Plant Hormones and Signal Transduction - 12 Flashcards
Define signal
environmental input that initiates one or more plant responses
Define receptor
the physical component that biochemically responds to a signal
What do receptors consist of
proteins or pigments associated with proteins (if light receptors)
What are the 4 chain of events that the signal transduction pathways typically involve
signal -> receptor -> signal transduction -> response
signal transductions can cause both rapid and slow responses, explain the difference in responses
rapid responses involve electrochemical responses
longer/slower involve changes in gene expression
plant responses to environmental signals can differ ____ and/or ___
time or spatially
Define cell autonomous response vs. non-cell autonomous response (is how plant responses differ spatially) and examples
cell autonomous = response to environmental signal where both the signal reception and response occur in the same cell (ex. guard cell)
non-cell = signal reception occurs in one cell and the response occurs in a different cell (ex. stomata)
where are the 4 places receptors can be located
plasma membrane, cytosol, endomembrane system, or nucleus
or found in more than 1 cellular location!
Define kinase
an enzyme that catalyzes the transfer of a phosphate group from ATP to a specified molecule (most common modification)
Define secondary messenger and what is the most common one
Ca2+
released in response to the primary messengers which are transported to the site of action to evoke the main physiological response
What are strategies for kinases to amplify signal transduction pathways (2)
Kinases = elevate weak initial signaling events above the threshold of detection or to propagate throughout the cytoplasm
Explain the processes of activation and termination of the secondary messenger Ca2+
signal induced activation of Ca2+ permeable ion channels in cytoplasm, activated sensor proteins interact and link signals to changes in activity -> can activate calmodulin by binding or phosphorylate target proteins, pumps and exchangers remove Ca2+ from cytoplasm and terminate signal
What is the secondary messenger Ca2+ mostly involved in
plant defenses and symbiotic interactions
what other factor can regulate Ca2+ fluxes
membrane lipids
Aside from Ca2+, what is another important secondary messenger
protons
Define hormones as chemical messengers
chemical messengers produced in one cell and modulate cell processes in another cell. they interact with specific proteins that function as receptors linked to cell signal transduction pathways
Explain the pathway of hormones
signal perception increases hormone biosynthesis -> hormone transported to site of action -> perception of hormone occurs by the receptor -> results in transcriptional or posttranscriptional events that induce a response -> suppress synthesis by negative feedback by catabolism or sequestration -> ready for next signal input
Plant development is regulated by what 9 major hormones
- auxin
- gibberellins
- cytokinins
- ethylene
- abscisic acid
- brassinosteroids
- salicylic acid
- jasmonates
- strigolactones
Auxin function
plant growth, growth regulator, embryo development in seeds, lateral branching, delaying leaf senescence
define polar auxin transport
directional auxin movement that functions in development and growth responses
Gibberellins function
transition to flowering, fruit development, growth promoting regulators
Cytokinins function
breaking bud dormancy, leaf senescence, formation of apical meristems, produced during mycorrhizal formation
What can cytokinins do in the presence of auxins
can stimulate plant tissue to produce parenchyma cells in undifferentiated masses called callus (cells that cover plant wound)
Ethylene function
fruit ripening, leaf and flower senescence, epinasty
Abscisic acid function (ABA)
promotes senescence, stomatal closure, seed maturation, responses to pathogens
Function of brassionosteriods (BRs)
sex determination, elongation growth and photomorphogenesis
Define salicylic acid and jasmonates
involved in plant defence responses to herbivory and pathogen infection
Strigolactones function
promote symbiotic interactions with arbuscular mycorrhizal fungi, stimulate activity of cambium and secondary growth
What is hormone concentration determined by
by the balance between the rate of increase of the hormone concentration (biosynthesis, uptake, activation, release) and rate of decrease of concentration (efflux, sequestration, degradation, inactivation)
What are the 3 factors that makes regulation of hormone levels complicated
- may be augmented by secondary or intersecting biosynthesis mechanisms
- variants of a hormone can cause variability in the biological activity
- may be multiple mechanisms for removing active hormones from the system
What hormone is toxic at high cellular concentrations and what can it be used for
auxins
used for herbicides
how is auxin regulated (2)
- by being conjugation into conjugated forms and oxidatively degraded
- sequestered in ER
What is the difference between natural and synthetic auxins
synthetic auxins can be herbicides because they are less subject to homeostasis control (sequestration and degradation) than natural auxins
What are the 3 regulatory mechanisms for gibberlin biosynthesis and catabolism pathway
- gibberelin inactivation (GA 2-oxidases)
- methylation
- conjugation to sugars
hormonal signaling involves transmission from _____ to ____
site of synthesis
site of action
What are the 3 types of hormones in terms of transmission
- endocrine hormones
- paracrine hormones
- autocrine effectors
Define endocrine hormones
hormones transported to sites of action distant from the site of synthesis
Define paracrine hormones
hormones that can act on cells adjacent to the site of synthesis
Define autocrine effectors
hormones that function in the same cells in which they are synthesized
Explain why most plants have paracrine activities
because plants lack a fast-moving circulatory system so they have paracrine activities which transduces to nearby cells to cause an effect
What is the most common electrical signaling in plants
action potential
Define action potential
depolarization of the plasma membrane of a cell generated by voltage-dependent ion channels
What kind of system do the cellular receptors for ethylene and cytokinins resemble
2-component regulatory systems
define 2-component regulatory systems
consist of membrane bound histidine kinase sensor protein and soluble response regulator protein
Explain signal movement through a 2-component regulatory system
the sensor proteins receive the input signal, undergo autophosphorylation, then pass signal on to response regulators by transferring phosphoryl group, then bring response
Where are cytokinin and ethylene receptors localized
localized to endoplasmic reticulum membrane
What do the largest class of plant receptor kinases consist of
receptor-like serine/threonine kinases (RLKs)
function of RKLs
relay information to the cell interior by phosphorylation of serine or threonine residues of target proteins
Define protein phosphatases
enzymes that remove phosphate groups from proteins that also have a role in signal transduction pathways
Explain why plant hormone pathways employ negative regulators
negative regulators are inactivating repressors which allow for faster activation of downstream response genes. the pathways function by inactivating repressor proteins
How do auxins, jasmonates, and gibberellins signal
by inactivating repressor proteins, directly targeting the stability of repressor proteins and thereby inducing a transcriptional response
What are the 4 mechanisms in which plants terminate signals
- degradation
- inactivation of conjugation to ligands
- sequestration
- inactivation by dephosphorylation
How is the integration of signal transduction pathways accomplished
through cross-regulation
Define agonistic and antagonistic interactions with other signals
agonistic = additive or positive interactions
antagonistic = negative or inhibitory interactions with other signals
Define primary cross-regulation
direct signaling pathways regulating shared transduction component
Define secondary cross-regulation
output of one signaling pathway regulates a second signaling pathway
Define tertiary cross-regulation
outputs of 2 distinct pathways exerting influence on one another
