Imidacloprid Disturbs the Nitrogen Metabolism and Triggers an Overall Stress Response in Maize Seedlings

Imidacloprid (IMI) protects crops from pests; however, its potential toxicity to plants and underlying mechanisms are still poorly understood. We investigated the effects of IMI on maize seedlings under different nitrogen sufficiency conditions. Our measurement of the maize seedlings’ growth traits and physiological indicators found that a 5 ppm IMI treatment stunted the maize’s growth and enhanced membrane lipid peroxidation under a nitrogen-supplied condition, but that it promoted an increase in biomass and alleviated chlorosis in maize shoots under nitrogen deficiency. These results suggest that IMI causes serious toxicity in maize seedlings under nitrogen-sufficient conditions. The content of IMI indicated that the leaf was the main site of IMI accumulation in maize, and that NO₃⁻ was beneficial for the transportation of IMI from the roots to the leaves. The three groups of seedlings, which received 0 (−N), 4 (N) or 10 mmol L⁻¹ NO₃⁻ (NN), were either treated or not treated with 5 ppm IMI. The six sets of transcriptome profiles from the shoots and roots were compared using Illumina sequencing. Transcriptome analysis revealed that IMI treatment led to changes in the expression of the genes involved in multiple biological processes, including nitrate transporter, nitrogen assimilation, nitrogen-regulatory factors, detoxification-related genes and several antioxidant-related genes in maize roots. The above results and the data for the nitrate content, glutamine synthetase activities and nitrate reductase activities showed that IMI disturbed nitrogen absorption and metabolism in maize seedlings. Glutathione S-transferase genes, C-type ATP-binding cassette (ABC) transporter 4, anthocyanins and lignin may play an important role in the detoxification of IMI in maize. These findings have helped us to elaborate the underlying detoxification mechanisms of IMI in plants, which is highly important in the cultivation of anti-pesticide crop varieties.