Effect of NH₄NO₃ Dressing on Activities of Nitrate Reductase and Invertase in NC89 Tobacco Leaves during Later Growth Stage

The effects of dressing rate and time on the activities of key enzymes in carbon and nitrogen metabolism, nitrate reductase (NR)and invertase (Inv), in NC89 tobacco leaves during later growth stage were studied by pot experiments.The results showed that:1)the activities of NR and Inv decreased with the advance of maturity of upper and lower leaves;2)the activities of NR and Inv in lower-leaf raised and Inv/NR decreased with the delay of dressing and the increase of dressing rate;3)the activities of NR and Inv and Inv/NR in upper leaves were lower while dressed earlier or with less N.The metabolism of carbon and nitrogen was relatively harmonious during the maturing of upper and lower leaves in the treatments dressed on 30 days after transplanting with 30% of total N.