Abstract:

In order to study the differences of nitrogen metabolism and secondary metabolism of different flue-cured tobacco varieties at maturity stage, and explore the appropriate nitrogen application amount for different flue-cured tobacco varieties, we used ‘NC71’, ‘Yunyan105’ and ‘Yuyan13’ as the research materials. The experiment was set up with three treatments: low nitrogen (30 kg/hm²), medium nitrogen (45 kg/hm²), and high nitrogen (60 kg/hm²). Determination of key enzyme activities of nitrogen metabolism and the contents of its products and secondary metabolites at maturity stage was carried out. The result showed that the nitrate reductase (NR) activities of ‘NC71’ high nitrogen treatment, ‘Yuyan13’ low nitrogen treatment and ‘Yunyan105’ medium nitrogen treatment were 1.474 U/g, 1.395 U/g and 1.533 U/g, respectively. The glutamate synthase (GOGAT) activities were 218.447 nmol/(mg·min), 192.276 nmol/(mg·min) and 203.052 nmol/(mg·min), respectively. The contents of total phenols were 6.652%, 6.539% and 6.076%, respectively. The differences of the above indicators did not reach a significant level. Correlation analysis showed that the correlation coefficient between nitrate reductase activity and carotenoids was 0.855, reaching a very significant level. Nitrate reductase activity was significantly positively correlated with free amino acids, nicotine and total phenols, and the correlation coefficients were more than 0.6. Glutamine synthetase (GS) activity was significantly positively correlated with the secondary metabolites, and the correlation coefficients were more than 0.5. Changing the activities of nitrate reductase and glutamine synthetase could affect the contents of secondary metabolites of nitrogen metabolism, which was conducive to the improvement of tobacco quality. In conclusion, there are significant differences in the appropriate nitrogen application amount among different flue-cured tobacco varieties. It is important to use nitrate reductase and glutamine synthetase activities to measure nitrogen application amount at maturity stage.

Key words: flue-cured tobacco, maturity stage, nitrogen metabolism, secondary metabolism, suitable nitrogen application amount, enzyme activity