The contents of proline and activities of key enzymes involved in proline metabolism in the leaves and roots were investigated for two wheat cultivar seedlings(differing in drought tolerance) exposed to PEG-6000 stress and recovery.The results showed that:(1)The root length and the root dry weight of ‘Pubing 143’(drought tolerant) were little affected little by PEG stress,whereas the root length and the root dry weight of ‘Zhengyin 1’(drought sensitive) decreased significantly.Under PEG stress the increasing range(75.0%) of proline content in the roots of ‘Pubing 143’ was more than that in ‘Zhengyin 1’(37.7%) at 36 h and the proline contents of both genotypes tended to be equal to their respective control after recovery from drought;(2)The activities of P5CS(synthesize proline from glutamate) and δ-OAT(synthesize proline from ornithine) increased significantly in the leaves of ‘Pubing 143’ under PEG stress,which indicated that two biosynthetic pathways were enhanced in the drought-tolerance cultivar ‘Pubing 143’ under PEG stress.P5CS activity increased while the change of δ-OAT activity was not obvious in ‘Zhengyin 1’ at 36 h,which indicated that the leaves of drought-sensitive cultivar ‘Zhengyin 1’ synthesized proline from ornithine primarily under PEG stress.Under PEG stress the activities of P5CS and δ-OAT were less affected in both wheat varieties roots;(3)PDH activity had a significant decrease at 36 h under PEG stress and increased significantly after recovery in the leaves of ‘Pubing 143’.PDH activity increased significantly compared with control in leaves of ‘Zhengyin 1’ under PEG stress.However,the activity of PDH decreased significantly in both wheat varieties roots.These results suggested that proline was mainly synthesized in the leaves of wheat and the accumulation of proline in the roots of ‘Pubing 143’ was associated with increased P5CS activity in leaves and transport of proline.