hormones + plant development Flashcards
plant adjustment to enviro
plants constantly adjust to enviro conditions
- require communication btw cell + tissue to coordinate metabolic, growth, and morphological responses
define signal
environmental input that initiates one or more plant responses
define receptor
physical component that biochemically responds to signal
receptors transduce and ?
amplify signal to trigger cell response
how receptors transduce signal + trigger cell response
modify activity of other proteins
employ intracellular signaling molecules, second messengers
what are secondary messengers ?
small intracellular molecules and ions that are rapidly produced or mobilitzed ot relatively high levels after signal perception to modify activity of target proteins
initial response of signal transduction?
secondary signals (hormones) transported to site of action initiate the main physiological response
roles of hormones as response
- signal - do something else in plant to elicit response
2. do response itself.
JA as example of hormone signalling
saliva elicitor (signal) - bind to receptor, - systemic produced to stimulate biosynthesis of JA. response is biosynthesis of JA. but JA can act systemically = secondary signal to target cells.
plant hormones - phytohormones
- function
regulation and coordination of plant growth, development and metabolism. depend on movement of chemical signals from one plant to another.
chemical signaling molecules transmit signal between cells + initiate physiological responses.
- regulate stages of life
- coordinate cell activities, pattern formation, reproduction
what needs to be regulated for effective signals?
concentrations of plant hormones. tightly regualted by +/- factors.
= enables tiely responses to signals,
= maintain sensitivity to same signal in future
- most hormones derived from multiple precursors and biosynthetic
diff btw human/plant hromones
human: transported somewhere else
plant: can be local or distant action
how many major hormones?
auxins gibberellins cytokinins ethylene abscisic acid salicylic acid jasmonic acid brassinosteroids strigolactone
auxins - essential for?
plant growth. signalling is key regulator of virtually every aspect of plant growth and development
= growth, phototropism, gravitropism, organogenesis, branching, embryonic patterning, stem cell maintenance
how was auxin discovered?
early studies of coleoptile bending during phototropism
- intact seedling bends towards light.
- tip excised no nurvacture
- opague tiip = no curvature
= mica sheet on side further from light = no curvature
= mica sheet on side closer to light = curvature.
- tip removed, gelatin placed between tip = normal curvature (lipid-soluble layer in between
four naturally occurring auxins in plants
- indole -3-ascetic acid (IAA) most abundant + physiologically important
- Indole-3-butyric acid (IBA) storage auxin
- 4-chloro-IAA
- phenylacetic acid (PAA)
auxing metabolism
auxins producced through several pathways, most is IAA pathway called IPyA
IAA path assoc withrapdily dividing + gorwing tissue.
Auxin levels are also controlled by conjugation, leaing to storage or degradation
conjugates are biologically inactive
- reversible conjugation = storage. hydrolyzed to free.
- irreversible conjugation leads to IAA degradation
- oxidation of IAA-hexose = IAA degradation
Gibberellins
- major forms?
- primary effect?
diverse group of chemically related plant hormones with varying levels of biological activtiy.
Major bioactive forms: GA1,3,4,7
primary effect = cell elongation
- stem elongation, seed germination, transition to flowering, fruit development
Gibberellin + stem elongation
promote elongation, stimulate internode elongation.
GA - gibberellin + flowering/fruit development
GA induce bolting + flowering of long-day plants grown during short days
GA biosynthesis
begins in plastic and sequentially oxidied in ER to give GA12.
- all GAs derived for GA12 by oxidation in cytosol.
Active GA controlled by regulated synthesis + deactivation
cytokinins -function
promote cell division + shoot growth
delay leaf senescence
apical dominance
regulate auxin action and distn
formation an dactivity of apical meristems
contribute to enviro signaling and pathogen response
regulate nutrient allocation
cytokinin metabolism
N6 substituted adenine-related compounds
- synthesized in plastids of roots.
- isopentenyl side chain from DMAPP transferred to isopentenyl transferase to ADP/ATP => zeatin
CK metabolism
altering expression of CK biosynthetic enzymes affects CK-regulated plant growth.
- CK added or removed from active pool by modifications or transport.
- active CK inactivate by conjugation to glucose or aa (reversible or irreversible)
- CK irreversibly deactivated via cytokinin oxidase
ethylene
gaseous hormone promotes fruit ripening.
- bc gas - moves freely btw + within tissue.
-ethylene produced by one fruit ripen another
= organ senescence
= growth of etiolated sseedlings
ethylene metabolism
derived from AA metionine via biosynthetic pathway
- methionine -> s-adenosylmethionine -> 1-aminocyclopropance-1-carboxylic acid (ACC) by ACC synthase
ACC oxidized to ethylene
- regulated by expression + stability of ACS and ACO (unstable; continually synthesied + degraded)
- stress induced phosphorylation of ACs stabilies it, increasing ethylene accumulation.
- no ethylene catabolsim, just diffuses out
Abscisic acid (ABA)
hormone that controls plant abilities to survive stressful conditions
- > ABA mediates tolerance of salinity, dehydration + temp stress
- > promotes seed maturation + dormancy
- > ubiquitous in plants biosynthetic and signaling pathway are conserved - early adaptation to terrestrial enviro
ABA metabolism
synthesized in almost all cells that contain chloroplasts or amyloplasts + has been detected in every major organ and tissue
where is ABA synthesized
plastid and cytoplasm. derived from zeaxanthin, carotenoid intermediate
ABA homeostasis
ABA levels in tissue change rapidly during development + in response to enviro.
- ABa increase with drought stress + during seed maturation
- Levels of active ABA regulated by changes in synthesis + deactivation by conversion to inactive forms, oxidation conjugation
carotenoid cleavage by? correlated to?
NCED highly correlated with ABA levels and key regulatory event in ABA synthesis.
- expression of NCED is induced by water stress + during seed maturation
ABA controlled by inactivation pathwasy
irreversibly deactivated by conversion to phaseic acid during recovery from water deficit and during seed germination. [phaseic acid helps increse water intake, degrades ABA almost completely
- reversible glucose conjugation = highly hydrophilic compound - ABa stored + transported long distance.
salicylic acid + jasmonic acid
primary signaling compounds function in plant defense responses to herbivory and pathogen infection
auxin transport - 2 distinct pathways
- PAT: polar auxin transport. directional cell-to-cell auxin movement via auxin transport proteins.
-> slow, regulated, carrier-mediated cell-to-cell directional transport from the shoot to root.
=> active, requires energy - unregulated bulk flow.
where are auxin concentrations highest
shoot apex, yougn leaves + root apex.
