Effects of different growth temperatures on alkaloid content and nicotine metabolism in roots, stems and leaves of tobacco (Nicotiana tabacum L.) plants
Alkaloids, especially nicotine content, significantly influences quality and flavour types of tobacco leaves, which is differentially regulated by various environmental conditions. To investigate the effects of different growth temperature on alkaloids and nicotine content as well as gene expression of nicotine metabolism-related enzymes in roots, stems and leaves of 12-leaf-old tobacco (Nicotiana tabacum L.) plants, the tobacco cultivar Yunyan 87 was cultivated in artificial climate chambers setting at three different growth temperature (mean temperature at 30.5, 23.5, and 16.5 °C with daily fluctuation). The results showed that the different growth temperatures influence growth, alkaloids and nicotine content as well as gene expression of seven nicotine metabolism-related enzymes in tobacco plants. The higher growth temperature at 30.5 °C lowered nicotine, anatabine, anabasine and nornicotine content in roots, stems and leaves. On the other hand, the lower growth temperature at 16.5 °C raised the alkaloid content in root and stem, and the medium growth temperature at 23.5 °C made leaves maintain the highest alkaloid content as compared with the lower and higher temperature treatments. RNA-seq and qPCR results showed that the seven gene expression of nicotine metabolism-related key enzymes was consistent with the change of nicotine content. These results suggested that the higher growth temperature quickly stimulated the synthesis of nicotine and translocation to tobacco leaves, the lower temperature inhibited the nicotine translocation, and the medium growth temperature was helpful for the long lasting accumulation of nicotine, which led to the highest nicotine content in tobacco leaves.