Annls of Botny 17: 285 292, 211 doi:1.193/o/mcq24, ville online t www.o.oxfordjournls.org Cdmium induces hypoderml periderm formtion in the roots of the monocotyledonous medicinl plnt Merwill plume Alexnder Lux 1,2, Mrek Vculík 1, Michl Mrtink 1, Desn Lišková 2, Mnoj G. Kulkrni 3, Wendy A. Stirk 3 nd Johnnes Vn Stden 3, * 1 Deprtment of Plnt Physiology, Fculty of Nturl Sciences, Comenius University in Brtislv, Mlynská dolin B-2, SK-842 15 Brtislv, Slovk Repulic, 2 Deprtment of Glycoiotechnology, Institute of Chemistry, Slovk Acdemy of Sciences, Dúrvská cest 9, SK-845 38 Brtislv, Slovk Repulic nd 3 Reserch Centre for Plnt Growth nd Development, School of Biologicl nd Conservtion Sciences, University of KwZulu-Ntl Pietermritzurg, Privte Bg X1, Scottsville 329, South Afric * For correspondence. E-mil rcpgd@ukzn.c.z Received: 1 Septemer 21 Returned for revision: 5 Octoer 21 Accepted: 5 Novemer 21 Pulished electroniclly: 29 Novemer 21 Bckground nd Aims Merwill plume is n importnt Africn medicinl plnt. As the plnts grow in soils contminted with metls from mining ctivities, the dnger of humn intoxiction exists. An experiment with plnts exposed to cdmium (Cd) ws performed to investigte the response of M. plume to this hevy metl, its uptke nd trnsloction to plnt orgns nd rection of root tissues. Methods Plnts grown from seeds were cultivted in controlled conditions. Hydroponic cultivtion is not suitle for this species s roots do not tolerte qutic conditions, nd dditionl stress y Cd tretment results in totl root growth inhiition nd deth. After cultivtion in perlite the plnts exposed to 1 nd 5 mg Cd L 21 in hlf-strength Hoglnd s solution were compred with control plnts. Growth prmeters were evluted, Cd content ws determined y inductively coupled plsm mss spectroscopy (ICP-MS) nd root structure ws investigted using vrious stining procedures, including the fluorescent stin Fluorol yellow 88 to detect suerin deposition in cell wlls. Key Results The plnts exposed to Cd were significntly reduced in growth. Most of the Cd tken up y plnts fter 4 weeks cultivtion ws retined in roots, nd only smll mount ws trnslocted to uls nd leves. In rection to higher Cd concentrtions, roots developed hypoderml periderm close to the root tip. Cells produced y cork cmium impregnte their cell wlls y suerin. Conclusions It is suggested tht the hypoderml periderm is developed in young root prts in rection to Cd toxicity to protect the root from rdil uptke of Cd ions. Secondry meristems re usully not present in monocotyledonous species. Another interprettion explining formtion of protective suerized lyers s result of periclinl divisions of the hypodermis is discussed. This process my represent n s yet unknown defence rection of roots when exposed to elementl stress. Key words: Cdmium, environmentl stress, medicinl plnts, Merwill plume, monocotyledonous plnts, periderm, plnt ntomy, root structure. INTRODUCTION South Afric hs lrge concentrtion of metl, minerl nd col-mining industries with high rtes of wste disposl (Cooke nd Johnson, 22). The gold nd col-mining industries re responsile for lowering ph levels of South Africn rivers y the phenomenon known s cid mine dringe (Coetzee, 1995). The wste from mining industries contins hevy metls such s led, cdmium (Cd), mercury, luminium, zinc, copper, mgnesium nd mngnese (Deprtment of Wter Affirs, 1986; Wren nd Stephenson, 1991). Compred with other metls or metlloids, Cd hs higher tendency to ccumulte in plnt tissues (Kt-Pendis nd Pendis, 1984) nd is considered s highly mutgenic nd crcinogenic y the Interntionl Agency for Reserch on Cncer (IARC, 1993; Filipic nd Hei, 24). Consumption of edile plnt mteril with high Cd content my cuse toxicity in humns (Jckson nd Allowy, 1992; FAO/WHO, 1995). Due to its high toxicity, the mximum permissile limit of Cd in medicinl plnts set y the World Helth Orgniztion (WHO) is.3 p.p.m. In recent investigtion y Street et l. (28), Cd exceeded the limits recommended y the WHO (1998) in ul nd tuer smples of South Africn medicinl plnts otined from street mrkets. In nother study, Cd ccumultion in uls of smll nd medium-sized plnts of Tulghi species used medicinlly incresed with incresing Cd concentrtion (Street et l., 21). Buls of mture Merwill plume plnts ccumulted 24-fold more Cd thn the WHO guidelines when irrigted with 2 mg Cd L 21. At the sme time, the ul extrcts showed incresed nticteril ctivity (Street et l., 29). Cdmium hd detrimentl effect on the root growth of Bowie voluilis, which is nother importnt ulous medicinl plnt in South Afric (Street et l., 27). In most of these studies, it ws indicted tht uls of medicinl plnts hve tendency to ccumulte Cd. However, the uptke mechnism of Cd is still uncler. Downloded from http://o.oxfordjournls.org/ t University of KwZulu Ntl, Medicl Lirry on Jnury 3, 213 # The Author 21. Pulished y Oxford University Press on ehlf of the Annls of Botny Compny. All rights reserved. For Permissions, plese emil: journls.permissions@oup.com
286 Lux et l. Cdmium nd hypoderml periderm formtion in roots As roots of seedlings represent the primry contct zone of plnts in soils, ntomicl ltertions occurring during Cd uptke my hve n effect on ccumultion processes nd vegettive growth of the plnts when they re exposed to this metl. The root rection of vrious plnt species ws recently reviewed y Lux et l. (211). Inhiition of root growth nd rnching s result of the inhiitory effect of Cd on cell division ws oserved y Fusconi et l. (26) nd M et l. (21). Species-specific rections nd chnges in root tissue orgniztion nd development occur fter Cd tretment (Lunáčková et l., 23). Chnges in the development of root poplsmic rriers were shown to e relted to Cd uptke nd trnsloction (Lux et l., 24; Mrtink nd Lux, 24; Vculík et l., 29). Considering these fcts, elevted concentrtions of Cd in the rhizosphere my influence root growth nd development of M. plume plnts. In the present contriution, two types of cultivtion of n extensively used medicinl plnt in South Afric, M. plume, were tested for the evlution of uptke nd trnsloction of Cd. An ntomicl study ws performed to investigte the possile effect of Cd tretment on root structure. MATERIALS AND METHODS Growth conditions nd experimentl design Seeds of Merwill plume (Lindl.) Spet, otined from the Botnicl Grden of the University of KwZulu-Ntl in Pietermritzurg, South Afric, were germinted on wet filter pper in Petri dish for 1 d. Therefter, the young seedlings were trnsferred to perlite nd irrigted with tp wter for 4 weeks nd then y hlf-strength Hoglnd s solution for 8 weeks in the greenhouse t Comenius University in Brtislv, Slovki. Two different types of cultivtion were pplied: (1) cultivtion of experimentl plnts directly in hydroponic solution (hydroponics) nd (2) cultivtion of plnts in perlite, which ws irrigted with the sme solutions s used for hydroponics. For hydroponics, the first set of prepred young plnts with lredy developed uls ws trnsferred to 5 L continers filled with hlf-strength Hoglnd s solution. Another set of plnts for perlite ws trnsferred to 1 L pots filled with perlite nd plced in growth chmer. The plnts in oth experiments were grown for 4 weeks t 25 8C, 6 % humidity, 16/8 h light/drk photoperiod, PAR 15 mmol m 22 s 21. For oth experiments, three different tretments were used: (1) control irrigted with hlf-strength Hoglnd s solution; (2) Cd 1 irrigted with hlf-strength Hoglnd s solution contining 1 mg Cd L 21 ; nd (3) Cd 5 irrigted with hlfstrength Hoglnd s solution contining 5 mg Cd L 21. Cdmium ws pplied in the form of Cd(NO 3 ) 2.4H 2 O. The hydroponic solution ws chnged weekly. The pots contining perlite were irrigted with 2 ml of solution on the first dy t the strt of the experiment nd fterwrds with n dditionl 1 ml of solution every seventh dy for 4 weeks. Growth prmeter determintion The plnts were hrvested nd fresh weights of roots, uls nd leves were determined. The totl root length ws recorded nd expressed s cumultive root length per plnt (CRL). The length of individul roots ws clculted from the CRL divided y the numer of roots on ech plnt. The sme mesurements nd clcultions were done with the leves. Fresh roots, uls nd leves were dried t 7 8C for 3 d nd fter tht the dry weight of these orgns ws determined. Determintion of Cd concentrtion Dried smples of roots, uls nd leves were nlysed for Cd y inductively coupled plsm mss spectroscopy (ICP-MS). The smples were dissolved in HNO 3 nd the Cd concentrtion ws determined y n Eln 6 spectrometer (Pe Sciex, Cnd). Antomicl oservtions Series of hnd sections of roots were prepred t 1 mm intervls from the root pex to the se. For suerin visuliztion in fluorescence microscopy, the free hnd sections were stined y.1 % Fluorol yellow 88 dissolved in lctic cid for 3 min nd wshed in distilled wter ccording to Lux et l. (25). The smples were plced into drop of.1 % FeCl 3 dissolved in 5 % glycerin prior to oservtion. The sections for right-field oservtions were stined with toluidine lue. The sections were oserved under n Zeiss Axioskop 2 plus epifluorescence microscope (Jen, Germny) nd documented y n Olympus DP 72 digitl cmer. Sttisticl nlyses The experimentl dt shown in the figures re mens of 12 replictes + s.e. from independent experiments repeted three times. The significnce ws compred t the.5 level using Student s t-test (Sttgrphics Centurion XV, v. 15.2.5, SttPoint, Inc.). RESULTS AND DISCUSSION Growth of the plnts The growth of M. plume plnts in hydroponics ws poor, nd only in control conditions did some new dventitious roots form. These exhiited limited growth. The roots of plnts treted with Cd were stunted nd no new root formtion occurred. The mjority of roots in oth Cd tretments grdully died (Fig. 1). The growth prmeters of plnts from this experiment re shown in Tle 1. It ws cler tht cultivtion in hydroponics is not fesile for this species. The growth of plnts cultivted in perlite under control conditions ws dequte nd plnts exhiited increses in oth root nd shoot growth (Figs 2 nd 3). Use of solid sustrte is necessry for this species. Street et l. (29) used sterilized cid-wshed qurtz snd wetted with Hoglnd s solution for cultivtion of this species. In our experiments the growth of M. plume plnts ws retrded fter Cd ppliction; the root system ws reduced in comprison with the control nd leves were shorter nd nrrower, nd yellowish compred with those of control plnts (Fig. 1). Shorter leves of M. plume were oserved fter CdCl 2 tretment, ut Downloded from http://o.oxfordjournls.org/ t University of KwZulu Ntl, Medicl Lirry on Jnury 3, 213
Lux et l. Cdmium nd hypoderml periderm formtion in roots 287 A B Control 1 mg Cd L 1 5 mg Cd L 1 FIG. 1. Effect of cdmium on 17-week-old Merwill plume plnts grown for 4 weeks in (A) hydroponics nd (B) perlite. Three different tretments were used: control (C); 1 mg Cd L 21 (Cd1); nd 5 mg Cd L 21 (Cd5). Scle rs ¼ 1 cm. TABLE 1. Growth prmeters of Merwill plume plnts grown for 4 weeks in hydroponics Tretment Growth prmeter Control Cd1 Cd5 Root f. wt (g).94 +.17.534 +.16.483 +.19 Root d. wt (g).51 +.9.33 +.12.26 +.8 Lef f. wt (g).49 +.83.131 +.32.1 +.18 Lef d. wt (g).32 +.45.127 +.9.123 +.26 Bul f. wt (g).134 +.48.95 +.29.11 +.54 Bul d. wt (g).13 +.75.17 +.57.13 +.24 CRL (cm) 18.22 + 3.45 1.62 + 2.21 9.38 +.81 ARL (cm) 4.742 + 1.46 2.948 +.46 2.818 +.48 Downloded from http://o.oxfordjournls.org/ t University of KwZulu Ntl, Medicl Lirry on Jnury 3, 213 Three different tretments were used: control, hlf-strength Hoglnd s solution; Cd1, hlf-strength Hoglnd s solution contining 1 mg kg 21 Cd; nd Cd5, hlf-strength Hoglnd s solution contining 5 mg kg 21 Cd. ARL, verge root length; CRL, cumultive root length (mens + s.e., different letters represent significnt differences t P,.5). without sttisticlly significnt differences etween control nd treted plnts (Street et l., 29). However, Cd t 2 mg L 21 resulted in significnt reduction of fresh weight of leves, uls nd roots, when compred with the control (Street et l., 29). Similrly in our experiment in the plnts treted with Cd(NO 3 ) 2.4H 2 O, the fresh nd dry weight of roots were significntly lower,.5 %, fter cultivtion in hydroponics with 1 mg Cd L 21 when compred with the control plnts. This difference ws even higher when the higher Cd concentrtion (5 mg Cd L 21 ) ws used. However, the difference etween 1 nd 5 mg Cd L 21 ws not significnt. The sme trend ws oserved for the leves. The min differences were oserved with uls; the fresh nd dry weights of uls of plnts treted with 1 mg Cd L 21 were not different
288 Lux et l. Cdmium nd hypoderml periderm formtion in roots Fresh weight (g) 1 8 6 4 2 Root C Cd1 Cd5 from those of the controls. After higher Cd ppliction (5 mg Cd L 21 ), the fresh nd dry weights of uls were lower, out 5 %, when compred with the control nd 1 mg Cd L 21 -treted plnts (Figs 2 nd 3). The numer of dventitious roots ws lower in plnts cultivted with Cd; the men numers for control, 1 mg Cd L 21 nd 5 mg Cd L 21 were 6.5, 6. nd 4.9, respectively. CRL s well s the verge length of roots (ARL) ws not different etween control nd 1 mg Cd L 21 -treted plnts. However, oth CRL nd ARL were significntly different etween the control nd 5 mg Cd L 21 tretments nd lso etween oth Cd tretments (Figs 4 nd 5). The inhiition of root growth ws proly cused y Cd-induced depolymeriztion of microtuules of the cell cytoskeleton nd chromosome errtions, which resulted in lower mitotic ctivity of meristemtic cells (Fusconi et l., 26; Seth et l., 28), nd thus inhiition of root elongtion. Cumultive lef length per plnt nd lso the verge length of leves were significntly different etween the control nd oth tretments. The growth of roots of crrot nd rdish seedlings ws inhiited t 2 mg Cd L 21 nd this inhiitory effect incresed with incresing concentrtions of Cd in oth liquid culture nd pot experiments (Chen et l., 23). In the present study, the inhiitory effect ws more pronounced t 5 mg Cd L 21, suggesting tht Lef Plnt prt Bul F IG. 2. Effect of cdmium on fresh weight of 17-week-old Merwill plume plnts grown for 4 weeks in perlite. Three different tretments were used: control (C); 1 mg Cd L 21 (Cd1); nd 5 mg Cd L 21 (Cd5). Mens ( + s.e.) with different letters re significntly different (P,.5). Dry weight (g) 2 15 1 5 C Cd1 Cd5 Root Lef Bul Plnt prt FIG. 3. Effect of cdmium on dry weight of 17-week-old Merwill plume plnts grown for 4 weeks in perlite. Three different tretments were used: control (C); 1 mg Cd L 21 (Cd1); nd 5 mg Cd L 21 (Cd5). Mens ( + s.e.) with different letters re significntly different (P,.5). A Cumultive lef length (cm) B Cumultive root length (cm) 5 4 3 2 1 5 4 3 2 1 M. plume seedlings re more sensitive to Cd thn the seedlings of crrot nd rdish. Recently, Street et l. (29) showed tht 2 mg Cd L 21 negtively ffected the fresh weight of leves, uls nd roots of mture plnts of M. plume exhiiting high ccumultion of Cd in the roots. This suggests tht inhiition of root growth t high Cd concentrtion my ffect nutrient nd wter uptke, resulting in inhiition of shoot elongtion. However, there is not enough informtion on the mechnism of Cd toxicity in the root system, which is the min orgn for uptke in plnts (Chen et l., 23). Cdmium concentrtion Lrge differences were found in ccumultion of Cd y different plnt orgns of M. plume (Fig. 6). Roots ccumulted considerly higher mounts of Cd when compred with the uls nd leves. This phenomenon is well known for mny plnt species. It is ssumed tht this is one of the min mechnisms to protect the ove-ground prts of plnts ginst toxic Cd effects (Lux et l., 211). The concentrtion of Cd significntly incresed in roots treted with 1 mg Cd L 21 nd even more Cd ws found in roots when grown t higher Cd stress (5 mg Cd L 21 ). The sme tendency ws oserved in ulous species cultivted t 5 nd 25 mm Cd (Soudek et l., 29). Similrly to the roots, the Cd concentrtions in the other plnt orgns were elevted correspondingly with incresing concentrtion of Cd in the medi. However, the C Cd1 Cd5 Tretment F IG. 4. Effect of cdmium on cumultive lef nd root length of 17-week-old Merwill plume plnt grown for 4 weeks in perlite. Three different tretments were used: control (C); 1 mg Cd L 21 (Cd1); nd 5 mg Cd L 21 (Cd5). Mens ( + s.e.) with different letters re significntly different (P,.5). c Downloded from http://o.oxfordjournls.org/ t University of KwZulu Ntl, Medicl Lirry on Jnury 3, 213
Lux et l. Cdmium nd hypoderml periderm formtion in roots 289 A 1 Averge lef length (cm) 8 6 4 2 B 1 Averge root length (cm) 8 6 4 2 C Cd1 Tretment Cd5 FIG. 5. Effect of cdmium on verge lef nd root length of 17-week-old Merwill plume plnts grown for 4 weeks in perlite. Three different tretments were used: control (C); 1 mg Cd L 21 (Cd1); nd 5 mg Cd L 21 (Cd5). Mens ( + s.e.) with different letters re significntly different (P,.5). Cd concentrtion (mg kg 1 d. wt) 7 6 5 4 3 2 1 Root Bul Lef concentrtion of Cd ws more thn eight times higher in the roots thn in the leves nd uls when plnts were grown in 1 mg Cd L 21. The differences etween plnt prts were considerly igger when the higher Cd concentrtion (5 mg Cd L 21 ) ws used. Comprle results were otined with C Cd1 Cd5 Tretment FIG. 6. Effect of cdmium ppliction on cdmium concentrtion in roots, uls nd leves of 17-week-old Merwill plume plnts grown for 4 weeks in perlite. Three different tretments were used: control (C); 1 mg Cd L 21 (Cd1); nd 5 mg Cd L 21 (Cd5). Mens ( + s.e.) with different letters re significntly different (P,.5). c c d CdCl 2 tretment of the sme species y Street et l. (29). The concentrtion of Cd in the roots ws pprox. 15 times higher compred with the uls nd out 3 times higher when compred with the leves. The concentrtion of Cd ws the sme in the leves nd the uls when lower Cd concentrtion (1 mg Cd L 21 ) ws used, nd out twice s high in the uls thn in the leves t higher Cd tretment (5 mg Cd L 21 ) (Fig. 6). Soudek et l. (29) hve oserved tht experimentlly tested ulous plnts retined on verge 75 % of ccumulted Cd in the roots, nd only 18 % nd 7 % in the uls nd leves, respectively. Despite the trnsloction fctor eing quite low in M. plume, the Cd ccumulted in the uls exceeded, t ll experimentl vrints, the limit for mximum Cd content (.3 p.p.m.) set y the WHO for medicinl plnts. Another medicinl plnt species, Tulghi violce, ccumulted Cd in its uls in the rnge of 3.4 8.7 mg g 21 d. wt depending on the size of test plnts fter 6 weeks tretment with 2 mg L 21 Cd. Tulghi violce ccumulted Cd in the leves t the level of 2.1 1.2 nd 5.5 2.9 mg g 21 t 2 nd 5 mg L 21, respectively, depending on plnt ge the older the plnt, the less ccumultion (Street et l., 21). Severl plnt species, such s Thlspi cerulescens, Aridopsis hlleri nd Sedum lfredii, cn ccumulte Cd in concentrtions exceeding even the level set for hyperccumultors (which is 1 mg Cdg 21 d. wt) (Slt et l., 1995; Zho et l., 26; Deng et l., 27; Bnsov et l., 28). Usully importnt crop plnts, such s mize, rice, whet nd sunflower, do not rech this hyperccumultion limit when treted with Cd concentrtions, 1 mg kg 21 of soil (Greger nd Lnderg, 28; Fessler et l., 21; Liu et l., 21). Monocotyledonous ulous plnt species, such s Allium cep, Allium stivum, Allium schoenoprsum nd Allium porrum, ehve similrly, ut in some cses they cn exceed the hyperccumultion limits when grown under specific conditions, mostly in hydroponics nd t high Cd concentrtions in the medi (Soudek et l., 29). Allium schoenoprsum ws le to ccumulte this metl to.17 nd 2 mg g 21 in roots nd leves, respectively, during 28 d of 5 mm Cd tretment (Brzni et l., 24). Root ntomy The dventitious roots of M. plume seedlings show the typicl structure of monocotyledonous root (Fig. 7A). One lyer of rhizodermis is formed y smll cells s the outermost tissue. The cortex is reltively rod, with one-lyered hypodermis. Hypoderml cells re rdilly extended nd develop Csprin nds nd suerin lmelle 1 15 mm from the root pex (Fig. 7B, C); this lyer cn e clssified s exodermis (Peterson nd Peruml, 199). Corticl prenchym is multilyered nd cells re lterntively rrnged with smll intercellulr spces. The single-lyered endodermis develops Csprin nds close to the root pex, t distnce of pprox. 3 mm. A secondry stte of endoderml development (suerin lmelle development) occurs pprox. 3 mm from the root pex. The centrl cylinder is nrrow; it consists of one-lyered pericycle, 6 12 rdilly rrnged poles of xylem nd phloem elements, nd centrl prenchymtous region. Downloded from http://o.oxfordjournls.org/ t University of KwZulu Ntl, Medicl Lirry on Jnury 3, 213
29 Lux et l. Cdmium nd hypoderml periderm formtion in roots A D B C F IG. 7. Cross-sections of dventitious roots of Merwill plume. Plnts were grown in control conditions in perlite (A C) nd treted with 5 mg kg 21 Cd (D F). Roots in control conditions exhiit the typicl structure of monocotyledonous roots formed y single-lyered epidermis nd single-lyered exodermis (A, B); exoderml cells develop suerin lmelle close to the root pex, s shown in C fter Fluorol yellow 88 stining in fluorescence microscopy. After cdmium tretment the hypoderml periderm is formed in the peripherl corticl zone close to the root pex (D F). Cork cmium produces cells y periclinl division (E); these ecome impregnted y suerin, s shown in F fter Fluorol yellow 88 stining in fluorescence microscopy. The distnces of sections from the root pex re 5 mm (A, B, D, E) nd 3 mm (C, F). Arevitions: ep, epidermis; ex, exodermis; me, mesodermis (mid-corticl lyers); en, endodermis; cc, centrl cylinder; sterisks indicte periclinl divisions in cork cmium. Scle rs: (A, D) ¼ 1 mm, (B, C, E, F) ¼ 5 mm. E F Downloded from http://o.oxfordjournls.org/ t University of KwZulu Ntl, Medicl Lirry on Jnury 3, 213 The oldest prt of M. plume root, close to the ul, is chrcterized y the presence of contrctile zone. Contrctile roots pull uls down into the soil. The ssocition etween contrctile roots, wter uptke nd hitt ridity ws investigted for gves, yuccs nd loes y North et l. (28). Cdmium ppliction in our experiments t higher concentrtion (5 mg Cd L 21 ) cused chnges in the root tissue orgniztion nd development. Exposure to Cd induced the formtion of cork cmium in corticl tissues internlly, djcent to the exodermis (Fig. 7D). Cells divided periclinlly nd the derivtives impregnted their cell wlls with suerin (Fig. 7E, F). Hypoderml periderm formtion occurred in the young, su-picl prt of the root. The first periclinl divisions were present pprox. 5 mm from the root pex. The root of most monocotyledons is covered y the originl primry epidermis during their whole life; under some conditions it ecomes lignified or even suerized. These cell wll modifictions my reduce the growth of plnt orgns nd cn ffect the trnsport of nutrients nd wter. Only few studies of periderm formtion in monocotyledons hve een completed, mostly focused on rorescent monocotyledons (Dickinson, 2). In ulous plnts, wound periderm formtion ws oserved in roots fter infection cused y
Lux et l. Cdmium nd hypoderml periderm formtion in roots 291 FIG. 8. Cross-section of dventitious roots of n dult Merwill plnt growing in soil (Botnicl Grden of University of KwZulu-Ntl, Pietermritzurg, South Afric) stined with Fluorol yellow 88 in UV light. The formtion of multiserite cell lyers with suerized cell wlls (*) resemling typicl periderm occurs fter injury of the root surfce. Scle r ¼ 1 mm. vrious species of Penicillium (Sltink, 1971). Exceptionl periderm is sometimes present elow the exodermis in some species of Asprgles (Kuff et l., 2). We suggest tht formtion of hypoderml periderm in young su-picl prts of Merwill roots represents defence rection of roots exposed to toxic metl tretment. Periderm, with impermele cell wlls, impregnted y suerin my reduce rdil uptke of Cd ions y roots. The formtion of protective su-epiderml lyers in response to Cd tretment is interpreted here s hypoderml periderm or wound periderm formtion. It cn proly lso e interpreted s multiserite hypodermis. This interprettion is sed on multiserite hypodermis shown in roots of some monocotyledonous species y Sego nd Mrsch (1989), Sego et l. (2) nd Heimsch nd Sego (28), nd in Iris y Meyer et l. (29). These studies showed developmentl schemes of multiserite exodermis nd hypodermis which cn e formed from the root picl meristem (RAM), in some cses mny millimetres ehind the tip. Exodermis sent in control conditions nd induced y slt stress ws found in roots of dicotyledonous plnt species (cotton) y Reinhrdt nd Rost (1995). These dt suggest the possiility of formtion of su-epiderml lyers oserved y us s result of meristemtic ctivity derived from the RAM. We cn support our opinion out the formtion of secondry meristem in su-epiderml root lyers of Merwill in response to stress y dditionl oservtions. Adventitious roots of dult plnts growing in soil (Botnicl Grden of University of KwZulu-Ntl, Pietermritzurg, South Afric) were investigted. In wounded or dmged res of older root prts, formtion of multiserite cell lyers with suerized cell wlls resemling typicl periderm (wound periderm) of dicotyledonous roots ws oserved (Fig. 8). Depending on interprettion, we cn cll these structures in monocotyledonous plnt species hypoderml periderm, or regrd their formtion s result of dditionl divisions of corticl cells. Otherwise we cn ccept the possiility of cork cmium formtion resulting in periderm lyers in monocotyledons. Conclusions Accumultion of toxic mounts of hevy metls in plnts represents helth thret for humns. Medicinl plnts used in trditionl medicine re little studied with respect to Cd intke. The cpcity of M. plume, n intensively trded medicinl plnt of South Afric, ws studied here. The dt show tht this plnt cn ccumulte considerle mounts of Cd. Plnts limit shoot Cd ccumultion y restricting Cd movement to the xylem through oth the symplsmic nd the poplsmic pthwys. Restriction of poplsmic movement of Cd ws found in vrious plnt species y root cell wll modifictions nd impregntions, ccelerted mturtion of poplsmic rriers exodermis nd endodermis nd lignifiction of peripherl root tissues. In roots of M. plume, erly formtion of hypoderml periderm close to the root pex occurs fter Cd tretment. Periderm is only rrely developed in roots of monocotyledonous plnts; therefore, nother interprettion my e dditionl periclinl division of hypoderml lyers. We hypothesize tht this process nd production of secondry tissues impregnted y suerin in M. plume treted y Cd hve functionl significnce in reducing the rdil trnsport of toxic Cd ions to the xylem nd susequently to the shoot. This my e novel defence rection of plnts exposed to Cd. ACKNOWLEDGEMENTS We thnk the Ntionl Reserch Foundtion RSA Slovk Collortive Project, South Afric nd the Slovk Reserch nd Development Agency (grnt APVV SK-ZA-7-7) for finncilly supporting the ilterl collortive project, nd the Slovk Grnt Agency VEGA (1/472/1). The uthors re grteful to oth referees for vlule nd stimulting comments nd suggestions. LITERATURE CITED Bnsov V, Hork O, Nduinsk M, Cimporov M, Lichtscheidl I. 28. Hevy metl content in Thlspi cerulescens J. et C. Presl growing on metlliferous nd non-metlliferous soils in Centrl Slovki. Interntionl Journl of Environment nd Pollution 33: 133 145. Brzni O, Dudi N, Khdk UR, Goln-Goldhirsh A. 24. Cdmium ccumultion in Allium schoenoprsum L. grown in n queous solution. Chemosphere 57: 1213 1218. Chen YX, He YF, Luo YM, Yu YL, Lin Q, Wong MH. 23. Physiologicl mechnism of plnt roots exposed to cdmium. Chemosphere 5: 789 793. Coetzee MAS. 1995. Wter pollution in South Afric: its impct on wetlnd iot. In: Cown G. ed. Wetlnds of South Afric. Pretori, South Afric: Deprtment of Environmentl Affirs nd Tourism. Cooke JA, Johnson MS. 22. Ecologicl restortion of lnd with prticulr reference to the mining of metls nd industril minerls: review of theory nd prctice. Environmentl Reviews 1: 41 71. Deng DM, Shu WS, Zhng J, et l. 27. Zinc nd cdmium ccumultion nd tolernce in popultions of Sedum lfredii. Environmentl Pollution 147: 381 386. Deprtment of Wter Affirs. 1986. Mngement of the wter resources of the Repulic of South Afric. Pretori, South Afric: Deprtment of Wter Resources. Dickinson WC. 2. Integrtive plnt ntomy. Acdemic Press, Sn Diego. Fessler E, Roinson BH, Gupt SK, Schulin R. 21. Uptke nd lloction of plnt nutrients nd Cd in mize, sunflower nd tocco Downloded from http://o.oxfordjournls.org/ t University of KwZulu Ntl, Medicl Lirry on Jnury 3, 213
292 Lux et l. Cdmium nd hypoderml periderm formtion in roots growing on contminted soil nd the effect of soil conditioners under field conditions. Nutrient Cycling in Agroecosystems 87: 339 352. FAO/WHO. 1995. Joint committee on food dditives nd contminnts. Position pper on cdmium (Prepred y Frnce). 27th session. The Hgue, The Netherlnds, 2 24 Mrch 1995, p. 32. Filipic M, Hei TK. 24. Mutgenicity of cdmium in mmmlin cells: impliction of oxidtive DNA dmge. Muttion Reserch 546: 81 91. Fusconi A, Repetto O, Bon E, et l. 26. Effects of cdmium on meristem ctivity nd nucleus ploidy in roots of Pisum stivum L. cv. Frisson seedlings. Environmentl nd Experimentl Botny 58: 253 26. Greger M, Lnderg T. 28. Role of rhizosphere mechnisms in Cd uptke y vrious whet cultivrs. Plnt nd Soil 312: 195 25. Heimsch C, Sego JL. 28. Orgniztion of the root picl meristem in ngiosperms. Americn Journl of Botny 95: 1 21. IARC. 1993. Beryllium, cdmium, mercury nd exposure in glss mnufcturing industry: monogrphs on evlution of crcinogenic risk to humns, vol. 58. Lyon, Frnce: IARC, 119 239. Jckson AP, Allowy BJ. 1992. The trnsfer of cdmium from griculturl soils to the humn food chin. In: Adrino DC. ed. Biogeochemistry of trce metls. Boc Rton, FL: Lewis Pulishers, 19 158. Kt-Pendis A, Pendis H. 1984. Trce elements in soils nd plnts. CRC, USA. Kuff F, Rudll PJ, Conrn JG. 2. Systemtic root ntomy of Asprgles nd other monocotyledons. Plnt Systemtics nd Evolution 223: 139 154. Liu J, Co C, Wong M, Zhng Z, Chi Y. 21. Vritions etween rice cultivrs in iron nd mngnese plque on roots nd the reltion with plnt cdmium uptke. Journl of Environmentl Sciences 22: 167 172. Lunáčková L, Šottníková A, Msrovičová E, Lux A, Streško V. 23. Comprison of cdmium effect on willow nd poplr in response to different cultivtion conditions. Biologi Plntrum 47: 43 411. Lux A, Šottníková A, Optrná J, Greger M. 24. Differences in structure of dventitious roots in Slix clones with contrsting chrcteristics of cdmium ccumultion nd sensitivity. Physiologi Plntrum 12: 537 545. Lux A, Morit S, Ae J, Kori I. 25. An improved method for clering nd stining free-hnd sections nd whole-mount smples. Annls of Botny 96: 989 996. Lux A, Mrtink M, Vculík M, White PJ. 211. Root responses to cdmium in the rhizosphere: review. Journl of Experimentl Botny doi:1.193/jx/erq281 (in press). M LJ, Zhng Y, Bu N, Wng SH. 21. Allevition effect of lgintederived oligoscchrides on Vici f root tip cells dmged y cdmium. Bulletin of Environmentl Contmintion nd Toxicology 84: 161 164. Mrtink M, Lux A. 24. Response of roots of three popultions of Silene dioic to cdmium tretment. Biologi 59: 185 189. Meyer CJ, Sego JL, Peterson CA. 29. Environmentl effects on the mturtion of the endodermis nd multiserite exodermis of Iris germnic roots. Annls of Botny 13: 687 72. North GB, Brinton EK, Grrett TY. 28. Contrctile roots in succulent monocots: convergence, divergence nd dpttion to limited rinfll. Plnt, Cell nd Environment 31: 1179 1189. Peterson CA, Peruml CJ. 199. A survey of ngiosperm species to detect hypoderml Csprin nds. II. Roots with multiserite hypodermis or epidermis. Botnicl Journl of the Linnen Society 13: 113 125. Reinhrdt DH, Rost TL. 1995. Slinity ccelertes endoderml development nd induces n exodermis in cotton seedling roots. Environmentl nd Experimentl Botny 35: 563 574. Sltink GJ. 1971. The infection of uls y Penicillium sp. Act Horticulture 23: 235 241. Slt DE, Blylock M, Kumr NPBA, et l. 1995. Phytoremedition novel strtegy for the removl of toxic metls from the environment using plnts. Biotechnology 13: 468 474. Sego JL, Mrsh LC. 1989. Adventitious root development in Typh gluc, with emphsis on the cortex. Americn Journl of Botny 76: 99 923. Sego JL, Peterson CA, Enstone DE. 2. Corticl development in roots of the qutic plnt Pontederi cordt (Pontedericee). Americn Journl of Botny 87: 1116 1127. Seth CS, Misr V, Chuhn LKS, Singh RR. 28. Genotoxicity of cdmium on root meristem cells of Allium cep: cytogenetic nd Comet ssy pproch. Ecotoxicology nd Environmentl Sfety 71: 711 716. Soudek P, Kotyz J, Lenikusová I, Petrová Š, Benešová D, Vněk T. 29. Accumultion of hevy metls in hydroponiclly cultivted grlic (Allium stivum L.), onion (Allium cep L.), leek (Allium porrum L.) nd chive (Allium schoenoprsum L.). Journl of Food, Agriculture nd Environment 7: 761 769. Street RA, Kulkrni MG, Stirk WA, Southwy C, Vn Stden J. 27. Toxicity of metl elements on germintion nd seedling growth of widely used medicinl plnts elonging to Hycinthcee. Bulletin of Environmentl Contmintion nd Toxicology 79: 371 376. Street RA, Kulkrni MG, Stirk WA, Southwy C, Vn Stden J. 28. Vrition in hevy metls nd microelements in South Africn medicinl plnts otined from street mrkets. Food Additives nd Contminnts 25: 953 96. Street RA, Kulkrni MG, Stirk WA, Southwy C, Adillhi HS, Chinsmy M, Vn Stden J. 29. Effect of cdmium uptke nd ccumultion on growth nd nticteril ctivity of Merwill plume n extensively used medicinl plnt in South Afric. South Africn Journl of Botny 75: 611 616. Street RA, Kulkrni MG, Stirk WA, Southwy C, Vn Stden J. 21. Effect of cdmium on growth nd micronutrient distriution in wild grlic (Tulghi violce). South Africn Journl of Botny 76: 332 336. Vculík M, Lux A, Luxová M, Tnimoto E, Lichtscheidl I. 29. Silicon mitigtes cdmium inhiitory effects in young mize plnts. Environmentl nd Experimentl Botny 67: 52 58. World Helth Orgniztion. 1998. Qulity control methods for medicinl plnt mterils. Genev, Switzerlnd. Wren CD, Stephenson GL. 1991. The effect of cidifiction on the ccumultion nd toxicity of metls to freshwter invertertes. Environmentl Pollution 71: 25 241. Zho FJ, Jing RF, Dunhm SJ, McGrth SP. 26. Cdmium uptke, trnsloction nd tolernce in the hyperccumultor Aridopsis hlleri. New Phytologist 172: 646 654. Downloded from http://o.oxfordjournls.org/ t University of KwZulu Ntl, Medicl Lirry on Jnury 3, 213