Post on 20-Jan-2016
Response to Signals in Plants
Chapter 39
Signal Transduction Pathway 1. Receptors receive a
stimulus and activate the secondary messengers
2. Secondary messengers ______ the signal in other proteins
3. Cells respond to the signal 1. _____________ pathway2. Transcriptional
regulation
Signal Transduction Pathway1. Light signal activates
__________ receptor which initiates two signal transduction pathways
2. Each transduction pathway activates kinase protein
3. Kinase proteins activate the expression of genes that result in a _______ (de-etiolation) response
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Plant HormonesHormone: _____________ produced in one part of an organisms body, which _______ another part of the body where it binds with a specific receptor and initiates a response in target cells or tissues
Auxin (IAA) Cytokinins Gibberellins (GA) Abscisic acid (ABA) Ethylene Brassinosteroids Jasmonates Strigolactones
Hormone: Auxin (IAA)Primary location produced: Shoot apical meristem Young leaves
Major functions: Stimulates _____________ Promotes lateral and
adventitious root formation Regulates ______________ Phototropism and
gravitropism Promotes secondary growth
Polar Transport of AuxinAuxin is transported from apex to shoot
Cell wall is _____ Auxin ion picks up H+ Diffuses across plasma membrane
Cytosol is _______ Auxin loses H+ Uses energy to pump out H+ to
maintain pH Leaves cell through carrier proteins
Cell Elongation in Response to Auxin
3Low pH activates__________, which separate microfibrilsand polysaccharides
Hormone: CytokininsPrimary location produced in plant: Roots
Major functions: Regulate _________ (cytokinesis) and influence pathway of differentiation
More cytokinins = development of shoot buds More auxins = more root growth
Control apical dominance = apical bud __________________ of axillary buds
Promote lateral bud growth Stimulate seed germination Delays senescence (death or deterioration of plant parts)
Apical Dominance
Hormone: Gibberellins (GA)Primary location produced in plant: Apical meristems of roots and buds Young leaves Developing seeds
Major functions: Stimulate ____________ and _________ Pollen development and tube growth Promotes _____________ and
germination Stimulates flowering and fruits (with
auxin)
Gibberellins Role in Germination1. After being activated
by water, gibberellins are released, which signal the aleurone
2. Aleurone releases _____________, which breakdown endosperm
3. Nutrients provide energy to developing embryo
Hormone: Abscisic acid (ABA)Primary location produced in plant: All plant cells
Major functions: ______ growth Controls stomata under water stress Promotes seed dormancy (counteracts
gibberellins) Promotes leaf senescence (programed
death)
Hormone: EthylenePrimary location produced in plant: Most plant cells
Major functions: Triple response of seedlings
1. Slow stem elongation2. Thickening of stem3. Horizontal growth of stem
Promotes ______ ___________ (detachment) Senescence
Movement in PlantsTropism: a directional growth response toward or away from a stimuli
_____________: directional growth in response to light
Caused by concentration of Auxin on shaded side
Movement in PlantsGravitropism: directional growth in response to _____
Caused by sedimentation of _______ in plant cells.
Movement in Plants Thigmotropism: directional growth in response to _____
Plant Response to LightBlue-light photoreceptors Initiate phototropism Opening of ______ Slowing of seed leaf stem
(hypocotyl) after seedling breaks ground
Phytochromes (receptors that absorb mostly red-light) De-etiolation (greening)
Seed germination Triggered by accumulation
of red and far-red phytochromes Red phytochrome (Pr)
______ growth Far-red phytochrome (Pfr)
________ growth
Shade avoidance Pr and Pfr ratio dictate growth
Plant Response to Light
Responses to Pfr:• Seed germination• Inhibition of vertical growth and stimulation of branching• Setting internal clocks• Control of flowering
Daily and Seasonal Plant Responses Circadian rhythms: around 24-hr cycles that are not
directly controlled by a known environmental variable
Photoperiodism: a physiological response to photoperiod (interval an organism is exposed to light in a 24-hr period) Flowering (short-day vs. long-day) Critical night length
Short-day and Long-day Plants Short-day plants:
require light period ______ than some critical period
Long-day plants: require light period _____ than some critical period
Critical Night Length Some plants require a
critical night length (ex. 12-hrs) to flower
Flowering can be turned on or off by activating the red (Pr) and far-red (Pfr) phytocrome receptors
Flowering Hormone Flower inducing hormone
(______) can initiate flowering in plants not-triggered by photoperiod
Plant Response to Environmental StressesDrought stress Reduce transpiration
Close _______ Release of __________
Inhibits growth of young leaves Change leaf shape Deeper root growth Drop leaves
Dormant Encilia californica
Oxygen deprivation Formation of aerial root _____ of root cortex cells
to create air tubes Ethylene
Plant Response to Environmental Stresses
Salt Stress Salt glands Production of
compatible solutes Maintain water
potential
Plant Response to Environmental Stresses
Heat Stress ________ proteins
Chaperone proteins
Plant Response to Environmental Stresses
Cold Stress Alter lipid concentration of
membranes Changes in solute concentration
of cytosol ________ proteins
Plant Response to Environmental Stresses
Plant Response to PathogensPAMP triggered immunity
Pathogen-associated molecular patterns (PAMPs) = ________________ specific to certain pathogens
Effectors act to cripple host plants innate immune response R proteins
Hypersensitive response = localized ___________ near infection site
Lesions
Systemic acquired response = signaling molecules activate defense system in entire plant
Plant Response to Pathogens1. Pathogen effector binds with R protein in host
plant cell
2. R protein initiates a signal transduction pathway
3. __________________. Infected area is sealed off, with cell walls reinforced. Anti-microbial molecules are released and infected area dies.
4. Infected cells release signaling molecule
5. Signaling molecule transported throughout plant
6. Signaling molecule initiates signal transduction pathway
7. _____________________. Plant cells produce molecules that protect the cell from pathogens.
Plant Response to HerbivoresHerbivory: animals eating plants
Recruitment of _____________
Plant Response to HerbivoresProduction of _______________
Tannins Opium
Plant Response to Herbivores Timing of flowering