于輝,向言詞

湖南科技大學(xué)生科院,重金屬污染土壤生態(tài)修復(fù)與安全利用湖南省高校重點(diǎn)實(shí)驗(yàn)室,湘潭 411201

1 前言

隨著現(xiàn)代工業(yè)的發(fā)展、工業(yè)“三廢”的排放以及礦藏的大量開采,農(nóng)田土壤重金屬污染問題日趨嚴(yán)重。根據(jù)環(huán)保部2014年4月發(fā)布的“土壤污染狀況調(diào)查公報(bào)”[1],耕地土壤點(diǎn)位超標(biāo)率為19.4%,在無機(jī)污染物中鎘排在首位。鎘在土壤中具有高度移動(dòng)性,容易被作物吸收,由此引起的農(nóng)產(chǎn)品污染事件屢有發(fā)生,也引起了社會(huì)的廣泛關(guān)注。近年來,利用品種間的差異,選育低鎘積累的作物品種成為了降低作物受鎘污染風(fēng)險(xiǎn)的有效策略之一[2],目前相關(guān)的研究在水稻(Oryza sativaL.)[3]、玉米(ZeamaysL.)[4]、辣椒(Capsicum annuumL.)[5]、花生(Arachis hypogaeaL.)[6]) 和甘薯(Ipomoea batatas(L.)Lam.)[7]等多種農(nóng)作物中已陸續(xù)開展。作物籽實(shí)(果實(shí))中鎘的累積與鎘的轉(zhuǎn)運(yùn)過程有關(guān),包括根系對鎘的吸收、鎘從根向莖葉的木質(zhì)部轉(zhuǎn)運(yùn)以及營養(yǎng)器官向生殖器官的韌皮部轉(zhuǎn)移。而鎘在植物體內(nèi)的遷移運(yùn)輸與其在細(xì)胞內(nèi)的分布和結(jié)合形態(tài)密切相關(guān)[8-9]。對這些過程的了解是開展低鎘積累品種選育的前提。本文分析了鎘積累型不同的作物品種根系對鎘的吸收、鎘向地上部的運(yùn)輸和分配及鎘在細(xì)胞內(nèi)的分布和結(jié)合形態(tài)的差異,探討引起品種間鎘積累差異的生理機(jī)制,旨在為鎘低積累作物品種的選育提供理論基礎(chǔ)。

2 根系吸收與作物鎘積累的關(guān)系

鎘進(jìn)入植株體內(nèi)首先要通過根系。Laporte等[10]發(fā)現(xiàn)向日葵(Helianthus annuusL.)鎘含量與根吸收能力有關(guān),高鎘品種根部鎘含量高于低鎘品種。Yan等[11]發(fā)現(xiàn)秈-粳雜交稻(Oryza sativaL.)籽粒鎘含量與根中鎘含量顯著正相關(guān)。Li等[12]對大蔥(Allium fistulosumL.)的研究中也有相似的結(jié)果。但在大豆(Glycine max)[13]、茄子(Solanum melongena)[14]和辣椒(Capsicum annuumL.)[15]等作物中卻發(fā)現(xiàn),低鎘品種根部鎘含量高于高鎘品種,籽實(shí)(果實(shí))鎘含量與根吸收相關(guān)性不大,因此根系吸收和鎘積累型的關(guān)系因植物種類而異。即使是同種植物不同基因型也存在差異。如Yan等[11]的報(bào)道,4種基因型水稻35個(gè)品種中,6個(gè)秈-粳雜交稻粒鎘濃度與根的濃度成正相關(guān),而秈稻、溫帶粳稻和熱帶粳稻則與鎘的轉(zhuǎn)運(yùn)或地上部的再分配有關(guān)。趙云云等[16]發(fā)現(xiàn)供試的大豆中,部分品種籽粒鎘與根系鎘成正相關(guān),而有些品種則相反。造成這些結(jié)果的原因可能與植物不同品種的根系形態(tài)和根際環(huán)境有關(guān)。

有研究表明,不同鎘積累特性的品種其根系形態(tài)存在差異。如吳啟堂等[17]發(fā)現(xiàn),水稻高鎘品種汕優(yōu)63的根干質(zhì)量、根長、根冠比和吸水量均高于低鎘品種野奧絲苗;Li等[18]報(bào)道,與非超積累生態(tài)型東南景天(Sedum alfredii)相比,超積累生態(tài)型具有細(xì)而多的分支根;Lu等[19]比較了不同花生品種,發(fā)現(xiàn)高鎘積累品種的細(xì)根較多;以上特性使得高鎘積累品種根部具有高的鎘含量。但硬質(zhì)小麥[20]、蕹菜[21]和辣椒[15]的低鎘品種根部鎘含量高于高鎘品種。對其根系形態(tài)比較顯示,硬質(zhì)小麥低鎘品種根表面積和根尖數(shù)目高于高鎘品種,而辣椒和蕹菜中則相反。進(jìn)一步分析發(fā)現(xiàn),辣椒根長、根總表面積和根尖數(shù)目與鎘轉(zhuǎn)運(yùn)系數(shù)成正相關(guān),因此低鎘品種根部對鎘的轉(zhuǎn)運(yùn)能力較低。但對蕹菜分析顯示,總根長、總表面積及總體積與鎘的轉(zhuǎn)運(yùn)系數(shù)和遷移率無顯著相關(guān),平均直徑與二者顯著負(fù)相關(guān),故認(rèn)為低鎘積累品種根平均直徑的增大減弱了鎘向地上部轉(zhuǎn)運(yùn)的能力。Xin等[22]對比鎘積累型不同的甘薯,根部鎘積累無顯著差異,但低積累品種總根長和比根長短,根尖分泌的低分子量有機(jī)酸多,從而減弱了鎘從根向莖的轉(zhuǎn)移。

鎘積累型不同的生態(tài)型或品種,其根際土壤的特性亦存在差異,且與根際土壤重金屬的生物有效性及吸收積累特性的差異有關(guān)[23]。東南景天超積累生態(tài)型根際pH值低于非超積累生態(tài)型,其根際對鋅、鎘的活化吸收明顯高于非超積累生態(tài)型,根際酸化是重要機(jī)理[23-24]。在蕹菜中也發(fā)現(xiàn)品種的鎘積累與土壤pH呈顯著負(fù)相關(guān)[21,25],蕹菜低鎘品種根際較高含量的有機(jī)質(zhì)、較低的酸化和還原能力,導(dǎo)致其對土壤鎘的活化能力較低,從而降低了植株對鎘的吸收積累。

3 鎘的運(yùn)輸對作物可食部位積累鎘的影響

鎘被根系吸收后通過木質(zhì)部運(yùn)輸?shù)角o、葉和花等器官的各個(gè)組織,有學(xué)者認(rèn)為此轉(zhuǎn)運(yùn)過程是決定地上部鎘含量的關(guān)鍵因素[9]。Su等[9]報(bào)道,不同品種的花生(Arachis hypogaeaL.)其鎘濃度差異主要源于木質(zhì)部的轉(zhuǎn)運(yùn)能力。Harris和Taylor[26]比較了鎘積累型不同的近等基因系硬質(zhì)小麥(Triticum aestivumL.)幼苗根系的吸收和轉(zhuǎn)運(yùn)能力,經(jīng)過相同時(shí)間處理后,高鎘積累型木質(zhì)部汁液中鎘濃度是低鎘積累型的 1.7-1.9倍。Uraguchi等[8]對水稻低鎘品種Sasanishiki(秈稻)和高鎘品種Habataki(粳稻)鎘積累特性進(jìn)行分析,發(fā)現(xiàn)盡管Sasanishiki根部鎘的累積量高于Habataki,但后者莖和籽粒中的鎘是前者的兩倍。進(jìn)一步研究發(fā)現(xiàn),除這兩個(gè)品種外,其他69個(gè)不同基因型水稻木質(zhì)部汁液中的鎘與籽實(shí)鎘含量均成正相關(guān),故認(rèn)為鎘從根到莖的木質(zhì)部運(yùn)輸能力是決定其積累型的主要因素。類似的現(xiàn)象在Arao等[27]和 Mori 等[14]對茄子(Solanum melongenaL.)的研究中也有發(fā)現(xiàn)。

鎘被轉(zhuǎn)運(yùn)到地上部后,通過韌皮部轉(zhuǎn)移到籽實(shí)中,此部分的研究多集中在禾谷類作物。Tanaka等[28]報(bào)道,水稻籽實(shí)中91%—100%的鎘來源于韌皮部的轉(zhuǎn)移。Kato等[29]分析發(fā)現(xiàn),三個(gè)水稻品種籽粒鎘含量與木質(zhì)部汁液鎘無關(guān),而與韌皮部中鎘的濃度正相關(guān)。鎘經(jīng)由韌皮部轉(zhuǎn)移到籽粒中一般認(rèn)為有以下兩種途徑[11,30]:(1)鎘首先積累在營養(yǎng)器官,籽實(shí)形成期通過再分配經(jīng)韌皮部轉(zhuǎn)移進(jìn)入籽粒。(2)根持續(xù)吸收鎘,在莖節(jié)通過木質(zhì)部-韌皮部的轉(zhuǎn)運(yùn)直接進(jìn)入籽粒。為了進(jìn)一步了解籽實(shí)鎘積累的發(fā)生途徑和時(shí)間,部分學(xué)者開展了營養(yǎng)生長和生殖生長期作物吸收轉(zhuǎn)運(yùn)鎘的研究。如Rodda等[31]對水稻水培,進(jìn)行花前、花后和持續(xù)給鎘三個(gè)處理,發(fā)現(xiàn)籽實(shí)中的鎘60%是由開花前營養(yǎng)器官積累的鎘轉(zhuǎn)移而來,40%來自于灌漿期,由根部吸收,在莖桿基部、葉軸和花梗直接發(fā)生木質(zhì)部到韌皮部的快速轉(zhuǎn)移。Kashiwagi等[32]發(fā)現(xiàn)水稻籽實(shí)中的鎘主要來源于抽穗前的營養(yǎng)器官,尤其是旗葉中鎘的轉(zhuǎn)移。抽穗后根對鎘的吸收及向莖的轉(zhuǎn)運(yùn)受限,此時(shí)根系吸收的鎘不會(huì)影響籽實(shí)中鎘含量。Yan等[11]對兩種鎘積累型水稻幼穗分化前、幼穗分化后、成熟早期和成熟中期分別給鎘兩周,成熟期收獲,也證實(shí)營養(yǎng)器官的轉(zhuǎn)移是籽實(shí)鎘積累的重要因素。進(jìn)一步實(shí)驗(yàn)發(fā)現(xiàn),葉是重要的鎘源器官,葉的衰老加速鎘釋放,相對應(yīng)的農(nóng)藝性狀是高鎘品種Milyang23葉衰老速度顯著高于低鎘品種Chucheong,與Huang等[15]對辣椒的研究觀點(diǎn)相似。然而Fujimaki等[33]用無損成像方法探明,水稻中鎘進(jìn)入莖稈和莖節(jié)部位后,被轉(zhuǎn)運(yùn)到穗中而不是葉片。Tavarez等[34]、Harris和Taylor[26]用小麥的近等基因系為材料,在籽實(shí)形成期的不同階段收獲,發(fā)現(xiàn)灌漿期沒有發(fā)生從葉到籽粒的鎘轉(zhuǎn)移,根部持續(xù)從土壤吸收鎘,在莖桿中通過木質(zhì)部-韌皮部轉(zhuǎn)移進(jìn)入籽粒,鎘積累型的差異主要源于根到莖的木質(zhì)部轉(zhuǎn)運(yùn)。故而認(rèn)為營養(yǎng)期葉中積累的鎘多存在于細(xì)胞中較穩(wěn)定的部位,不易被轉(zhuǎn)載到韌皮部進(jìn)入?yún)R器官。Kubo等[35]以4個(gè)日本普通小麥為對象,分別在苗期、拔節(jié)期、開花期和灌漿期給鎘直到成熟,發(fā)現(xiàn)盡管籽粒中的鎘量主要來自營養(yǎng)器官的轉(zhuǎn)移,但品種積累型差異受到木質(zhì)部-韌皮部鎘直接運(yùn)輸?shù)挠绊?與前人的報(bào)道又有不同。

綜合來看以上的研究報(bào)道并沒有達(dá)成一致的觀點(diǎn),造成這種現(xiàn)象的原因可能與研究對象的不同以及實(shí)驗(yàn)條件的差異有關(guān)。有報(bào)道顯示即使同一植物生長過程中器官之間對鎘的積累規(guī)律也可能發(fā)生變化,如水稻秀水11(低鎘品種)苗期葉中鎘含量高于秀水110(高鎘品種),而成熟期前者葉中鎘含量低于后者[36]。

4 鎘在細(xì)胞內(nèi)的分布和結(jié)合形態(tài)與鎘積累的關(guān)系

植物吸收鎘后,根據(jù)各自的應(yīng)激策略將其區(qū)隔在細(xì)胞的不同部位,如通過與細(xì)胞壁的結(jié)合及液泡區(qū)室化等途徑阻滯鎘的遷移運(yùn)輸。在對蕹菜(Iomoea aquaticaForsk.)[37-38]、菜心(Brassica parachinensisL.)[39]和水稻等[40]的研究中發(fā)現(xiàn),鎘大部分被固定在細(xì)胞壁,向其它部位的轉(zhuǎn)移被減弱。而在美洲商陸(Phytolacca americanaL)[41]和遏藍(lán)菜(Thlaspi caerulescens)[42]中,細(xì)胞中的鎘大部分儲(chǔ)存在可溶部分(液泡中)。苧麻(Bechmeria niveaGaud)根中48.2%—57.6%的鎘分布在細(xì)胞壁[43],而辣椒根中細(xì)胞壁只結(jié)合了一小部分鎘(8%—17%)[44],可溶部分的鎘比例很高。這可能是不同植物對鎘不同的應(yīng)激反應(yīng)。鎘的亞細(xì)胞分布是形成品種鎘積累型差異的一個(gè)重要因素。He等[45]發(fā)現(xiàn)鎘敏感性(高鎘)的水稻突變體比野生型的細(xì)胞器中鎘含量高。比較菜心[39]和蕹菜[38]的亞細(xì)胞分布,低鎘品種根部細(xì)胞壁結(jié)合鎘的濃度和比例高于高鎘品種,從而大部分鎘被滯留在根部。辣椒[44]和水稻[40]低鎘品種莖葉中細(xì)胞壁的鎘比例高于高鎘品種,降低了鎘進(jìn)一步向果實(shí)(籽實(shí))的轉(zhuǎn)移。鎘離子穿過細(xì)胞壁進(jìn)入細(xì)胞后,可以不同的化學(xué)結(jié)合形態(tài)存在。在各種結(jié)合形態(tài)中,乙醇可提取態(tài)(與無機(jī)鹽結(jié)合的鎘)和水溶態(tài)鎘(與有機(jī)鹽結(jié)合的鎘)遷移活性最強(qiáng),氯化鈉提取態(tài)次之(與蛋白質(zhì)和果膠酸鹽結(jié)合的鎘),醋酸(與磷酸鹽結(jié)合的鎘)和鹽酸(與草酸鹽結(jié)合的鎘)提取態(tài)遷移活性最弱。比較低鎘和高鎘水稻中鎘結(jié)合形態(tài)表明,高鎘品種中水溶態(tài)和乙醇提取態(tài)鎘的比例高于低鎘品種[40]。但在對不同品種煙草(Nicotiana tabacumL.)鎘化學(xué)形態(tài)分布研究中發(fā)現(xiàn),高鎘積累型根內(nèi)遷移性較弱的醋酸提取態(tài)分配比率高于低鎘積累型[46]。Zhou等[47]發(fā)現(xiàn)低鎘莧菜(Amaranthus mangostanusL.)莖中氯化鈉提取態(tài)鎘比例很低,認(rèn)為與蛋白質(zhì)結(jié)合的鎘可能是造成鎘積累差異的主要因子,而菜心[39]低鎘品種中這部分比例則較高。辣椒[44]低鎘品種根中無機(jī)態(tài)鎘(乙醇提取態(tài))所占比例最大,研究者認(rèn)為這部分鎘可能以螯合態(tài)的形式進(jìn)入了細(xì)胞質(zhì),且區(qū)隔在液泡中的比例要高于高鎘品種,故可溶部分的鎘比例相應(yīng)較高。莖葉中乙醇提取態(tài)和水溶態(tài)鎘較低,則減弱了鎘向果實(shí)的轉(zhuǎn)移。綜上,鎘在細(xì)胞內(nèi)的分布和結(jié)合形態(tài)與其在植物體內(nèi)的遷移運(yùn)輸密切相關(guān),不同植物及品種間存在差異。但以往此方面的研究主要集中在植物幼苗時(shí)期,而鎘的運(yùn)輸和在籽實(shí)的積累是長期持續(xù)的過程,且不同的發(fā)育期對鎘的積累規(guī)律可能發(fā)生變化[36],因此單一生長期提供的數(shù)據(jù)缺乏系統(tǒng)性和全面性。

5 結(jié)論與展望

綜上所述,不同作物籽實(shí)(果實(shí))積累鎘的差異受到多方面的影響。有些作物中鎘累積與根吸收能力成正相關(guān),而有些則相關(guān)性不大,鎘含量主要取決于根向地上部的轉(zhuǎn)運(yùn)能力或者地上部的再分配。鎘的亞細(xì)胞分布和結(jié)合形態(tài)影響著鎘的遷移運(yùn)輸,與高鎘積累品種相比,低鎘作物品種細(xì)胞壁鎘和遷移活性較弱的鎘形態(tài)比例往往高于前者,由此降低了鎘的進(jìn)一步轉(zhuǎn)移。

目前,在對低鎘積累作物品種的篩選和機(jī)制研究方面取得了一定的成效,但是,還有很多研究工作需要開展,主要包括以下方面:

(1)闡明根際環(huán)境對植物吸收積累鎘的綜合影響,鎘脅迫下不同積累型品種根際的動(dòng)態(tài)調(diào)節(jié)過程,特別是根系分泌物、根際微生物對土壤重金屬鎘的形態(tài)轉(zhuǎn)化及生物有效性的影響,低積累鎘的作物品種根際微生物環(huán)境特點(diǎn)等。

(2)利用豐富的基因資源,篩選可食部位低鎘積累、非可食部位高鎘積累的作物品種,對鎘污染土壤進(jìn)行邊修復(fù)邊利用。同時(shí)結(jié)合目前對鎘的認(rèn)識(shí)與分子生物學(xué)方法,運(yùn)用物理和化學(xué)誘變、分子標(biāo)記輔助育種、耐性基因的分離與克隆技術(shù)等,培育出新品種。

(3)作物不同的發(fā)育期對鎘的積累規(guī)律會(huì)發(fā)生變化,而目前對于鎘在各生育時(shí)期植株體內(nèi)的動(dòng)態(tài)變化過程了解不深,對重要農(nóng)作物鎘積累的途徑和再分配規(guī)律有待進(jìn)一步深入研究,以保障我國主要農(nóng)產(chǎn)品的安全生產(chǎn)。

參考文獻(xiàn)

[1]中華人民共和國環(huán)境保護(hù)部.全國土壤污染狀況調(diào)查公報(bào)[EB/OL].http://www.zhb.gov.cn/gkml/hbb/qt/201404/t20140417_270670.htm,2014-04-17.

[2]GRANT C A,CLARKE J M,DUGUID S,et al.Selection and breeding of plant cultivars to minimize cadmium accumulation[J].Science of Total Environment,2008,390:301–310.

[3]蔡秋玲,林大松,王果,等.不同類型水稻鎘富集與轉(zhuǎn)運(yùn)能力的差異分析[J].農(nóng)業(yè)環(huán)境科學(xué)學(xué)報(bào),2016,35(6):1028–1033.

[4]杜彩艷,張乃明,雷寶坤.不同玉米品種對鎘鋅積累與轉(zhuǎn)運(yùn)的差異研究[J].農(nóng)業(yè)環(huán)境科學(xué)學(xué)報(bào),2017,36(1):16–23.

[5]XIN Junliang,HUANG Baifei,LIU Aiqun,etal.Identification of hot pepper cultivars containing low Cd levels after growing on contaminated soil:uptake and redistribution to the edible plant parts[J].Plant and Soil,2013,373:415–425.

[6]SHIGuangrong,SU Gengqiang,LU Ziwei,etal.Relationship between biomass,seed components and seed Cd concentration in various peanut(Arachis hypogaeaL.)cultivars grown on Cd-contaminated soils[J].Ecotoxicology Environmental Safety,2014,110:174–181.

[7]XIN Junliang,DAI Hongwen,HUANG Baifei.Assessing the roles of roots and shoots in the accumulation of cadmium in two sweet potato cultivars using split-root and reciprocal grafting systems[J].Plant and Soil,2017,412:413–424.

[8]URAGUCHIS,MORIS,KURAMATAM,etal.Root-to-shoot Cd translocation via the xylem is the major process determining shoot and grain cadmium accumulation in rice[J].Journal of Experimental Botany,2009,60:2677–2688.

[9]SU Ying,WANG Xüming,LIU Caifeng,et al.Variation in cadmium accumulation and translocation among peanut cultivars as affected by iron deficiency[J].Plant and Soil,2013,363:201–213.

[10]LAPORTE M A,STERCKEMANC T,DAUGUETD S,et al Variability in cadmium and zinc shoot concentration in 14 cultivars of sunflower(Helianthus annuusL.)as related to metal uptake and partitioning[J].Environmental&Experimental Botany,2015,109:45–53.

[11]YAN Yongfeng,CHOI D H,KIM D S,et al.Absorption,translocation,and remobilization of cadmium supplied at different growth stages of rice[J].Journal of Crop Science&Biotechnology,2010,13(2):113–119.

[12]LI Xuhui,ZHOU Qixing,WEI Shuhe,et al.Identification of cadmium-excluding welsh onion(Allium fistulosumL.)cultivars and their mechanisms of low cadmium accumulation [J].Environmental Science& Pollution Research,2012,19:1773–1780.

[13]SUGIYAMA M,AE N,ARAO T.Role of roots in differences in seed cadmium concentration among soybean cultivars–proof by grafting experiment[J].Plant and Soil,2007,295(1):1–11.

[14]MORI S,URAGUCHI S,ISHIKAWA S,et al.Xylem loading process is a critical factor in determining Cd accumulation in the shoots ofSolanummelongena andSolanumtorvum [J].Environmental& Experimental Botany,2009,67(1):127–132.

[15]HUANG Baifei,XIN Junliang,DAI Hongwen,et al.Root morphological responses of three hot pepper cultivars to Cd exposure and their correlations with Cd accumulation[J].Environmental Science and Pollution Research,2015,22(2):1151–1159.

[16]趙云云,鐘彩霞,方小龍,等.華南地區(qū)夏播大豆品種鎘耐性及籽粒鎘積累的差異[J].大豆科學(xué),2013,32(3):336–34.

[17]吳啟堂,陳盧,王廣壽.水稻不同品種對Cd吸收累積的差異和機(jī)理研究[J].生態(tài)學(xué)報(bào),1999,19(1):104–107.

[18]LI Tingqiang,YANG Xiaoe,LU Lili,et al.Effects of zinc and cadmium interactions on root morphology and metal translocation in a hyperaccumulating species under hydroponic conditions[J].Journal of Hazardous Materials,2009,169:734–741.

[19]LU Ziwei,ZHANG Zheng,SU Ying,et al.Cultivar variation in morphological response of peanut roots to cadmium stress and its relation to cadmium accumulation[J].Ecotoxicology & Environmental Safety,2013,91:147–155.

[20]BERKELAAR E,HALE B.The relationshipbetween root morphology and cadmium accumulation in seedlings of two durum wheat cultivars[J].Canadian Journal of Botany,2000,78(3):381–388．

[21]龔玉蓮,楊中藝.蕹菜典型品種的根系形態(tài)學(xué)特征及與Cd吸收積累的關(guān)系[J].華南師范大學(xué)學(xué)報(bào)(自然科學(xué)版),2012,44(3):100–106.

[22]XIN Junliang,HUANG Baifei,DAI Hongwen,et al.Characterization of root morphology and root-derived low molecular weight organic acids in two sweet potato cultivars exposed to cadmium[J].Archives of Agronomy and Soil Science,2017,63(5):723–734.

[23]LI Tingqiang,DI Zhenzhen,ISLAM E,et al.Rhizosphere characteristics of zinc hyperaccumulatorSedum alfrediiinvolved in zinc accumulation[J].Journal of Hazardous Materials,2011,185:818–823.

[24]LI Tingqiang,LIANG Chengfeng,XUAN Han,et al.Mobilization of cadmium by dissolved organic matter in the rhizosphere of hyperaccumulatorSedum alfredii[J].Chemosphere,2013,91:970–976.

[25]GONG YuLian,YUAN JianGang,YANG ZhongYi,et al.Cadmium and lead accumulation by typical cultivars of water spinach as responding to different soil conditions[J].Fresenius Environmental Bulletin,2010,19:190–197

[26]HARRIS N S,TAYLOR G J.Cadmium uptake and partitioning in durum wheat during grain filling[J].BMC Plant Biology,2013,13:103–118.

[27]ARAO T,TAKEDA H,NISHIHARA E.Reduction of cadmium translocation from roots to shoots in eggplant(Solanum melongena)by grafting ontoSolanum torvumrootstock[J].Soil Science&Plant Nutrition,2008,54:555–559.

[28]TANAKA K,FUJIMAKIS,FUJIWARA T,etal.Quantitative estimation of the contribution of the phloem in cadmium transport to grains in rice plants(Oryza sativaL.)[J].Soil Science&Plant Nutrition,2007,53:72–77.

[29]KATO M,ISHIWAWA S,INAGAKI K,et al.Possible chemical forms of cadmium and varietal differences in cadmium concentrations in the phloem sap of rice plants(Oryza sativaL.)[J].Soil Science&Plant Nutrition,2010,56:839–847.

[30]YONEYAMA T,GOSHO T,KATO M,et al.Xylem and phloem transport of Cd,Zn and Fe into the grains of rice plants(Oryza sativaL.)grown in continuously flooded Cd-contaminated soil[J].Soil Science&Plant Nutrition,2010,56:445–453.

[31]RODDA M S,LI G,REID R J.The timing of grain Cd accumulation in rice plants:the relative importance of remobilization within the plant and root Cd uptake post-flowering[J].Plant and Soil,2011,347:105–114.

[32]KASHIWAGI T,SHINDOH K,HIROTSU N,et al.Evidence for separate translocation pathways in determining cadmium accumulation in grain and aerial plant parts in rice[J].BMC Plant Biology,2009,9:8–17.

[33]FUJIMAKI S,SUZUI N,ISHIOKA N S,et al.Tracing cadmium from culture to spikelet:noninvasive imaging and quantitative characterization of absorption,transport,and accumulation of cadmium in an intact rice plant[J].Plant Physiology,2010,152:1796–1806.

[34]TVAREA M,MACRI A,SANKARAN R P.Cadmium and zinc partitioning and accumulation during grain filling in two nearisogeniclinesofdurum wheat[J].Plant Physiology&Biochemistry,2015,97,461–469.

[35]KUBO K,KOBAYASHI H,FUJITA M,et al.Varietal differences in the absorption and partitioning of cadmium in common wheat (TriticumaestivumL.) [J].Environmental&Experimental Botany,2016,124:79–88.

[36]WANG Feijuan,WANG Min,LIU Zhouping,et al.Different responses of low grain-Cd-accumulating and high grain-Cd accumulating rice cultivars to Cd stress[J].Plant Physiology&Biochemistry,2015,96:261–269.

[37]WANG Junli,YUAN Jiangang,YANG Zhongyi,et al.Variation in cadmium accumulation among 30 cultivars and cadmium subcellular distribution in 2 selected cultivars of water spinach(Iomoea aquaticaForsk.)[J].Journal of Agricultural&Food Chemistry,2009,57:8942–8949.

[38]XIN Junliang,HUANG Baifei,YANG Junzhi,et al.Comparison of cadmium subcellular distribution in different organs of two water spinach (Ipomoea aquaticaForsk.)cultivars[J].Plant and Soil,2013b,372:431–444.

[39]QIU Qiu,WANG Yuntao,YANG Zhongyi,et al.Effects of phosphorus supplied in soil on subcellular distribution and chemical forms of cadmium in two Chinese flowering cabbage(Brassica parachinensisL.)cultivars differing in cadmium accumulation[J].Food&Chemical Toxicology,2011,49,2260–2267.

[40]YU Hui,XIANG Zuoxiang,ZHU Yun,et al.Subcellular and molecular distribution of cadmium in two rice(Oryza sativaL.) genotypes with different levels of Cd accumulation[J].Journal of Plant Nutrition,2012,35:71–84.

[41]FU Xiaoping,DOU Changming,CHEN Yingxu,et al.Subcellular distribution and chemical forms of cadmium inPhytolacca americanaL[J].Journal of Hazardous Materials,2011,186:103–107.

[42]Ma Jianfeng,Ueno D,Zhao Fangjie,et al.Subcellular localisation of Cd and Zn in theleavesof aCd hyperaccumulating ecotype ofThlaspi caerulescens[J].Planta,2005,220,731–736.

[43]WANG Xin,LIU Yunguo,ZENG Guangming,et al.Subcellular distribution and chemical forms of cadmium inBechmerianivea(L.)Gaud [J].Environmental&Experimental Botany,2008,62:389–395.

[44]XIN Junliang,HUANG Baifei.Subcellular distribution and chemical Forms of cadmium in two hot pepper cultivars differing in cadmium accumulation [J].Journalof Agricultural and Food Chemistry,2014,62:508–515.

[45]HE Junyu,ZHU Cheng,REN Yanfang,et al.Uptake,subcellular distribution,and chemical forms of cadmium in wild-type and mutant rice[J].Pedosphere,2008,18:371–377.

[46]李彥娥,趙秀蘭.鎘脅迫下不同品種煙草鎘化學(xué)形態(tài)分布研究[J].中國農(nóng)學(xué)通報(bào),2013,29(16):69–73.

[47]ZHOU Yihui,XUE Meng,YANG Zhongyi,et al.High cadmium pollution risk on vegetable amaranth and a selection for pollution-safe cultivars to lower the risk[J].Frontiers of Environmental Science&Engineering,2013,7(2)219–230.