Nitrate is a nutrient signal that triggers complex regulation of transcriptional networks to modulate nutrient-dependent growth and development in plants. This includes time- and nitrate concentration-dependent regulation of nitrate-related gene expression. However, the underlying mechanisms remain poorly understood. Here we identify NIGT1 transcriptional repressors as negative regulators of the Arabidopsis NRT2.1 nitrate transporter gene, and show antagonistic regulation by NLP primary transcription factors for nitrate signalling and the NLP-NIGT1 transcriptional cascade-mediated repression. This antagonistic regulation provides a resolution to the complexity of nitrate-induced transcriptional regulations. Genome-wide analysis reveals that this mechanism is applicable to NRT2.1 and other genes involved in nitrate assimilation, hormone biosynthesis and transcription. Furthermore, the PHR1 master regulator of the phosphorus-starvation response also directly promotes expression of NIGT1 family genes, leading to reductions in nitrate uptake. NIGT1 repressors thus act in two transcriptional cascades, forming a direct link between phosphorus and nitrogen nutritional regulation.

BackgroundDexmedetomidine is a highly selective central α2-agonist with anesthetic and analgesic properties for patients in intensive care units. There is little information about the relationship between dosage and plasma concentration during long drug infusions of dexmedetomidine in critically ill patients, especially in Asians. In addition, the administration of dexmedetomidine with a dosage of 0.2–0.7 μg/kg/h in Japan is different from that with a dosage of 0.2–1.4 μg/kg/h in European countries and the USA. There has been concern about obtaining an effective concentration with a small dosage and estimating the relationship between dosage and plasma concentration. We conducted a prospective, observational, cohort study measuring plasma dexmedetomidine concentrations.MethodsPlasma dexmedetomidine concentrations of 67 samples from 34 patients in an intensive care unit for 2 months were measured by ultra performance liquid chromatography coupled with tandem mass spectrometry using single-blind method, and the correlation coefficient between dosages and plasma concentrations was estimated. Exclusion criteria included young patients (<16 years) and samples obtained from patients in which the dosage of dexmedetomidine was changed within 3 h.ResultsAmong the patients, 20 (58.8%) of the 34 received dexmedetomidine at 0.20–0.83 μg/kg/h, and in 40 of the 67 samples for which dexmedetomidine had been administered, this occurred for a median duration of 18.5 h (range, 3–87 h). The range of the dexmedetomidine plasma concentration was 0.22–2.50 ng/ml. By comparison with other studies, with a dosage of 0.2–0.7 μg/kg/h, the patients in this setting could obtain an effective dexmedetomidine concentration. The plasma dexmedetomidine concentration was moderately correlated with the administered dosage (r = 0.653, P < 0.01). The approximate linear equation was y = 0.171x + 0.254. The range of Richmond Agitation-Sedation Scale was 0 to -5.ConclusionsWe concluded that, with a dosage of 0.2–0.83 μg/kg/h, the patients in this setting could obtain an effective dexmedetomidine concentration of 0.22–2.50 ng/ml. In addition, the plasma dexmedetomidine concentration was moderately correlated with the administered dosage (r = 0.653, P < 0.01).Trial registrationUniversity Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) UMIN000009115.

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