中文摘要：

用50 mmol·L^-1KNO3溶液处理的甜菜幼苗提取总RNA,通过RT-PCR法从甜菜总RNA中分离得到一个硝酸还原酶基因,其cDNA长2 760 bp,包含了完整的基因编码序列,与已公布的硝酸还原酶基因序列相似性达99%。同时利用活体测定法检测了经缺氮胁迫不同时间后甜菜叶中NR活性,并利用NR片段引物进行半定量RT-PCR,检测了基因的表达量。结果表明,随着缺氮处理时间的延长,甜菜叶中的NR活性随诱导时间增加活性逐渐降低,在缺氮处理1 h,其活性便有明显的降低;而NR的mRNA受缺氮胁迫下调表达,暗示着NR基因的表达与氮诱导相关。

英文摘要：

Nitrate Reductase （NR） plays a key role in the metabolism of nitrate. The activity of NR is conducive to reduce the concentration of nitrate in plants. The homolog cDNA with 2 760 base pairs of nitrate reductase gene was obtained by RT-PCR fiom total RNA using Beta vulgaris treated by 50 mmol· L^-1 KNO3 as material in this research. DNA sequence analysis showed that it contains the entire open reading frames that encode deduced protein with 905 amino acid residues and shows 99% sequence identity to Beta vulgaris nitrate reductase gene. The results showed that the activity of NR rapidly decreased in the first lh and gradually decreased when the time of N-absent treatment was prolonged. Furthermore, the expression of NR was down-regulated in the seedlings of Sugar Beet under N-absent stress. It suggested that the mRNA transcription of NR might be related with the induction of N.