Differentiation of shoot is controlled by:

A high cytokinin to auxin ratio triggers shoot formation but inhibits root induction, whereas, a low ratio produces the opposite effect. Plant growth regulators (cytokinin, auxin) are widely used to control differentiation in cultured plant cells and tissues. Related Theory In the root meristem, auxin induces the meristematic cell division, whereas cytokinin promotes the cell to swith from the meristematic to differentiated state through inhibiting auxin signalling. Auxin at low concentrations limits the action of cytokinin. An increase in cytokinin level counteracts this inhibitory effect and leads to an inhibition of auxin stgnalling. At higher concentrations of both hormones, these antagonistic interactions between cytokinin and auxin are absent