Nopaline
Nopaline is an opine, a modified amino acid found in certain plant tumors caused by the bacterium Agrobacterium tumefaciens. Specifically, nopaline is a derivative of L-arginine and α-ketoglutarate, condensed to form N2-(1,3-dicarboxypropyl)-L-arginine.
Nopaline is synthesized by the enzyme nopaline synthase, encoded by the nos gene located on the Ti (tumor-inducing) plasmid of Agrobacterium. The bacterium utilizes nopaline as a source of carbon and nitrogen. The presence of nopaline (and other opines) in the plant tissue provides a selective advantage to Agrobacterium, facilitating its proliferation within the plant.
Different strains of Agrobacterium are classified based on the specific opines they produce. Nopaline strains produce nopaline, while other strains produce different opines like octopine or agropine. This classification is useful in understanding the interactions between Agrobacterium and its host plants. Opines like nopaline are not typically found in healthy plant tissue. They are unique markers of Agrobacterium-induced tumors (galls).
The study of nopaline and other opines has been crucial in understanding the mechanism of horizontal gene transfer from bacteria to plants, and in developing genetic engineering tools for plant biotechnology.