Identification of Cd Accumulation and Translocation Ability for the Root of 20 Rice Cultivars

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1 Journl of Agriculture Food nd Development, 218, 4, Identifiction of Cd Accumultion nd Trnsloction Ability for the Root of 2 Rice Cultivrs Xu Fengli, Hu Hongqing *, Zhu Jun nd Fu Qingling College of Resources nd Environment, Huzhong Agriculturl University, Key Lbortory of Arble Lnd Conservtion (Middle nd Lower Reches of Yngtze River), Ministry of Agriculture, Hubei 437, Chin Abstrct: There ws certin difference in the ccumultion nd trnsloction cpcity of Cd in 2 rice genotypes by hydroponics. The different detoxifiction mechnism of Cd in rice roots ws explored from microcosmic perspective. The results showed tht the ccumultion of Cd in Jponic rice ws lrger thn tht in Indic rice. The Cd content in root ws higher thn tht in stem/lef, nd the trnsfer fctor vried in 1.22% %. The non-protein-sulfhydryl substnce in root ply certin role in Cd detoxifiction in the rice root. The content of Cd in the root cell wll ws higher thn in other components, nd the content of non-protein thiol (NPT) mterils in root ws significntly correlted with the ccumultion of Cd. The Cd tolernce of these genotypes rice ws obviously different, but the mechnism of detoxifiction of rice root ws ll relted to the cell wll nd the content of NPT in the cell. Keywords: Rice genotypes, Cd, subcellulr distribution, NPT. 1. INTRODUCTION Globlly, mny pddy fields re subject to Cd pollution due to humn ctivities such s the indiscriminte dischrge of industril nd mining wstes, improper sludge disposl nd irrtionl use of chemicl fertilizers. In Chin, bout h of griculturl soils re polluted by vrious contminnts [1]. Rice is the min food for more thn hlf of the world's popultion. The ccumultion of Cd in rice cn enter the humn body through the food chin nd cuse hrm to humn beings, especilly in Southest Asi [2]. Different genotypes of rice cultivrs hve gret differences in ccumultion nd root tolernce to Cd [3, 4, 5]. Therefore, it is essentil to study the ccumultion nd trnsfer of Cd in rice roots of vrious genotypes. Toxicity of Cd on rice cnnot be ignored, even t low Cd concentrtions. The plnt will lso pper necrosis nd produce Cd-contining grin. Rice roots ply significnt function in the bsorption nd trnsfer of metl Cd, nd once the root bsorbs Cd, it will be complexed by the cell wll (polyscchrides) nd / or low moleculr weight compounds, inhibiting its trnsfer to bove ground [6, 7]. There re two kinds of mechnism for plnt detoxifiction of Cd, the deposition of rice root cell wll nd the intrcellulr ction of the vcuolr [8, 9]. Root gene expression produce nonprotein thiol mterils (NPT), minly including glutthione (GSH), phytocheltin synthse (PCs) nd other mterils contining thiol (-SH), which plys * Address correspondence to this uthor t the College of Resources nd Environment, Huzhong Agriculturl University, Key Lbortory of Arble Lnd Conservtion (Middle nd Lower Reches of Yngtze River), Ministry of Agriculture, Hubei 437, Chin key role in the Cd detoxifiction of plnts [1, 11]. Clemens et l. [12] suggests tht Cd cn bind to PC in the plnt cytoplsm to form PC-Cd complex, then trnsport to the vcuole by trnsport proteins to constitute sulfur-contining high moleculr weight complex, which is stored in the vcuole, decrese the concentrtion of free Cd 2+ in the cytosol nd reduces the toxicity of Cd. This study investigted the differences in Cd ccumultion in 2 genotypes of rice from the micro level, so s to identify the detoxifiction mechnisms. Differentil centrifugtion nlysis ws used to compre the sub cellulr distribution of Cd ccumultion in these genotypes of rice to revel the mechnism of Cd uptke. In ddition, through the explortion for the Cd tolernce differences in 2 genotypes of rice cultivrs nd the expression of NPT in rice roots, it will provide scientific bsis for screening of rice resistnt to Cd nd the mechnism of Cd detoxifiction in rice root cytoplsm. 2. MATERIALS AND METHODS 2.1. Rice Vrieties Twenty rice cultivrs (13 indic styles, 7 jponic styles) were selected, including indic conventionl rice, indic two-line hybrid rice, indic three-line hybrid rice, jponic conventionl rice, jponic two-line hybrid rice nd jponic three-line hybrid rice. Specific cultivrs re listed in Tble Experiment Method Rices were cultivted with rice specil nutrient solution from Interntionl Rice Reserch Institute in E-ISSN Interntionl Journl of Green Technology

2 Identifiction of Cd Accumultion nd Trnsloction Ability for the Root of 2 Journl of Agriculture Food nd Development, 218, Vol. 4, 11 Tble 1: Bsic Sitution of Tested Rice Vrieties Codes Nmes Styles Mle ( ) Femle ( ) 1 Ludo Q7 indic conventionl rice Bsmti-Superfine Hunghuzhn 2 Hunghuzhn indic conventionl rice Fenghuzhn Hungxinzhn 3 Huilingyou996 indic two-line hybrid rice R S 4 Aofuyou 383 indic three-line hybrid rice Ao R383 Aofu A 5 Gunglingyou 35 indic two-line hybrid rice R35 Gungzhn 63-4S 6 Huyou 352 indic two-line hybrid rice Huhui 352 Hu 528A 7 Shenyou 957 indic three-line hybrid rice α-7 Shen 95A 8 Y lingyou 9 indic two-line hybrid rice R9 Y58S 9 Lingyou 289 indic two-line hybrid rice R S 1 Qunyou 822 indic three-line hybrid rice YR822 Qun 9311A 11 E Lingyou 476 indic two-line hybrid rice R476 E nong 1S 12 II you 331 indic three-line hybrid rice Minhui 331 Ⅱ-32A 13 Ju 2 you 18 indic three-line hybrid rice Ehui18 Jufeng2A 14 E xing No. 2 jponic two-line hybrid rice * * 15 Xingyubo jponic conventionl rice * * 16 Jiyou No. 2 jponic three-line hybrid rice Jihui 3 J 6A 17 Wnjing 55 jponic conventionl rice 955 Chunjingnuo 18 Ejing 912 jponic conventionl rice Bonong 12 Ewn 9 ho 19 E Jingz No. 3 jponic two-line hybrid rice Minhui 128 N588S 2 Ewn 17 jponic conventionl rice 955 Chunjing 3 jing * An unknown prents. PVC pots (height 3 cm, dimeter 25 cm). The rice seeds with full grin shpe were selected nd soked in 3% H 2 O 2 (w/w) for 1 min nd clened with deionized wter. After two weeks of cultivtion in deionized wter, the rice seedlings were trnsferred to 1/8 diluted specil nutrient solution. When the seedlings grew to four-lef, they were treted with the complete nutrient solution contining 2. µmol/l cdmium (CdCl 2 ), which ws djusted ph round 5.5 with dilute NOH or HCl solution nd replced every ten dys. The quntittive nutrient solution ws dded every two dys. These were set up 4 repetitions. Ech pot hs three poles in the cover. Two strins were put per hole nd controlled pest timely Smple Collection nd Anlysis Rice plnt smples were collected fter 4 dys in Cd stress, rinsed 3 times with tp wter, wshed 3 times with deionized wter nd seprted the roots, stems nd leves. The fresh smples were preserved for determintion of NPT content nd subcellulr distribution of Cd in roots. When the smples were collected, the height of rice plnts ws mesured. After the smples were collected, they were soked t 15 for.5 hour, dried t 6, nd their dry mss were weighed. The dried plnts were milled through the 1 mm-sieve, digested with 4:1 nitric cid- perchloric cid, nd the Cd content ws determined with tomic bsorption spectrometry (AAS) Subcellulr Distribution of Cd in Rice Roots Different frctionl centrifugtion technique ws used to isolte the cellulr components of ech orgn: cell wll frction (F1), orgnelle frction (F2), membrne frction (F3), nd cell fluid frction (F4). The detiled method is: the fresh plnt smple 1 g ws dded with 1 mmol L -1 Tris-HCl buffer (ph=7.4, 2.5% AsA), ground in n ice bth, nd the homogente ws centrifuged to seprte ech cell component. The filter residue ws F1. F2 component ws centrifuged nd precipitted t 25 g, other ws precipitted t 15 g s F3 component fter centrifugtion, nd superntnt is F4 component. Ech buffer ws replenished with the sme volume of buffer before

3 12 Journl of Agriculture Food nd Development, 218, Vol. 4 Xu, et l. centrifugtion. The resulting residue nd precipitte were ssyed for nlysis. The cell wll nd unbroken residue were wshed with deionized wter, filtered by quntittive filter pper nd dried t 6, nd 1 ml of HNO 3 -HClO 4 (4:1, V/V) mixture ws dded. After overnight, digestion ws performed t 2. Cd content ws determined through AAS. The orgnelle pellets were trnsferred to smll beker with deionized wter, evported to dry on hot plte, digested with 2 ml of concentrted nitric cid nd clrified. The superntnt ws cidified for the determintion of Cd content with AAS Determintion of Non-Protein Sulfhydryl The fresh smple 1. g ws dded 2. ml of 5% (V/V) SSA (5-sulfoslicylic cid) (contining 6.3 mmol L -1 DTPA, ph<1), nd dded smll mount of wshed qurtz snd in 4. The smples were ground, mixed nd centrifuged (8 g) in low-temperture (4 ) for 15 min. And the superntnt liquid ws reserved. The superntnt 3 µl ws took into 1 ml glss test tube, dded 63 µl.5 mol L -1 K 2 HPO 4 (ph 7.5) nd 25 µl 6.3 mmol L -1 2-nitrobenzoic cid (DTNB), plced for 2 min t room temperture, nd used for the colorimetric determintion of non-protein thiol t 412 nm Index Clcultion nd Dt Anlysis When rice ws hrvested, the dry weight of root nd stem (lef) rtio (R/S) ws used to evlute growth nd helth indictors [13]. Trnsfer fctor (TF%) [14]= Cd content of stem nd lef (mg/kg dry weight)/ Cd content of root (mg/kg dry weight) 1. All dt ws sttisticlly nlyzed using SPSS RESUIL AND ANALYSIS 3.1. Plnt Height nd Biomss of Rice t Different Cd Concentrtions The growth sttus of ech genotype rice ws shown in Tble 2 nd Figure 1. According to Tble 2, the length of rice root ws cm nd the length of Tble 2: Length of Roots, Stems nd Leves t Hrvest of Different Rice Vrieties (cm) Codes of Rice The Length of Rice Roots(cm) The Length of Rice Stems nd Leves(cm) 1 2.1±1.82 gh 28.2±.95 l 2 3.8±1.86 bc 48.6±11.4 def 3 24.±.53 efg 53.1±1.1 b 4 3.2±.75 bc 57.±.66 bc 5 2.3±1.41 fgh 36.3±1.58 ijk ±.31 gh 4.1±1.1 ghij ± ±.93 efgh ±.5 h 41.4±1.1 ghi ± ±2.25 bcd ±1.62 b 51.5± ±.84 b 6.±1.65 b ±.78 bcd 57.2±.96 bc ±.49 b 57.6±2.1 bc ±.44 fgh 46.7±1.78 efg ±.72 h 31.2±2.86 kl ± ± ± ±1.25 fghi ±.25 h 34.1±2. jkl ±1.4 fgh 52.5± ±.4 def 39.2±1.17 hij The vlues re men ± SE (n = 3). Different letters in the sme column indicte significnt difference between the rice cultivrs t P <.5.

4 Identifiction of Cd Accumultion nd Trnsloction Ability for the Root of 2 Journl of Agriculture Food nd Development, 218, Vol. 4, 13 stems nd leves cm. The differences between the root length nd the length of stems nd leves of rice t tested Cd concentrtions were obvious, nd the plnt heights of "E Lingyou 476", "Jiyou No. 2" nd "Lingyou 289" were longer compred with others nd were 91.8 cm, 59.3 cm nd 89. cm respectively. In Figure 1, the dry mtter biomss of rice in "Ejingz No. 3", "E Lingyou 476", "Aofuyou 383" nd "Lingyou 289" were higher thn tht of other vrieties nd their vlues ll were bove 1.4 g/per. While "Ludo Q7" hd the lowest plnt height nd dry mtter weight in this biologicl stge. Compred with the lrgest "E Lingyou 476", the difference in plnt height ws.9 times, nd the biomss ws 6.14 times lower thn the mximum biomss "E Jingz No. 3" Dry weight(g/per) Stems nd leves Roots R/S showed tht the totl ccumultion of Cd in jponic rice ws mg/kg. The ccumultion of totl Cd in jponic rice cultivrs No. 14 E xing No. 2, No. 15 Xingyubo, No. 16 Jiyou No. 2 nd No. 17 Wnjing 55 were 47.9, 462.1, nd mg/kg, respectively. However, in indic rice, especilly the ccumultion of Cd in indic rice cultivrs No. 9 Lingyou 289, No. 1 Qunyou 822, No. 11 E Lingyou 476 nd No. 12 "II you 331 were 186.7, 183.8, nd 17. mg/kg, respectively. These results indicted tht the ccumultion mount of Cd in jponic rice ws higher thn tht in indic rice universlly. Acoumultion of Cd in rice (mg/kg) hi defg bcd def efghefghi Stems nd leves efghi fghi ghi i hi efghi Roots b bc bc.2. Figure 1: Dry weight t hrvest of different rice vrieties (g/plnt). Figure 2: The ccumultion of Cd t hrvest of different rice vrieties (mg/kg). Thus, there ws significnt difference in the response of different genotype rice growth under the sme Cd stress. But it could be seen tht there ws no significnt difference in growth helth sttus (R/S) fter Cd stress tretment in rice. Overll, the growth height nd dry mtter weight of rice genotypes differed gretly Cd Accumultion of Rice During the 4-dy growth of rice under Cd stress, the Cd ccumultion in different orgns nd the Cd trnsfer fctor (TF%) were showed in Figure 2 nd 3. In 2 rice cultivrs, the Cd content of rice root rnged from to mg/kg, but tht of stems nd leves ws mg/kg. The ccumultion of Cd in rice ws minly concentrted in the roots, while its content in stems nd leves is less. In Figure 2, it TF(%) fghi i fgh bcd f b efg hi ghi ghi fghi efg f defg efg efg Figure 3: Trnsfer fctor of root-stem nd lef t hrvest of different rice vrieties (TF%). bc bc

5 14 Journl of Agriculture Food nd Development, 218, Vol. 4 Xu, et l. As could be seen from Figure 3, there were significnt differences in the trnsfer fctors of these rice cultivrs. The rice cultivrs with lrger trnsfer fctors were Aofuyou 383, Huyou 352 nd EJingz No. 3. In prticulr, vrieties Huyou 352 whose trnsfer fctor ws s high s 11.12%, while the minimum trnsfer fctor ws Lingyou 289, which is only 1.22%. For the cultivr Ludo Q7, the ccumultion content of Cd nd the trnsfer fctor were smll, but the growth sttus ws poor, probbly becuse the growth of the rice cultivr ws slow to grow nd metbolize under Cd stress, resulting in decrese in the bsorption nd trnsport cpcity of Cd Distribution of Cd in Rice Root Subcellulr It could be seen in Figure 4 tht, for the ll rice genotypes, the ccumultion of Cd in the rice root ws minly distributed in the cell wll component (F1), nd tht in the cell fluid (F4) ws the second. The Cd cumulnt of F1 nd F4 in No. 9 Lingyou 289, for instnce, were 55.11% nd 24.27% respectively. The ccumultion of Cd in the rice roots orgnelles component (F2), nd the membrne structure constituent (F3) ws reltively smll, such s F1 (62.51%), F4 (23.62%), F2 (7.76%) nd F3 (6.11%) in No. 1 ludo Q7. The lrgest proportion of F1 components in Cd content ws the cultivr Huilingyou 996 with rtio of 7.1%, nd the smllest ws cultivr No. 15 Xingyubo with Cd rtio of 41.96%. The subcellulr distribution rtio of Cd in rice root_%_ F4 F3 F2 F1 Figure 4: The subcellulr distribution of Cd in root system of different rice vrieties. Although the Cd distribution mount of F1 ws the lest in Xingyubo mong these rice genotypes, the order of distribution in ech component of Xingyubo ws still F1 (41.96%) > F4 (22.3%) > F2 (21.9%) > F3 (13.83%). This indicted tht the Cd minly deposited in the cell wll of rice roots, nd it did not vry gretly mong these genotypes NPT Content of Rice Root under Cd Stress It showed in Figure 5 tht the NPT content rnge in different rice genotypes ws mg/kg. No. 9 Lingyou 289, No. 1 Qunyou 822 nd No. 11 E lingyou 476 hd fewer NPT content, 2.41 mg/kg, 1.69 mg/kg nd 1.47 mg/kg, respectively, while the content of Cd in jponic rice ws generlly higher, mg/kg in "Ejing 912", which ws the highest The NPT concention of root(mg/kg)18 2 hij b jk h ij h ef e ijk l kl d Figure 5: The NPT content of root t hrvest of different rice vrieties (mg/kg) Accumultion of Cd in rice roots(mg/kg) ij fg g e e r=.536 p=.15 The NPT concention of rice root(mg/kg) Figure 6: The correltion between Cd ccumultion nd NPT content in rice root. d

6 Identifiction of Cd Accumultion nd Trnsloction Ability for the Root of 2 Journl of Agriculture Food nd Development, 218, Vol. 4, 15 Apprently, the NPT contents were different in the roots of tested rice genotypes. In Figure 6, the ccumultion of Cd in roots of rice ws significntly correlted with the expression of NPT in roots (P <.5). This suggested tht the uptke of Cd in rice roots stimulted the expression of NPT, llowing more Cd to bind to NPT nd reducing the Cd ccumultion in the shoot. Therefore, the expression of NPT in rice roots is n importnt substnce tht inhibits the metstsis of Cd in plnts. 4. DISCUSSION The discrepncy in bsorption nd ccumultion of Cd in different rice genotypes ws significnt, nd Cd ws minly present in the root prt of rice, the sme s Li reported [15]. The roots of rice re in direct contct with the Cd-contining environment nd the metl re trnsported through the root system to the ground. Simultneously, the present study found tht Cd ws minly concentrted in cell wlls of roots, nd the content of Cd in the soluble components of rice root cells ws only inferior to tht of cell wll, which might be relted to the deposition of cell. At present, the rice cell wll fixtion nd vcuole comprtmentliztion ply n importnt role in reducing Cd toxicity. Cd is minly combined with the crboxyl group nd hydroxyl group (-COOH/-OH) in the cell wll, inhibiting its entrnce into the cytoplsm nd reducing the toxic effects of metl on rice [16, 3]. Vcuolr comprtmentliztion of plnt cells is one of the importnt detoxifiction mechnisms in rice. Gene OsHMA3 locted on the cell membrne cn trnsfer Cd into the vcuole nd inhibit the metstsis of Cd [17]. The presence of Cd could induce NPT-SH synthesis in rice roots. Shi nd Pn [18] similrly indicte tht Cd cn promote to produce NPT. The prt of Cd bsorbed by rice roots exists in the form of NPT- SH-Cd (PCs-Cd, GSH-Cd, etc.), complexes in the vcuole nd inhibits Cd trnsfer to the shoot [19, 2, 21], but the Cd content of the soluble components in the rice root system ws correlted with the trnsfer fctor (TF) of Cd [22]. Therefore, the trnsfer of metl, which ccumulted in rice root, would be suppressed. These results not only showed tht rice cell deposition ws the min detoxifiction mechnism, but lso explined the resons the more Cd in rice roots thn stems nd leves. It could be found tht the ccumultion mount of Cd nd NPT in jponic rice ws higher thn tht in indic rice universlly. Although study hs pointed out tht the ccumultion of Cd in indic rice ws greter thn tht of jponic rice [23], the reltionship between the expression of NPT in the roots of rice nd the ccumultion of Cd hs not been nlyzed. Our study held tht the ccumultion mount of Cd nd NPT were significntly positively correlted. The previous studies hve shown tht the GSH content in root for low-cd rice vrieties is higher thn tht for high-cd rice cultivrs [24]. Phytocheltin (PC), s kind of NPT, plys n importnt role in the metstsis bility of Cd in rice cells. It ws found tht the dded Cd down regulted the metl trnsporter genes IRT1 nd NRAMP1, while up regulted the expression of the PC synthse gene (PCS1) in plnt [25]. The detoxifiction mechnisms of different rice vrieties re similr, but the differences in Cd ccumultion between indic rice nd indic rice my be relted to the content nd species of NPT in rice. The results of this study only reflected the reltionship between Cd nd NPT content in rice roots, nd we should further explore the differences in gene expression between indic nd jponic rice, nd find out the contribution of specific proteins to the detoxifiction mechnism of Cd. CONCLUSION Under the sme Cd level stress, the tolernce bility of severl genotypes of rice ws existentil discrepncy, but the mechnism of Cd tolernce ws bsiclly the sme. Generlly, the mechnism of detoxifiction in these rice genotypes ws relted to the cell wll nd intrcellulr NPT expression in rice roots. Cd ccumultion in rice roots ws significntly correlted with its expression of NPT, nd Cd in the rice genotypes ws minly distributed in cell wll components, followed by cytosolic components. There ws no significnt difference in R/S mong the rice cultivrs, while the ccumultion of Cd nd the rootshoot trnsfer fctor in ll cultivrs, especilly jponic cultivrs, were higher thn tht in indic cultivrs. Considering the difference in the growth sttus nd Cd ccumultion nd trnsport cpcity of 2 genotype rices, it is considered tht the "Lingyou 289" rice cultivrs re more resistnt to Cd. ACKNOWLEDGEMENT The work ws finncilly supported by the Ntionl Science nd Technology Support Pln of Chin (215BAD5B2). REFERENCE [1] Liu F, Liu X, Ding C nd Wu L. The dynmic simultion of rice growth prmeters under cdmium stress with the ssimiltion of multi-period spectrl indices nd crop model.

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