Rational metabolic-flow switching is an effective strategy that we previously proposed to produce exogenous high-value secondary metabolite(s) in cultured plant cells. Specifically, it involves redirecting a highly active inherent metabolic pathway to a pathway producing related exogenous compounds. The success of this strategy depends on the identification of at least one highly active metabolic pathway in host plant cells that can be redirected to produce a target compound following the introduction of exogenous biosynthetic gene(s) via genetic transformation. Active metabolic pathways may be predicted on the basis of the major metabolites that accumulate in cells. In previous proof-of-concept studies, we demonstrated that cultured cells of a temperate bamboo species (Phyllostachys nigra; Pn) are an appropriate host for producing phenylpropanoid-derived compounds. However, developing a series of host plant cells with a variety of metabolic properties is necessary to maximize the utility of rational metabolic-flow switching. In this study, we established cultured cells of two tropical bamboo species (Dendrocalamus giganteus and Dendrocalamus brandisii). By analyzing the metabolites that increased in abundance in response to phytohormone treatments, we determined that exogenous gibberellin A3 (GA3) substantially induced the accumulation of an unknown metabolite in D. giganteus (Dg) cells. This compound was isolated and identified as serotonin (5-hydroxytryptamine). After optimizing the culture conditions, the serotonin production titer in Dg suspension cells reached 360 mg l-1. These findings indicate that Dg cells are potentially suitable for the bioproduction of exogenous tryptophan-derived indolic compounds via rational metabolic-flow switching.