菲与NH4-N和NO3-N共存对作物根系硝酸还原酶活性的影响

Nitrate reductase activity of crop roots in the presence of phenanthrene and NH_4^+-N,NO_3^--N

作物根系多环芳烃(PAHs)与氮素吸收的相互作用研究对于通过施肥措施保障农产品的安全与强化PAHs污染环境的植物修复效果具有重要意义。本文以菲为PAHs代表,采用活体测定法研究了小麦、大豆和莴苣根系硝酸还原酶(NR)活性对硝态氮和铵态氮与菲共存下的响应。结果表明:无论菲处理与否,两种形态的氮素均能明显提高作物根系NR活性,硝态氮促进根系NR活性效果更好;铵硝混合氮处理中,小麦和莴苣根系NR活性随着硝态氮比例增加而增大,而大豆在硝态氮和铵态氮比为1∶1时NR活性最大。同一氮素水平,菲或无菲处理的作物根系NR活性因作物品种不同差异较大;在单一硝态氮或单一铵态氮存在下,根系NR活性从大到小依次为小麦、大豆、莴苣;铵硝混合氮存在下,作物根系NR活性大小顺序与硝态氮或铵态氮处理相同。与无菲处理相比,菲处理对小麦、大豆、莴苣的NR活性都有促进作用;在硝态氮和菲处理下,米氏常数从小到大为小麦、大豆、莴苣,而亲和力从大到小是小麦、大豆、莴苣;菲处理作物根系NR的米氏常数均小于相应的无菲处理,而亲和力则相反。表明,菲增强了根系NR与NO-3的亲和力是菲与不同形态氮共存促进作物根系NR活性的重要原因。

Investigation regarding interaction of root uptake of polycyclic aromatic hydrocarbons （PAHs）and nitrogen is beneficial for the safe production of crop foods and enhancement in phytoremediation of PAH-contaminated soil and water. To characterize the response of nitrate reductase（NR） to the presence of phenanthrene（ a model compound of PAHs）and nitrogen, in vivo measurement in NR activity of wheat（ Triticum aestivum） , soybean （Glycine max ）and lettuce （Latuca sativa ）roots was employed at different con- centrations of nitrate and ammonium and different ratios of ammonium to nitrate with or without phenanthrene in reaction solution. Nitrate, ammonium and the mixture of nitrate and ammonium all increased NR activity in both phenanthrene and phenanthrene-free treatments. Nitrate reductase activities in NO]-fed crop roots were the highest. NR activities of wheat and lettuce roots increased with a decrease in ratio of NH~/NOj. However, in combined ammonium and nitrate treatments, NR activity of soybean was the highest at 1：1 ratio of NH~/NO~. NR activity varied with crop species as well. NR activity of soybean was lower than that of wheat, and higher than that of lettuce. Whatever was supplied with NaNO3 , NHaC1 or the mixture of NO3 and NH4, compared to phenanthrene-free treatments, a marked increase in NR activity was observed in phenanthrene treatments. At the same nitrate and phenanthrene level, Km value in Michaelis-Menten equation for wheat was lower than that for soybean. Km value for lettuce was higher than that for soybean. The presence of phenanthrene apparently stimulated the affinity between NR and NO3. Taken together, it is concluded that phenanthrene enhances NR activity of roots due to the stimulation of affinity of NR and nitrate in the presence of phenauthrene.