| Abstract: | The accumulation of betacyanin, in dark-grown Amaranthus tricolorseedlings, in response to cytokinins or red light, occurs mainlyin two specific tissues, the lower epidermal cells of the cotyledons(with the exception of guard cells), and the endodermis of thehypocotyl. The possible significance of this ‘spatialpattern of competence’ is discussed, together with theconcept of target cells in relation to plant hormones. The effect of removing exogenously supplied cytokinin at varioustimes during a 24 h induction period is reported. There is noevidence that cytokinins act by a ‘triggering’ effectwith a long half life, the response in the target cells beingthe same as that expected from the amount of cytokinin and cytokininmetabolite remaining in the tissue at the time of extraction.Either continuous presence of cytokinin is needed or any triggeraction is short lived, and continuous ‘re-triggering’is needed to achieve maximum response. Key words: Amaranthus tricolor, Betacyanin synthesis, Cytokinin action, Target cells |
