Different types of tobacco plants were studied to see how they process nitrogen. The researchers looked at three different genotypes of tobacco plants and found that each one had different levels of certain enzymes related to nitrogen metabolism. One genotype had higher nitrate reductase activity in its leaves, while another had higher activity in its roots. Glutamine synthetase activity was higher in a different genotype's leaves and roots. The amount of soluble protein also varied between the genotypes. Overall, the researchers found that the levels of these enzymes did not always match the nitrogen levels in the plants.