Excessive sulfur supply reduces arsenic accumulation in brown rice

Transcription

1 Plnt Soil Environ. Vol. 59, 213, No. 4: Excessive sulfur supply reduces rsenic ccumultion in rown rice J. Fn 1, X. Xi 2, Z. Hu 3, N. Zidi 4, C. Liu 5 1 Stte Key Lortory of Soil nd Sustinle griculture, Institute of Soil Science, Chinese cdemy of Sciences, Nnjing, P.R. Chin 2 Institute of Environment nd Sustinle Development in griculture, Chinese cdemy of griculture Sciences, eijing, P.R. Chin 3 College of Resources nd Environment, University of Chinese cdemy of Sciences, eijing, P.R. Chin 4 Soils nd Crops Reserch nd Development Centre, griculture nd gri-food, Queec, Cnd 5 Jingsu Key Lortory of griculturl Meteorology, College of pplied Meteorology, Nnjing University of Informtion Science nd Technology, Nnjing, P.R. Chin STRCT The ojective of this study ws to investigte the influence of excessive sulfur (S) supply on iron plque formtion nd rsenic (s) ccumultion in rice plnts. comined soil-snd pot experiment ws conducted y using two s levels (, 2 mg/kg) comined with three S concentrtions (, 6, 12 mg/kg). The results showed tht excessive S supply significntly decresed s concentrtion in rown rice, ut s concentrtion in root incresed with incresing rte of S supply. Moreover, ioconcentrtion fctors for leves nd stems were 8 35 fold of tht for rown rice, indicting tht s ws minly ccumulted in rice leves nd stems insted of rown rice. Furthermore, excessive S supply significntly decresed trnsloction fctor of s compred to tretment without S supply. These results indicted tht excessive S my reduce s trnsloction from soils nd roots to grin. The mechnism could e scried to excessive S tht induced the decrese of s vilility, the increse of iron plque formtion under s stress, nd the increse of glutthione in rice leves nd roots. Therefore, excessive S cn reduce s ccumultion in rown rice exposed to s contminted soils though it my result in loss of rice yield. Keywords: rsenic toxicity; glutthione; iron plque; Oryz stiv L.; plnt uptke rsenic (s), n extremely toxic metlloid pollutnt, is distriuted in soil through nthropogenic ctivities, such s pesticide nd hericide ppliction, mining, or irrigtion with contminted groundwter (Hu et l. 27). Rice grown on s-contminted pddy soil cn ccumulte high levels of s, pproximtely 1-fold lrger thn other cerels (Lomi et l. 29). Thus, s uptke y rice plnts is recognized s mjor route of s trnsfer into food chin which hs the potentil to ecome new disster for popultion in Southest si (Heikens et l. 27). Therefore, it is crucil to understnd the mechnism of s uptke y rice nd to find strtegies for reducing s ccumultion in grin for enhnced food sfety. Pddy rice (Oryz stiv L.) oxygentes its rhizosphere, resulting in the formtion of n iron oxyhydroxide plque (Hnsel et l. 21). The effect of iron Supported y the Open Fund Project of the Stte Key Lortory of Soil nd Sustinle griculture, Project No , nd y the Ntionl Nture Science Foundtion of Chin, Grnts No nd

2 Vol. 59, 213, No. 4: Plnt Soil Environ. plque on plnt uptke of hevy metls or nutrients my depend on the mount of iron plque on the root surfce (Hu et l. 27). The Fe hydroxides in soil nd solution hve very strong inding ffinity for rsente (so 4 3 ) nd possile cpcity to oxidize rsenite (so 3 3 ) to rsente (Liu et l. 24). The iron plque my ct s rrier or uffer to s uptke due to the dsorption nd immoiliztion of metls y iron plque (Liu et l. 24). Reduced glutthione (GSH), low moleculr weight tri-peptide, is the most undnt source of non-protein thiol in plnt cells (Khn et l. 28). GSH hs function in the detoxifiction of hevy metls through the formtion of phytocheltins (PCs) (Hssn et l. 25), which cn e trnsported to the tonoplst, tken up y ctive trnsport systems, nd deposited in the vcuole, thus decresing the toxicity of hevy metls (Shrm nd Dietz 26). s in pddy soils predominntly occurs in its reduced form, rsenite, which cn rect with GSH nd/or PCs forming s-pcs or s-gs complex (Tuli et l. 21). Once formed in roots nd leves, they could e trpped s peptide-thiol complexes such s γ-glutmylcysteine, precursor of GSH (Dhnkher et l. 22). Nonetheless, there re no reports on the interctions etween excessive S, iron plque development, GSH nd s ccumultion in rice. The ojective of this study ws to investigte these interctions under greenhouse culture. MTERIL ND METHODS Experimentl design. The topsoil ( 2 cm) from Putin city, Fujin province, Chin ws used for the pot experiment. The soil clssified s Typicl Hplquept contined 797 mg/kg totl S, 35.1 mg/kg C(H 2 PO 4 ) 2 extrctle S, 3.96 mg/kg totl s,.36 mg/kg HCl extrctle s. There were six tretments with two levels of s (N 2 HsO 4 7 H 2 O) (, 2 mg s/kg) comined with three S levels (N 2 SO 4 ) (, 6, 12 mg S/kg). Ech tretment hd four replictes. rhizog system with soil-snd comintion ws used to collect rhizosphere nd non-rhizosphere soils seprtely. The rhizogs were mde of nylon net with mesh size of 4 µm nd filled with 5 g cid-wshed qurtz snd. In totl 2 kg dried soil ws plced in ech pot, ll of which received sed dressing of nutrients s Fn et l. (21). Rice (Oryz stiv L.) seeds were sterilized in 1% H 2 O 2 (v/v) solution for 3 min, followed y thoroughly wshing with deionized wter. The seeds were germinted in moist filter pper t 25 C. In ech pot, two uniform germinted seeds were trnsplnted nd grown for 16 dys. Soil ws kept sumerged with deionized wter for the whole growth period. Smpling nd nlysis. efore hrvesting, two pieces of fresh penultimte leves of ech plnt were smpled nd GSH content ws nlyzed ccording to DTN [5,5'-dithilis-(2-nitrovenzoic cid)] method (Griffith 198). Rice plnts were hrvested nd divided into roots, shoots nd seeds. Hlf of the fresh roots were used for the extrction of iron plque y scoric citrte cetic (C) method (Go et l. 27). Qurtz snd collected from rhizosphere ws extrcted y.1 mol/l HCl (Hu et l. 27). In C extrcts nd HCl solution, s concentrtion ws determined y tomic fluorescence spectrometry, nd Fe, Mn nd S concentrtions were determined y inductively-coupled plsm opticl emission spectroscopy. Soil totl S ws digested y Mg(NO 3 ) 2 (utters nd Chenery 1959). Dried rice plnts were digested ccording to Fn et l. (21). regent lnk nd stndrd reference mteril (Shru, GW 762, Ntionl certified reference mterils) were included to verify the ccurcy nd precision of nlysis. The recovery is 95.8%. Dt nlysis. In order to study the trnsloction pttern of s in rice plnts, ioconcentrtion fctor (CF) nd trnsloction fctor (TF) ws clculted ccording to Singh et l. (21). nlysis of vrince (NOV) followed y the lest significnt difference (LSD) test nd correltion nlysis were performed using the Windows-sed SPPS 13. (SPSS Inc., Chicgo, US). RESULTS Effect of excessive S on rice iomss nd s uptke. In S tretments, s supply decresed dry weight of root (P <.1) nd grin (P <.5). nd in +S tretments, s ddition lso showed similr decresing trend on dry weight of root, shoot nd grin compred to s tretments. Furthermore, dry weight of root, shoot nd grin tended to decrese with the increse of S levels (Figure 1). The verge s concentrtions in roots were 7.5, 11.3, nd 66.9 fold those in leves, stems, rown rice nd husk in +s tretments, respectively, while the corresponding vlues in s tretments were 3.2, 4.9, 77.3 nd 38.8 respectively (Tle 1). Furthermore, S ddition significntly 17

3 Plnt Soil Environ. Vol. 59, 213, No. 4: Shoot weight (stems + leves) Root weight (g/pot) (g/pot) Grin weight (g/pot) s +s Figure 1. Effect of S ppliction on iomss of rice (Different lower- nd upper-cse letters indicte significnt difference t P <.5 (LSD test) for S levels nd s levels) (P <.5) decresed s concentrtions in rown rice, leves, stems (not significnt in +s tretments) nd husk in oth +s nd s tretments. Furthermore, CF for leves nd stems were 8 35 fold tht for rown rice nd 5 2 fold tht for husk (Tle 2), indicting tht s ws minly ccumulted in rice leves nd stems. Moreover, S supply significntly decresed CF of s for leves, stems, rown rice nd husk compred to S tretments. The TF shows movement of hevy metls from root to rown rice. In the present study, TF of s ws significntly lower with S supply thn without S supply (Tle 2), suggesting tht S ppliction my inhiit s trnsfer from rice root to grin. Effect of excessive S on GSH in leves nd iron plque on the root surfce. GSH concentrtions in rice leves were relted to S nd s levels (Figure 2). In s tretments, GSH content tended to incresed with S levels lthough their difference ws not sttisticlly significnt (P >.5). In +s tretments, 12 mg S/kg supply significntly increse GSH in rice leves compred to nd 6 mg S/kg tretments (Figure 2). The ppliction of S significntly decresed C-extrctle Fe nd Mn in iron plque on the root surfce of rice in s tretments (Tle 3). In +s tretments, S supply showed higher Fe, Mn (P <.5) nd s (P <.5) thn tretments without S. s ddition significntly incresed C-extrctle s in iron plque (P <.1). Compred to s tretments, s ddition hd higher C-extrctle S ut the difference ws significnt only in 12 mg S/kg ddition tretment. Elements in rhizosphere qurtz snd nd nonrhizosphere soil. In s tretments, HCl-extrctle Fe in the rhizosphere ws significntly higher with 12 mg S/kg ddition thn with nd 6 mg S/kg (Figure 3). Compred to s tretments, s ddition significntly incresed HCl-extrctle s in the rhizosphere in ll S levels tretments (Figure 3). The concentrtions of SO 4 2 were significntly higher (P <.1) in the non-rhizosphere soils with S ddition thn without S ddition (Figure 3). In +s tretments, 12 mg S/kg ddition hd significntly higher soil ph thn tretments with nd 6 mg S/kg ddition (Figure 3). In tretments with nd 6 mg S/kg ddition, soil ph in +s tretment ws significntly lower (P <.5) thn in s tretment. ut in 12 mg S/kg ddition tretment, soil ph in +s tretment ws significntly higher (P <.1) thn in s tretment. GSH content in leves (mg/kg FW) s +s Figure 2. Effect of S ppliction on glutthione (GSH) content in the penultimte leves of rice. Different lower- nd upper-cse letters indicte significnt difference t P <.5 (LSD test) for S levels nd s levels 171

4 Vol. 59, 213, No. 4: Plnt Soil Environ. Tle 1. Effect of sulfur ppliction on concentrtions (mg/kg dry weight) of s in rice S levels 6 12 Roots Leves Stems rown rice Husk s +s s +s s +s s +s s +s 19.4 ± ± ± ± 15.5 c 7. ± ± ± ± ± 5.6 ± 17.4 ± 3.6 ± 11.2 ± ± 5.4 ± 14.5 ± 3.6 ± 12.5 ± c nlysis of vrince for s levels.4 ± ± ± ± ±.9 ±.42 ± 1.51 ±.3. 6c.6.54 c.19 ± 1.23 ±.29 ± 2.7 ± P <.1 P <.1 P <.1 P <.1 P <.1 6 P <.1 P <.1 P <.1 P <.1 P <.1 12 P <.1 P <.1 P <.1 P <.1 P <.1 S levels s P <.5 P <.1 ns P <.5 P <.5 Vlues re mens ± stndrd devitions; ns not significnt. Vlues followed y different letter within column indicte significnce t P <.5 (LSD test) for S levels DISCUSSION The results from the present study strongly suggested tht excessive S ppliction could significntly decrese s uptke y rown rice, which could e scried to three principl mechnisms. Firstly, excessive S supply incresed the formtion of iron plque on the root surfce under s stress (Tle 3). Iron plque my e rrier or uffer to the uptke of s (Liu et l. 24). significnt, positive correltion etween s in roots nd iron plque ws found (Tle 4), indicting tht iron plque my ct s uffer to the uptke of s y rice roots. However, no significnt reltionship ws found etween s content in rice leves, grin, husk nd s in iron plque (Tle 4). Moreover, the lower CF nd TF of s in rown rice with S supply (Tle 2) indictes tht s trnsloction from soils nd roots to rown rice ws inhiited y S. ll these results suggested tht excessive S induced the trnsformtion of iron plque my induce s uptke nd e trpped in rice roots ut cn reduce s trnsloction from roots to shoots nd grin. This my e scried to S induced expression of genes controlling s ccumultion nd trnsport in rice under s stress (Ri et l. 211). Secondly, S supply induced GSH formtion in rice (Figure 2), which cn rect with s forming s-pcs or s-gs complex (Tuli et l. 21). nd s-pcs or s-gs complex cn then e tken up into the Tle 2. Effect of sulfur ppliction on ioconcentrtion fctor (CF) nd trnsloction fctor of s in rice S levels 6 12 CF-leves CF-stems CF-rown rice CF-husk Trnsloction fctor s +s s +s s +s s +s s +s 38.3 ± ± ± ± ± 12.7 ± 11.6 ± 8. ± ± 11.1 ± 15.1 ± 9.7 ± ± 1.1 ± ±.63 ± ±.96 ± nlysis of vrince for s levels 4.21 ± 1.77 ± ± 1.3 ± ± 1.64 ± ±.16 ± ±.7 ± ±.7 ±.3.3 P <.1 P <.1 P <.5 P <.1 ns 6 ns ns ns ns ns 12 ns P <.5 ns ns ns S levels s P <.5 P <.1 P <.5 P <.1 ns Vlues re mens ± stndrd devitions; ns not significnt. Vlues followed y different letter within column indicte significnce t P <.5 (LSD test) for S levels 172

5 Plnt Soil Environ. Vol. 59, 213, No. 4: Tle 3. Effect of sulfur ppliction on concentrtions of scoric citrte cetic (C)-extrctle Fe, Mn, s nd S in iron plque on root surfce of rice S levels Fe (g/kg) Mn s S (g/kg) s +s s +s s +s s +s 15.6 ± ± ± ± ± ± 4. c.6 ±.4 c.8 ±.3 c ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±.1 nlysis of vrince for s levels ns ns P <.1 ns 6 ns ns P <.1 ns 12 ns ns P <.1 P <.1 S levels s P <.5 P <.5 P <.1 P =.54 Vlues re mens ± stndrd devitions; ns not significnt. Vlues followed y different letter with column indicte significnce t P <.5 (LSD test) for S levels () Fe in the rhizosphere Mn in the rhizosphere Mn in the rhizosphere s in the rhizosphere s +s c () 2 SO 2-4 concentrtion in in soil soil Figure 3. () Effect of S ppliction on.1 mol/l HCl-extrctle Fe, Mn nd s concentrtions in the rhizosphere of rice; () effect of S ppliction on C(H 2 PO 4 ) 2 -extrctle SO 4 2, HCl-extrctle s concentrtions nd ph in the non-rhizosphere of rice. Different lower- nd upper-cse letters indicte significnt difference t P <.5 (LSD test) for S levels nd s levels HCl extrctle s in soil Soil ph s +s 173

6 Vol. 59, 213, No. 4: Plnt Soil Environ. vcuole, susequently decresing s trnsporttion from rice roots nd leves to rown rice (Zho et l. 21). Thirdly, excessive S supply my decrese s vilility y forming indiscerptile s 2 S 3 or FesS. cterium, such s Desulfotomculum uripigmentum, ws reported to induce precipittion of s 2 S 3 y its reduction of s(v) to s(iii) nd S(VI) to S( II) under noxic conditions with excessive S (Figure 3) (Newmn et l. 1997). nd in the environment with high Fe (II) or FeS, FesS my e formed y coprecipittion of s with Fe nd S (Frquhr et l. 22). Furthermore, higher soil ph, resulted y s ddition nd excessive S supply (Figure 3), my promote the formtion of these indiscerptile compounds. Therefore, due to the integrtion of these mechnisms, excessive S supply could significntly inhiit s uptke nd ccumultion in rown rice exposed to s contminted soils. REFERENCES utters., Chenery E.M. (1959): rpid method for the determintion of totl sulphur in soils nd plnts. nlyst, 84: Dhnkher O.P., Li Y.J., Rosen.P., Shi J., Slt D., Senecoff J.F., Sshti N.., Megher R.. (22): Engineering tolernce nd hyperccumultion of rsenic in plnts y comining rsente reductse nd γ-glutmylcysteine synthetse expression. Nture iotechnology, 2: Fn J.L., Hu Z.Y., Zidi N., Xi X., Wu C.Y.H. (21): Excessive sulfur supply reduces cdmium ccumultion in rown rice (Oryz stiv L.). Environmentl Pollution, 158: Frquhr M.L., Chrnock J.M., Livens F.R., Vughn D.J. (22): Mechnisms of rsenic uptke from queous solution y interction with goethite, lepidocrocite, mckinwite, nd pyrite: n X-ry sorption spectroscopy study. Environmentl Science nd Technology, 36: Go M.X., Hu Z.Y., Wng G.D. (27): Extrction nd elementl nlysis of iron plque from the surfce of rice roots. Environmentl Chemistry, 26: (In Chinese) Griffith O.W. (198): Determintion of glutthione nd glutthione disulfide using glutthione reductse nd 2-vinylpyridine. nlyticl iochemistry, 16: Hnsel C.M., Fendorf S., Sutton S., Newville M. (21): Chrcteriztion of Fe plque nd ssocited metls on the roots of mine-wste impcted qutic plnts. Environmentl Science nd Technology, 35: Hssn M.J., Wng Z., Zhng G. (25): Sulfur llevites growth inhiition nd oxidtive stress cused y cdmium toxicity in rice. Journl of Plnt Nutrition, 28: Heikens., Pnullh G.M., Mehrg.. (27): rsenic ehviour from groundwter nd soil to crops: Impcts on griculture nd food sfety. Reviews of Environmentl Contmintion nd Toxicology, 189: Hu Z.Y., Zhu Y.G., Li M., Zhng L.G., Co Z.H., Smith F.. (27): Sulfur (S)-induced enhncement of iron plque formtion in the rhizosphere reduces rsenic ccumultion in rice (Oryz stiv L.) seedlings. Environmentl Pollution, 147: Khn N.., Singh S., Umr S. (28): Sulfur ssimiltion nd iotic Stress in Plnts. Springer-Verlg, erlin, Heidelerg. Liu W.J., Zhu Y.G., Smith F.., Smith S.E. (24): Do iron plque nd genotypes ffect rsente uptke nd trnsloction y rice seedlings (Oryz stiv L.) grown in solution culture? Journl of Experimentl otny, 55: Lomi E., Scheckel K.G., Pllon J., Crey.M., Zhu Y.G., Mehrg.. (29): Specition nd distriution of rsenic nd locliztion of nutrients in rice grins. New Phytologist, 184: Newmn D.K., everidge T.J., Morel F. (1997): Precipittion of rsenic trisulfide y desulfotomculum uripigmentum. pplied nd Environmentl Microiology, 63: Ri., Tripthi P., Dwivedi S., Duey S., Shri M., Kumr S., Tripthi P.K., Dve R., Kumr., Singh R., dhikri., g M., Tripthi R.D., Trivedi P.K., Chkrrty D., Tuli R. (211): rsenic tolernces in rice (Oryz stiv) hve predominnt role in trnscriptionl regultion of set of genes including sulphur ssimiltion pthwy nd ntioxidnt system. Chemosphere, 82: Shrm S.S., Dietz K.J. (26): The significnce of mino cids nd mino cid-derived molecules in plnt responses nd dpttion to hevy metl stress. Journl of Experimentl otny, 57: Singh., grwl M., Mrshll F.M. (21): The role of orgnic vs. inorgnic fertilizers in reducing phytovilility of hevy metls in wstewter-irrigted re. Ecologicl Engineering, 36: Tuli R., Chkrrty D., Trivedi P.K., Tripthi R.D. (21): Recent dvnces in rsenic ccumultion nd metolism in rice. Moleculr reeding, 26: Zho F.J., McGrth S.P., Mehrg.. (21): rsenic s food chin contmintion: Mechnisms of plnt uptke nd metolism nd mitigtion strtegies. nnul Review of Plnt iology, 61: 1 5. Received on Decemer 3, 212 ccepted on Jnury 28, 213 Corresponding uthors: Dr. Zhengyi Hu, University of Chinese cdemy of Sciences, College of Resources nd Environment, 19, Yuqun Rod, 149 eijing, P.R. Chin phone: , fx: , e-mil: zhyhu@ucs.c.cn 174