| The effect of osmotic stress on endogenous polyamines content and their metabolism enzyme activity in tobacco plants were investigated by hydroponic experiment using polyethylene glycol(PEG6000) as osmoticum.The results showed that the contents of putrescine(Put),spermidine(Spd) and spermine(Spm) in tobacco roots increased significantly under osmotic stress,and with the decreasing of osmotic potential,the changing ranges of these polyamines were more significant compared with control.It was also found that the content of Put in the roots increased during osmotic stress for 12 h at the osmotic potential of-0.5 MPa and 18 h at the osmotic potential of-0.25 MPa,respectively;afterwards,the Put content in two stress-treated roots all decreased.The contents of Spm and Spd in the roots were the highest with osmotic stress for 6 h,after that they gradually declined.The changing trends of Put content and ADC activity in the leaves were compatible with Put content in the roots,while both the Spd content and PAO activity reached their peaks with osmotic stress for 18 h,then decreased obviously.There were not significant changes in Spm content and ODC activity in the leaves during osmotic stress.In addition,it was found that there was a significant positive relationship between Put content and ADC activity in the leaves,which suggested that the major pathway of Put biosynthesis in the leaves under osmotic stress was from arginine decarboxylation by the function of ADC,and the accumulation of Put in the plants could enhance the drought-resistance of tobacco. |