Development of shoot and root in tissue culture is determined by

Development of shoot and root in tissue culture is determined by cytokinin and auxin ratio.
The pioneering work has shown that a high auxin/cytokinin ratio induces root regeneration, whereas a low ratio promotes shoot induction.
High cytokinin-to-auxin ratios correlated with the shooty phenotype of transformed tissues propagated in vitro in the absence of added growth hormones.