Plant Movement

8/19/2019 Plant Movement

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Plant Movement Plant movement is the result of irritability protoplasm, which is sensitive and respond to internal external stimuli.Unicellular plants or lower plants like many algae can freely move in water. Higher plants are firmly fixed in the soil

and therefore the movement in some organs only change their direction or position is called movement of curvature.

Stimulus

"The changes in the environment which induces a change in the plant is called stimulus."

Response

"Reaction of the plant to the stimulus is called response."

Irritability

"The fundamental property of protoplasm by which is meant its ability toappreciate and respond to change in their environments."

Types of Movement

1. Turgor Movement

These movements are caused by change in the cell volume due to turgor changes and are reversible.

xample is rolling up of leaves in dry weather.

!. Growth Movement

"rowth movement are the changes in the position of plant organs due to enlargement of cells or due to increase in

number of cells. The growth movement are irreversible, i.e. the plant parts cannot come back to the original position.

(i) utonomic or !pontaneous

These movements are independent of any external stimuli for example, in twig plants, the tip of the stem grows at

une#ual rate in different segments and thus causes the twining around the support. These movements are also

called Notation.

(ii) Paratonic Movements

They are caused by external stimuli. $epending on the direction and types of response, the Paratonic %ovements areclassified into following categories&

a. Tropic Movements (Tropism)

b. Tactic Movements (Taxes)


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c. Nastic Movements (Nasties)

(a) Tropic Movements

These are directional movements and are in response to stimulus, which comes mostly from one direction. They

growth may be towards the stimulus or at the specific angle to the stimulus. $epending on the types of the stimulus

the tropic movement are classified as under&

• Phototropism

'timulus is light. (or example shoot is positively phototropism and root is negative phototrophic.

• Geotropism

'timulus is gravity. )oots are positively and shoot are negatively geotropic.

• hemotropism

'timulus is come chemical substances. "rowth of pollen tube towards ovary is the result of secretion of chemical

substance by the ovule.

• #rotropism

'timulus is water. )oots are positively hydrotropic.

• PT$ or Thigmotropism

'timulus is solid surface or touch. Tendrils are positively haptotropic.

(b) %astic Movements

The *astic %ovements are non+directional, i.e. they are independent of the direction of the stimulus. The stimulus

may act from any direction of response will always be same. xamples are opening and closing of buds to formshoot.

• &ntensity (Photonasty)

(or example leaves of some plants like ewelweed become hori-ontal during day and drop at night. (lowers of some

plant open during day and close in the morning.

• Termonasty

rocus flower opens when it is war and closes when it is cold.

• 'aptonasty

/eaves of %imosa Pudica 0Touch+me+not plant drop when they are touched.


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• !eismonasty

2f %imosa Plant is given a sharp blow, its leaflets at the top fold and drop.

(c) Tactic Movement (Taes)

Tactic movement is the movement of an entire cell or organism in response to an external stimulus. The direction of

the movement is obtained by the direction of the stimulus.

Special Terms on Types of Plant Movements

Ben G. Bareja, Feb. 2013

Plant movements do exist. Although, unlike animals, lants are in!aable o" lo!omotion in

that the# are unable to move "rom one la!e to another, or er"orm some "eat like shaking

o" hands as humans do, the# are still !aable o" some "orm o" movement.

Plant organs move to$ard s!ar!e resour!e or other$ise se!ure "ood, or use it as an

adatation to es!ae or minimi%e injur# "rom harm"ul external "a!tors, or ensuredeveloment. &hus, "or examle, the rimar# root moves do$n$ard $here it !an obtain

$ater and mineral nutrients "rom dee do$n $hile the shoot moves u$ard to be exosedto light "rom the sun' !arnivorous lants exhibit movement to tra inse!ts $hi!h are to

be!ome sour!es o" nutrition' !ertain "lo$ers !lose at night to revent !hilling injur# or $henthere is intense heat' the ollen tube $hi!h !arr# serms moves to$ard the ovule $hi!h,

a"ter "ertili%ation, "orms into a seed' and the stomata oen and !lose as a me!hanism toregulate transiration andhotos#nthesis under various environmental !onditions.

For !enturies the subje!t o" lant movement has in "a!t o!!uied the s!ienti"i! !ommunit#"or $ant o" deeer understanding o" lant gro$th and develoment. (no$ing the exa!t

"un!tions o" these movements, their environmental re)uisites, and their !ontrol $ouldbene"it !ro rodu!tion. *t is ossible to a!hieve in!reased gro$th and rodu!tivit# b#

maniulating the environment or the internal !ontrol me!hanisms o" these movements.

Belo$ are some o" the terms used in des!ribing se!i"i! t#es o" lant movements that

o!!ur naturall#+

1. Circumnutation or nutation rotar# or heli!al, or siral attern o" movement o" lant

organs, su!h as stems, tendrils and roots, $ithout h#si!al !onta!t $ith an# obje!t.

http://www.cropsreview.com/plant-nutrients.htmlhttp://www.cropsreview.com/transpiration.htmlhttp://www.cropsreview.com/what-is-photosynthesis.htmlhttp://www.cropsreview.com/transpiration.htmlhttp://www.cropsreview.com/what-is-photosynthesis.htmlhttp://www.cropsreview.com/plant-nutrients.html


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Tropic Movements -movements o" !urvature that resond to the dire!tion o" the external

stimulus. ovement ma# be to$ard the same dire!tion as the stimulus -ositive troism/,

oosite -negative troism/, or at an# intermediate angle -bet$een 0 and 0/. &roi!resonses are due to di""erential gro$th in tissues adja!ent and a$a# "rom the stimulus/+

2. Phototropism the movement o" lant organs, su!h as the stem and !oleotile, inresonse to illumination b# a unilateral -or unidire!tional/ light. Phototroi! resonse ma#

bepositive, as $hen the stem ti bends to$ard a light sour!e, ornegative $hen it bendsa$a# "rom the same light sour!e. eaves normall# orient at intermediate angles $ith

rese!t to light dire!tion and are so des!ribed as plagiotropic.

3. Geotropism or Gravitropism the unidire!tional resonse o" lants to gravitational

ull. ommon terms alied in des!ribing resonses o" lant organs to the dire!tion o"gravitational ull are+ positive gravitropism the organ, e.g. the rimar# root, gro$s

do$n$ard to$ard the dire!tion o" the ull o" gravit# -!enter o" the earth/' negative

gravitropism the organ, e.g. the shoot, moves u$ard in oosite dire!tion to the !entero" the earth' orthogravitropic the arallel alignment o" the rimar# lant axis -rimar#root and stem/ $ith the dire!tion o" the ull o" gravit#' diagravitropic the organ, e.g.

stolons and rhi%omes, gro$s erendi!ular to the ull o" gravit#' plagiogravitropic theorgan, notabl# the lateral stems and roots, orient at some intermediate angle -bet$een 0

and 0/ $ith rese!t to the linear dire!tion o" the gravitational ull' agravitropic theorgans do not resond or has little sensitivit# to the ull o" gravit#.

4. Chemotropism lant movement in resonse to a !hemi!al substan!e. An examle is

the gro$th o" the ollen tube to$ard the substan!es se!reted b# the stigma and st#le andon to the ovule or embr#o sa!. Plant roots elongate to$ard a sul# o" essential mineral

nutrients. A se!ial t#e o" !hemotroism is aerotropism or oxytropism, the bending

resonse to air, arti!ularl# ox#gen.

5. Electropism or Galvanotropism movement o" !urvature in resonse to ele!tri!al

!urrent.

6. Heliotropism also !alled 7solar tra!king,8 is a lant movement in $hi!h the organs o"

lants tra!k the sun a!ross the sk#. &he resonding organ ma# be oriented erendi!ular,arallel, or obli)uel# to the sun9s ra#s. :xamles+ sun"lo$er -Helianthus annuus/ and

!omass lant -Silphium laciniatum/.


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;. Hydrotropism the gro$th o" lant arts, i.e. the roots, in resonse to moisture or$ater. &he root exhibits ositive h#drotroi! resonse b# moving to$ard the $ater sour!e.

nlike troisms, there is no ronoun!ed bending to$ard or against the dire!tion o"stimulus. &hese lant resonses !an be either gro$th movements $hi!h are ermanent or

turgor movements $hi!h are reversible./+

12. Epinasty the bending o" an organ, su!h as etioles, leaves, and edun!les, to$ard theground not due to gravit#. &he bending resonse is due to higher rate o" longitudinal

gro$th at the uer than at the lo$er side o" the organ.

13. Hyponasty the u$ard bending o" an organ -reverse o" einast#/.

14. Hydronasty lant movement -"or examle the oening and !losing o" some "lo$ers/in resonse to atmosheri! humidit#.

15. Nyctinasty the slee movement -oening and !losing/ o" lant organs, su!h as leaves

and "lo$ers, due to da# and night eriods o" dail# rh#thm. &he leaves o" man# n#!tinasti!lants oen during the da# or art o" the da# and !lose at night. ?#!tinasti! movement

!aused b# !hange in light intensit# is !alled photonastic -n. photonasty/ $hile that !ausedb# !hange in temerature is !alled thermonastic -n.thermonasty/.

16. Seismonasty movement in lants in resonse to tou!h as $ell as other "orms o"h#si!al !onta!t or me!hani!al disturban!e su!h as shaking, $ounding, $ind, raindros, and

intense heat or burning. *n the !ase o" the sensitive lant -Mimosa pudica/, a lea"let, lea", orgrou o" leaves raidl# "olds and bends in resonse to the external stimulus.

1;. Thigmonasty or haptonasty lant movement in resonse to tou!h or h#si!al!onta!t $ithout regard to the dire!tion o" the stimulus. &higmonasti! movements are

exemli"ied b# the !losing o" the inse!teating lant @enus9s "l#tra -Dionaea muscipula/ andthe bending o" the glandular hairs o" sunde$ -Drosera s./ as a result o" !onta!t $ith an

inse!t.

=:F:=:?:


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A=C*? . 1


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The movement o plant structures in response to stimuli is veryinteresting. The stimuli might be in the orm o light, touch,chemicals, temperature, gravity or water. Thus the agency or actorthat causes movement is called stimulus. ot all parts o the plantact at the site o perception to stimuli. !nly certain regions orstructures are capable o receiving the stimuli and such structures ororgans are called perception site. The site o perception need not bethe structure that responds to movement. "n act, in many cases thesite o response and the site o perception are di#erent.onetheless, the stimulus has to cross through the plasmamembrane o the cell or cells ound in such structures that receivesthe stimulus. $lasma membrane has all the inbuilt components andthe potentiality to receive stimulus and transmit it into intracellularmilieu or proper response.

There is a time lag between the time at which the stimulus isapplied and the time at which the response begins. This time iscalled reaction time. "t may vary and depends upon the intensity o stimulus and the %ind o response. " the stimulus is wea%, theremay not be any response at all, but i the stimulus is ade&uate or inright &uantity the response is positive. The time re&uired to causethe proper stimulus is called presentation time. !nce the plant body responds to the stimulus say sleeping

movement 'change in the position direction(, structures involvesalways come bac% to their original position. This process is calledrecovery and the time re&uired is reerred to as relaxation time,which again varies rom species to species. " the stimulus isprovided repeatedly the receiver structures do not respond with thesame intensity as the frst instance, but it slows down. This e#ect isdue to atigue. Such behavior is probably due to the loss o samematerial components re&uired or the response. " the stimulation iscontinued at increased re&uency, the plant organs do not respondand behave as i they are dead structures. Such a state is called

Tetanus or extreme atigue. ow it is believed that stimulation'&uantity( causes irritation at the site o perception and the producto irritation are then transported to the site o response, where thestructures respond and perorm movement. )ll these events initiatewith signal, and the receptor that receives the signal becomesactive and induces signal transduction pathway in the cell cells.

There will be a cascade o events that fnally leads to the response.


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$lants endowed with di#erent structural adaptation and di#erentpotentialities exhibit di#erent types o movement either voluntarilyor involuntarily. Based on the behavior as pattern, movement*sstimulus, the plant movements have been grouped into physicalmovements and vital movements. P"ysi#al Movements$

The structures involved in this type o movement are mostlydead. %ero#"asy$ Structures li%e the wall o ruits, sporangia,capsules, have di#erential wall thic%enings. +uring dry weatherconditions, they loose water to atmosphere. Because o this, thethic% walls contract as a result they brea% open along with the line o

dehiscence, where the cell walls are thin andsusceptible. Hy&ro#"asy$ ertain structures, made up o hydrophilic substances, are capable o imbibing water as well. +ueto imbibition o water they swell. +ue to imbibition o waterperistomial teeth in -oss capsules, elators in e&uisetum, etc. showmovements. "n act such movements help in the dispersal o spores. ital Movements$ $lant movements due to the activity o living structures are called

vital movements. They are urther classifed into di#erent %inds. "nsome plants, particularly unicellular algae, the entire cell movesrom place to place or rom one position to the other or theprotoplasm by itsel shows continuous ux by physicaldisplacement. "n others, where the plant body is fxed in the soil,certain structures show bending or curvature movements./urthermore, some o the movements are auto regulated andpropelled by innate mechanisms but other movements are inducedby stimuli.

"n this case the entire living cell is involved either in the movemento protoplasm or the entire body o the plant cell rom one place toanother. These movements may be autonomous and induced. Autonomous$ Protoplasmi# Streamin'$


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$rotoplasm is not a static uid. 0ith all its complicated structuresthe entire protoplasmic uid is in constant sweeping motions. Thesestreaming movements can be observed under high resolution lightmicroscopes. /or example, in the cells o staminal hairs o tradescantia, the streaming is locali1ed and in each o these areasthe direction is cloc%wise or anticloc%wise. Tiny particulates areseen swept along with the stream in a particular direction andparticular directed path. Such compartmentali1ed movements are%nown as yclosis. But in 2lodea and other plants, the protoplasmshows uniorm movement, but in one direction. !ne can observechloroplasts movement along the cytoplasmic streaming. Suchmovements are called 3otational -ovements. $rotoplasmic streaming is due to the activity o contractile proteins

ound associated with other microtubule networ% ound within thecytoplasm. "t is an active process microtubules play an importantrole in such intra cellular movements. These structural elementscontain motor proteins and they perorm the movements. Theenergy re&uired or this process is derived rom )T$ molecules.

These movements help in the even distribution o chemicalcomponents. )nd the protoplasmic movement across theplasmodesmata brings about the transportation o materials romone cell to another. )uxin has been ound to accelerate the rate o protoplasmic movements. )ddition o colchicine and cytochalasin B

totally inhibits the movement, thereby indicating the involvement o microtubules and microflaments. 3espiratory poisons li%e +$,4, also inhibit the movement, thus suggesting that these areactive movements. 2ven amoebae show such movements. /or thatmatter all living cells exhibit autonomous movements. Paratoni# movements$


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These movements are stimulated by external agents li%e light,chemical heat, etc. Hence they are called taxis or tactic

movements.www.tutorvista.com

P"otota#ti# Movement$ 5nicellular algae suspended in a testtube moves towards the light source to obtain solar energy orphotosynthesis. " the light is very intense, they move away rom

light6 this may be due to the raise in temperature. The movement inthese cases is due to locomotor structures li%e agella or cilia. Thebeating o these structures propels the cells towards light. Theagellar activity utili1es )T$. Hence these movements are active.


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www.imagejuicy.com

("emota#ti# Movement) ertain agellated or non7agellatedbacteria move towards the source o ood by lashing their agella orby tumbling. "n these cases, the stimulus is chemicals. Similarly,the movement o spermato1oids in lower organisms li%e Bryophytesis directional, because the chemicals released by mature archegoniaprovide the chemo stimulus. Sensing the chemicals, the agellatedspermato1oids swim towards archegonia and enter the nec% canaland bring about ertili1ation. T"ermota#ti#$ )gain lower organisms sense the temperature andmove towards the compatible temperature or move away i thetemperature is incompatible. Sensing the change in thetemperature by the plants is autonomic but the cells always showdirectional movements.)ll the above mentioned movements involve signal transductionpathway. 2lucidation o these pathways at molecular level isnecessary and exciting.

Movements of (urvature$ $lants with their fxed plant body cannot move rom place to place,but certain structures show bending movements which may bedirectional or non7directional or they may be autonomous orinduced. However, some o the plant movements are due to the

http://www.imagejuicy.com/images/plants/a/adiantum/21/http://www.imagejuicy.com/images/plants/a/adiantum/21/


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growth o the cells or due to change in the turgidity o the cells.Based on the above eatures movement o curvature has beenurther classifed such as8

Autonomi# Gro*t" Movements$ Nutatory) $lant structures li%e tendrils and stem tips exhibitdi#erential growth alternately. This results either in sideward orcircular movements. ertain sub cylindrical stems 'at or angular(due to di#erential growth at the sides show 1ig 1ag movement. !nthe other hand, cylindrical tendrils in search o getting a hold on to asubstratum, a waves o growth activity ta%es place around thetendril. That is why it appears as i it is moving in circles. Such type

o movements is called circumnutatory movement. The growthactivity o the above said structures is in7built and they show arhythmic pattern. 0hether the hormonal uxes are responsible orthis type o growth movement or any other innate mechanisminvolved is not %nown. But the treatment o these stems with )B)inhibits the movements, indicating that these are phytohormonemediated.

!p"emeral Movements$

+uring the development o leaves and oral organs, the growthpattern determines the growth direction o the structures. /orexample, leaves expand laterally by continuous radial divisions andexpansions. Similarly sepals and petals because o continuousgrowth o cells at the base on the inner surace ma%e the oweropen. The hypocotyl hoo% o the bean seed straightens up becauseo one sided growth due to expansion cells on that side. Suchgrowth movements are called 2phemeral. !nce the movementreaches certain stage, the bending movement stops.

Autonomi# Tur'our Movement$ +esmodium gyrans '"ndian telegraphic plant( and 2leiotis sorriahave trioliate compound leaves. "n the ormer case, central leaetis larger and straight. But the lateral two leaets are smaller whichshow regular upward and downward movements. Such movementsare observed only during daytimes but not at night. Such rhythmic


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gyratory movements re&uire about 97: minutes or the completiono one cycle. This is due to autonomic turgour changes in the cellsound in the swollen pulvinus o the leaets. How light brings aboutturgour changes or is it due to phytochrome mediated responses orhormonal responses is not clear.

www.biology;isc.weebly.com Paratoni# Nasti# Movements$ $aratonic movements are induced by external stimuli. 0hatevermay be the point or direction o stimulus applied the movement o

the plant structures is already predetermined and they exhibitmovement only in one direction. -ost o the movements areturgour movements, but growth movements are not uncommon. /orexample, the opening o hypocotyl hoo% o germinating beanseedling, opening o circinately coiled leaves o erns and cycas arethe examples o growth mediated nastic movements. +i#erentialdistribution o growth hormone in the adaxial 'dorsal( suraces o theleaves6 it is this that is mainly responsible or such growthmovements. These movements are permanent and they do notshow temporary day and night uctuations.

P"otonasty$ -any leguminous plants, with their pulvinous bases,show characteristic sleeping movements and they show a rhythmicpattern o opening o lea7lets in the day and closing in the eveningwith a precision o a cloc%. "n act, such movements are attributedto circadian rhythm operated by an inbuilt biological cloc%.

http://biology4isc.weebly.com/plant-movement.htmlhttp://biology4isc.weebly.com/plant-movement.html


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www.s10.lite.msu.edu

The photonastic mechanism has been explained on the basis i hormonal distribution in the cells o the pulvinus. +uring daytimes,auxin is ound in greater amount at the upper region o the pulvinus,because o this the cells become more turgid and lea lets open.

The same process is reversed during night because o theredistribution o auxin to lower side which causes olding by the wayo turgour changes. "nvestigations into such movements have shown that these arephytochrome mediated, because red and ar red lights are verye#ective in opening and olding o leaets. $hytochrome being anexcitable molecule in response to light it is %nown to bring aboutchanges in the permeability o membranes. Thus the turgourmovements bring about so called sleeping movements. )dded to

this the change in the permeability also involves the e


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www.mentalfloss.com

The plant +rosera consists o leaves arranged in a rosette pattern. The lea blades are at and rac%et shaped. The upper surace is

made up o colorul glands which secrete stic%y ?uice, where youvery high activity o golgi complex. There are a large number o sensitive tentacles spread out at the margins. The tentacles have asensitive broad base and a terminal glandular globosely head whichalso secretes ?uice. "n sunlight, these structures glisten li%e dewdrops6 hence the name sundew plant.

http://mentalfloss.com/article/18044/hunting-strategies-carnivorous-plantshttp://mentalfloss.com/article/18044/hunting-strategies-carnivorous-plants


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http8@@www.puchen.org@ "nsects, mista%ing the glistening ?uice or honey, settle down onthese suraces where their legs get stuc% because o the stic%y ?uiceand they cannot escape. )s insects have nitrogenous compounds intheir body, they di#use and sensiti1e the tentacles, becausenitrogen compounds act as signals, in response, they immediatelyold upon the insect and the same gets trapped. "n this casenitrogenous compounds ound in insects provide the stimulus. !nthe other hand, i a metal piece is placed, tentacles do not old,instead i a piece o meat is dropped, the tentacles closeimmediately. However, ater digestions, tentacles open slowly andthis process ta%es ew hours. Such chemonastic movements areound in utricularia, >enus y trap, etc.


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www.top-10-list.org

T"ermonasty8 /lowers in Tulips and rocus are very sensitive totemperature variations. )ccordingly the accessory whorls may beclosed or open. These movements are %nown to be due to turgour

changes rather than growth movements. Siesmonasty$ -imosa pudica 'Touch me not plant(, Biophytum,eptunia oleracea, +esmanthus are very sensitive to touch, rathershoc% generated by the touch. -imosa pudica has pinnatelycompound leaess with a swollen pulvinus at the base every leaet.

Touching the leaves is believed to cause a seismic shoc% to theleaves and this stimulus is transmitted all along the rachisdownwards and reaches the basal pulvinus o the lea. Theirritability caused, due to touch is actually transmitted through sieve

tubes, because these are the only structures which are capable o transmitting the stimulus as ast as A.97C cm@sec. The materialbasis or the transpiration stimulus has been ound to be )B) and)B) mediated ions. )s the )B) ions di#use along the rachis, it alsotrans7di#uses into pulvinus o the leaets.

http://top-10-list.org/2010/05/11/top-ten-insect-eating-plants/http://top-10-list.org/2010/05/11/top-ten-insect-eating-plants/


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www.prezi.com

http8@@www.gettyimages.in@

http://prezi.com/kgcmctn9wkfz/cell-communications-mimosa-pudica/http://prezi.com/kgcmctn9wkfz/cell-communications-mimosa-pudica/http://www.gettyimages.in/http://prezi.com/kgcmctn9wkfz/cell-communications-mimosa-pudica/http://www.gettyimages.in/


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Basal turgor movements6 http&33fabacademy.org3http8@@en.wi%ipedia.org@

The mechanism o upward movement o pinnules and downwardbending o the entire lea at the base is now considered as due tothe activity o the motor cells ound in the pulvinus. )natomicalstudies indicate that at the lower region the pulvinus consist o thinwalled parenchymatous cells, which are loosely arranged with lot o intercellular spaces. ells also contain many contractile vacuoles.

The cell membranes and vacuolar structures have contractileproteins. These vacuoles are loaded with 4= ions when the leaetsare open. These motor cells are highly sensitive and active. Such

cellular organi1ation is also ound at the upper region o the pulvinusound at the base o the leaets. 0hen the stimulatory hormone )B), which is also called as stresshormone 'released due to irritability( reaches these speciali1ed cells,they are stimulated to contract, collapse and extrude water and 4=ions into intercellular spaces. This action brings about the


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collapsing o cells on this side and the lea downwards. Similarlymechanism is involved in the olding o leaets upwards. Therecovery ta%es place within 97AC minutes. The opening processta%es place by active pumping in o 4= ions bac% into cells. The4@)T$ase pumps are supposed to be ound in the cell membranes.

This active process re&uires energy. " the production o )T$ isinhibited by respiratory inhibitors li%e +$ or 4 recovery does notta%e place. " plants are %ept is continuous dar%, they ail to produceany siesmonastic responses, which suggest the siesmonasticmovements are )T$ dependent active processes. Paratoni# Tropi# Movements$

These movements are due to growth activity. The curvature

movement is always directional, either towards the stimulus or awayrom the stimulus. -ost o these are phytohormone mediatedmovements. P"ototropism8 $hototropic movement is mostly exhibited by stemtips6 or they always bend towards the light source. The actionspectrum o the light has been ound to be at blue light. The bluelight is now %nown to bring about une&ual distribution o activeauxins than the total auxin content. The pigment or absorption o blue light has been ound to be ryptochrome. The older view o

destruction o auxin and the lateral movements o auxins inresponse to light has been more or less ruled out. The di#erence inthe &uantity o active auxin brings about di#erential growth and alsocurvature. +etails o this process have been explained elsewhere.


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www.blog.gurukpo.com

www.scoop.it

http://www.blog.gurukpo.com/plant-movementshttp://www.scoop.it/t/plant-biology-teaching-resouces-higher-education/p/4015625709/2014/02/09/plant-cell-review-phototropism-growing-towards-an-understanding-of-plant-movementhttp://www.blog.gurukpo.com/plant-movementshttp://www.scoop.it/t/plant-biology-teaching-resouces-higher-education/p/4015625709/2014/02/09/plant-cell-review-phototropism-growing-towards-an-understanding-of-plant-movement


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"n plants, auxin unctions as a master controller o development, pattern ormation,

morphogenesis, and tropic responses. ) sophisticated transport system has evolved to allow

the establishment o precise spatiotemporal auxin gradients that regulate specifc

developmental programs. ) critical unresolved &uestion relates to how these gradients can

be maintained in the presence o open plasmodesmata that allow or symplasmic exchange

o essential nutrients and signaling macromolecules. Here we addressed this conundrum

using genetic, physiological, and cell biological approaches and identifed the operation o

an auxin7DSL: eedbac% circuit that regulates the level o plasmodesmal7locali1ed callose in

order to locally downregulate symplasmic permeability during hypocotyl tropic response.

This system li%ely involves a plasmodesmal switch that would prevent the dissipation o a

orming gradient by auxin di#usion through the symplasm. This regulatory system may

represent a mechanism by which auxin could also regulate symplasmic delivery o a wide

range o signaling agents. http8@@www.cell.com@developmental


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$hototropism o the sporangiophore 'ruiting body( o the 1ygomycete, $hycomyces

bla%esleeanus 'photograph by +.S. +ennison(. www.uni7marburg.de

$hototropic movement in in one o the ungi called $hycomycsblacesleeanus

The apoprotein cry in association with avins bring aboutphotoptropism, it gets activated by absorbing blue light andautophosphorylation o ser@thr residues, that leads to transport o ions to one side and brings about bending movement. Geotropism8 Drowth o roots towards soil and the stem away romthe soil in response to gravitational orce is an inbuilt mechanismendowed in stem tip and root tip o the plant. urvature movemento roots towards gravitational is termed as positive geotropism andthe movement o the stem away or against gravitational orce iscalled negative geotropism. However in some plants, rhi1omes andrunners grow parallel to the surace o the soil. Such a response iscalled digeotropism. The obli&uely growing stems show plagiogeotropism '/or details reer the hapter )uxin(.

The di#erential response o stem tip and root tip to the samegravitational orce is due to their di#erent innate structural andunctional potentials. Though both structures are derived rom thesame embryonic cell and possess the same genetic potential they

behave di#erently probably this is because o the programming o process driving the development o in such structures. Themechanism o geotropism has been explained on the assumptionthat di#erential responses are due to di#erent concentrations o auxins. The concentration o auxin that promotes the growth o thestem apex inhibits the growth o the root tip. !n the other hand, theconcentration o auxin that is e#ective in the growth o the root tipis not ade&uate or the growth o the stem tip. This conceptsuggests that stem apex re&uires higher concentration o auxins orits growth and roots re&uire low levels o auxins as optimal

concentration or the normal growth. " a seedling is placed on the soil hori1ontally, due to mass action o gravitational orce, auxins move downwards in both stem apex androot apex. "n the stem apex, as more and more o auxinaccumulates at the lower suraces the cells ound in this region growaster than the upper cells, thus the stem curls upwards. But in

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roots, as more o auxin accumulates at the lower region, the higherconcentration inhibits the growth o cells ound at the lower surace,but the cells at upper surace grow aster because o lowerconcentration o auxin. /urthermore, the root cap being thepreceptor o gravitaropism produces )B), which on translocationbasipetally, reaches the lower cells by sheer gravity. 0ith theaccumulation o more and more o )B) at lower cells, the growth o these cells is urther inhibited, but the cells at the upper region grownormally and thus bring about the downward growth curvature orroots. ("emotropism8 $ollen tubes and certain ungal hyphae exhibitchemotropic movements, because they grow towards organicnutrient rich media. "n the case o pollen tubes, the direction o

growth is dictated by the chemical gradient generated by theembryo sac. This chemical gradient greatly acilitates the growthmovement o pollen tube towards the embryo sac, irrespective o the position o ovules in the ovary. Hy&rotropism8 Drowth o roots towards water is calledhydrotropism. 0hatever may be the positions o seedlings, asshown in the fgure, the roots curl towards water. This positivegrowth curvature might be due to greater water potential, probablyacts as the motive orce or the growth o root tip. Stem and other

structures are insensitive to water and they do not show anyhydrotropic curvature movements. T"i'motropism8 $lants with wea%er stem spread around andre&uire support or their growth. -any o the climbers havedeveloped hoo%s, pads and tendrils or getting a frm oot hold ontothe substrate6 which may be a roc% or a wooden stic% or any suchhard structure. /or example, in the case o tendrils o cucurbita andother species the terminal regions are sot, tender. The terminalregion o the tendrils consists o a number o fne pits, which are

highly sensitive to touch. 0hen the tendril comes in contact withany supporting structures, the pits get stimulated and the same istransmitted a ew millimeters basally. This results in the di#erentialgrowth o the tendril on one side. This causes the curvature in thetendrils and fnally they coil around the stem the supportingstructure. The time re&uired or such coiling ater the stimulus is

?ust E to 9 minutes. !nce the initial reaction is set in at the basal


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region, the tendrils coil round the support and thus draw the climbernearer to the support. "t is suspected that auxins and )B) areinvolved in thigmotropic curvatures. )B) inhibits the growth o thecells in the region o the contact and auxins stimulate the growth o the cells on the opposite side and bring about eh growth curvaturecalled Fcoiling*.

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Plant Movement