玉米硝酸盐累积及其在适应持续低氮胁迫中的作用

旱地作物吸收氮素的主要形态是硝酸盐，硝酸盐的积累与再利用对植物适应低氮土壤环境具有重要意义。本试验利用两个硝酸盐累积能力不同的玉米自交系478（硝酸盐积累低）和W312（硝酸盐积累高）为研究材料，研究玉米的硝酸盐累积及其在适应持续低氮胁迫中的作用。结果表明，W312的硝酸还原酶活性和NR基因的表达都弱于478，而体内氨基酸含量显著较低。对一个可能与液泡膜硝酸盐转运有关的氯离子通道蛋白基因（ZmCLC）的表达分析发现，478的ZmCLC表达显著强于W312。说明W312硝酸盐积累能力强主要是由于其较弱的氮同化能力，而不是硝酸盐向液泡的运输能力强。在砂培体系并持续缺氮条件下，W312叶绿素含量（SPAD值）显著高于478，表明植株体内较高硝酸盐累积有助于W312适应持续缺氮的土壤环境。

Nitrate accumulation in maize and its role in adaptation to lasting low nitrogen environments

Nitrate is the major nitrogen (N) form in aerial soils. Accumulation and subsequent reutilization of nitrate in plants can be important for adaptation to low N environments. Using two maize inbred lines differing in nitrate accumulation ability, nitrate accumulation in maize and its relation to adaptation of low nitrogen environments were investigated. In comparison to inbred 478, inbred W312 accumulated significantly more nitrate in shoot. The activity of nitrate reductase (NR) as well as the expression of two maize NR genes (ZmNR1 and ZmNR2) was lower in W312. Correspondingly, the total amino acids content in W312 was also lower. The putative chloride channel ZmCLC, which homolog in Arabidopsis was demonstrated to be responsible for nitrate transport into vacuole, was cloned. The expression of ZmCLC in W312 was lower than in 478, especially at low N stress conditions. It was conclude that the higher nitrate accumulation in W312 is due to its lower nitrate assimilation ability rather than the activity of nitrate transport toward the vacuoles. At low N conditions in a sand culture system, the chlorophyll content of W312 was much higher than that of 478, suggesting that the higher ability of nitrate accumulation may be beneficial for the adaptation of plants to the lasting low N stress.