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近年来,随着工业化进程的不断加快,镉(Cd)、汞(Hg)和铅(Pb)等重金属的污染问题愈加严重[1]。其中,水体镉污染尤为严峻,我国部分江河湖泊受到不同程度的镉污染[2]。例如,龙江河发生的严重镉污染事件,水体的镉含量超标80倍[3]。安宁河镉含量最高曾达0.6 mg·L−1,远远超过国家地表水Ⅴ类标准(GB 3838-2002)[4]。海河总镉含量也曾超过地表水Ⅱ类标准的16.7%~83.9%[5]。水体中的镉不仅能直接通过饮用水进入人体,还会通过富集于水生动植物中再经食物链累积,最终通过饮食被摄入人体。进入人体的镉会沉积在骨骼、皮肤和肾脏等组织中,进而造成组织器官的损伤甚至癌变,严重影响人体健康[6-9]。因此,水体镉污染的治理至关重要。
去除水体重金属的方法常见的有物理方法、化学方法和生物方法[10]。与物理、化学方法相比,生物修复方法具有低成本、无二次污染、高效率等优点[11]。其中,植物修复技术通过超富集植物从污染水体中摄取重金属并将其富集在体内,从而实现对污染水体的修复[12],具有巨大发展潜力。决定植物修复技术修复重金属污染效果和应用价值的最关键之处,是找到合适的重金属超富集植物[13]。通常,重金属超富集植物是指富集后重金属含量能超过1 000 mg·kg−1(干质量)的植物,而重金属含量仅需超过100 mg·kg−1(干质量)则可被定义为镉超富集植物[14]。
浮萍,由于生长速度快、污染物去除效率高,是一种理想的污染水体修复材料和研究污染物胁迫理论的模式植物[15]。浮萍共有5属36个种,生长速度快,其生物量每16~24 h增加1倍,有利于前期的育种扩繁[16-17]。浮萍是形态最简单的开花水生植物,仅有叶状体和根,可以避免离子的长距离运输,离子转运效率极高[18]。浮萍能在温度为10~40 ℃、pH为5.0~9.0条件下生长,环境适应能力强[19-20]。浮萍对Cu、Zn、Cd、Pb等重金属都有一定富集和耐受能力[21-22],并在采集收获、加工应用等方面表现出较大优势,已受到广泛关注[23]。
然而,有关浮萍在重金属耐受和富集方面的研究目前都还主要集中在少数品种上,缺乏系统的研究[21,24-29]。多根紫萍(Spirodela polyrrhiza)对镉非常敏感,其相对生长速率和光合色素含量在1 μmol·L−1的镉胁迫7 d后显著降低,被认为是一种具有开发应用价值的重金属指示物[24-25]。而少根紫萍(Landoltia punctata)在3 mg·L−1 的镉处理10 d后,富集系数和对水体中镉的去除率分别可达到为770和72.43%,具有明显的高富集优势[26]。由此可见,由于基因型不同,不同种属的浮萍对重金属镉的富集效果差异较大。因此,比较不同浮萍种属间镉富集效果的差异,筛选最适合的浮萍品种,对进一步应用植物修复技术具有现实意义。
本研究为筛选出最适于治理水体镉污染的浮萍品种,通过30 mg·L−1 镉处理7 d初筛90株浮萍株系,以叶片颜色变化为判断标准,获得7株优势浮萍株系。对该7株浮萍株系进行了种属鉴定和进一步复筛,在0.5 mg·L−1(低质量浓度)和10 mg·L−1(高质量浓度)镉浓度下处理7 d,比较了7株浮萍株系的生长速率、叶绿素含量、对镉的富集效果和去除率,以期筛选出对镉富集效果最佳的浮萍品种,为今后利用最佳浮萍品种治理水体镉污染提供参考。
耐镉浮萍筛选、鉴定及其对镉的富集效果
Screening, identification and enrichment effects of cadmium-tolerant duckweeds
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摘要: 近年来,水体镉污染日益严峻,筛选超富集植物用于其治理具有重要意义。本研究以90个浮萍株系为实验材料,采用30 mg·L−1 的镉处理7 d,获得7个镉耐受优势株系。通过Blast比对和构建系统发育树鉴定该7个浮萍株系的种属,确定为Spirodela polyrhiza、Lemna japonica、Lemna minor和Landoltia punctata。通过低质量浓度(0.5 mg·L−1)和高质量浓度(10 mg·L−1)镉处理7 d,进一步比较和研究了7个优势株系对镉的富集效果。结果表明,低浓度镉处理后,5个株系的镉富集量超过100 mg·kg−1;高浓度镉处理后,7个浮萍株系的镉富集量超过1 200 mg·kg−1,生物富集系数大于120,对水体中镉的去除率高于70%。其中,4号株系(L. japonica)为本次筛选出的最佳株系,其镉富集量、生物富集系数和对水体中镉的去除率分别达到2 834.30 mg·kg−1、283.43和82.50%。Abstract: In recent years, the cadmium pollution in water has become severe, and it is of great significance to screen hyperaccumulators for its treatment. In this study, 90 duckweed strains were taken as experimental materials and treated with 30 mg·L−1 cadmium for 7 days, then 7 cadmium-tolerant dominant strains were obtained. Through Blast comparison and construction of phylogenetic trees, the species of these 7 duckweed strains were identified as Spirodela polyrhiza, Lemna japonica, Lemna minor and Landoltia punctata. After treatment with low concentration (0.5 mg·L−1) and high concentration (10 mg·L−1) cadmium for 7 days, the enrichment effects of 7 dominant strains were further studied and compared. Under low concentration cadmium treatment, the cadmium concentration of 5 duckweed strains exceeded 100 mg·kg−1. Under high concentration cadmium treatment, the cadmium concentration of 7 duckweed strains exceeded 1 200 mg·kg−1. The bioconcentration factors were higher than 120, and the water cadmium removal rates were higher than 70%. Among them, 4 duckweed strain (L. japonica) was the best strain selected in this study, and its cadmium concentration, bioconcentration factor and water cadmium removal rate reached 2834.30 mg·kg−1, 283.43 and 82.50, respectively.
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Key words:
- duckweed /
- heavy metal cadmium /
- species identification /
- hyperaccumulators /
- water pollution
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表 1 浮萍株系编号和采集信息
Table 1. Duckweed species number and collection place
株系编号 采集地 经纬度 1 北京市昌平区 E116°42'47'' N40°10'92'' 2 贵阳市花溪区 E106°39'23'' N26°26'59'' 3 贵阳市花溪区 E106°39'57'' N26°26'49'' 4 北京市昌平区 E116°42'47" N40°10'92" 5 重庆市大足区 E105°51′1″ N29°27′48″ 6 重庆市大足区 E105°45′28″ N29°27′57″ 7 重庆市大足区 E105°45′23″ N29°27′55″ 表 2 7个浮萍Blast种属鉴定结果
Table 2. Species identification of 7 duckweed strains by Blast
株系编号 atpF-atpH比对序列 atpF-atpH序列相似性/% rpS16比对序列 rpS16 序列相似性/% 种属 1 MN419335 99.28 KJ503285 99.69% Spirodela polyrhiza 2 KX212888 99.00 KX212891 99.38% Lemna minor 3 KX212888 98.49 KX212891 99.69% Lemna minor 4 KJ921747 99.70 EU568887 94.80% Lemna japonica 5 KJ921747 99.11 EU568887 94.80% Lemna japonica 6 KJ630555 99.30 KJ503327 99.70% Landoltia punctata 7 KJ630555 97.25 KJ503327 99.60% Landoltia punctata -
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