Some external agents, including wound tumor virus, Agrobacterium tumefaciens and Agrobacterium rhizogenes, could initiate tumors on plants

The effect of exogenous auxin and cytokinin on cell proliferation and differentiation varies with the tissue system, and depends on the endogenous levels of the two hormones in the tissue. In this report, cytokinin (N-benzyladenine, BA) and auxin (indole-3-acetic acid, IAA) were used to treat young seedlings, leaf explants, and genetic tumors of a Nicotiana hybrid. Exogenous BA markedly accelerated genetic tumor formation in young seedlings, while exogenous IAA inhibited it on young seedlings but not on leaf explants. Genetic tumors showed low sensitivity to exogenous BA and IAA. RAPD analysis of the genomes of the genetic tumors and normal tissue suggested that tumor formation is related to genomic instability.