Polyamines are involved in chilling tolerance in tobacco (Nicotiana tabacum) seedlings

To better understand the role of polyamines (PAs) and their metabolism in responses to chilling stress in tobacco plants, this study investigated changes of endogenous PA contents, PA synthetase and oxidase activities, seedling growth and membrane permeability in tobacco (Nicotiana tabacum) cvs. MSk326 (MK, chilling-sensitive variety) and Honghuadajinyuan (HD, chilling-tolerant variety) under chilling stress. Chilling stress significantly reduced the shoot and root dry weights but improved PA contents, especially of putrescine, in the two tobacco cultivars, with higher contents in the tolerant variety. Moreover, stepwise regression analysis indicated that the relative growth rate of tobacco seedlings under chilling stress was positively correlated with endogenous PA contents, putrescine and spermidine, particularly. The above results suggested that the resistance of tobacco seedlings to chilling stress was promoted mainly by putrescine and spermidine. And further study specified that the higher PA contents in the chilling-tolerant tobacco variety were related to higher PA synthetase activities [arginine decarboxylase (ADC) and ornithine decarboxylase (ODC)] and lower oxidase activities (diamine oxidase and polyamine oxidase) under chilling stress. Again, the study demonstrated that PA biosynthesis in tobacco seedlings was mainly dependent on the ODC pathway under chilling stress, through ADC and ODC inhibitor application and recovery treatments. Compared with the ADC inhibitor (d-arginine), the ODC inhibitor (2-fluoromethyl ornithine) more significantly inhibited PA contents and increased membrane permeability in tobacco seedlings under chilling stress. In summary, the research findings suggested PAs play an important role in regulating the chilling tolerance of tobacco seedlings.