纳米银影响桑树组培苗生长的原因初探

Impact of Silver Nanoparticles on the Growth of Tissue Culture-Derived Mulberry Plants

纳米银作为新型抗菌材料得到广泛应用,同时也通过多种途径排放入环境,在土壤和自然水体中富积,对环境微生物及植物产生毒副作用。本研究分析纳米银对桑树生长的影响。在土壤中按20mg/Kg,40mg/Kg(土壤干重)添加纳米银,对照组不添加纳米银,栽种4月龄桑树组培苗,观察桑树的生长情况。移栽4个月后对土壤中可培养细菌、真菌和放线菌进行了比较,测定纳米银在桑叶叶片、桑树木质部、韧皮部及根部的蓄积量;最后测定桑叶叶片中叶绿素含量、过氧化氢酶、过氧化物酶、硝酸还原酶等的酶活性。结果显示低浓度纳米银早期促进桑树发芽,但后期桑叶提前枯黄。添加纳米银土壤中可培养细菌、真菌和放线菌的数量均显著低于对照组。纳米银在桑树各部位的分布,根>茎>叶,木质部的含量相对衡定。桑叶中过氧化氢酶,过氧化物酶的酶活性显著高于对照组,而硝酸还原酶的活性显著低于对照组。桑叶叶绿素a和叶绿素b含量差异不显著。实验结果表明,土壤中低浓度纳米银可短期促进桑树生长,但高浓度对桑树有致死性作用。

Silver nanoparticles have got extensive application as an antimicrobial material.However,there is increasing concern about the accumulation of silver nanoparticles in soil and natural water bodies and the subsequent ecotoxicity to microorganisms and plants.In the present study,we analyze the impact of silver nanoparticles on mulberry,one kind of plants usually used in remediation of heavy metal contamination.A batch of 12 strains of 4 month old tissue culture derived mulberry plants were planted in 3 flowerpots,of which two contained silver nanoparticles at the rate of 20 and 40 mg/kg,respectively,and the third contained no silver nanoparticles.Four months after transplantation,the numbers of bacteria,fungi and actinomycetes in the soil were counted,and the accumulation of silver nanoparticles in the soil and in the roots,phloem,xylem and leaf of the mulberry plants was investigated based on a standard nitration reaction with HNO 3.The activities of POD,CAT and nitrate reductase and the chlorophyll content in leaves were measured.The results showed that silver nanoparticles at a low concentration(20 mg/Kg)promoted bud germination of the plants at their early growth stage but advanced the yellowing of their leaves at the late growth stage,and that the community of culturable bacteria,fungi and actinomycetes decreased significantly as compared with the control group.The distribution of silver nanoparticles in the organs of mulberry was in the order of root>xylem>leaf and their content in the xylem was relatively constant.The activities of POD and CAT significantly increased,but nitrate reductase activity significantly decreased in the test groups,in a dose dependent manner.The above data suggested that silver nanoparticles could inhibit the growth of mulberry in a concentration of 20mg/kg in soil.