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