Original Research Accumulation of Pb and Cd and its Effect on Ca Distribution in Maize Seedlings (Zea Mays L.)

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1 Polish Journl of Environmentl Studies Vol. 14, No. 2 (2005), Originl Reserch Accumultion of Pb nd Cd nd its Effect on C Distribution in Mize Seedlings (Ze Mys L.) E. Młkowski 1 *, R. Kurtyk 1, A. Kit 2, W. Krcz 1 1 Deprtment of Plnt Physiology, Fculty of Biology nd Environmentl Protection, University of Silesi, 28 Jgiellońsk St, Ktowice, Polnd 2 Deprtment of Anlyticl Chemistry, University of Silesi, 9 Szkoln St, Ktowice, Polnd Received: 29 June, 2004 Accepted: 10 August, 2004 Abstrct In the present study the ccumultion of Pb nd Cd in mize seedlings (Ze mys L., cv. K33 x F2) nd its effect on the content of C in their orgns were investigted. The influence of both metls on dry weight yield ws lso studied. Concentrtions of Pb, Cd nd C were mesured in 15 mm-long picl root segments s well s in whole mesocotyls nd coleoptiles fter 24 h of incubtion of seedlings in hydroponic solutions. It ws observed tht in Pb- or Cd-treted mize seedlings the dry weight of root picl segments ws mrkedly incresed, wheres in the shoots it ws less ffected. It ws lso found tht the content of both metls in mize seedling orgns rose with incresing concentrtions of Pb or Cd in the hydroponic solutions. The highest concentrtions of both metls were observed in roots, in which the ccumultion of Pb ws 10-fold higher thn tht of Cd. By contrst, higher ccumultion of Cd thn Pb ws found in mesocotyl nd coleoptile. These dt suggest tht the mechnisms of Pb nd Cd trnsloction from roots to shoots re different nd tht the ccumultion of C in roots nd its trnsloction to shoots ws less ffected by Pb thn Cd. Keywords: Pb nd Cd, C ccumultion, roots, mesocotyls, coleoptiles, Ze mys L. Introduction Hevy metls re present in soils s nturl components or s result of humn ctivities. Metl-rich mine tilings, metl smelting, electroplting, fossil fuel combustion, intensive griculture, nd wste disposl on lnd re the most importnt humn ctivities tht contminte soils with lrge quntities of the toxic metls [1]. Among toxic metls, Pb nd Cd pper to be the most dngerous to the environment. These non-essentil elements re tken up through the roots of mny plnt species nd ccumulted in ll plnt orgns. Tken up in excess, Pb nd Cd cn cuse deficiencies or dverse ion distribution within the plnt [2, 3, 4, 5, 6], disturb metbolism of nucleus [7], photosynthesis [8] or reduce rte of growth [9, 10, 11]. *Corresponding uthor; e-mil: mlkowsk@us.edu.pl Mny reserchers hve investigted the uptke nd ccumultion of Pb nd Cd in different plnt species [2, 12, 13, 14, 15, 16]. However, the mechnism of ccumultion of hevy metls is still not completely understood. Among crop plnt species, mize is one of the most importnt nd is grown throughout the world. It lso cn be used successfully in phytoextrction, which is new technology for removing hevy metls from contminted soils [17]. The uptke of Pb nd/or Cd [13, 18, 19, 20] nd effects of both metls on minerl nutrition [21, 22] in mize hve been studied previously. These experiments were conducted with mize plnts older thn 10 dys, wheres informtion concerning the uptke of Pb nd Cd nd their interction with other ions t the erly stges of mize seedling development is poorly documented. For exmple, Wierzbick nd Obidzińsk [23] conducted experiments on the effect of Pb on imbibition nd germintion of mize seeds, but they did not mesure uptke of Pb or C.

2 Dry weight, % of control Dry weight, % of control 204 It ws reported tht Pb nd Cd uptke ffected ccumultion of C in orgns of vrious plnt species [3, 16, 24, 25, 26, 27]. Bsed on these observtions, it ws postulted tht the hevy metls could compete with C for entry into plnt cells nd ffect ccumultion nd distribution of C in plnts [16, 24, 26, 28]. Recently, it hs been documented tht uptke of Pb nd Cd by plnt cells is medited by C 2+ chnnels nd/or crriers nd disturbs ccumultion of C [17, 29]. In the present work the ccumultion of Pb nd Cd nd its effect on C distribution in roots, mesocotyls nd coleoptiles of mize seedlings t their erly stges of development were investigted. The influence of both metls on dry weight yield ws lso studied. Mteril nd Methods The experiments were crried out with etiolted 3-dy-old mize seedlings (Ze mys L., cv. K33 x F2) tht were trnsferred to hydroponic continers filled with control solution of the following composition: KCl (1 mmol dm -3 ), NCl (0.1 mmol dm -3 ) nd CCl 2 (0.1 mmol dm -3 ) or to the solution with the sme slt composition, contining dditionlly PbCl 2 or CdCl 2 t finl concentrtion of 0.1 mmol dm -3 or 1.0 mmol dm -3. The control solution with the slt composition mentioned bove is used routinely in our lbortory [30, 31]. The initil ph of the solutions ws djusted to with 0.1 N NOH or 0.1 N HCl. The plnts were grown in the solution in the drk t 27ºC for 24 h. After this time roots were rinsed 2-fold with distilled wter nd blotted dry with tissue pper. Then 15 mm picl segments of seminl roots, whole mesocotyls nd coleoptiles (with the first lef removed) were smpled nd the plnt tissue ws dried t 80 C for 3 dys to determine its dry weight. In the current study the picl root segments, insted of whole roots, were used to sses the effect of Pb nd Cd on C ccumultion nd distribution, becuse the uptke of C nd its trnsloction to shoots is much higher in picl thn in bsl root zones [32]. For metl nlyses, dry plnt tissue ws digested with ultr-pure concentrted nitric cid (Merck). The concentrtions of Pb, Cd nd C were mesured by emission spectrometry with excittion by n rgon inductively-coupled plsm technique (ICP-AES). Stndrd solutions of metls (Merck) were used s reference. All chemicls were of nlyticl grde. All experiments were replicted t lest four times, with 100 seedlings in ech replicte. Dt were nlyzed using the computer softwre Sttistic for Windows, version , SttSoft Inc., Tuls, USA (Licence SP NET5). Differences between individul tretments nd control were nlyzed using one-wy ANOVA nd LSD test. Sttisticl significnce ws defined t p < Results Młkowski E. et l. As cn be seen in Fig. 1 the dry weight of the 15 mm long picl root segments ws lmost twofold greter, s compred to the control (100 %), when mize seedlings were exposured to both 0.1 mmol dm -3 nd 1.0 mmol dm -3 Pb. However, mesocotyl nd coleoptile dry weight did not significntly differ, s compred to the control solution, in plnts treted with 0.1 mmol dm -3 or 1.0 mmol dm -3 Pb (Fig. 1). In turn, when mize seedlings were treted with 1.0 mmol dm -3 Cd n increse of dry weight of both root segments nd mesocotyls ws observed (Fig. 2). By contrst to Pb, Cd t 1.0 mmol dm -3 decresed dry weight of coleoptiles. However, in plnts treted with Cd lrge vritions in dry weight yields were observed nd differences mong mens of dry weight of control nd Cd-treted plnts were not sttisticlly significnt (Fig. 2). The dt in Tble 1 indicte tht ccumultion of Pb nd Cd in mize seedling orgns incresed with incresing concentrtions of both metls in the hydroponic solutions. The content of Pb in root segments, t both concentrtions of hevy metls used, ws pproximtely tenfold higher s compred to Cd. The dt in Tble 1 lso suggest tht trnsport of Cd from roots to shoots ws less restricted thn tht of Pb nd its level in mesocotyl nd coleoptile t 0.1 mmol dm -3 ws mrkedly higher thn tht of Pb. Plnts from 1.0 mmol dm -3 tretments hd significntly higher concentrtion of Cd thn Pb in coleoptile but there ws no sttisticlly significnt difference in concentrtion of both metls in mesocotyls. Figure 3 shows comprison of the effects of both metls nd the control tretment on ccumultion of C in seedling orgns. The dt indicte tht following exposure of seedlings to Pb t both concentrtions (0.1 mmol dm -3 nd 1.0 mmol dm -3 ), the ccumultion of C in root segments ws enhnced 2- to 2.7-fold s compred to c d b b Pb 0.1 mmol/l Pb 1.0 mmol/l Fig. 1. Effects of Pb on dry weight (mg) of mize seedling orgns (Ze mys L.), shown s percent of control. Vlues re mens (n = 4). Columns mrked with the letter re not significntly different from the control using LSD test (p < 0.05). Columns mrked with the sme letter re not significntly different from ech other using LSD test (p < 0.05). b b

3 Dry weight, % of control Accumultion of Pb nd Cd Tble 1. Effects of different concentrtions (0.1 nd 1.0 mmol/l) of Pb or Cd in the hydroponic medium on concentrtions (mg/kg d.w.) of both metls in the orgns (root, mesocotyl, coleoptile) of mize seedlings. Vlues re mens ± SE (n=4). Concentrtion of metls in the hydroponic medium Plnt orgn Cd 0.0 mmol/l (control) 1.8 ± ± ± 0.37 Cd 0.1 mmol/l ± 630 b 91.5 ± 11.6 b 25.5 ± 5.7 b Cd 1.0 mmol/l 10,010.5 ± 650 c ± 33.0 b 70.0 ± 6.0 c Pb 0.0 mmol/l (control) 5.2 ± 0.20 d 0.3 ± ± 0.13 Pb 0.1 mmol/l 40,293.3 ± 1261 e 52.0 ± 9.2 c 11.0 ± 4.5 d Pb 1.0 mmol/l 113,404.7 ± 9532 f ± 7.0 b 39.0 ± 7.5 b Mens followed by the sme letter in column re not significntly different from ech other using the LSD test (P < 0.05). control solution. In plnts treted with 0.1 mmol dm -3 Cd, the concentrtion of C ws 3-fold greter thn in the control. Contrry to Pb, Cd t higher concentrtion (1.0 mmol dm -3 ) decresed content of C by 30%, s compred to the control, but the difference ws not sttisticlly significnt (Fig.3A). In mesocotyls the effect of Pb on C ccumultion showed no definite tendency, wheres Cd decresed the C content in these orgns (Fig. 3B). In coleoptiles Pb nd Cd hd no sttisticlly significnt effect on C concentrtion (Fig. 3C). Discussion The dt presented in this pper show tht dry weight of the 15 mm long picl root segments ws enhnced, s compred to the control, by exposure of mize seedlings to both Pb concentrtions, wheres dry weight of mesocotyls nd coleoptiles ws not significntly ffected 200 Clcium concentrtion in roots [mg kg -1 d.w.] Clcium concentrtion in mesocotyls [mg kg -1 d.w.] A B Cd 0.1 mmol/l Cd 1.0 mmol/l Clcium concentrtion in coleoptiles [mg kg -1 d.w.] C Fig. 2. Effects of Cd on dry weight (mg) of mize seedling orgns (Ze mys L.), shown s percent of control. Vlues re mens (n = 4). Columns mrked with the letter re not significntly different from the control using LSD test (p < 0.05). Columns mrked with the sme letter re not significntly different from ech other using LSD test (p < 0.05). Fig. 3. Effects of Pb nd Cd on ccumultion of C in mize (Ze mys L.) seedling orgns: A concentrtion of C in roots; B concentrtion of C in mesocotyls; C concentrtion of C in coleoptiles. Vlues re mens (n = 4). Columns mrked with the sme letter re not significntly different from ech other using LSD test (p < 0.05).

4 206 (Fig. 1). Similr results hve recently been demonstrted by Młkowski et l. [27], who showed tht in mize seedlings exposed to Pb (t 0.1 mmol dm -3 nd 1.0 mmol dm -3 ) the dry weight of root picl segments (8 mm) ws mrkedly incresed, wheres the dry weight of shoots ws not significntly ffected. In the cse of Cd-treted mize seedlings (Fig. 2) the higher dry weight of roots nd mesocotyls (sttisticlly insignificnt) ws found t 1.0 mmol dm -3. By contrst to roots nd mesocotyls, dry weight of coleoptiles ws not chnged by Cd (Fig. 2). However, there is no dt concerning the effect of Cd on dry weight of mize seedlings t their erly stges of development. Becuse of different experimentl conditions (e.g. concentrtion of Cd, time of exposure, seedlings growth stges), direct quntittive comprison of our dt for Cd with the results presented by other uthors [22, 33, 34] is difficult. The higher dry weights of root picl segments, in the presence of Pb or Cd, found in the present study, my hve been due to the fct tht roots in plnts treted with both metls were shorter but thickened (dt not shown). The dt on ccumultion of Pb nd Cd hve clerly shown tht both metls were strongly ccumulted in roots, but substntilly lower mounts were observed in mesocotyls nd coleoptiles. It ws lso found here tht ccumultion of Pb in mize root picl segments ws 10- fold higher s compred to Cd (Tble 1). These results re in greement with the dt obtined by other uthors for different plnt species [2, 5, 15, 28]. It ws proposed by Brennn nd Shelley [35] tht very high ccummultion of Pb in roots might be connected with prepicittion of the metl t the root surfce s morphous Pb-phosphte. It is noteworthy tht trnsport of Cd to shoots ws higher s compred to Pb (Tble 1). These dt suggest tht mechnisms of trnsloction of Pb nd Cd from roots to shoots re different. Similr results for trnsloction of Pb nd Cd were lso reported by Burzyński [2] nd Kim et l. [28] in experiments with Cucumis stivus nd Oryz stiv, respectively. Since the trnsport of C 2+ ions by chnnels or trnsporters is inhibited by Pb nd Cd [17, 29], it would be expected tht the ccumultion of C in the presence of the hevy metls should be reduced. As indicted from results presented here this ws not the cse, becuse incresed Pb ccummultion in root tips (Tble 1), ws connected with higher uptke of C (Fig. 3A). Wierzbick [36] hs recently reported tht Pb stimulted thickening of the cell wlls in roots, which ws result of the synthesis of new cell wll polyscchrides. This new cell wll should crete new binding sites for divlent ctions nd enhnce their ccumultion in roots. Results shown in the present study might suggest tht ccumultion of Pb nd C in mize root picl segments might be relted to binding of both divlent ctions to the newly synthesised cell wll. Accumultion of Pb in plnt cell wlls ws lso observed by other uthors [36, 37, 38]. Cdmium t higher concentrtion (1.0 mmol dm -3 ) decresed the content of C in root segments by 30% s compred to the control (not sttisticlly significnt) Młkowski E. et l. (Fig.3A). These dt suggest tht Cd, contrry to Pb, should compete with C for entry to the root cells. Results presented in the current study showed tht ccumultion of C in roots nd its trnsloction to shoots were less ffected by Pb thn Cd. It is proposed tht this phenomenon is relted to binding of higher mount of Pb, s compred to Cd, in the root poplst (cell wlls). Cdmium, which is not bound in the poplst could compete with C for trnsport systems. Thus, we conclude tht effects of Cd on ccumultion nd distribution of C in mize seedlings, contrry to Pb, might be cused vi competition for the trnsport systems cross the plsm membrne but not vi competition for the binding sites on the cell wll. References 1. ROSS S.M. 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