Abstract: This thesis introduced the study of cytokinin_signal transduction by using mutants (cytokinin_receptors and some related proteins are probably involved in cytokinin_signal transduction) and the hypothesis for cytokinin_signal transduction pathway: once cytokinin is accepted by receptors (CKI1, IBC6 or GCR1), it will become typical information via transduction_system. On the one hand, this typical information may regulate genetic expression which might lead to the change of response to the range of cytokinin concentration by regulating receptor level. In addition, genetic expression may have cell exhibit relevant physiological responses. On the other hand, this typical information may activate MAPK cascade, which result in relevant physiological responses.