Role of cytokinin in Nicotiana genetic tumors — A working hypothesis

Abstract

There are three prerequisites for the development of genetic tumors in Nicotiana; distantly related species must be crossed interspecifically, the hybrid plants must be exposed to stress conditions and an elevated level of cytokinin must be present. These events occur sequentially. First, the interspecific hybrid plants appear to produce a unique tumor‐inducing factor (Ti‐factor). Second, stress conditions trigger the synthesis signal molecule(s) which in turn stimulate synthesis of increased levels of cytokinin. Third, the elevated level of cytokinin acts upon the Ti‐factor to initiate uncontrolled growth. The predominant shooty/leafy morphology of genetic tumors reflects the high level of endogenous cytokinin, and this hormone appears to play a pivotal role in the development of these tumors.