Abstract: To understand the mechanism of γ-aminobutyric acid (GABA) in plant growth and development,the seedlings of Nicotiana tabacum (SR1) were cultured in 1/2 MS medium plus three different GABA concentrations.The results showed that GABA can stimulate the growth of Nicotiana tabacum seedlings at a low concentration (1mmol/L),and the length of primary roots is significant longer than that of the control (higher about 30%);The expression of MAPK was promoted under the treatment of a low GABA concentration (1mmol/L).However,the elongation of primary roots was inhibited at a high GABA concentration (10-100 mmol/L),demonstrating the typical feature of ethylene response effect.The expression of ACS1 was enhanced by different GABA concentration,100 mmol/L in leaves and 10 mmol/L in roots.Different expression of MAPK and ACS1 to GABA signals may be involved different signal transduction pathway.