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.