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烟叶采收晾制后，体内硝酸还原酶活动剧烈下降，晾制后４ｄ，叶肉内该酶活性即下降至０，晾制后两周主脉内此酶活性下降至０．且两种电子供体间无显著差异．烟叶体外硝酸还原酶活动晾制开始时很低，晾制３周后增加．整个晾制过程中叶肉、主脉硝酸盐含量均无显著变化．晾制后两周主脉亚硝酸盐含量很低，但是晾制后３周开始逐渐增加，叶肉亚硝酸盐在整个晾制过程中无变化．晾制后３周，主脉亚硝酸盐含量增加，与体外硝酸还原酶活动相关，这可能是微生物的酶起作用．
After the tobacco leaves were harvested for air-drying, the activity of nitrate reductase decreased sharply in the body. After 4 days of air-curing, the enzyme activity in the leaves decreased to 0, and the enzyme activity in the main vein decreased to 0 after two weeks of air-curing. There was no significant difference between the two electron donors. The activity of nitrate reductase in vitro was low at the beginning of air-curing, and increased after 3-week airing. There was no significant change in the contents of mesophyll and main vein during the whole process of air-curing. Two weeks after drying, the content of nitrite in the main artery was very low, but began to increase 3 weeks after the air-curing. The nitrite in the leaves did not change during the whole air-curing process. Three weeks after drying, the content of nitrite in the main artery increased, which was related to the activity of nitrate reductase in vitro. This may be due to the action of microorganisms.