Dynamic changes of activities of key enzymes in carbon and nitrogen metabolism in flue-cured tobacco of different positions after topping and correlation analysis.

The variations of activities of nitrate reductase,amylase and invertase in the flue-cured tobacco leaves in different positions at topping and 10 d,20 d,30 d after topping were studied.The results showed that: 1) From topping to 20 d after topping,the activity of nitrate reductase in the upper leaves was higher than that in the cutters and lower leaves.From topping to 10 d after topping,the activity of nitrate reductase in the cutters and lower leaves rose rapidly.2) The activity of amylase of tobacco leaves in the 3 positions decreased during the whole stage in general and was very low and similar to that at topping.There was a peak activity value of amylase in the cutters and upper leaves 10 d after topping and another 20 d after topping respectively.3) The activity of invertase in the upper leaves was higher than that in the cutters and the lower leaves during the whole stage.The activity of invertase in the cutters and lower leaves showed continuous declining trend and the declining speed in the lower leaves was larger than in the cutters.4) The activity of amylase was correlated significantly and negatively with the activity of nitrate reductase and invertase in the upper leaves.There was also an obvious negative correction between the activity of amylase and that of invertase.