ch. 39 pt. 1 Flashcards
how do plants respond to signals from the environment?
altering growth and development
what do signal transduction pathways link?
signal to response
steps of signal transduction pathway
reception of signal, transduction, response
what happens to a potato left growing in darkness
process pale stems, unexpanded leaves, and short roots
- etiolation
etiolation
morphological adaptations for growing in darkness
etio
cause
what happens after etiolated potato is exposed to light
undergoes de-etiolation, shoots/roots grow normally
how do proteins function?
by changing shape
what do receptor proteins do in response to the stimulus
change shape
receptor in de-etiolation
phytochrome capable of detecting light
second messengers
transfer/amplify signals from receptors to other proteins that cause responses
2 types of second messengers
calcium ions (Ca2+) and cyclic GMP (cGMP)
how does the phytochrome receptor respond to light?
- opening Ca2+ channels, increase Ca2+ levels in cytosol
- activating enzyme that produces cGMP
phytochrome
plant color
how is GMP different from cGMP
GMP undergoes dehydration synthesis to from cGMP
ase
enzyme
kin
movement
what does a kinase do
catalyze transfer of a phosphate group from ATP to specified molecule
- substrate +ATP -> ADP + substrate
de-etiolation signal pathway process
- phytochrome activated by light
- cGMP produced and Ca2+ channel opened, activate protein kinases
- protein kinases activate transcription factors in nucleus
- trasncription
- translation
- de-etiolation
what does a signal transduction pathway lead to
regulation of one or more cellular activities
what do most responses to stimulation involve
change in activity of enzymes
how can a change in activity of enzymes (response) occur
- transcriptional regulation
- post-translational modification
post-translational modification
modification of existing proteins in signal response
- often involves phosphorylation of specific amino acids
- cGMP and Ca2+ directly activate protein kinases
phosphorylation
activation
dephosphorylation
inactivation
how do protein kinases often work?
in a cascade linking initial stimuli to gene expression through phosphorylation of transcription factors
transcriptional regulation
- transcription factors bind directly to specific regions of DNA and control transcription of specific genes
- some transcriptional factors activators that increase transcription
- others are repressors that decrease transcription
what does de-etiolation activate:
enzymes that
1. function in photosynthesis directly
2. supply chemical precursors for chlorophyll production
3. affect levels of plant hormones that regulate growth
what do plant hormones do
help coordinate growth, development, and responses to stimuli
what are plant hormones
chemical signals that modify or control specific physiological processes within a plant
what are plant hormones also called
plant growth regulators
growth promoters
auxins, cytokinins, gibberellins
growth inhibitors
ethylene, abscissic acid
are plant hormones produced in high or low concentrations
low
effects of hormones
each hormone has multiple effects, but multiple hormones can influence single process
what do plant responses to hormones depend on
concentration and combination of specific hormones
major plant hormones
- auxin
- cytokinins
- gibberellins
- abscisic acid
- ethylene
- brassinosteroids
- jasmonates
- strigolactones
overview of auxin
stem elongation, formation of lateral adventitious roots, phototropism/gravitorpism
cytokinins overview
cell division in shoots/roots, modifies apical dominance to promote lateral bud growth, movement of nutrients into sink tissues
gibberellins overview
stem elongation, pollen development, seed development/germination, sex determination
abscisic acid overview
inhibits growth, stomatal closure during drought stress, seed dormancy, senescence
ethylene overview
ripening of fruit, leaf abscission, senescence
brassinosteroids overview
cell expansion/division in shots, xylem/phloem differentiation
jasmonates overview
fruit ripening, floral development, nectar secretion, response to herbivory/pathogen invasions
strigolactones overview
seed germination, attraction of mycorrhizal fungi to root
tropsim
any response resulting in curvature of organs toward or away from stimulus
- phototropism
- thigmotropsim
- gravitropism
Darwin and Darwin
phototropism only occurs when tip is illuminated
Boysen-Jensen
phototropism occurs when tip is separated by permeable (not impermeable) barrier
auxin
any chemical that promotes elongation of coleoptiles
indolacetic acid
common auxin in plants
what is the transport of auxin referred to as?
polar
- produced in shoot tips, transported down the stem
what do auxin transporter proteins do
move hormone from basal end of one cell into apical end of neighboring cell
does the direction of auxin change in response to gravity?
no
acid growth hypohtesis
- auxin stimulates proton pumps in plasma membrane
- H+ moves into cell, lowers pH in cell wall and increases membrane potential
- reduced pH activates expansins
- osmotic uptake of water into cell increases turgor pressure
- increased cell wall plasticity combined with increased turgor pressure enables cell to elongate
expansins
enzymes that loosen the fabric of the cell wall
what does auxin also do?
alter gene expression and stimulates sustained growth response
reduced auxin flow from the shoot stimulates what?
growth in lower branches
what does auxin transport play a role in?
- phyllotaxy
what does polar transport of auxin from leaf margins direct?
leaf venation pattern
what is the activity of the vascular cambium under control of?
auxin
what is the organization of female angiosperm gametophytes likely regulated by?
auxin gradient
auxin functions
- vascular cambium
- organization of female angiosperm gametophytes
- plant development
- acid growth/cell elongation
indolebutyric acid
auxin that stimulates adventitious roots, used in vegetative propagation of plants by cuttings
synthetic auxins
used in herbicides (2,4-D) that kill edicots by causing hormonal overdose
- monocots able to inactivate these hormones
what do developing seeds produce?
auxin - promotes fruit development
cytokinins
stimulate cytokinesis
where are cytokinins produced
actively growing tissues (roots, embryos, fruits)
how does cytokinins work together with auxin?
to control cell division and differentiation
apical dominance
terminal bud’s ability to suppress development of axillary buds
what is apical dominance under the control of?
sugar, cytokinins, auxin, and strigolactone
what happens when the apical bud is removed:
- increases sugar availability
- decreases auxin/strigolactone levels
- initiates axillary bud growth
cytokinins and anti-aging of plant organs
- inhibiting protein breakdown
- stimulating RNA and protein synthesis
- mobilizing nutrients from surrounding tissues
