Silver nitrate-positive opines in crown gall tumors

Abstract

Agrobacterium tumefaciens strains harboring octopine- or agropine-type Ti-plasmids induce crown gall tumors on Kalanchoë tubiflora, sunflower or carrot, that contain agropine, mannopine, mannopinic acid, and agropinic acid. Since oxidation of these compounds on electrophoretograms by an alkaline silver nitrate reagent yields darkly stained spots due to reduction of the silver ions, they are called ‘silver nitrate-positive’. These silver nitrate-positive compounds are not present in normal plant tissues nor in tumors induced by A. tumefaciens strains that contain a nopaline-type Ti-plasmid. All four compounds are opines since octopine- and agropine-type Ti-plasmids, but not nopaline-type Ti-plasmids, confer on the bacterial host the ability to catabolize them for growth. Silver nitrate-positive opines were always present in primary octopine- or agropine-type crown gall tumors. However, cultured crown gall tumors frequently did not contain detectable silver nitrate-positive opines even though other types of opines, such as octopine, were usually present.