Used for the quantitative detection of nitrate reductase (NiA) enzyme activity in plant tissues. This ELISA kit enables researchers to measure changes in NiA levels under different environmental conditions, such as nitrogen availability, light exposure, and stress factors. It is widely applied in plant physiology and agricultural research to study nitrogen metabolism, optimize fertilizer use, and develop crop varieties with improved nitrogen use efficiency. The assay is suitable for high-throughput analysis and provides a reliable tool for monitoring enzyme activity in leaves, roots, and other plant parts.