The effect of a synthetic cytokinin, 6-benzylaminopurine (BAP), on gene expression of Rho1Ps in shoot apex segments of garden pea was examined by Northern blot hybridization using 32Plabelled 560 bp partial Rho1Ps cDNA fragment as the probe. The application of 10-12 M BAP, the lowest concentration tested, for 24h to the segmetns strongly activated the synthesis of Rho1Ps transcripts as much as 7 times compared with those in BAP-untreated segments. In addition, the Rho1Ps transcripts synthesis was enhanced by BAP in a concentration dependent manner, suggesting that BAP is concretly involved in the Rho1Ps gene expression in the segments. A time course analysis of BAP on Rho1Ps gene expression exhibited that BAP was closely related not only to the Rho1Ps transcripts synthesis but also to the degradation of Rho1ps transcripts.