plant response to stress-1226620207280901-9

7/26/2019 plant response to stress-1226620207280901-9

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Plant Response to Stress

BC39P- Plant

Biochemistry

Dr. W. McLaughlin


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Stresses

External conditions that adversely aect

gro!th" develo#ment" or #roductivity$tresses trigger a !ide range o #lant

res#onses%& altered gene ex#ression

& cellular meta'olism

& changes in gro!th rates and cro# yields


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Types of Stress

Biotic - im#osed 'y other organisms

Abiotic - arising rom an excess or deicitin the #hysical or chemical environment

& Biotic and a'iotic stresses can reduceaverage #lant #roductivity 'y ()* to +,*"

de#ending on the cro#


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Plant Response to Abiotic Stress

arising rom an excess or deicit in the #hysical

or chemical environment


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Environmental conditions that can

cause stress

!ater-logging

drought high or lo! tem#eratures

excessive soil salinity

inadeuate mineral in the soil too much or too little light


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Phytotoxic compounds

/one


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Resistance or sensitivity of plants

to stress depends on:

the s#ecies

the genoty#e develo#ment age


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Ho plants respond to

environmental stress


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Stress resistance mechanisms

0voidance mechanisms&

#revents ex#osure to stress 1olerance mechanisms

& #ermit the #lant to !ithstand stress

0cclimation& alter their #hysiology in res#onse stress


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Stress resistance


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!han"es in "ene expression to

stress

0 stress res#onse is initiated !hen #lants

recogni/es stress at the cellular level$tress recognition activates signal transduction

#ath!aysthat transmit inormation !ithin the

individual cell and throughout the #lant

Changes in gene ex#ression may modiygro!th and develo#ment and even inluence

re#roductive ca#a'ilities


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Plant response to stress


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Re"ulation of plant stress

responses

Abscisic acid #ABA$

%asmonic acidEthylene

!alcium


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&ene expression results in:

2ncrease amounts o s#eciic m40

Enhance translation$ta'ili/e #roteins

0ltered #rotein activity

0 com'ination o the a'ove


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Stresses involvin" ater deficit

Water related stresses could aect #lants i the

environment contains insuicient!ater to meet'asic needs


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Environmental conditions that can

lead to ater deficit

drought

hy#ersaline conditions lo! tem#eratures

transient loss o turgor at midday


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'actors that can affect the

response of a plant to ater deficit

duration o !ater deiciency

the rate o onset i the #lant !as acclimated to !ater stress


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Tolerance to drou"ht and salinity

smotic ad5ustment&

a 'iochemical mechanism that hel#s #lantsacclimate to dry and saline conditions

Many drought-tolerant #lants can regulate theirsolute #otentials to com#ensate or transient orextended #eriods o !ater stress 'y ma6ingosmotic ad5ustments" !hich results in a netincrease in the num'er o solutes #articles#resent in the #lant cell


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(smotic ad)ustment


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(smotic ad)ustment

smotic ad5ustment occurs !hen the

concentrations o solutes !ithin a #lant cellincreases to maintain a #ositive turgor

#ressure !ithin the cell

1he cell actively accumulates solutes and as a

result the solute #otential 7s8 dro#s"#romoting the lo! o !ater into the cell


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Solutes that contribute to osmotic

ad)ustments


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!ompatible solutes #osmolytes$

Com#ati'le solutes tend to 'e neutrally

charged at #hysiological #" either non-ionic or/!itterionic" and are excluded rom hydration

shells o macromolecules.

& 2n contrast" many ions can enter the hydration shellso a #rotein and #romote its denaturation


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!ompatible ions


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(smolytes

Mem'rane-associated carriers and

trans#orters are #ro'a'ly involved indierentially distri'uting osmolytes !ithin

the cell and throughout the #lant


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Proline

distri'ution o #roline in osmotically

stressed #lants involves a trans#orter t!oArabidopsiscD40 encoding #roline

trans#orters !ere cloned 'y unctional

com#lementation


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Proline * "lycine betaine

:lycine 'etaine accumulation in osmotically stressed#lants resulted rom increased rates o synthesis"

!hereas" !ith #roline" synthesis and cata'olisma##ears to 'e co-ordinately regulated in res#onse to!ater stress

:lycine 'etaine is synthesised and accumulated 'y

many algae and higher #lants and is not 'ro6endo!n 'y #lants:enetic evidence indicates that accumulation o

glycine 'etaine #romotes salt tolerance


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+annitol

the reduced orm o the sugar mannose and is

'roadly distri'uted among #lants salt stress inhi'its sucrose synthesis and

#romotes accumulation o mannitol

mannitol concentrations increase in res#onse

to osmotic stress


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+annitol

mannitol accumulation a##ears to 'e regulated'y com#eting #ath!ays and decreasing rates omannitol consum#tion and cata'olism

2n celery" salt stress inhi'its sucrose synthesis'ut does not seem to aect the en/ymes thatsynthesise mannitol

$alt stress also do!n-regulate ,A.-dependent mannitol dehydro"enase" theen/yme that oxidises mannitol in celery


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Trans"enic plants

transgenic to'acco andArabidopsis#lantsengineered to ex#ress the E. coligene or 40D;-de#endent mannitol-


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-Pinitol

cyclic sugar alcohol" is a ma5or solute in

mem'ers o the Pine =amily and Bean =amily its concentrations are higher among halo#hytic

s#ecies and those ada#ted to drought.

in leaves" #initol is localised to the chloro#last

and cystol 'ut not in the vacuoles


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(smotin

a'undant al6aline #rotein

discovered in cultured to'acco cells that had'een acclimated to >?+ mM 4aCl

molecular si/e o ?(-6Da

localised in the vacuole

classiied as a patho"enesis-related7P8

#rotein


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(smotin

1ranscri#tion o an osmotin gene is induced 'yat least


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(xidative Stress

xidative stress results rom conditions

#romoting the ormation o active oxygen

s#ecies that damage or 6ill cells


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Environmental factors that cause

oxidative stress

air #ollution 7increased amounts o o/one or sulurdioxide8

oxidant orming her'icides e.g. #arauat dichloride heavy metals drought heat and cold stress !ounding A light intense light that stimulate photoinhibition


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(xidative stress


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Reactive oxy"en species #R(S$

=ormed during certain redox reactions and

during incom#lete reduction o oxygen or

oxidation o !ater 'y the mitochondrial or

chloro#last electron transer chain

$inglet oxygen" hydrogen #eroxide" su#eroxide

anion" hydroxyl and #erhydroxyl radicals


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(/one and oxidative stress

ydrocar'ons and oxides o nitrogen 74"

4?8 and sulur 7$x8 react !ith solar A

radiation to generate o/one 738.

/one is a highly reactive oxidant


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The ne"ative effects of o/one on

plants

decreased rates o #hotosynthesis

lea in5ury reduced gro!th o shoots and roots

accelerated senescence

reduced cro# yield


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(/one ama"e

alters ion trans#ort

increases mem'rane #ermea'ility inhi'its ;-#um# activity

colla#ses mem'rane #otential

increases Ca?;

u#ta6e rom the a#o#lasmxidative damage to 'iomolecules


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Resistance to o/one

tili/es either avoidanceor tolerance

0voidance involves #hysically excluding the#ollutant 'y closing the stomata" the #rinci#al

site at !hich o/one enters the #lant

1olerance - 'iochemical res#onses that induce

or activate the antioxidant deence systemand#ossi'ly also various re#air mechanisms


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Tolerance to oxidative stress

Stress conditions, antioxidants and antioxidant enzymes

Antioxidant or antioxidant enzyme Stress condition

Anionic peroxidases Chilling, high CO2

Ascorbate peroxidase Drought, high CO2, high light intensity, ozone, paraquat

Catalase Chilling

Glutathione Chilling, drought, -irradiation, heat stress, high CO2, ozone, SO2Glutatione reductase Chilling, drought, high CO2, ozone, paraquat

olyamines De!iciency o! ", , Ca, #g, #n, S, or $% drought, heat, ozone

Superoxide dismutase Chilling, high CO2, high light , increased O2, ozone, paraquat, SO2


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Salicylic acid and ethylene

/one ex#osure results in increased amounts o ??"!hich stimulate the #roduction o $0

esults in a transient increase in the num'er otranscri#ts that encode defence-related secondarymetabolitese.g. #hytoalexins" cellular 'arriermolecules e.g. lignins" callose" and extensins" P#roteins e.g. 7


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Heat Stress

1he ty#ical res#onse to heat stress is a

decrease in the synthesis o normal #roteins"

accom#anied 'y an accelerated transcri#tion

and translation o ne! #roteins 6no!n as heat

shoc0 proteins7$Ps8


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Heat shoc0 proteins


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Heat shoc0

may arise in leaves& When trans#iration is insuicient

& !hen stomata are #artially or ully closed and

irradiance is high

may arise in germinating seedlings

& When the soil is !armed 'y the sun may arise in organs !ith reduced ca#acity or

trans#iration e.g. ruits


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Resistance or sensitivity of plants

to heat stress

Duration

$everity o the stress$usce#ti'ility o dierent cell ty#es

$tage o develo#ment


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Acclimation to heat stress


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!lasses of HSPs

Protein class Size (kDa) Location

&S'(( '((-'') cytoplasm

&S*( +(-*) cytoplasm,

&S.( /*-.' , cytoplasm, mitochondria

&S/( '(-/( chloroplasts, mitochondria

sm&S '0-1( cytoplasm, chloroplast, , mitochondria


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Plant Response to Biotic Stress

im#osed 'y other

organisms


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Patho"en attac0 strate"ies

necrotrophy" in !hich the #lant cells are 6illed

biotrophy" in !hich the #lant cells remain alive hemibiotrophy" in !hich the #athogen initially

6ee#s cells alive 'ut 6ills them at later stages

o inection


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'ailure of a patho"en to cause

disease

1he #lant s#ecies attac6ed is una'le to su##ortthe lie-strategy o the #articular #athogen

1he #lant #ossesses #reormed structural'arriers or toxic com#ounds

Deence mechanisms are activated such that

the invasion remains locali/edEnvironmental conditions change and the

#athogen #erish


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Successful patho"en infection *

disease occurs:

nly i the environmental conditions are

avoura'le

2 the #reormed #lant disease deenses are

inadeuate

2 the #lant ail to detect the #athogen

2 activated deense res#onses are ineective


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Preformed defense: Secondary

metabolites

Plants #ossess dierent secondary meta'olites

!ith antimicro'ial #ro#erties

may 'e #resent in their 'iological active orm or

may 'e store as inactive #recursors that are

converted to their active orms 'y host

en/ymes in res#onse to #athogen attac6 ortissue damage


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Secondary metabolites

#re-ormed inhi'itors are the saponinsand the

"lucosinolates


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Saponins

:lycosylated com#ounds" classiied as eithertriter#inoids" steroids" or steroidal glycoal6aloids

0 'iologically active triter#inoid sa#onin ound inthe roots o oat #lants" avenacin A-1" is highlyeective against the root inecting 1a6e-allungus" a ma5or #athogen o cereal roots

1his #athogen aects !heat and 'arley" 'ut notoat #lants


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plant response to stress-1226620207280901-9