Cytokinin habituation

Cytokinins are potent morphogenetic substances known to regulate organogenesis in cultured tissues (92). Studies of cytokinin habituation suggest that cell heritable states of cytokinin requirement are maintained by a regulatory positive-feedback... 

Tissues from different parts of the tobacco plant differ both in cytokinin requirement and in their competence for habituation in culture. In contrast to pith tissue, tissue cultured from explants of the leaf lamina exhibits a non-inducible C phenotype. 

These tissues do not become habituated under conditions that induce the habituation of pith tissue (58). Tissue cultured from the cortex of the stem exhibits a constitutive phenotype primary explants of cortex do not require exogenous cytokinin for proliferation. The great majority (95 to 99%) of single-cell clones isolated from leaf- and cortex-derived cultures show the phenotype of their parent tissues. Therefore, it appears that cells in the stem-cortex and leaf are determined to express different cytokinin requirements in culture and that these states are inherited at the cellular level. 

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