重金属Cd^(2+)、Pb^(2+)胁迫对小白菜生理及其BcMT2a基因表达的影响

Effects of Heavy Metal Cd^(2+) and Pb^(2+) Stress on Physiology and the Expression of BcMT2a Gene in Brassica campestris L.

为探明小白菜对Cd^(2+)、Pb^(2+)单一及其复合胁迫的响应机理,以不同浓度Cd^(2+)、Pb^(2+)处理小白菜幼苗,对其生物量、生理指标(POD、SOD、CAT活性及MDA含量)及Cd^(2+)、Pb^(2+)在小白菜中的富集情况进行研究,同时克隆与重金属富集相关的金属硫蛋白基因BcMT2a并对其表达特异性进行分析。结果表明:除低浓度Cd^(2+)(10mg/L)对小白菜的根长和地上部分生长有一定的促进作用外,Cd^(2+)、Pb^(2+)及Cd^(2+)—Pb^(2+)处理对小白菜根长和地上部分生长均有一定的抑制作用,且随着浓度的升高,抑制作用逐渐增强;抗氧化酶系统中,POD与SOD活性较高,且与CAT活性均呈现先升后降的趋势。Cd^(2+)浓度为40mg/L时,MDA含量达到最大值。Cd^(2+)、Pb^(2+)在小白菜各组织中的积累顺序依次为根>茎>叶,且Pb^(2+)在一定程度上能够促进Cd^(2+)的吸收。BcMT2a基因编码的蛋白主要存在于细胞核中,属于易突变亲水性蛋白,该基因的相对表达量在一定浓度范围内可随着Cd^(2+)、Pb^(2+)及Cd2—Pb^(2+)浓度的升高而增加,且相对表达量的趋势与抗氧化酶系统结果基本一致,说明小白菜在受到Cd^(2+)、Pb^(2+)及Cd^(2+)—Pb^(2+)胁迫时,抗氧化酶系统与BcMT2a基因有明显的应答,可增加小白菜对Cd^(2+)、Pb^(2+)的耐受性。

In order to explore the response mechanism of Brassica campestris to the Cd（2＋）,Pb（2＋） single and combined stress（Cd（2＋）—Pb（2＋））,a culture room experiment was conducted,where the Brassica campestris seedlings were treated with different concentrations of Cd（2＋） and Pb（2＋）.The biomass,the content of antioxidant defense enzyme activities[i.e.,peroxidase（POD）,superoxide dismutase（SOD）,catalase（CAT）activities]and malondialdehyde（MDA）,and the enrichment of heavy metal ions were measured.In addition,the metallothionein gene BcMT2a which was associated with heavy metal enrichment was cloned and its expression was also analyzed.The results were as follows：except the low concentration of Cd（2＋）（10 mg/L）,which could promote the root length and aboveground growth of Brassica campestris,both the Cd（2＋） and Pb（2＋） single and combined stress could inhibit the development of root length and the growth of aboveground of Brassica campestris.And with the increasing concentrations of heavy metal ion,the inhibition effects were gradually strengthened.The order of inhibition effects of heavy metal ions was Pb（2＋）〉Cd（2＋）—Pb（2＋）〉Cd（2＋）.In the antioxidant enzyme system,POD and SOD activity were higher,and showed a trend of increasing first and decreasing then,as well as CAT activity.MDA content reached the maximum when Cd（2＋）concentration was40 mg/L.The order of heavy metal ions accumulation in the organs of Brassica campestris was root〉stem〉leaf.The protein encoded by BcMT2a gene is a hydropathy and mutant protein predominantly present in the nucleus.In a certain concentration rage,the relative expression of BcMT2a increased with the increase of Cd（2＋）,Pb（2＋）and both combined concentrations,and the trend of relative expression was consistent with theresult of the antioxidant enzyme system.These findings indicate that the antioxidant enzyme system and BcMT2a have a clear response under the different concentrations of Cd（2＋）,Pb（2＋）and Cd（2＋）—Pb（2＋）in Brassica campestris,and they can increase the tolerance of Brassica campestris to Cd（2＋）and Pb（2＋）stress.