Zhong, FenglinFenglinZhongWang, ShubinShubinWangLin, JunfangJunfangLinRoan, Su-fengSu-fengRoanLin, BiyingBiyingLinZhou, XiangzhuXiangzhuZhouIOU-ZEN CHENLin, YizhangYizhangLinPang, JieJiePangWu, ShuangShuangWu2020-02-272020-02-2720180167-6903https://scholars.lib.ntu.edu.tw/handle/123456789/466742Optimal fertilization management is critical for romaine lettuce (Lactuca dolichophylla K.) cultivation, a major economical vegetable in China. Herein, we chose a romaine lettuce genotype (Lactuca sativa L.) known for “year-round production” and as “high-yielding,” to examine the effect of varied nitrogen (N) fertilizer forms on nitrate (NO3−) accumulation. We cloned NO3− reductase (NR) and nitrite (NO2−) reductase (NiR) of romaine lettuce and analyzed their expressions at different growth stages in response to different N forms. Five N treatments with varying NO3−-N:NH4+-N ratios were examined. Our results showed that lettuce leaf NO3− content decreased significantly with the increase of NH4+-N in fertilizer. The lowest NO3− content was observed when NO3−-N:NH4+-N ratio was 0:100. NR and NiR activity and expression initially were upregulated by the increase in NO3− content, with the highest level at 70:30 NO3−-N:NH4+-N ratio, but quickly declined thereafter. We also found the temporal activation pattern of N transporters was different from that of NO3− reductase and NO2− reductase, suggesting there is a coordination between N translocation and N reduction in lettuce leaves to maintain proper N homeostasis. These findings provide insights into the role of NO3−-N:NH4+-N ratio in regulating NO3− assimilation, balancing N metabolism, and reducing NO2− toxicity in vegetable production. © 2018, Springer Science+Business Media B.V., part of Springer Nature.Lactuca dolichophylla K; Nitrate reductase; Nitrite reductase; Nitrogen accumulation; Nitrogen resources[SDGs]SDG2journal article10.1007/s10725-018-0404-6WOS:000440115000001