Nopaline is primarily used in plant biotechnology and genetic engineering, especially in the study of crown gall tumors caused by Agrobacterium tumefaciens. It serves as a key example of an opine, which are compounds synthesized in infected plant tissues and utilized by the bacteria as a nutrient source. Because nopaline and its biosynthetic pathway are encoded by genes on the Ti (tumor-inducing) plasmid, it plays an important role in classifying Agrobacterium strains and their host range. The nopaline synthase gene (nos) is also used in molecular biology as a selectable marker or part of gene expression systems in transgenic plants. Additionally, the promoter region of the nos gene is widely used to drive constitutive expression of foreign genes in plant transformation experiments.