Metabolite profiling of spinach (Spinacia oleracea L.) leaves by altering the ratio of NH_4^+/NO_3^- in the culture solution(Plant Nutrition)

To observe the effect of different forms of N, we have applied metabolic profiling using gas chromatography mass spectrometry to evaluate the metabolite composition of spinach. The aim of the present study was to find an appropriate indicator of overall metabolic response to N source. The effect of the NH_4^+/NO_3^- ratio on spinach tissue was investigated, comparing two cultivars that differed in their ability to use N. There was wide variation in NH_4^+/NO_3^- absorption without any distinct growth inhibition in either cultivar. Statistical analysis revealed that the metabolites could be broadly divided into two types, correlating either positively or negatively with NH_4^+ uptake in the culture solution. Principal component analysis (PCA) was an effective tool that extracted the indexes of the effect of the ratio of N forms as PCA scores. Close relationships between metabolite profiles and NH_4^+ uptake were observed, indicating that metabolic profiling is able to distinguish the invisible metabolic change in mature leaves of spinach and may provide a new tool for the investigation of quality features or rhizosphere nutritional condition.