Properties of Crowngall Cells - Infection by A. tumefaciens produces tumour like growth from which roots and/or shoots may sometimes be produced. But infection by A. rhizogenes gives rise to 'hairy roots', which may often show negative geotropism; in some species, shoots may regenerate from the roots giving rise to complete plants.

Both hairy root and crowngall cells (free of Agrobacterium cells) are capable of growing in culture on a growth regulator (GR)-free medium, while normal plant cells need exogenous auxin and or cytokinin. Thus these plant cells have undergone cancerous or oncogenic alteration; they generally induce tumour when grafted onto a healthy plant.

The crowngall and hairy root cells also synthesize unique nitrogenous compounds called opines, which are neither produced by normal plant cells nor utilized by them. Agrobacterium cells use opines as their carbon and nitrogen source; the bacteria are usually present in the intercellular spaces of crown galls. The crowngall cells continue to produce opines even when they are cultured in vitro; even the plants regenerated from these cells produce them.