plant signal response

Biology V23.0012 with Velhagen at New York University

About this deck

By: Fariya Islam
Textbook:

Biology with MasteringBiology? (with WebCT Access Code Card -- Generic) (8th Edition)
Created: 2011-05-12
Size: 59 flashcards
Views: 4

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development/response to signal

1) light

2) circadian clock

3) pathogens, herbivores

4) gravity

5) internal signals, hormones

exogenous signals

light (quantity, quality, duration, direction)

mechanical (wind, herbivores)

atmospheric humidity

other plant proximity

soil nutrients/water

pathogens

gravity

CO₂

endogenous signals

mostly growth regulators & hormones

growth regulators (cytokine, ethylene, auxin, gibberellin)

mechanical (growth related tissue compression/tension)
developmental regulators (mobile RNA)

metabolites (sugars, glutamates)

A. thaliana mutants

identify how signals are perceived

plant signaling similar to animal cell signaling

reception - transduction - response

hormone/environmental stimulus -- receptor -- relay proteins/second messengers (small molecules/ions) -- activation of cellular responses

phototropism

response to light

hormones*

light signal at tip (cover tip), signal is mobile chemical (separate tip by gelatin block and mica)

Went experiment: auxin hormone causes phototropism

- expose plants to unilateral light

- excise tip and extract chemical messenger (auxin)

- place auxin on control plant w/excised tip, show that application of auxin to one side causes curvature

- plant bends to light bc of more auxin on dark side

plant hormone action

- plant hormones control growth and development via changes in 1) cell division 2) cell elongation 3) cell differentiation

like animal hormones:

- produced in very low [ ]

- minute amount has profound effect

- are transported

plant hormones & effects

growth enhance
auxin- elongation
cytokinin- division
gibberellin- GA seed germination
bassinosteroid- stem division/elongation
growth inhibit
abscisic acid- ABA promote seed dormancy
ethylene- promote wiltin/fruit ripening
brassinosteroid- inhibit root growth

auxin

moves long distances through phloem
also moves cell-to-cell via auxin transport proteins

made in shoot --> to high [ ] in roots

auxin moves cell-to-cell transport: chemiosmotic model or acid growth hypothesis

auxin charged anion in cytoplasm IAA-

in acidic cell wall some auxin uncharged IAAH

IAAH cross plasma memb into cell where it deprotonated IAA-, can exit only w/specific auxin transporters PIN

auxin moves cell-to-cell transport: chemiosmotic model or acid growth hypothesis

auxin stimulates ATPase/proton transport into cell wall

this acidification loosens cell wall and it can expand - pressure released and water can enter until cell expands and pressure potential = solute potential

auxin growth & acid growth hypothesis

- region of cell elongation: auxin transport stimulates plasma membrane proton pumps, lowering pH in cell wall

- which activates expansion enzymes that break polysaccharide cross links b/w cellulose microfibrils

auxin growth & acid growth hypothesis

- increasing voltage potential also enhances ion uptake into cell (lowers water pot. inside cell) causing osmotic uptake of water

- uptake of water into cells with looser walls elongates the cell

cytokinins: cell division/differentiation

made in roots

produced in actively growing tissues like roots, embryos, fruits

works w/auxin: ratio cytokinin:auxin important in specifying root v. shoot cell differentiation

cytokinin and auxin control organogenesis in tissue culture

tobacco leaf disc in sterile culture dishes on medium of various hormones

different [ ] --> roots and shoot

[cytokinin]=[auxin] --> undifferentiated

cytokinin:auxin ratio

high auxin, low cytokinin --> roots

low auxin, high cytokinin --> shoots

same auxin & cytokinin --> nothing

brassinosteroids

induce cell elongation/division in stems

similar in structure to animal sex hormones

dwf4 - A.t mutant defective in brassinosteroid synthesis

synthesis or signaling mutants?

spray w/hormone

gibberellins GA

induces seed germination

promoting factors: light, GA

GA & seed germination

water imbibe in seed -- release GA from embryo signals seed to break dormancy, germinate

cell respond to GA: synthesis digestive enzymes, hydrolyze stored nutrients in endosperm, a amylase

sugar/nutrients consumed during growth of embryo into seedling

during germination, GA induces expression of nutrient-mobilizing enzymes

breakdown of starch in endosperm initiated by GA produced by embryo or

GA added during malting process of barley seeds

water washes away ABA (inhibits germination)

GA promotes growth through cell expansion & division

induces expression of cell-cycle regulatory proteins cyclins

promotes elongation by cell wall loosening and stabilizing orientation of cortical microtubules (help direct growth)

GA responses: stem elongation

A. t mutants in GA synthesis or signaling

abscisic acid ABA

promotes seed dormancy/inhibits seed germination

inhibitory: ABA; promoting: light, GA

seed dormancy

survival value, ensure seed will germinate in optimal conditions:

- ABA levels up 100x during seed maturation

- high levels ABA in seed- production of special proteins, help seed withstand dehydration (part of maturation)

- water washes ABA, germination

maize mutant in ABA signal transduction

mutants in ABA signal transduction causes precocious germination:

- embryos that germinate while seed still on plant

- ABA cannot transduce its signal to inhibit embryo growth

ethylene

- gaseous hormones

- main effects: 1) fruit ripening 2) leaf abscission/senescence (programmed cell death)

- response to mechanical stress

- gas -- effects can be transmitted to other parts of a plant to other plants

ethylene & fruit ripening

burst of ethylene production in fruit triggers ripening

commercial gassing of tomatoes

ethylene causes leaf abscission

leaves fall off trees in fall

causes abscission in neighboring plants

ethylene & triple response

allows growing shoot to avoid obstacles (rocks in soil) as it elongates

increasing triple response:

1) slowing of stem elongation

2) stem thickening

3) curvature to enable horizontal growth

(when plants wounded - more ethylene production)

A. t ethylene triple response mutants

ein mutant - insensitive, tall even w/ethylene

eto mutant - overproducing, response even w/o ethylene

ctr mutant - constitutive, receptor/signal transduction mutant, response w/ethylene inhibitor

light

-direction, intensity, wavelength (colors)

-action spectrum: relative response of biological process to diff. light wlengths, use to test which wlengths of light affect:

phototropism, repression of hypocotyl elongation, germination, flowering time

different light qualities perceived by different photoreceptors effects different processes

1) phototropins (blue)- bend towards light

2) cyptochromes (blue)- de-etiolation, no light=hypocotyl elongation

3) phytochromes (red/far red)- flowering time

photoperiodism-flower induction
photomorphogenesis- de-etiolation and photoperiosdism

action spectra --> phototropism mediated by blue light perception

phototrophic bend toward light caused by photoreceptor cryptochrome, sensitive to blue light

A. t mutants impaired in phototropism

encode photoreceptor: phototropin

CRY & PHY

photoreceptors are proteins linked to chromophores that absorb light

A. hy (hypocotyl) mutants = light-insensitive

light (red/blue) inhibits hypocotyl elongation in WT plants

Hy mutants are impaired in red or blue light perception or signal transduction

structure of phytochrome: red/far red receptor

2 identical subunits- polypeptide dimer

chromophore- coval. attached R/FR light absorbing molecule

domain 1- photoreceptor activity (receive)

domain 2- kinase activity (absorb)

phytochrome holoprotein=polypep. dimer + cov. attached chromophore (absorber)

phytochromes exist in 2 photoreversible states

conversion of phytochrome P_r (inactive) form to P_fr (active) form by red light triggers developmental responses (seed germination, flowering control)

experiment: action spectrum for light induced germination of lettuce seeds

red light increased germination (activates phytochrome)

far red light inhibited germination (inactivates phytochrome)

response depended on last flash

effect of light on biological clock

phytochrome conversion Pr to Pfr mark sunrise (low FR), sunset (FR enriched light)

provide biol. clock w/env. light cues

photoperiod- relative length of night/day

env. stimulus to detect time of yr

photoperiodism- physio. response to photopd
flowering time

circadian clock in plants

24 hour

exists in absence of light

light can reset when rhythm begins

circadian clock gates signaling pathways: flowering

flowering gene (FT flowering times)

short --> long day
flower growth

photoperiod control of flowering involves phytochrome

short day: long night, (crysanthemum in Fall)

long day: short night, (iris in Spring)

flash of light

critical period

reversible effects of red and far red on photoperiodic response

critical dark period

FT = florigen: flower promoting signal

in shoot apical meristem

gravitropism

response to gravity

shoots up, roots down

plants may detect gravity by settling of statoliths

specialized plastids containing dense starch grains

bend toward gravity

thigmotropism

response to touch

occurs in vines and climbing plants

tendrils wind around solid support (grape vines)

thigmotropism: mimosa

- rapid leaf movements in response to mechanical stimulation

- examples of transmission of electrical impulses called action potentials

A. t also sensitive to touch

weekly tocuhing = shorter plants, activation of touch-induced genes

environmental stresses on plant survival/growth/reproduction

- salt
- cold

- heat

- pathogens

plant defense against pathogens

- 1st line of defense: physical barrier, skin (epidermis/periderm)

avirulent pathogens makes signal (Avr=signal) recognized by plant R gene (receptor) - host can mount response

signal molecule (ligand) from Avr gene product of bacterial pathogen
receptor coded by R allele of plant - plant mounts resistant response

if bacteria has specific Avr gene allele recognized by plant R gene - plant responds

disease progression occurs if there is no avr:R gene interaction

- no avr: plant diseased

- avr & no R: plant diseased

- pathogen & no R: plant diseased

no gene-for-gene recognition bc of one of the above 3 conditions, pathogen will be virulent, causing disease

Avr:R gene recognition mounts hypersensitive response HR against an avirulent pathogen

1) avr-r recognit.

2) signal transd. -> HR response: lesions to kill bacteria + infected cells

3) dying plant releases salicylic acid signal

4) signal distributed

5) chemical initiates signal transd. pathway

6) systemic acquired resistance SAR activated

About this deck

By: Fariya Islam
Textbook:

Biology with MasteringBiology? (with WebCT Access Code Card -- Generic) (8th Edition)
Created: 2011-05-12
Size: 59 flashcards
Views: 4

About StudyBlue

“Simply amazing. The flash cards are smooth, there are many different types of studying tools, and there is a great search engine. I praise you on the awesomeness.”
Dennis