The Relationship Between Nitrogen Metabolism During Senescencing And Flue-Curing And Qulity Of Tobacco Leaf

The experiments were carried out, through regulating the applied N level and flue-curing conditions, to evaluate the nitrogen metabolism and it's relationship to flavor quality of tobacco leaf. It was found out that during the senescing process of tobacco leaf growing at field, as the leaf senescing, the content of abscisic acid (ABA) and malondialdehyde (MDA) increased while the changing model of the activity of superoxide dismutase (SOD) was a mono-peak curve with the peak appearing at sometime between the physiological ripeness stage and harvesting. And the content of ABA and MDA and the activity of SOD decreased when the applied N level increased.The content of protein, amino acid (AA), nitrate and nitrate reductase (NR) activity had different changing models. With the stalk position rising, protein content decreased, NR activity increased, AA content was a mono-valley curve , and nitrite content was a mono-peak curve, whereas, all of them had positive correlation with the N-applying level.SOD,ABA and MDA had close correlation to N metabolism. Under low N level, the correlation was significant at the 5% level of significance between SOD and MDA and total nitrogen, nitrite reductase, protein but was not under high N applied level. The correlation between ABA and major N nitrogen compounds excluding amino acid and nitrate was highly significant under all N-applying level. So ABA was proposed to be the physiological index to evaluate the senescing degree of tobacco leaf.There were big effects of temperature and moistrue conditions in curing process on nitrogen compounds content in tobacco leaf. The studies indicated that total nitrogen content was higher in tobacco leaf cured under high temperature yellowing (HTY), low moisture yellowing (LMY) or low moisture color-fixing (LMC) conditions. The curing temperature had less effect on nicotine than curing moisture. The nicotine content was high in tobacco leaf cured under high moisture yellowing (HMY).The degradation of protein and the accumulation of amino acid weremainly occurring in yellowing stage and color fixing stage. Protein was degraded more quickly in yellowing stage than in color-fixing stage and amino acid was on the contrary. That's to say, the degradation of protein and the accumulation of amino acid didn't happen paralleledly. Under the conditions of LTY, HMY and HMC, the proteinase activity was high and could standing much longer time which resulted in more protein was hydrolyzed and more amino acid was accumulation. And mat's the reason why the content of protein was low and the content of amino acid was high in the tobacco leaf cured under these conditions. Also, the condition of LTY and HMY made for the nitrite reductase activity and the accumulation of nitrate. The content of nitrite and nitrate increased synchronously and reached the highest point at the end of color fixing and then decreased.Correlation analysis showed that the correlation among total nitrogen, nicotine, protein, amino acid was highly significant at 1% level. Each monomial smoking score and most of nitrogen compounds had close correlation. The multi-regression equations between aroma, irritancy, taste, strength, sweetness and general quality existed at 10% level of significance.After considering the above-motioned study results synthesizly, we think that the medium applied N level and low temperature yellowing or high moisture curing condition is good for the quality of tobacco leaf.