Effects of External Inorganic Nitrogen Concentration on Metabolism, Growth and Activities of Key Carbon and Nitrogen Assimilatory Enzymes of Laminaria Saccharina (Phaeophyceae) in Culture1

The growth rate of Laminaria saccharina (L.) Lamour. is dependent on inorganic nitrogen in culture. Growth rates were saturated between 5 and 10 μmol · L−1 nitrate. The activities of ribulose‐1,5 bisphosphate carboxylase, phosphoenolpyruvate carboxykinase, mannitol‐1‐phosphate dehydrogenase, nitrate reductase and glutamine synthetase also varied with the concentration of inorganic nitrogen in the medium. All enzyme activities were lowest at 2.5 μmol · L−1 nitrate (the lowest concentration used) increasing to a maximum activity between 10 and 30 μmol · L−1 nitrate. Most enzyme activities followed a hyperbolic curve resembling those described by the Michaelis‐Menten equation, with different half‐saturation constants.