Ni胁迫对不同基因型谷子幼苗生长及氮素代谢的影响

Effect of Ni on the growth and nitrogen metabolism in foxtail millet seedlings of different genotypes

采用盆栽土培法,研究了不同浓度Ni2+(0、25、50、100、150、200 mg/kg)对4种基因型谷子(13-36、B-7、晋谷51号、晋谷52号)幼苗生长,Ni2+富集与转运能力,叶片中硝态氮、氨态氮、可溶性蛋白质、脯氨酸含量及氮代谢相关酶硝酸还原酶(NR)、谷氨酰胺合成酶(GS)、谷氨酸合酶(GOGAT)、谷氨酸脱氢酶(GDH)活性的影响。结果表明:Ni2+胁迫下,4种基因型谷子幼苗的根长、苗长、生物量随Ni2+浓度增加逐渐降低,体内Ni2+含量逐渐增加,与对照组差异显著(P<0.05)。在所试浓度范围内,4种基因型谷子幼苗叶片中的硝态氮含量、NR、GS、GOGAT活性表现为低浓度(25—50mg/kg)增高和高浓度(50—200 mg/kg)降低,而GDH活性在Ni2+浓度为100mg/kg以上时下降,氨态氮含量在50—150 mg/kg处理组中为对照的1.14—3.02倍。不同浓度Ni2+处理后,4种基因型谷子幼苗叶片中的脯氨酸含量均有不同程度的提高,而可溶性蛋白质含量呈明显下降趋势。实验结果证明,Ni2+胁迫抑制了谷子幼苗对硝态氮的吸收,降低了叶片中NR、GS、GOGAT活性,影响了氨的同化作用,使谷子幼苗的氮素代谢发生紊乱,不同基因型谷子对Ni2+胁迫的毒性效应存在差异。4种基因型谷子对Ni2+的耐性顺序为13-36>B-7>晋谷51>晋谷52。

Nowadays, soil pollution by Ni2~ is getting more severe in some place of China. Nickel （Ni） is an essential microelement of plants, however, large Ni^2＋ accumulation in crops leads to necrosis of plant leaf, lignification of stem and growth inhibition of root. The mechanisms of the Ni^2＋ toxicity are not well understood for nitrogen metabolism of higher plants. In this study, pot culture was conducted to investigate the effects of Ni^2＋ on the growth of roots and shoots, biomass, the uptake and accumulation of Ni^2＋, the contents of nitrate nitrogen, ammonium nitrogen, free proline and soluble proteins, the nitrogen metabolism key enzymatic activities including nitrate reductase （NR）, glutamine synthase （GS）, glutamate synthase （GOGAT）, glutamate dehydrogenase （GDH） in four genotypes （13-36, B-7, Jingu 51, Jingu 52） of foxtail millet （Setaria italica （L.） Beauv ） seedlings from Shanxi, China. The foxtail millet seeds were cultured in incubators at 26℃ for germination with no light, then planted in the pots spiked with five different Ni^2＋ concentration, namely 25, 50, 100, 150, 200 （mg/kg）. The experimental results showed that with the rise of Ni^2＋ concentration the root length, shoot length and biomass declined and the accumulation of Ni^2＋ increased gradually, which formed a sharp contrast with the control group （P〈0.05）. In the range of test Ni^2＋ concentration, the content of nitrate nitrogen, the activities of NR, GS, GOGAT of four genotypes of foxtail millet characterized by increasing at low concentration （25--50mg/kg） and declining at high concentration （50--200 mg/kg）. The activities of NR, GS, GOGAT reached the peak values when exposed to 50mg/kg Ni2＋. The nitrate nitrogen contents and NR activities in 13-36 were higher than other three genotypes （P〈0.05）. The activities of GS and GOGAT in 13-36, B-7, Jingu51 were 1.69, 1.47, 1.19 and 2.84, 1.03, 3.17 times than those of control group in 50mg/kg Ni2＋ exposure. However, The GDH activities decreased when the Ni^2＋ concentration higher than 100mg/kg. Ni2＋ treatments increased the accumulation of ammonium nitrogen in range of 50 to150 mg/kg in the leaves of four foxtail millet and were 1.14 to 3.02 times than control group. Besides these, with the increasing of Ni^2＋ concentration, the content of free proline increased, the soluble protein decreased. Synthesize the above results, we found that Ni2＋ treatments impaired N assimilation in foxtail millet seedlings by restraining the absorption of nitrate nitrogen and inhibiting the activities of NR, GS and GOGAT, which lead to nitrogen metabolism disturbance. And the toxicity effect was different among different genotypes of foxtail millet. Further, Ni2＋ stress inhibited the growth of foxtail millet. The tolerance order of four foxtail millets to Ni^2＋ was 13-36〉B-7〉Jingu51 〉Jingu52.