape to far red light cytochrome and germination occurs
if the cytochrome is hit with far red light then what happens?
the cytochrome changes shape to red light cytochrome and germination is inhibited and nothing occurs
circadian rhythms
cycles that are about 24 hours long and are governed by an internal “clock”
-clock depends on synthesis of a protein regulated through feedback control and may be common to all eukaryotes
photoperiod
the relative lengths of night and day, is the environmental stimulus plants use
most often to detect the time of year
photoperiodism
physiological response to photoperiod
short day plants
plants that flower when a light period is shorter than a critical length (of darkness)
long day plants
plants that flower when a light period is longer (if it passes the critical length of darkness)
day neutral plants
controlled by plant maturity
-not photperiod
is photoperiod controlled by night length or by day length
night length
after how long of the photoperiod do plants flower?
-Some plants flower after only a single exposure to the required photoperiod
• Other plants need several successive days of the required photoperiod
photoperiod is detected by what part of the plants?
by leaves (which cue buds to develop as flowers)
florigen
the flowering signal (when buds are cued to develop as flowers)
short day /long night plants have their flowers bloom only when…
- they spent atleast the minimal amount of hours (according to critical dark period) in dark
- continuous dark hours in dark as well
long day/short night plants have their flowers bloom only when….
- when hours in darkness are less than the critical dark period
- when the hours in darkness (if over the critical dark period) is interrupted by a red light
gravitropism
response to gravity
-roots show positive gravitropism; shoots show negative gravitropism
thigmomorphogenesis
changes in form that result from mechanical disturbance
thigmotropism
growth in response to touch
-occurs in vines and other climbing plants
action potentials
-rapid leaf movements in response to mechanical stimulation are examples of transmission of electrical impulses
abiotic stresses
nonliving stresses
-ex) drought, flooding, salt stress, heat stress, and cold stress
biotic stresses
living stresses
-ex) herbivores and pathogens
what happens to plants during drought
- plants reduce transpiration by closing stomata, slowing leaf growth, and reducing exposed surface area
- Growth of shallow roots is inhibited, while deeper roots continue to grow
what happens to plants during flooding
Enzymatic destruction of root cortex cells creates air tubes that help plants survive oxygen deprivation during flooding
what happens to plants with salt stress
Salt can lower the water potential of the soil solution and reduce water uptake
• Plants respond to salt stress by producing solutes tolerated at high concentrations
• This process keeps the water potential of cells more negative than that of the soil solution
what happens to plants during heat stress
Excessive heat can denature a plant’s
enzymes
heat shock proteins
help protect other proteins from heat stress
what happens to plants under cold stress?
Cold temperatures decrease membrane fluidity
• Altering lipid composition of membranes is a response to cold stress
• Freezing causes ice to form in a plant’s cell walls
and intercellular spaces
• Many plants, as well as other organisms, have antifreeze proteins that prevent ice crystals from growing and damaging cells
what do plants do to fight of living stresses like herbivores?
Plants counter excessive herbivory with physical defenses, such as thorns and trichomes, and chemical defenses, such as distasteful or toxic compounds
• Some plants even “recruit” predatory animals
that help defend against specific herbivores
-Plants damaged by insects can release volatile chemicals to warn other plants of the same species
what do plants do to protect against pathogens
-A plant’s first line of defense against infection is
the barrier presented by the epidermis and periderm
• If a pathogen penetrates the dermal tissue, the second line of defense is a chemical attack that kills the pathogen and prevents its spread
• This second defense system is enhanced by the inherited ability to recognize certain pathogens
virulent pathogen
one that a plant has little specific defense against
avirulent pathogen
one that may harm but does not kill the host plant
gene for gene recognition
recognition of elicitor molecules by the protein products of specific plant disease resistance (R) genes
what is the hypersensitive response
– Causes cell and tissue death near the infection site
– Induces production of phytoalexins and PR proteins, which attack the pathogen
– Stimulates changes in the cell wall that confine the pathogen
systemic acquired resistance
causes systemic expression of defense genes and is a long-lasting response
salicylic acid
ynthesized around the infection site and is likely the signal that triggers systemic acquired resistance
