Foliar application of nano urea results in higher biomass, chlorophyll, and nitrogen content than equimolar bulk urea through differential gene regulation in Arabidopsis thaliana

Abstract

Indian Farmers Fertilizer Cooperative (IFFCO)′s liquid nano urea formulation (NUF) was applied to one-month-old Arabidopsis thaliana plants grown in vermiculite as a 0.4% foliar spray twice at an interval of 10 days and compared with sprays of equimolar bulk urea. NUF resulted in a 51 ± 14.9% increase in biomass, 29.5 ± 9.1% in chlorophyll, 8.4 ± 3.1% in nitrogen, and 4.5 ± 0.3% in amino acid content of the leaves, compared to bulk urea. NUF′s zeta potential of -54.7 mV and particle size of ≃27.7 nm, measured by dynamic light scattering and transmission electron microscopy, make it suitable for stomatal uptake. We conducted a differential gene expression analysis by mRNA sequencing to understand the molecular basis of the phenotypic gains under NUF rather than urea. NUF resulted in significantly higher expression levels of 211 genes (log2fold-change > 0.5, FDR < 0.05) involved in the biosynthesis of carbohydrates, amino acids, nucleotides, lipids, phytohormones, and secondary metabolites, cell wall biosynthesis and modification, growth and developmental processes, cell cycle, and stress response than bulk urea. On the other hand, 1,286 genes (log2fold-change < -0.5) involved in cell death, abscission, senescence, nitrogen transport and metabolism, and biotic stress response showed lower expression levels upon NUF application than bulk urea. Our results suggest that although NUF foliar spray suppresses nitrogen uptake genes, possibly due to nitrogen excess, it enhances growth by up-regulating the synthesis of essential biomolecules and growth-promoting genes, compared to bulk urea.