In Tobacco callus; which one shall induce shoot differentiation in combination of auxin and cytokinin

In Tobacco callus; a higher concentration of cytokinin and a lower concentration of auxin shall induce shoot differentiation in a combination of auxin and cytokinin.
For callus initiation, a high concentration of auxins and a low concentration of cytokinins were used, whereas a high concentration of cytokinins and a low concentration of auxins were used for shoot-bud differentiation.
An intermediate ratio of auxin and cytokinin promotes callus induction, while a high ratio of auxin-to-cytokinin or cytokinin-to-auxin induces root and shoot regeneration, respectively.