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CHAPTER 2 

## icarf. * Understanding the Minimal Toxicity of Lead in Plants DAVI D E . KOEPP E Department

of Agronomy, University of Illinois, USA 1 . INTRODUCTIO N Th e presenc e o f

indigenou s leadi

n th e earth' s crus t

a t concentration s averaging 1 6 ^g/g soi l (D e Treville , 1964) , it s recent depositio n nea

r highway s an dothe r

pollutan t source s (Koeppe , 1977) , an dth e knowledg e tha t lea di s highly toxi c t o variou s physiologica l processe s hav e brough t int o focu s ove

r th e las t 15-2 0 year s th e questio n of th e effect s o f lea do n highe r plants . Thi s ha s seemeda n especially relevant

questio n whe

n consideratio n ha s been give n t o th e fact

tha t certai n highe

r plant s probabl y suffe r alea dinsul t tha t i s greater than tha t impose don any othe r

living organism . Recent

man-effectedlea

ddeposit s hav e been nea r highway s through th e burnin g of

leade dgasoline s by automobile s (Canno n an d Bowles , 1962) , i

n soil s nea r building s painte dwit

h leade dpaint s (Getze /

al., 1977) , o n agricultural land s fertilize dwit h sewag e sludg e (Hinesly et al., 1972 ) an din variou s localize dsituation s nea r meta l ore deposits , mining , smeltin g an dothe r

industrial operation s (Antonovic s et al., 1971) . Pesticide s containin g lea

dhave , dependen t

o n usage , lef

t substantia l lead residue s i n orchard s an dothe r

agricultura l area s wher

e they hav e been spraye d(Schuck an dLocke , 1970) . 

### 2 . UPTAK E O F LEA

D B Y PLANT S Lea di s availabl e t o plant s fro

msoil an daeroso l sources . Th e actual uptak e an dassociatio n oflea d wit

h plant s i s affecte

d(t o varyin g degrees ) by almos t al l environmenta

l factor s (Zimdah l an dKoeppe , 1977) . In aver y genera l wa y i t ha s been observe dtha t

th e lea dconten t (i n and/o r on ) of plant s 5 5

>. . ^*:iJs«aW. . .• J «*fta--rtJto. ; ,jtiaaifciw!*r"S*a^ ^

## <K fc 

## ' ; > ^ v ','' : . 5 6 Effect of Heavy Metal

Pollution on Plants

~ % generally reflects th e extent of leadinsult , o r

wha t can b e terme d biologically-availabl e lead . Th e chemica l for moflea d a s i

t impact s plant s i s of critical importance , however, ' a s thi s i s afacto r i n movement s int o plants , in translocatio n an din th e toxi c effectivenes s of lea dwithi n th e plant

Plant s growin g nea

r highway s ar e usuall y expose dt o more leadtha n mosToflTe r location s (z.imdah l an dHassett , l*) J /7) . Ih e sourc e o f

thi s leacG s primaril y fromaeroso l automobil e exhaus t particulate s a s lea

dhalogen s wfiic h ar e no t

water soluble!(Rolf

e an dReinbold . 1977, . Eve n lea d incorporate dint o soil s i s nearl y alway s tightl y boun dt o organi c o r colloida l materials , o r

in aprecipitate dform ; al l o f which serv e t o reduc e th e uptak e - of ' lea dinf o plan t root s by conventional processe s involvin g solubl e ioni c movemen t (Zimdah l an dKoeppe , 1977) . Thes e observation s ar e supporte d by experiment s which sho w tha t increase dcation-exchang e capacit y (Baumhard t

an dWelch^JSI^Mille r

et al., 1975a ; Mille

r et al., 19756 ; Mott o et al., 1970),4owere3j) H (Co x an dRains , 1972 ; Lagerwerf f et al., 1973 ; Mille

r et al., 1975a ; Mille

r et al., 19756 ; Zimdah l an dFoster , 1976 ; Joh n an dVa

n Laerhoven , 1972) , organi c matte r (Liebhard t

an dKoske , 1974) , phosphoru s (Hassett etal., 1976 ; Mille

r an dKoeppe , 1971 ; Rolfe , 1973 ; Zimdah l an dFoster , 1976 ; Sun g an dJeong , 1977 ) an dothe r lead

precipitatin g anion s (Rolf

e an dReinbold , 1977 ; Karamano s et al., 1976 ; Sung , 1976

) reduce dth e uptak e o

f lea dint o plan t

roots . Aside fromth e genera

l lo w availabilit

y t o plant s of

soi l lead , th e movemen t o r translocatio n o

f lea dfro mabsorbin g roots , o r

roo t hairs , i s apparentl y impede db y anumber of biochemica

l and/o r physica l processe s involvin g lea

d binding , inactivatio n and/o r precipitation . Earl y wor

k b y Hammett (1S»28 ) showe dlea

dt o b e localize din th e cell wall s an dnuclei o f absorbin g roots . Tandle r

an dSolar

i (1969 ) foun dtha t

lea dwa s boun dt o orthophosphat e ion s withi n th e nucleolu s o f onio n roo t

tip s fixed in alea

d solution . Othe r

studie s hav e shown tha t

lea di s ofte n foundi n th e cytoplas m o f cell s associate dwit

h electron-dens e precipitate s localize di n membranou s inclusions , vesicle s or organelles . Malon e et

al. (1974 ) reporte d that th e root s o

f corn plant s expose dt o lea din hvdroponi c solutio n accumulate dasurfac e leadprecipitat e an dlea dcrystal s in th e cell walls

T They hypothesize dtha t

dictyo'som

e vesicle s wer

e responsibl e fo

r an activ e extrusio n o f

apparentl y solubl e lea

dfromroo t

cells . In corn , an encase d deposi t o f lea dsurrounde dby th e vesicula r membran e wa s observe dto migrate towardth e outsid e o f th e cel l wher e th e membran e surroundin g the deposi t fuse dwit h th e plasmalemma . Th e material surroundin g th e deposi t the n fuse dwit h th e cel l wall , resultin g i

n aconcentratio n oflea d deposit s i n th e cel l wal l outsid e th e plasmalemma . Simila r deposit s wer

e als o observe d 

### 1Lead: Understanding the Minimal Toxicity of

Lead in Plants 5 7 i n stem s an dleave s which woul dsuppor t th e hypothesi s tha t

onc e translocated , leadcoul db e 'extruded ' fromcell s throughou t th e plant . Th e impactio n o n plan t

leave s o f aeroso l leadparticle s fromautomobil e exhaus t ha s been wel

l documente d(se e Zimdah l an dKoeppe , 1977 fo r review) . Th e uptake int o plan t cell s of suc h leadha s been asourc e of muc h controversy . Zimdah l an dKoepp e (1977 ) conclude dfromaliteratur e revie w tha t little , i f any , aerosol-deposite dlea di n natur e i s accumulate d throug h th e cuticula

r barrie r of higher plan t leaves . Th e bryophyt e Rhytidiadelphus squarrosus di dtak e u p lea dfromtraffic exhaust , a s electron-dens e precipitate s wer e recognize dwithi n cytoplasmi c vesicle s o r vacuoles , chloroplasts , mitochondria , microbodie s an dplasmodesmat a (Ophu s an dGullvag , 1974) . Canno n an dBowle s (1962 ) reporte dtha t leadwa s associate dwit

h th e above-groun dportion s of

gras s grow n clos e t o road s in concentration s a s hig h a s 3000 ug/

g dry weigh

t of plan t matter . Schuck

an dLock e (1970 ) an d Wedding et

al. (1975 , 1976

) determine dtha t

substantia l leadparticulat e matter wa s deposite do n plan t

surfaces . Such depositio n wa s dependen t upo n th e characteristic s of

th e lea f surfac e a s wel

l a s th e windspeed , and , t o alesse r extent , othe r

environmental conditions . Seve n time s more lea

dwa s deposite do n pubescen t

sunflowe r leave s tha n o n glabrou s tuli p poplar leave s (Weddin g et

al., 1975) . These , an dadditiona l experiment s (Weddin g et al., 1975 ; Carlso n et

al., 1976 ) foun dn o re-entrainmen t of mono dispersedlea

dparticulate s fromalea f surfac e a t

win dspeed s u p t o 6- 7 m/s , eve n thoug h thes e wind s cause darapi dfluttering of th e tes t leaves . Wjtil e topicall y applie dlea

d wa s minimall y remove db y wind , i t wa s readil y remove d by simulate drai n conditions . A fallin g mis t wa s mor e effectiv

e tha n larg e raindrop s i

n leadremova

l (Carlso n e

r al., 1976) . Th e smalle

r drop s of mis t coalesce dint o large r

drops , ra n towardth e lea

f edg e an dfel

l off ; while th e larger , les s effectiv e drop s splashe dof

f a t impact . Itj s almos t

certai n tha t

plant s growin g nea

r highway s posses s elevate d Iga d levels , probabl y in aparticulat e form , associate dwit h leave s an dstems . Eve n i f thi s lea di s no t absorbe dint o th e plan t

cells , it s presenc e a s atopica l coatin g o n lea

f surface s mus t

b e considered . Doe s i t

hav e effect

s o n plan t processe s o r

thos e of th e microorganism s co-inhabitin g thes e plan t surfaces ? 3 . EFFECT S • Th e ubiquitou s presenc e oflea d i n soils , complicate dan daccentuate dno w b y man-effecte

dadditions , make s question s of leadeffec

t o n plant s of5 8 Effect of'Heavy Metal

Pollution on Plants critica l importanc e i n formulatin g bot h short

- an dlong-ter men vironmenta l policy . Th e importanc e o f thes e question s i s amplifie db y tw o possibl y conflictin g observation s tha t hav e bee n i n th e literatur e fo r man y years . Th e first

i s tha t lea di s highl y toxi c t o man y organism s unde r certai n conditions . Secondly , eve n thoug h ver y larg e concentration s o f lea dar e presen t i n localize dplan t

environments , an deve n associate di n o r o n plants , ther e ar e fe

w report s o f

lead-induce dtoxi c effect s o n plant s grow n i n natura l ecosystem s tha t hav e bee n severel y impacte dwith lead . > Thi s sectio n wil l conside r th e effect s o f

lea do n plant s whe n i t

i s availabl e fro mrootin g medi ao r

atmospheri c sources . I t wil l als o discus s som e o f th e studie s whic h specificall y as k jquestion s o f

th e effect s o f

lea do n in vitro physiologica l processes . Finally , th e associatio n oflea d wit h plant s wil l b e summarize dfro mth e large r ecosystem-foo dchai n vantag e point . 3.1 . Distributio n Whe n a n analysi s i s mad e o f ho w lea dma y influenc e plan t growth , question s relatin g t o uptake ! pattern s an dmechanism s o f depositio n (localization ) withi n th e plan t ar e ofte n th e firs t

t o b e considered . Al l studie s sho w tha t mos t lea dimpacte da t

th e roo t o r lea f surfac e remain s a t

tha t site withou t movement . Whe n root s ar e treated , very littl e lea di s translocate d int o edibl e fruit s (Baumhard t an dWelch , 1972 ; Te r

Haar , 1970 ; Zimdah l an dKoeppe , 1977) . Earl y studies , includin g thos e b y MacLea n et al. (1969) , Pag e an dGanj e (1970) , Aarkro g an dLipper t (1971) , an dman y others , hav e foun dth e lea dconten t o f fruits , vegetable s an dgrai n t o b e les s tha n i n othe r

vegetativ e plan t

parts . I n plant s expose dt o lead-contaminate d rootin g media , th e root s alway s contai n lea da t concentration s con siderabl y greate r

tha n othe r

above-groun dtissues . Heves v (1923. . i n on e o f th e earlies t

studie s o f

thi s problem , conclude dtha t lea di s boun di n th e root s subsequen t

t o roo t treatment , an dtha t

suc h bindin g serve s t o protec t th e remainin g plan t

part s fro minjury . Recen t studie s utilizin g variou s type s o f microscopica l an dhi.stochem.ca l technique s suppor t th e concep t

tha t larg e amount s o f

lea dar e boun dt o th e outsid e o f roots , th e 'free space' , a s wel l a s cel l wall s throughou t

th e root s (Malon e et

al., 1974) . Studie s wher e roo t metabolis mha s bee n controlled , sugges t tha t th e outsid e an dfree-spac e bindin g i s passiv e (Gore n an dWanner , 1971) . Les s i s know n abou t th e energetic s o f

th e intracellula r

lea ddeposit s associate dwit h organelle s an d vesicles . I t

seem s unlikel y tha t

th e dictyosom e vesicl e lea ddeposit s i n cor n reporte db y Malon e et

al. (1974 ) ar e passive , however , thei r studie s di d no t see k t o answe r

thi s questio n directly . Sharp e an dDenn y (1976 ) observe d tha t th e plasmalemm aacte da s abarrie r t o lea di n Potamogetonpectinatas.

## Ik^imf e vw^'mszvgtf^^S^/^^yLead: Understanding the Minimal Toxicity of

Lead in Plants 5 9 The movemen

t o f lea donc e i t i s clearl y withi n th e functiona l metaboli c region s o f th e root s ha s bee

n har dt o evaluate . Whethe r lea dmove s a s a

n ion , or a s achelate dcomplex , i s areasonabl e questio n bu t no t easil y answered . Chelatio n of

leadwit h EDT A doe s facilitate leadmovement . Wallace et al. (1976 ) an d Pate l et

al. (1977 ) observe dtha t

chelatin g agent s modifie dth e uptak e o

f heav y metal s fro

mthe ' soil , an d Marte n an d Hammon d(1966 ) foundtha t

th e presenc e o

f EDT A increase dlea

duptak e b y plants . Tanto n an dCrowd

y (1971 ) reporte dtha t

lead-EDT A entere droot s onl y i n th e shor t root-hai r zone , an dthat

th e roo t endoderm s appear s t o limit th e movemen t o f th e lea dchelate int o th e transpiratio n stream . Onc e i n th e transpiratio n stream , however , the y suggeste dtha t leadmovedpassively , an dtha t i t accumulate da t

th e evaporativ e surface s o f th e leaf . Th e possibilit y tha t lea dmove s int o an d withi n plant s in anaturall y chelate d for mi s suggestedfro

mwor k at th e Universit

y of Illinoi s wher

e naturall y exude d compound s wer

e foundwhich chelate dlea d(Gadd e an d Laitinen , .1972) . Onl y afe w report s are availabl e which asses s th e questio n o f th e chemica

l identit y o f lea di n plants . On e compound , lea dpyrophosphate , ha s bee n identifie di n th e root s of

pint o bea

n wher e th e lea dconcentratio n wa s 3 2 40 0 ug/ g dr y weigh t (Zimdahl , 1972) . Ther e ha s als o bee n areport tha t lea dorthophosphat e (Pb 3 (P0 4 ) 2 ) wa s presen t in soybea

n root s (see Zimdah l an d Koeppe , 1977) . Other studie s by Brown an d Slingsby (1972 ) wit h th e liche

n Cladonia rangiformis detecte dlea dboun dt o insolubl e anioni c site s i n exchangeabl e form , bu t externa l t o th e cell membranes . Th e potentiall y tight

an d nearly irreversibl e bindin g o f lea dt o mos t exchangeable surface s reporte db y soi l scientists , an dthos e report s referre d lo her e wit h plan t roots , adequatel y se

t th e stag e an dpredict , a priori, wh y plant s sho w s o littl e respons e t o potentiall y toxi c concentration s o f lea di n th e plan t environment . Numerou s experiment s hav e bee n conducted , however , whic h hav e quantitate dth e effect s of lea do n both genera

l yield parameter s (includin g gros s vegetativ e yieldan d grai n yield ) an d mor

e specifi c o r integrate dwhole-plant

physiologica

l processes . Thes e studie s wil l be considere di

n th e next sectio n o f thi s chapter . 3.2 . Aeroso

l Effect s Lea dparticle s deposite do n lea f surface s coul db e hypothesize dt o affec t plan t processe s i

n tw o genera

l modes . First , intracellula r physiologica

l processe s coul db e affecte

di f lea di s solubilize dan d move s into th e cell s o f th e leaf . I n Sectio n 2 th e possibilit y of thi s seems t o have bee n6 0 Effect of Heavy Metal

Pollution on Plants experimentall y discounted . Carlso n et al. (1976 ) mad e measurement s o f lea dmovemen t

fro mleaf

surface s (fumigate dwit h 1-3-w mdiamete r

PbCl 2 aerosol) , t o non-fumigate dplan t tissues . I n tw o experiment s a t least , severa l fully develope dleave s o f soybea n plant s wer e selectivel y fumigated . Followin g apost-fumigatio n period , th e lea dassociate dwit h th e fumigate d leave s wa s determined , a s wa s th e lea dconcentratio n o f severa l non fumigate dsin k

tissues , includin g newl y develope dleave s an ddevelopin g bea n pods . I n bot h th e abov e experiment s an dathir di n whic h th e lead concentratio n o f

fumigatio n wa s ver y hig h an dcondition s wer e optimize d fo r th e movemen t

o f lea dfro mth e sourc e leaf , negligibl e movemen t

int o and/o r withi n th e plan t

wa s observed . I n corollar y experiment s Carlso n et al. (1977 ) measure dth e rat e o f photosynthesi s o f

leave s afte r

topica l applicatio n o f

PbCl 2 particle s u p t o concentration s o f

700/ig/ g fres h lea f

weight . Photosynthesi s wa s no t reduce dsignificantl y wit h thi s iexten t o f lea f contaminatio n ove r

athre e week post-fumigatio n period . . : Th e questio n nex t

arise s a s t o whethe r

lea dparticle s ma y accumulat e in th e stomat ao f

leaves , thu s affectin g th e abilit y o f th e stomat at o ope n an d clos e diurnall y an dwit h environmenta l stress , suc h a s tha t impose db y wate r deficits . Fliickige r

et al. (1979 ) reporte dtha t

th e diffusiv e resistanc e o f aspe n leave s wa s reduce dwhe n th e surfac e wa s impacte dwit h chemicall y iner t 5-jimdiamete r

silic age l particles . Thei r interpretatio n o f

thi s situatio n wa s tha t particle s o f

aprope r

siz e wil l affec t

plant-wate r

relation s by blockin g stomata , thu s preventin g thei r closur e durin g ho t

an ddr y period s tha t woul db e require dt o preven t drough t injury . Carlso n et

al. (1976 , 1977) , however , argu e tha t 1-3-u mdiamete r

PbCl 2 particle s o n soybea n lea f surface s ar e no t

likel y t o physicall y bloc k stomata . The y poin t

ou t tha t t o physicall y bloc k

onl y 10 % o f

th e stomata l por e are ao f asoybea n lea

f wit h 1-y mdiamete r

PbCl 2 particle s woul drequir e abou t 700 0 w g PbCl 2 / g o f leaf . I n usin g thi s reasoning , an dthei r photosynthesi s rat e studies , the y conclud e tha t

stomata l blockag e wil l no t effec t decrease drate s of photosynthesi s unles s particulat e depositio n reache s extremel y hip, h values . "Othe r studie s o f

physiologica l processe s o f plant s expose dt o ai r pollutio n (includin g lead ) hav e bee n conducte dwit h plant s grow n a t varyin g distance s fro mhighways . A recen t experimen t

b y Fliickige r

et al. (1978 ) ha s correlate dP b collecte di n filters a t varyin g distance s fro ma highwa y wit h growth , peroxidas e activit y an dAT P formatio n in chloroplast s isolate dfro mth e expose dplants . Concentration s o f lead decrease drapidl y fro mth e highway , bein g reduce dt o 3 3 % a t adistanc e o f 1 0 mfro mth e highwa y border . Peroxidas e activit y wa s increase di n plant s7 ~^y m WVLead: Understanding the Minimal Toxicity of

Lead in Plants 6 1 a t 2 man d1 2 mdistanc e whe n compare dt o activit

y i n plant s at

4 2 mand . 18 6 mdistance . Th e formatio n o f AT P in isolate dchloroplast s an dplan t growt h exhibite da

n increasin g inhibitio n wit

h decreasin g distanc e fro

mth e highway ; plant s at

2 mdistanc e wer

e th e mos t

inhibited . Unfortunately , thes e author s wer

e no t abl e t o specificall

y isolate th e effect

s o f lea dfro m othe r pollutio n source s arisin g i

n th e vicinit

y o f highways . Andwhile i t

wa s inferre dtha t dus t an dexhaus t

gase s wer

e responsibl e fo

r th e observe d effects , th e author s suggeste dtha t th e exhaus t

gase s exerte dapredominan t influence . Steenke n (1973 ) directl y fumigated , wit h automobil e exhaust , anumber o f cultivate dplant s in greenhouses , seein g i n certai n situation s letha

l effect s o n olde r leaves , bu t

usuall y only sligh

t effect s o n younger

leaves . Interestingly , i

n complementar

y experiment s wher

e fumigatio n wa s wit

h Pb-fre e automobil e exhaust , th e effect s wer e eve n more sever

e at mos t exposur e levels . Althoug h Steenke n di dfindtes t plant s wit

h P b concentration s o f

35 0 mg Pb/k g dr

y matter , he wa s unabl e t o sho w an y statisticall y significan

t depression s o

f yieldan dgrowt

h du e solel

y t o lead . Smit h (1976) ha s foundtha t

th e lea dburde n of

plant s du e largely t o surface depositio n wa s a s hig h a s 200 x th e baselin e level s fo r unwashe d plants . H e wa s unabl e t o find, however , any acute an ddirec t effect s o f thi s lea do n th e roadsid e biota . Hi s wor k doe s poin t

i n anothe r directio n tha t w e wil l conside r later , tha t

bein g th e potentia l o

f atopical lea

dcoatin g t o exer t asubtle impac t

o n th e microflorao n th e plan t surfac e an dt o have food

chai n effect s ampnne q throug h foragin g insect s an danimals . * 1

3.3 . Whol e Plan t Effect s (Leadi n th e Rooting Medium

) Reports on th e effect

s of lea do n selecte daspect s o

f plan t growt h hav e appearedin th e literatur e fo r ove r 5 0 years . Bot

h growt h stimulation s an d reduction s hav e bee

n reporte dt o resul t

fromvaryin g lea

dconcentration s in th e rootin g media . Growt

h stimulations , mostl y at

lo w lea dconcentrations , hav e bee n reporte dfo

r severa l differen t plant s b y Keato n (1937) , Berr y (1923) , an dother s (se

e Tornaben e et

al., 1977 fo

r review) . Sinc e mos t

of thes e report s cam

e befor e th e definitio n o

f optimal condition s fo

r hydroponi c growt

h o f plants , i t

might b e suspecte dtha t

th e growt

h stimulation itsel

f wa s no t du e t o lead , bu t

possibly t o othe r

ion(s ) mad e availabl e a s aresul t

oflea d salt

treatment s t o th e rootin g media . Numerou s othe r studie s utilizin g lead-amende dhydroponi c cultur e hav e shown a significan t reductio n of

growt h wit h increasin g lea

dconcentrations . Evidenc e ha s als o bee

n presente dtha t

th e magnitud e o

f th e lea deffec t variou s inversel

y wit h th e phosphat e concentratio n of th e nutrien t

solutio n6 2 Effect of Heavy Metal

Pollution on Plants an dwit h th e phosphat e statu s of

th e plan t itself (Mille r an dKoeppe , 1971 ; Rolfe , 1973) . ;. s Othe r example s in which genera l decrease s in growt

h parameter s hav

e been determine dafte

r lea dtreatmen t

in hydroponi c cultur e includ e studie s wit h re dmapl e (Davi s an dBarnes , 1973) , oat s (Fiussell o an dMolinari , 1973) , soybean s (Huan g et ai, 1974) , corn (Carlso n et ai, 1975) , sunflowe

r (Carlso n et

al., 1975) , ric e (Fiussell o an dMolinari , 1973 ; Mukherj i and Maitra , 1976,1977) , lobloll y pin e (Davi s an dBarnes , 1973) , an dgroundsel (Briggs , 1976) . In mos t

of thes e situation s th e tim

e of treatmen t

wa s a significan t variabl e in th e exten t

of th e lead-induce dtoxicity . I n acomparativ e hydroponi c study t o determin e th e relativ e toxicit y o f lea dt o anumbe r

of differen t plants , Fiussell o an dMolinar i (1973 ) determine dth e following sequenc e of decreasin g sensitivit

y t o lead : „ Capsicum annuum > Beta vulgaris > Phalaris canariensis > Vicia sativa > Helianthus annum >Oryza sativa > Triticum vulgare > Avena sativa > Pisum sativum An exampl e o

f th e exten t of th e lea dtoxicit y i s tha t A. sativa, on e o

f the leas t sensitiv e species , showedaM % decreas e i n fres h weight , a23 % decreas e in dr

y weigh t an da2 6 % decreas e i

n chlorophyl l conten t

whe n grown fo r 21.day s i n nutrien t solutio n amende dwit

h 10" * M Pb(N0 3 ) 2 - Merakchiisk aet

al. (1976)

j reporte dtha t

Phaseolus vulgaris (bean) exhibite dreduction s i

n whol e plant , lea

f an droo t fres h weigh t afte r 1 0 days ' treatmen t wit h 10" 5 M PbCl 2 i

n hydroponi c solution . Th e reduction s wer e abou t twic e a s grea

t whe n th e PbCl 2 concentratio n wa s increase dt o 10" 3 M . Wit h th e 1 0 " 5 M PbCl 2 treatment , th e lengt h of th e whol e plan t

wa s reduce

d b y 3 4 % an dth e lengt

h o f th e roo t b y 7 0 % . Lea

f surfac e are awa s reduced 2 6 % , bu t measurement s of

th e lengt h o f th e aeria l par t o f th e plan t an dth e hypocoty l nod e eac h showedincrease s o f 16% . Wit h ric e {Oryza sativa) roo t growt h wa s completely inhibite db y 2 x 10~ 2 M lea

dacetate an dgerminatio n b y 10" ' M lea

dacetate (Mukherj i an dMaitra , 1976) . A

t 10" 3 M lea

dacetate , shoo t

growt h wa s inhibite db

y 9% , wherea s th e inhibitio n of , roo t growt h wa s 46% . Broye r et al. (1972 ) i

n experiment s wit

h Phaseolus vulgaris (bean , var . bus h blu e lake) , Hordeum vulgare (barley ) an dLycopersicon esculentuin (tomato ) observe donly slight reductio n i

n plan t to p an droo t

dr y weigh t following treatment s o

f u p t o 50/i g atom/litr e initia l lea dsupply . Possible reason s fo r th e lack o f observabl e lea

deffec t ma y hav e resulte dfrom.shorte r treatmen t time s an dmuch lowe

r lea dconcentration s ove

r th e entir e fi,Lead: Understanding the Minimal Toxicity of

Lead in Plants 6

3 duratio n of

th e treatmen t

period . Th e author s di dfindmos t of th e lead ^csnciatedwit

h th e root s an dlittl e wit

h th e plan t

tops . Thi s lea

dsorptio n t o th e root s o f barley wa s ver

y rapi dan dno t

influencedb

y temperature . I t

i s ofte n ver y difficul t t o compar e th e tota l amoun t of lea d treatmen t

wit h th e root s o f plants , an dherei n often reside s th e probabl e quantitativ e difference s i

n lead-effectedplan t

response . 'I n other experiments , lea

dsalt s hav e bee

n incorporate dint o anumber of differen t soils . Neithe r

alfalf ano r corn wer e affectedb

y lea dconcentration s : JipTo"212/ig/gi n Chester

silt loa msoi l (Lagerwerf

f et al., 1973) . Soybea

n (Glycine max. L. ) an dcorn (Zea mays L. ) wer e sown in asandy-cla

y soi l andwatere dwit

h fixed concentration s oflea d an dvariou s anion s (Sun g an d Jeong , 1977) . Whe

n th e plant s wer

e harveste dbefor

e flowering they showed no^sign s o

f jgad^toxicit y in spite o f 377 3 /i g Pb/g soih

_Tota l lea

d concentration s in th e plant s di dno t excee d3-6 4 /ig/ g dr y weight . In anothe r stud y wit h 500/ig/g P

b in th e soil , radish , carro t an dspinac h showed considerable uptak e o

f lea dbu t withou t reducin g yieldo r

toxicit y symptom s (Jude l an dStelte , 1977) . Othe r wor k ha s reveale dn o yield reductio n i

n alfalf aan dbromegras s grown o n soil s amende dwit h u p t o 100/i g Pb/g soi l (Karamano s et al., 1976) . I n man y o

f th e mor e recent «Midie s th e define

dpresenc e o

f anion s suc h aTphosphat e an dsulfat e ha s Tourer]lea

duptak e and/o r

effec t (see Sectio n 2) . On e o f th e more significan

t application s of

lea dt o agricultural soil s ha s bee n wit h numerou s othe r

heav y metal s an dothe r

major an dmino r micronutrient s i

n sewage sludge . Wit

h the . ever-present

possibilit y tha t a numbe r o f thes e metal s beside s lea

dmigh t b e toxi c t o plants , i t

ha s no t bee n possibl e t o isolate any distinc t

lea deffect s fromsuc h sludg e applications . I n actuality , th e presenc e o

f s o man y othe r competin g ion s probabl y serve s t o reduce th e uptak e an dany effec t o f lead . Severa

l studie s hav e questioned , however , whethe r combination s o

f heavy metal s tha t

are know n plan t toxin s migh

t "a t certai n concentration s ac t synergistically (o r

antagonisti

cally) . Tw o report s fro

matrac e elemen

t researc h projec t

a t th e Universit

y o f Illinoi s serve t o illustrat e thi s point . In astudy b y Mille r et al. (1977 ) varyin g concentration s o

f lea dan dcadmiu mwer

e incorporate dint o a sand y loa msoi l wit h arelatively lo

w cation-exchang e capacity . In measurements o f

10-3 1 day s ol dcorn shoot s ther e wa s atendenc y fo r soi l lea dt o increas e th e plan t

cadmiu mconcentratio n an dth e tota l cadmiu m uptake . Conversely , soi l cadmiu mreduce dth e tota l lea duptak e an din som e case s lea dconcentratio n o

f th e shoots , Statistical analyse s show tha t bot h lea dan dcadmiu mindividually reduce dcorn shoo t growth , an d tha t ther e wa s apositiv e interactio n o

f th e tw o metal s o n growth . I n anothe r6 4 Effect of Heavy Metal

Pollution on Plants stud y b y Carlso n an dBazza z (1977) , seedling s o f

America n sycamor

e (Plantanus occidentalis L. ) wer e grow n in Drummer

silt y cla y loa msoi l treate dwit

h variou s concentration s o f lead , cadmiu mo r

lea dplu s cadmium . Plan t

growt h an dheavy metal conten t wer e measure dafte

r 9 0 day s o f treatment . Concentration s of both cadmiu man dlea

dwer e increase di

n th e plan t

tissue , an droo t

growth , wood

y stemgrowth , ne

w stemgrowt

h an dfoliag e growt

h Wer e synergistically affecte

dby th e lead

cadmiu mtreatment . Tha t is , th e effec

t o f th e tw o heavy metal s togethe r wa s greater

than th e su

mof th~ y pfT^ct s n f thrTin^jrhij^ljigw y meta i treatmeats . . Researc h wit

h severa l plant s includin g Lactuca sativa L., Raphanus' sativus, Oleifera sp. , Setaria itdlica L. , Raphanus sativus radicula L . and Tagetes sp . by Kraus e an dKaise r (1977 ) assessedth e interactio n oflea d and sulfu r dioxid e fumigation . In thei r studies , neither

th e uptake and translocatio n o

f lead , no r it s effect s o n yieldwer

e influencedby th e sulfu

r dioxid e treatment . ! A s aresult o f observation s of

th e uptak e an deffec

t oflea d o n th e genera

l growt h o f plant s i n th e field an dth e literatur e cite dhere , alon g wit h man y othe r studie s to o numerou s t o mention , th e following concept s hav e emerged . First , tha t

lea di s take n u p by plant s wit

h th e magnitud e o

f uptak e bein g correlate dinversel y t o soi l o r

othe r artificia l rooting-medi a condition s tha t

bin d lead . Suc h bindin g o f lea dreduce s it s activit

y (in~ a physica l chemistr y sense) i n th e soi l o r

rooting-mediu msolution . In othe r words ^ goo dagricultural practic e in monocultura l o r natura l systems shoul dvirtuall y negate th e uptak e an deffec t oflea d unde r

field conditions . I n th e absenc e o

f agricultural disturbance , i t seems tha t

P b uptak e fro

mth e soil woul db e foun donly unde r condition s wher

e th e soil s wer

e ligh t an d ha dlow fertilit

y levels , low organi c matte r level s and/o r

alow cation

exchang e capacity . Eve

n here , wher

e som e lea duptak e i s likely , studie s hav e shown tha t

9 0 % o r more o f th e lea dtake n int o root s i s tightl y boun dthere , riot availabl e to r

translocatio n t o othe r

part s of th e plant , an dno t

a n effectiv e toxin , 'th e cnance s tha t

enoug h lea

dca n b e take n u p b

y any highe

r plan t unde r natura l condition s t o effec t atoxi c respons e see

mremote . Under controlle dlead-treatmen t conditions , toxi c response s influencin g physiologica

l parameter s othe r

tha n genera

l growt h hav e bee n quantitated , an dar e th e subjec t

o f th e next sectio n of

thi s chapter . 3.4 . Specific In Vivo Lea

dEffect s (Leadi n the Rooting Medium

) Thi s sectio n wil

l revie w studiesii n which plant s wer e expose dt o high lea

d concentration s i

n th e rootin g medium , an di n whic h th e respons e t o lea

do f <* 'Lead: Understanding the Minimal Toxicity of

Lead in Plants 65 processe s othe r

tha n genera

l growt h wer e measured . Thes e effect

s migh t b e consideredin vivo a s compare dt o in vitro studie s wher e Pb wa s applie d directl y i n th e 'tes t tube ' t o enzymes , organelle s o r othe r subfractionate d cellula r components . Ga s exchange , particularl y th e uptak e o f C0 2 in photosynthesis , ha s bee n determine dfo

r severa l differen t plan t specie s treate dwit

h differen t concentration s o

f lea dfo r increasin g period s o

f time , Amon g th e plant s teste di n thes e experiments , soybea n (Glycine max. L. ) (Bazza z et al., 19746) , sunflowe

r (Helianthus annuus) (Bazza z et ai, 1975 ; Carlso n et

al., 1975 ; Bazza

z et ai, 1974a) , America

n sycamore (Plantanus occidentalis L. ) (Carlso n an dBazzaz, 1977) , corn (Zea mays L. ) (Bazza z et al., 1975 ; Carlson et al., 1975) , lobloll y pin e (Rolf e an dBazzaz, 1975) , autum n oliv e (Rolf e an dBazzaz , 1975 ) an dspruc e (Kelle r an dZuber , 1970

) exhibite d rprince d rate s o f photosynthesi s wit

h increase dsoi l lea

dconcenTfattons . Lik e mos t o f th e lead-effects experiments , th e effectiv e rooting-medi alea

d\ concentration s wer

e usuall y ver

y hig h a s compare dwit

h th e concentration s \ o f lea dencountere db

y almos t al l plant s growin g naturall y o r in J monoculture . Becaus e o

f th e technique s an dexj)gjir ignt ^ l prnrfflj"ir s ^ involved , fe

w correction s hav e bee

n madeTJetwee

n th e lea dconten t o f th e an dtKeir

_rate s of photosynthesis . On e study makin g thes e

(1974a) wh o reporte dfo r leave s measurements wa s don e b y bazza z et sunflowe r that a t lea f lea dconcentration s of

193 /i g Pb/g dr

y weigh t th e rat e o f ne t photosynthesi s wa s reduce db y 5 0 % . Rolf

e an dBazza

z (1975 ) found n o effec t of P b o n either

photosynthesi s o r

transpiratio n o f

lobloll y pin e (Pinus laedd) o r

autum n olive (Elaeagnus umbellata) a t tissu e con centration s below 6

0 an d72/ig/g dr

y weigh t respectively . At

thes e concentration s photosynthesi s wa s reduce di n lobloll y pin e by 1 1 % an di n autum n oliv e b y 17% . I n othe r

studie s carrie dou t

b y Bazza z an dco worker s (Bazza z et al., 1974a ; Bazza

z et al., 19746 ; Carlso n et

ai, 1975 ; Rolf e andBazzaz , 1975 ) there wa s astron g correlatio n betwee n lead

effecte ddecrease s i

n photosynthesi s an dconcomitan t decrease s i

n rate s o f transpiration . Th e suggestio n fro mthi s i s tha t

decrease s in th e rate s o f whole-plan t photosynthesi s ma

y b e du e t o induce dclosure o f stomat a rathe r tha n adirec t effec t o n th e proces s o

f photosynthesi s residin g directly withi n th e chloroplasts . Thi s poin t ma y b e questioned , however , a s report s ar e availabl e o

f in vitro effect

s of lea do n isolate dchloroplast s (Mile s et al., 1972 ; Bazza

z an dGovindjee , 1974 ; Won g an dGovindjee , 1976) . Th e possibilit

y of in vivo effect

s o f lea do n chloroplast s tha t

ma y b e responsibl e fo r cel l deat h ha s bee

n reporte dafte

r studie s wit

h th e hydrophyt e Ceratophyllum demersum (Rebechini an dHanzely , 1974) . In6 6



### 2 0 r ^ i/fU ) ,-.•-. . 1

160^

. 3 rvN'ff ^ 

## G^ Y to? ' -,< : ,0^^ f 

### £ 

## '•- V 1. 1 Effect of Heavy Metal

Pollution on Plants thi s study , strikin g change s i n chloroplas t fine structur e resulte dfro m growt h i n a n aquati c mediu mcontainin g Pb(NO,) j chelate dwit h EDTA . Lead-expose dlea f

cell s exhibite dareductio n i n gran astacks , areductio n i n th e amoun t

o f strom ai n relatio n t o th e lamella r system , an dshowe dan absenc e o f

starc h grains . • I n bean , however , Yordanovan d Merakchiiska(1976 ) foun dtha t 10" 3 M PbCl 2 stimulate dphotosynthesi s o n aleaf-are abasis , bu t effecte da 15-2 0 % reductio n o n amg-chlorophyl l basis . Thes e author s als o reporte d n o significant

effect o n chloroplas t

lamella r protei n compositio n o r

spectra l propertie s o f

th e pigmen t

system . Th e membrane s o f proplastid s i n th e meristemati c cell s o f

lettuc e roo t

tip s di dsho w destructio n o f th e margina l membrane s afte r

treatmen t

wit h tetramethy l lea d(Heric h an dBobak , 1974) . Th e respiratio n o f

cor n roo t

tip s decrease db v 10-17 % afte r a1- h treatmen t wit h 20m

M lead , an db y 28-4 0 %"after a3- h treatmen t

(Koeppe , 1977) . Thes e respirator y decrease s wer e accompanie db y aconcomitan t decreas e o f

th e energ y charg e o f

th e treate dtissue . Lea dadde dt o asoybea n rootin g medi ao f sand-vermiculite , reduce d po dfres h weigh t

b y 3 5 % wit h dail y watering s o f 30 0 /i M lea d(Huan g et

ai, 1974) . Thi s reductio n wa s correlate dwit h decrease s i n shoot , root , leaf an d nodul e dr y weight ; an dwitf i nodul e ammonia , protei n an dcarbohydrat e content . Decrease s i n th e rat e o f photosynthesi s an dnodul e acetylen e concentratio n wer e als o observed . Pigmen t concentratio n change s i n leave s ar e ofte n avisibl e sig n o f elementa l toxicit y o r

deficiency . I n PbCl 2 -treate d Acer rubrum (re dmaple ) th e relativ e anthocyanin e conten t increase da s muc h a s 270 % (Davi s an d Barnes , 1973) . I n anothe r quantitativ e study , Pb(N0 3 ) 2 i n solutio n cultur e fo r 2 1 day s effecte dadecreas e i n chlorophyl l conten t oi Avena sativa (oat ) b y approximatel y 2 6 % (Fiussell o an dMolinari , 1973) . Othe r researcher s hav e referre dt o th e chlorotic , appearanc e o f leave s followin g lea dtreatment , bu t hav e usuall y no t

quantitate dth e los s o f chlorophyll . I n thes e studie s ther e hav e bee n fe

w attempt s t o correlat e achloroti c plan t appearanc e onl y wit h lea daccumulation . I n astud y b y Walke r

et al. (1977 ) wit h Zea mays L . (corn) , PbCl 2 wa s adde dt o asand y loa msoi l i n concentration s o f 125-250/ig/ g dr y soi l weight . After

20-3 0 day s treatmen t

th e plan t

concentration s o f

boron , manganese , coppe r

an dzin c >ver

e reduce dfro m20-3 9 % . Th e mod e oflea d actio n i n thi s stud y wa s no t questioned . Kanna n an dKeppe l (1976 ) di d observ e i n short-ter mexperiment s wit h pe a(Pisum sativum) seedling s tha t lea di n aHoagland' s nutrien t mediu mwa s highl y inhibitor y t o th e <W

'!•£< •

ft"P.1 4

Lead: Understanding the Minimal Toxicity of

Lead in Plants an dZn 2 + 6 7 absorptio n o

f Fe , Mn 2 + , an dZn 2 + ions . The y reasone dthat

th e inhibition wa s o

f aphysica l nature , lik

e blockin g th e entr

y o r bindin g o f th e ions t o th e ion-carrier . Severa l researcher s hav e measure dth e activitie s o f enzyme s i n generally crud e homogenate s o f

lead-treate dplants . Lea

dacetate ( 6 x 1_0" 2 M^injthe — liqiiif j medi aof

germinatin g ric e effecte

dabou t a50%"decreas e i

n th e activitie s o f proteas e an da-amylas e i

n endosper

mafte r fou r day s (Mukherj i an dMaitra , 1976) . Th e activit y of RNas e wa s reduce db y 17% , bu t tha t of DNase wa s stimulate db

y 12% . A comprehensiv e study o

f enzymes , selecte dnutrient s an dnitrogenou s compound s o

f soybea n leave s following 1 0 day s of Pb(NOf) , treatmen t

i n -Qlulin n r-nitiir p le d Le e et al. (1976 ) t o conclud e tha t lea dcause da

n advance i n senescenc e o

f th e seedlings . At

lea dconcentration s o

f 10 0 /ig/ml , ' lea f respiratio n wa s increase d22 % while severa l enzymes " showedlm e followin g effect s whe n compare dt o zero-leadtreate dcontrols : aci d phosphatase , +23% ; peroxidase , + 154% ; mali c dehydrogenase , +20% ; j-amylase , +280% ; an dglutamin e synthetase , -89% . Under th e sam e lea d treatment

phosphorus , calciuman dnitrat e decreased , bu t tota l fre e amin o acids , solubl e protein , ammoni aan dlea dincreased . I n lead-treate dyoun g cor

n plant s Maier

(1978 ) foun dtha t

th e activit y o f aci dphosphatas e decrease din th e root s bu t increase din th e leaves . In experiments wit

h othe r enzyme s Maier

(1977a) observe dtha t

NAD +

- dependen t malate dehydrogenas e increase din leave s o f Medicago sativa an dZebrina pendula, bu t

decrease din th e Medicago roots . Esteras e analyze dafte r in vivo lea

dtreatmen t

by Maie r (19776 ) increased , or decreased , a s di dit s number o f multipl e forms , wit

h th e lengt

h o f lea d treatmen t an dth e temperature . Severa l investigation s hav e foun dtha t variou s form s o

f lea dproduc e chromosoma

l lesion s o r

othe r disturbances . Include din thes e are tctramethyl lea

deffect s o n Lactuca sativa (Sekerkaan dBobak , 1974) , lea d acetat e on onio n roo t

ti p cell s (Mukherj i an dMaitra , 1976) . an ddi

- an d trialky l lea don onio n roo t

ti p cell s (Allium cepa) i n which spindl e disturbance s wer

e note d(Ahlberg et

ai, 1972) . Ye t another interactiv e effec

t o f lea di s suggeste di

n severa l studies , i n whic h th e hypothesi s i s advance dtha t th e rea l toxi c effec

t o f lea di s no t direc t o n an y cellula r component , bu t

rathe r indirec t b y killin g cell s throug h deprivatio n o

f phosphate . Thi s wa s recently argue db y Schulz e an d Bran d(1978 ) followin

g experiment s wit

h Chlamydomonas. an dhadbee n earlie r arguedwit

h les s dat ab

y Merakchiisk aet

al. (1976 ) i

n studie s wit

h lea d effect s o n Phaseolus vulgaris. "Z^'-J 16 8 Effect of Heavy Metal

Pollution on Plants 3.5 . Lea d Effect s o n In Vitro Plan

tSystem s Numerou s report s fro

mth e animal literatur e hav e shown tha t lea dforms mercaptideswit

h the—S H grou p o

f cystein e an dless-stabl e complexe s wit h othe r amin o aci dside chain s (see Vallee an dUlmer , 197 2 for review) . Lea

d ha s als o bee

n shown t o bin dan dalter th e activit

y o f many membranou s subcellula r particle s includingmitochondria,chloroplasts , nucleotide s and nuclei c acid s an dchromosome s (see Vallee an dUlmer , .197 2 fo r review) . Usin g mitochondri aisolate dfro metiolate dcor

n seedling s Koepp e and Mille r (1970 ) reporte dtha t

PbCl , stimulate dth e oxidatio n o f exogenou s NADH , bu t

inhibite dth e rate:o f

succinate oxidatio n b

y mor e than 80% . I

n areactio n mediumcontainin g sucros e o r KC 1 a s a n osmotican t

th e effec t o f lea do n th e oxidatio n rate s wa s immediate a s wa s th e reversa l o f th e lead

induce dsuccinate inhibitio n ;wit h th e additio n o

f inorgani c phosphate . Inorgani c phosphat e di dno t revers e th e stimulatio n o

f th e rat e of

NAD H oxidatio n b

y lead , possibly suggestin g a n irreversibl e bindin g oflea d o r that lea deffecte da n irreversibl e chang e i

n th e mitochondria l comple x responsibl e fo

r NAD H oxidation . Othe r dat astrongl y suggeste dlead

induce ddecrease s i

n oxidative 1 phosphorylation . I n asubsequen t study wit h isolate dplan t

mitochondri a(Bittel l et

ai, 1974 ) th e concentratio n o

f lea d effectin g a5 0 % inhibitio n of

j succinate oxidatio n wa s no t differen t fro m similarly effectiv

e concentration s of

cadmiu mo r

zinc . Lea d(0- 1 mM ) cause d a n extensiv e increas e in swelling o f mitochondri ai

n areactio n mediu

m containin g KC1 . In bindin g studie s i t wa s observe dtha t

th e maximum capacit y of amitochondrial suspensio n t o bin dlea dwa s nearl y 1 0 time s greate r tha n th e 5 8 n

M o f Cd 2 ; + , Zn 2 + , Co 2 + , Ni 2 + an dMn 2 + bound/m g mitochondrial protein . Th e affinit y wa s als o observe dt o b e ver y high fo r lead . Studie s b

y Goyer an dothe r worker s (Goyer , 1968 ; Goyer an dKroll , 1969 ; Goyer

et ai, 196 8 an d Scot

t et ai, 1971 ) detailin g th e effect s of lea d o n anima l mitochondri aindicate tha t lea dha s ver y simila r effect s o n bot h plan t an danima

l mitochondria . Effect s oflea d o n isolate dchloroplast s wer e firs t reporte db

y Mile s et ai (1972) . Thes e researcher s observe dtha t lea dinhibite dphotosyntheti c electro n transpor t

associated ! wit

h photosyste mII , bu t

ha dn o effec

t o n electro n transpor t

throug h photosyste mI . Fluorescenc e inductio n curve s indicate dtha t

th e primar

y sit e of lea dinhibitio n wa s o n th e oxidizin g sid e o f photosyste mII , betwee

n th e primar

y electro n dono r

of photosyste mI I and th e sit e o f wate r oxidation . Bazza

z an dGovindje e (1974 ) later observe dtha

t PbCl 2 either

stimulate do r

inhibite dphotosyste mI I activit y dependin g o

n th e p H of

the reactio n medium . Furthe r studie s wit

h isolate d maize chloroplast s b

y Won g an dGovendje e (1976 ) reporte dth e direc t inhibitio n 

## m?spt^: "c%i**&°;

Lead: Understanding ihe Minimal Toxicity of

Lead in Plants 69 b y lea do f th e reactio n centr e P70 0 o f photosyste mI . The y hypothesize d throug h observation s o f

th e dar k deca y rate s o f

P700 + , tha t

lea daltere dth e rat e o f electro n transfe r

t o P700 + . Thus , lea dwa s see n t o hav e tw o simultaneou s effects : a n inhibitio n o f P70 0 photooxidatio n an da n alteratio n o f

th e kinetic s o f

re-reductio n o f

P700 + . Th e photosyntheti c fixation o f CO , b y isolate dspinac h chloroplast s wa s observe d5y~Hamp p et

ai (1973a ) t o b e non-competitivel y inhibite db y lead . Thes e inhibition s wer e mos t pronounce da t

concentration s u p t o -y ijI 1 ~ 2 0 /tM , an dlikel y wer e correlate dwit h adrasti c reductio n i n AT P formatio n ff , ,-. —""B y irradiate dchloroplasts . Interestingly , eve n at^QOj^jconcentration s o f ..••• : ]j ! "~ lead , 15 % o f th e C0 2 fixation capacit y wa s no t inhibited . ~

" &•' "' " • • , r y r-y A s predicte dfro mnumerou s anima l studies , lea dals o affect s th e activit y

, ! >'• ' (_

' of

numerou s isolate dplan t enzymes . I n extract s o f root s o r

leave s o f spinach , Hamp p et

al. (19736 ) observe dth e inhibitio n o f ribulose-1,5

- diphosphat e carboxylas e an dribulose-5-phosphat e kinas e activit y a t 5/i M Pb(N0 3 ) 2 . Lea dstimulate dth e activit y o f pyruvat e kinas e u p t o concentration s o f

100 /iM . Bot h astimulatio n an dinhibition , dependin g o n lea dconcentration , wa s observe di n a n NAD + o r NADP + glyceraldehyde

3-phosphat e dehydrogenas e phosphoglycerat e kinas e system . In arecen t

stud y b y Maie r

(19776 ) in vitro lea dinhibition s o f esteras e activity wer e observe di n enzym e preparation s fro mZea mays, Medicago saliva an dZebrina pendula. Lea d( 2 x 10" 6

- 2 x 10" 3 M ) wa s foun di n experiment s b y Zeger s et al. (1976 ) t o inhibi t

th e IAA-induce d elongatio n o f Avena sativa coleoptil e segments . Thes e author s hypothesize dtha t lea dwa s interferin g wit h a factor(s ) directl y involve di n cel l elongation , suggestin g th e specifi c involvemen t

o f enzyme s i n th e wal l an dth e ATPas e associate dwit h th e plasmalemma . i I t

i s suspecte dtha t

man y othe r

enzym e system s woul db e inhibite db y leadi f th e studie s wer e conducte da s the y hav e bee n wit h in vitro anima l systems . •

4 . SUMMAR Y A s aresul t

o f localize dpollution , highl y elevate dlevel s o f lea dar e becomin g associate dwit h plan t

root s an dfoliage . Movemen t o f lea dint o highe r plant s ha s bee n convincingl y demonstrate dthroug h roots , bu t no t fro m lea dparticle s deposite do n leaf surfaces . Associatio n o f lea dwit h foliag e i s a s atopica l coating , wit h mor e lea ddeposite do n pubescen t leave s tha n

. ^..^^^.^^mi^Sme*-. ^.^iJSSCW-.--^>'^teWBt*.

- • - s .wj i fci^-\.. A .JaiUi«!»SJBL.«-.

- _Effect of Heavy*Metal

Pollution on Plants f§ij l

-is leave s wit h smoot h surfaces . Moderat e wind s effectin g afluttering lea

f £ motio n caus e littl e lea

dremoval . Rainfal l doe s remov e larg e quantitie s o f ^ leadTwit h slo w mist-typ e treatme^U s bein g th e mos t effective . Lead""d"eposit

s '~~ o n leave s have mtj e effec

t o n stnnhpta l apertur e an dga s exchange , bu t ar e o f . $ considerabl e importanc e a s potentia l toxin s t o th e microfloraassociate d; : witlTlea i surface s an dt o grazing ; herorvore s rangin g tro minsect s t o horses" . ' ; Quit e possibly th e mos t

importan t

effec t o f lea dassociate dwit

h plan t • foliage i s i n foodchain s wher

e plant s i n essenc e ac t

a s passive lea

dcarriers . '& Unde r certai n soil condition s (includin g lo w pH , lo w cation-exchang e f capacity , lo

w organi c matte r

level s an dlo

w phosphoru s levels ) larg e alnouiii s u f lea dca n be-taken u p b

y highe r plan t roots . Lea

d take n u p b y root s generally ha s noftoxiCyeffec t o n plants , excep t

at extremely high root medi aconcentration s tha t

hav e littl e relevanc e t o natura l conditions . Thi s genera l lac k o f lea d effec t fro mhigh lea

dconcentration s i

n root s ha s ledt

o th e hypothesi s tha t

mos t lea d|take n u p b y root s i s quickl y inactivate d throug h depositio n in^h e roots . Lea dphosphat e deposit s are formedo n roo t surfaces , i

n periphera

l extracellula

r space s (includin g cell walls ) an d within dictyosom

e vesicle s o

f roo t cell s outsid e th e endodermis . Environmenta

l factors , plan t

ag e an dplan t

speciatio n ar e importan t variable s i n lea duptak e b

y plan t roots . Generally , a

n alteratio n o

f any soi l vanable.wtiich make s lea

dmor e availabl e i

n soi l solutio n increase s roo t

lea d uptake . Mos t

studie s wit

h lea di n hvdroponi c solutio n sho w adirec t correlatio n wit

h tim e o f lea dtreatment , uptak e int o an dtranslocatio n within th e plant , an dtoxi c effect . Lea daddition s t o bot

h in vitro subfractionate dcellula r system s an dto root s have produce deffect

s on man y differen t enzyme s or

othe r integrate d subcellula r systems . On e i s ledjto suspec t tha t th e choic e o

f th e enzyme , organell e o

r whole-plant

proces s unde r

stud y ha s bee n i n many instance s a result o f th e expertis e an dinteres t

o f th e investigator s rathe r

than searche s fo r trul y critical lead-effectedrate-limitin g reactions . Effect s o f high lea d concentratio n have bee

n reporte do n photosynthesis , respiration , energ y relation s an da

n array ot selectedenzyme s a s wel

l a s yiel d(either tres h o r dr y weight , o r

grain) . Lea

dha s bee

n shown t o caus e chromosoma l aberration s an dt o becom e nAtimatel

y associate dwit

h man y differen t cellula r an dsubcellula

r membranes . Thi s association_f>ft< mresults in-the manifestatio n o

f toxi c lea deffects~"suc

h a s reduction s i

n th e activit

y o f phosphatas e an denzyme-boun dATPase . Lea daccumulation s in localize darea s nea r pollutio n source s probabl y have littl e direc t

effec t o n plant s grown i

n thes e areas . Thi s lac

k o f effec t mos t ofte n i s du e t o nearly irreversibl e bindin g o f lea dt o soil exchang e 

# •

4

< *

# .mmr^zgm sr^"-:r ^

Lead: Understanding Ihe Minimal Toxicity of Lead in Plants 7 1 surface s an dt o extracellula r roo t surfaces . Lea daeroso l particulate s d o no t enter plant s an dhav e n o demonstrabl e physica l effec t o n th e foliar

surfac e of plants . A t

thi s time , lea dca n b e hypothesize dt o pos e little , if any . proble mt o plant s themselves , wit h th e possibl e exceptio n o f area s wher e joi l fertility , organi c matte r an dcolloi dconten t

ar e ver y low . Her e onl y modes t lea dbindin g wil l occu r

i n th e plant' s p'ivi'-""T"Mn , TMTMPlea d wil l b e riirectl v availabl e lo r

uptake , an dsom e toxi c effect s o f lea dmigh t

b e 

## prearcrjdT ^ Th e mor e significant

rol e o f plant s wit h lea di n th e ecosyste mreside s i n foo dchai n situation s wher e atopica l lea dcoatin g ma y b e ingeste db y "hTfoTvore s grazin g o n thes e plants . Th e potentia l relevanc e o f thi s proble m i s supporte db y documente ddeath s o f horse s (Rabinowit z an dWetherill , 1972 ) grazin g i n lead-contaminate droadsid e areas . REFERENCE S Aarkrog.A.an d J . Lippert(1971) . Direc t contaminatio n o

f barley wit h 51 Cr , 59 Fe , "Zn , 203 Hg , an d 2l0 Pb . Radial. Bot. 11 : 463-72 . Ahlberg , J. , C . Ramel an dC . A . Wachtmeiste r (1972) . Organoleadcompound s show n t o be genetically active . Ambio 1 : 29-31 . Antonovics , J. , A . D . Bradsha w an dR.G.Turne r

(1971) . Heav

y meta l toleranc e i

n plants . Adv. Ecol. 7 : 1-85 . Baumhardt . G . R . an dL . F . Welc h (1972) . Lea

duptak e an dcor

n growt h wit h soil

appliedlead . J. Environ. Qual. 1 : 92-4 . Bazzaz , F . A. , R . W . Carlso n an dG . L . Rolf e (1974a) . Th e effec

t o f heav y metal s on plants . I . Inhibitio n of

ga s exchang e i

n sunflowe r b y lead , cadmium , nitrogen an dthallium . Environ. Pollut. 7 : 241-6 . Bazzaz , F . A. , G . L . Rolf

e andP . Windl e (1974/)) . Differin g sensitivit

y o f cor n and soybea n photosynthesi s t o lea

dcontamination . J. Environ. Qual. 3 : 156-8 . Bazzaz , F . A. , R . W . Carlso n an dG . L . Rolf e (1975) . Th e inhibitio n of cor n and sunflowe r photosynthesi s b

y lead . Physiol. Plunt. 34 : 326-9 . Bazzaz , M . B . an dGovindje e (1974) . Effect s of lea dchlorid e o n chloroplas t reactions . Environ. Lett. 6 : 175-91 . Berry . R . A . (1923) . Th e manurial propertie s oflead nitrate . J. Agric. Sci. 14 : 59-65 . Bittell , J . E. , D . E . Koepp e an dR . J . Mille r (1974) . Sorptio n of

heav y meta l cation s b y cor n mitochondri aan dth e effect s o n electro n an denergy transfe r reactions . Physiol. Plant. 30 : 226-30 . Briggs , D . (1976) . Genecologica l studie s oflea d toleranc e i

n groundsel . New Phvtol. 77 : 173-86 . Brown , D . H . an dD . R . Slingsby (1972) . Th e cellula r locatio n oflead an dpotassium i n the liche n Cladonia rangiformis (L. ) Hoffm . New Phytol. 71 : 297-305 . Broyer , T . C , C . M . Johnso n an dR . E . Paul l (1972) . Som e aspect s oflea d i

n plant nutrition. " Plant

and Soil. 2 : 301-13 .Effect of Heavy Metal

Pollution on Plants 7 2 Cannon , H . L . an dJ . M . Bowle s (1962) . Contaminatio n o f vegetatio n b y tetraethy l lead . Science. 137 : 765-6 . ; ' • *< S Carlson , R . W . an dF . A . Bazza z (1977) . Growt h reductio n i n America n sycamor e (Plantanus occidentalis L. ) cause db y Pb-C dinteraction . Environ. Pollut. 12 : 243-53 . , Carlson , R . W. , F . A . Bazza z an dG . L . Rolf e (1975) . Th e effec t

o f heav y metal s o n plants . II . Ne t

photosynthesislan d transpiratio n o f whol e cor n an dsunflower plant s treate dwit h Pb , Cd , Ni , Tl . Environ. Res. 10 : 113-20 . Carlson , R . W. , F . A . Bazzaz , J . J . Stuke l an dJ . B . Weddin g (1976) . Physiologica l effects , win dre-entrainment j an drainwas h o f

lea daeroso l particulate s deposite do n plan t

leaves . Environ. Sci. Technol. 10 : 1139-42 . _ • Carlson , R . W. , J . J . Stuke l an dF . A . Bazza z (1977) . Aeroso l studies . In : Environmental

Contamination by Lead and Other Heavy Metals. (G . L . Rolf e an dK.A . Reinbol d(eds)) , pp . 51-66 . Institut e fo r Environmenta l Studies , Urbana , Illinois . ' , Cox , W . J . an dD . W . Rain s (1972) . Effect s o f lim e o n lea duptak e b y five plan t . species . J. Environ. Qual. 1 : 167-9 . .. . : Davis , J . B . an dR . L . Barne s (1973) . Effect s o f soil-applie dfluoride an dlea do n growt h o f

lobloll y pin e an dre dmaple . Environ. Pollut. 5 : 35-44 . . ; DeTrevill e F (1964) . Natura l occurrenc e oflead . Arch. Environ. Health. 8:212-21 . : Fiussello , N . an dM . T . Molinar i (1973) . Effect s oflea d o n plan t growth . Allioma. 19

- 89-96 . ' Fliickige r W. ; H . Fliickiger-Kelle r an dJ . J . Oertl i (1978) . Effec t o f ai r pollutio n cause db y traffi c o n peroxidas e activit y o n AT P formatio n i n isolate d chloroplast s an do n growt h o f corn . Z. Pflanzenkr. Pftanzenshutz. 85 : Fliickiger ! W. , J . J . Oertl i an dH . Fliickige r (1979) . Relationshi p betwee n stomata l diffusiv e resistanc e an dvariou s applie dparticl e size s o n lea f surfaces . Z . Pftanzenphvsiol. 91 : 173-5 . ! Gadde , R . R. ' an dH . A . Laitine n (1972) . A n interdisciplinar y stud y o t environmenta l pollutio n b y lea dan dothe r metals . NS F Gran t

G I 31605 , Progres s Report . .,,,. , j n u / ' Get z L L A . W . Haney , R . W . Larimore , J . W . McNurney , H . V . Leiand , P . W . Price , G . L . Rolfe , R . L . Wortman , J . L . Hudson , R . L . Solomo n an dK . A . Reinbol d(1977 ) Transpor t an ddistributio n i n awatershe decosystem . In : Lead in the Environment

(W.|R . Bogges s (ed.)) , pp . 105-34 . Nationa l Scienc e Foundation . Washington , D.C . Goren , A . an dH . Wanne r (1971) . Di e Absorptio n vo n Blei un dKupfe r durc h Wurzel n vo n Hordeum vulgare. Ber. Schweiz. Bot. Ges. 80 : 334-40 . Goyer , R . A . (1968) . Th e rena l tubul e i n lea dpoisoning . I . Mitochondria l swellin g an daminoaciduria . Lab. Invest. 19 : 71-7 . Goyer , R . A . an dR . Krol l (1969) . Ultrastructura l transformatio n i n mito

chondri aisolate dfro mkidney s o f norma l an dlead-intoxicate drats . J. Cell. Biol. 41 : 393-400 . . , ' Goyer , R . A. , A . Krol l an dJ . P . Kimbal l (1968) . Th e rena l tubul e i n lea dpoisoning . II . In vitro studie s o f

mitochondria l structur e an dfunction . Lab. Invest. W 78-83 . i . . . Hammett , F . S . (1928) . Studie s i n th e biolog y o f metals . I . Th e localizatio n o t lea o b y growin g roots . Protoplasma. 4 : 183-6 . •> S.#»« ' 1 SR? c S'«gf*JS5Sj5f^, v S^r'^f*^ " i a'.^.t H P.2 0 

# ~ 1



# -m.- Lead: Understanding the Minimal Toxicity of

Lead in Plants 7 3 Hampp , R- , H . Ziegle r

an dI . Ziegle r

(1973a) . Th e effect

oflea d ion s o n th e 14 C0 2 - fixation an do n th e ATP-synthesi s b y spinac h chloroplasts . Biochem. Physiol. Pflanz. 164 : 126-34 . Hampp , R- . H . Ziegle r

an dI . Ziegle r

(19736) . Influenc e o f

lea dion s o n th e activit y o f enzyme s o f

th e reductiv e pentos e phosphat e pathway . Biochem. Physiol. Pflanz. 164 : 588-95 . Hassett , J . J. , J . E . Mille r an dD . E . Koepp e (1976) . Interactio n o f lea dan d cadmiu mo n cor n roo t

growt h an duptak e o f lea dan dcadmiu mb y roots . Environ. Pollut. 11 : 297-302 . Herich , R . an dM . Boba k (1974) . Influenc e o f

tetramethy l lea do n th e protoplast s o f plan t cells . Acta Biol. Acad. Sci. Hung. 25 : 289-98 . Hevesy , G . (1923) . Th e absorptio n an dtranslocatio n o f lea db y plants . A contributio n t o th e applicatio n o f th e metho do f

radioactiv e indicator s i n th e investigatio n o f

th e chang e o f

substanc e i n plants . Biochem. J. 17 : 439-45 . Hinesly , T . D. , R . L . Jone s an dE . L . Ziegle r (1972) . Effect s o n cor n b y application s o f heate danaerobicall y digeste dsludge . Compost Sci. 13 : 26-30 . Huang , C . Y. , F . A . Bazza z an dL . N . Vanderhoe f (1974) . Th e inhibitio n o f soybea n metabolis mb y cadmiu man dlead . Plant Physiol. 54 : 122-4 . John , M . K . an dC . Va n Laerhove n (1972) . Lea duptak e a s affecte db y lime , nitroge n an dsource s oflead . J. Environ. Qual. 1 : 169-71 . Judel , G . K . an dW . Stelt e (1977) . Po t experiment s o n lea duptak e b y vegetabl e plant s fro mth e soil . Z . Pflanzenernaeh, Bodenkd. 140 : 421-30 . Kannan , S . an dH . Keppe l (1976) . Absorptio n an dtranspor t o f Pb 2 + i n youn g pe a seedlings . Z. Naturforsch. 31 : 393-6 . Karamanos , R . E. , J . R . Bettan y an dJ . W . B . Stewar t (1976) . Th e uptak e o f

nativ e an dapplie dlea db y alfalf aan dbromegras s fro msoil . Can. J. Soil Sci. 56 : • ; 485-94 . Keaton , C . M . (1937) . Th e influenc e o f lea dcompound s o n th e growt h o f barley . f So/ 7 Sci. 43:401-9 . Keller , T . an dR . Zube r

(1970) . Lea duptak e an dlea ddistributio n i n youn g spruc e plants . Forstwiss Centralbl. 89 : 20-6 . Koeppe , D . E . (1977) . Th e uptake , distribution , an deffec t o f cadmiu man dlea di n plants . Sci. Tot. Environ. 7 : 197-206 . Koeppe , D . E . an dR . J . Mille r (1970) . Lea deffect s o n cor n mitochondria l respiration . Science. 167 : 1376-8 . Krause , G . H . M . an dH . Kaise r (1977) . Plan t

respons e t o heav y metal s an dsulphu r dioxide . Environ. Pollut. 12 : 63-71 . Lagerwerff

, J . V. , W . H . Armige r

an dA . W . Spech t

(1973) . Uptak e oflea d b y alfalf a an dcor n fro msoi l an dair . Soil Sci. 115 : 455-60 . Lee . K . C , B . A . Cunningham , K . H . Chung , G . M . Paulse n an dG . H . Lian g (1976) . Lea deffect s o n severa l enzyme s an dnitrogenou s compound s i n soybea n leaf

. J. Environ. Qual. 5 : 357-9 . Liebhardt , W . C . an dT . J . Kosk e (1974) . Th e lea dconten t o f variou s plan t

species a s affecte db y cycle-lite , mhumus . Commun. Soil Sci. Plant

Anal. 5 : 85-92 . MacLean , A . J. , R . L . Halstea dan dB . J . Fin n (1969) . Extractabilit y o f adde dlea di n soil s an dit s concentratio n i n plants . Can. J. Soil Sci. 49 : 327-34 . Maier , R . (1977a) . Th e effec t o f lea do n th e NAD + -dependen t malat e dehydrogenas e i n Medicago sativa L . an dZebrina pendula S . Z . ' Pflanzenphysiol. 85 : 319-26 .7 4 Effect of Heavy Metal

Pollution on Plants « Maier , R . (19776) . Influenc e o f lea do n th e activit y o f esteras e an dit s multipl e forms . Biochem. Physiol. Pflanzen. 171 : 455-68 . Maier . R . (1978) . Studie s o n th e effect oflea d o n th e aci dphosphatas e i n Zea mavs L . Z . Pflanzenphysiol. 87 : 347-54 : Malone . C . D. , D . E . Koepp e an dR . J . Mille r (1974) . Localizatio n o f lea d accumulate db y cor n plants . Plant Physiol. 53 : 388-94 . Marten , G . C . an dP . B . Hammon d(1966) . Lea duptak e b y bromegras s fro m contaminate dsoils . Agron. J: 58: 553-4 . Merakchiiska , M. , H . Karalovaan d I . Yordanov ( 1976) . Th e effect o f lea dapplie d throug h th e root s o n th e growt h o f Phaseolus vulgaris. Compi. Rend. Acad. BulgareSci. 29 : 1819-21 . [ Miles . C . D , J . R . Brandle , D . J . Daniel . O . Chu-Der , P . D . Schnor e an dD . J . Uhli k (1972) . Inhibitio n o f

photosyste mI I i n isolate dchloroplast s b y lead . Plant Physiol. 49 : 820-5 . ; Miller . J . E. , J . J . Hasset t an dD . E . Koepp e (1975«) . Th e effect o f soi l propertie s an d extractabl e lea dlevel s o n lea d uptak e b y soybeans . Commun. Soil Sci. Plant Anal. 6 : 339-47 . \ Miller , J . E.J.J . Hasset t an dD . E . Koepp e (19756) . Th e effect o f soi l lea dsorptio n capacit y o n th e uptak e o f lea db y corn . Commun. Soil Sci. Plant

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hig h an dlo w moto r

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th e hydrophyte , Ceratophvtlum demersum. Z. Pflanzenphysiol. 73 : 377-86 . #

10.

* &Lead: Understanding the Minimal Toxicity of

Lead in Plants 7 5 Rolfs-' . G . L . (1973) . Lea duptak e b y selecte dtre e seedlings . J. Environ. Qual. 2 : 153-7 . Rolfe . G . L . an dF . A . Bazza z (1975) . Effect s oflea d contaminatio n o n transpiratio n an dphotosynthesi s o f

lobloll y pin e an dautum n olive . For. Sci. 21 : 33-5 . Rolfe . G . L . an dK . A . Reinbol d(1977) . Environmental Contamination by Lead and Other Heavy Metals. Inst . Environ . Studies . Urbana , Illinois , 14 3 pp . Schuck , E . A . an dJ . K . Lock e (1970) . Relationshi p o f automotiv e lea dparticulate s t o certai n consume r

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lea di n th e leaf

tissu e o f PotamogeionpectinaiusL. J. Exp. Bol. 27:1155-62 . Smith , W . H . (1976) . Lea dcontaminatio n o f th e roadsid e ecosystem . J. Air Pollut. Conf. Assoc. 26 : 753-66 . Steenken , F . (1973) . Fumigatio n o f cultivate dplant s wit h lead-containin g an dlead

free automobil e exhaus t gases . Z . Pflanzenk. Pflanzenshuiz. 80 : 513-27 . Sung . M-W . (1976) . Studie s o n th e precipitatio n oflea d io n an dth e inhibitio n o f plan t growth . Korean J. Bol. 19 : 1-6 . Sung . M-W . an dY-H . Jeon g (1977) . Effect s o f variou s anion s o n absorptio n an d toxicit y oflea d i n plants . Korean J. Bol. 20 : 7-14 . Tandler , C . J . an dA . J . Solar i (1969) . Nucleola r orthophosphat e ions—electro n microscop e an ddiffractio n studies . J. Cell. Biol. 41 : 91-108 . Tanton , T . W . an dS . H . Crowd y (1971) . Th e distributio n o f lea dchelat e i n th e transpiratio n strea mo f

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