Abstract: In order to study the changes of nicotine content and expression of related genes in different types of tobacco germplasm, four tobacco types, including flue-cured tobacco K326, oriental tobacco Basma, burley tobacco TN90 and sun-cured tobacco Maryland were used as materials. Nicotine content in different leaves and the expression levels of nicotine metabolism related genes PMT, QPT, CYP82E5V2 and A622 were measured at different developmental stages. The results showed that with the passing of growth stage, the nicotine content increased slowly, and increased dramatically after topping. Except for Basma, the nicotine content continued to increase after topping, while in K326, TN90 and Maryland, the nicotine content increased sharply after topping, then decreased slowly, and gradually stabilized. PMT gene in different types of tobacco was expressed in different growth stages. Expression level of PMT was higher at the seedling stage, and its change trend was basically the same as that of the nicotine content. Expression level of QPT was higher in the early stage, then decreased, and reached a peak one week before topping. After topping, the expression level continued to increase, which was positively correlated with the change of nicotine content. Expression level of CYP82E5V2 remained at a high level in different growth stages, presenting a wave pattern, and increased in the bloom stage, and peaked before and after topping. However, expression level of CYP82E5V2 in Basma decreased when it was mature. Expression level of CYP82E5V2 was positively correlated with the change of nicotine content before the topping, and negatively correlated to a certain extent from the later topping stage to the mature stage. Expression level of A622 in K326 and Maryland rose in a wave-like manner, and remained at a high level at maturity, while in TN90 and Basma, expression level of A622 was higher one week before and after topping, then decreased, and increased again, the expression level was lower at maturity, and there was no obvious consistency with the change of nicotine content.

Key words: tobacco, nicotine, quantitative real-time PCR, gene expression