chapter 23 plant physiology

8/18/2019 Chapter 23 Plant Physiology

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BY: REEN

apter . Tropisms and

NasticMovement:

OrientingPlants in

Space


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TROPISM

the turning of all orpart of an organism ina particular directionin response to an

external stimulus. hese tropic

responses ma! either"e positi#e ornegati#e.


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Phototropism

is often deas a respounilateral

"ut can aloccur in pthat recei#from all si


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Phototropism

he magnitude of a light graacross an organ such as a coleopdependent on optical properties o

tissue as %ell as di&erences in inclight.


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coleoptilesOrgans such a

coleoptiles apfunction as ligpipes. his methat light app

the tip' for exa%ill "e transmthrough the coto cells furthethe organ.


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Phototropism: A l!e"light Response

()*+s• ,ro"a"ilit! of the chrom"eing a photoreceptor.

()-+s

• Suggestions that photoreare la#in molecules.

• Phototropin/ a 0a#o

pigment responsi"le


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Phototropism orients aplant #or optimalphotos$nthesis he singular impact of phototropism is

orients gro%th and leaf angle to%ard inlight in order to maximi1e light interceptphotos!nthesis.

,lants also use "lue light to control stopening and facilitate gas exchange as %to relocate chloroplasts %ithin the cell.


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,l

usligcohi

a#rechs mce


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L2ENCE RES,ON

C2R3ESluence response cur#es are geno"tained "! monitoring the respof the organ to di&erent total amof light 40uence5' usuall! "! usinsingle 0uence rate "ut varying t

presentation time.


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6nitial rise to$rst pea78

restricted to

the apex ofcoleoptiles

Reduced positi#eresponse: "endinga%a! from the light

Another rise inresponse to light8

extends moreto%ard the "asalregion of the

coleoptile


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Bunsen/Roscoe

Reciprocit! La%States that the product of a photochemicreaction is determined "! the total amouenerg! presented' regardless of 0uence rpresentation time.

he complexities of second positi#e cur#are due to su"se9uent e#ents in the signtransduction chain.


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E ,OORO,6CRES,ONSE 6S AR6B2

O A LAERALRE;6SR6B26ON O;62S6BLE A2


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Cholodn!/=ent

h!pothesisormulated in the late ()>+s as acom"ination of the ideas of N. Choloand . =. =ent in an attempt to expphototropism

States that unilateral illumination ina lateral redistri"ution of endogenouauxin near the apex of the organ.


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S!stematic Ree#aluaof the Cholodn!/=eh!pothesis "! =. R

Briggs


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RE?2LA6ON BY A A@O BL2E/SENS663E

LA3O,ROE6NS


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Phototropin,hotoreceptor for phototropism.

(>+7;a plasma mem"rane protein isphosphor!lated "! "lue light and conin the same area most responsi#e to

Extensi#e characteri1ation pro#ed thprotein is a 7inase that autophospho

in "lue light.


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N, ( or the Non/phototropich!pocot!l (

Encodes the (>+7;a protein'

=as a mutant isolated in Ara"idopsifailure to exhi"it phototropism and l

the (>+7;a protein. he N,( holoprotein %as su"se9ue

renamed phototropin ( 4phot(5 "ecaits functional role in phototropism.


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,hot ( has t%o 0a#inmononucleotide 4@N5

chromophores,hot ( photosensor! domain

has distincti#e domainscalled LO3 4light' ox!gen an

#oltage5> LO3 domains asites that "ind to

ma7e ,hototro

responsi#e to li


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Phot % Phot 2

• irst positi#e

cur#ature• Second positi#e

cur#ature• Second positi#e

cur#ature

• Stomatal

opening

• Stomatal

opening• A#oidance mo#t

of chloroplastsunder high lightintensities


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,OORO,6N AC636Y AN;S6?NAL CA6N

(. Autophosphor!lation of phototropina signi$cant role in the phototropicresponse' pro"a"l! "! initiating aphosphor!lation cascade.

>. ,hototropins ma! "e in#ol#ed in geregulation.


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&RA'ITROPISM

is the directionalgro%th of a plantorgan in response

to a gra#itational$eld %here rootsgro% do%n%ardsand shoots gro%

u %ards


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&ravit$

Omnipresent and non#ar!ing

Constant magnitude

can "e detected onl! "! the mo#

of some structure or structures %the cells


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&RA'ITROPISM IS MOR(T)AN SIMP*+ ,P AN-

-ONOrthogravitropic root and sho

the primar$

a/is align p0ith the direco# gravitap!ll.

diagra#itropic Organs %hich g


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plagiogravitropic Organs orieat some

intermedia

angle 1et04 and 54 tvertical6

agravitropic Organs th


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?ra#itational stimulation 4stimulus 9uantit! or is the product of the intensit! of the stimulus athe time o#er %hich the stimulus is applied:

d t a

%here a is the acceleration of mass due to gra4in g5

t is the time 4in seconds5 o#er %hich the stimuapplied.

&ravitational

Stim!lation


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minimum dose re9uired to inducegra#itropic cur#ature.

hreshold dose %ill #ar! depending the organism or experimental condi

Threshold -ose


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6s the minimum duration of stimulation reinduce a cur#ature that is Dust detecta"le.

is the inter#al "et%een the presentation ostimulus and the actual de#elopment of cu

Presentation Time

Reaction Time


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6s the minimum stimulus intensit!re9uired to induce a response.

hreshold intensities ha#e "eendetermined for a #ariet! of plant orgunder di&erent experimental condit

Threshold Intensit$.

occurring "e


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7 Phases o# Root

&ravitropismoccurs %ithin perhaps one sof orienting a root o& the #eand in#ol#es "ioph!sicalmechanisms 4e.g.' pressuresensing the direction ofgra#itational pull.

occurring "e( and (+ secfollo%ingreorientationin#ol#es thecon#ersion o"ioph!sical s

to a "iochemsignal.

occurs "et%een (+seconds and (+minutes ofreorientation and

in#ol#es aredistri"ution of auxin%ithin the root tip.


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the gra#it! detectingportion of the root cap.

consists of cells rich indense am!loplasts:organelles that are $lled%ith starch grains.

Col!mella


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Starch/Sh!pothe

?. a"

and E.Nemec

&ravit$ Perception

Statostarch


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Are a group of statoliths 4starch gracontained %ithin a mem"rane.

6n #erticall! oriented roots theam!loplasts reside at the lo%er endeach columella cell' to%ard the root

Am$oplasts


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(. ?ra#itropism is generall! a"sent in planspecies that ha#e no starch grains oram!loplasts.

>. here is a strong correlation "et%een thof starch sedimentation and presentatio

Am$oplast as the

gra#it!/sensingmechanism


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*. Loss of starch "! hormone treatmenmutation is accompanied "! a loss ofgra#iresponse.

-. Am!loplasts can "e displaced "! a hgradient magnetic $eld in place of gra#

Am$oplast as the

gra#it!/sensingmechanism


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hori1ontal orientation of the shoot or rooinduces a lateral translocation of auxin tolo%er side of the organ.

Auxin redistri"ution %ould "ias the gro%tfa#or of the lo%er side such that negati#egra#itropic organs 4e.g.' coleoptiles and s%ould turn up%ard.

Redistri!tion o#

A!/in


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the higher auxcontent on theside of the roo

inhi"its elongarelati#e to theside and the rocur#es do%n%

Redistri!tion o#

A!/in


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Roots at a hori1ontal position' the thcolumella cells on the lo%er side of root depolarize and those on the upside hyperpolarize.

stretch/acti#ated ion channels %ouldresponsi"le for the o"ser#ed changemem"rane potential in the columell%hich in turn %ould lead to the as!m

Changes in memranepotential


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it has "een sho%n that p of the rooapoplast decreases from p . to -%ithin > minutes of gra#istimulation

hese p changes in the root capprecede auxin/related p changes inelongation 1one "! a"out (+ minute

p) changes

Calci!


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Calci!m

,6N t i


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PIN protein *ocation Impor( Apical end of

cells in thestele

responsfor deli#the aux

stream root ap

,6N proteins

,6N t i


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PIN protein *ocation Impor> • root cap

• Epidermaland cortical

cell

mediat"asipetstream

auxin tthe celelongat1one.

,6N proteins

,6N t i


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PIN protein *ocation Import* Lateral %all

of thecolumella

cells

di#erts t0o% of auxin

laterall!centrifugto%ard tperipher

,6N proteins

NASTIC MO'(M(NTS


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Nastic mo#ements are plant mo#ements toccur in response to en#ironmental stimulunli7e tropic mo#ements' the direction oresponse is not dependent on the dir

o# the stim!l!s.

Some of the most spectacular plant mo#eare nastic mo#ements.

NASTIC MO'(M(NTS

( i t


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is the do%n%ard"ending of an organ'commonl! petiolesand lea#es %hose

tips are inclinedto%ard the ground.

(pinast$

) t


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Re#erse response of epinast!'%hich is said to "e induced "!gi""erellins.

he up%ard "ending of a leaf or other plant part' resulting from greater gro%th of the lo%erside than of the upper side.

)$ponast$

h t


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hermonast!

6s a nastic mo#ethat is associatechanges in temp

thermonastic moare permanent afrom alternatingdi&erential gro%t%o surfaces of tpetals.

@ t


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urgor @o#ements

(. leisurel! rh!thmic leaf mo#ementsn!ctinastic plants'

>. #er! rapid seismonastic mo#emenlimited num"er of species' and

*. thigmonastic or thigmotropic curlinthreadli7e appendages in clim"ingand #ines.

N+CTINASTIC


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N+CTINASTICMO'(M(NTS8night clos!re9All n!ctinastic responses

depend on re#ersi"leturgor changes in thepul#inus.

he extensor region isformed "! motor cellsthat lose turgor duringthe "ending mo#ement'

GG

ION *,;(S AN-


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ION *,;(S AN-R(S,*TIN& OSMOTIC

R(SPONS(Smotor cell #olume changes are due toosmotic %ater upta7e 4or loss5 as a resion accumulation 4or loss5 across the cmem"rane.

S%ollen extensor cells are characteri1ehigh protoplasmic HI and lo% apoplas

Role of ,otassium


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Role of ,otassium

HI exchange across the plasma mem"raoccurs through HI channels and that thechannels can "e regulated "! changing tmem"rane polarit!.

;epolari1ation of the mem"rane opens tchannels and allo%s HI to mo#e out of tdo%n its electrochemical gradient.

S(ISMONAST+


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S(ISMONAST+

a nastic mo#ement inresponse to a mechashoc7 rapid folding olea0ets of the sensiti

due to changes in tupressure caused "! #

three essential


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three essentialcharacteristics of the

seismonastic response(. he rapidit! of the response.>. 6t follo%s the GGall/or/none principle'

means that there is no o"#ious rela"et%een the intensit! of the stimulu

the extent of the response.

*. Excitation is propagated from the pstimulation.


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chapter 23 plant physiology

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