Nitrogen assimilation of plants is carried out by complicated biochemical processes. Plants can take up nitrogen from the soil in various forms. Independently of its form, nitrogen is transformed into ammonium, so that plants can utilise it.

Our objective was to examine under laboratory conditions how increasing molybdenum concentration acts on various nitrogen forms and how it affects the process of nitrate assimilation.

A dicotyledonous plant (sunflower, Helianthus annuus L. cv Arena PR) was selected as the subject of experiment. The molybdenum concentration was examined in the shoot and the root separately.

In the course of the experiment, it was established that molybdenum is indispensable for the undisturbed process of nitrate reduction, one of the important steps of nitrate assimilation. Proper molybdenum supply increases the activity of the nitrate reductase enzyme; therefore, the harmful accumulation of nitrate can be avoided.

The practical value of examining the correlation between molybdenum supply and nitrate reduction can be utilised especially in the production of leaf vegetables and root vegetables, as these plants contain much more nitrate than average. If it is made sure that the molybdenum concentration of the soil reaches the physiological molybdenum demand of plants (0.01 μM), it is possible to reduce their nitrate content, which is important from the aspect of human healthcare.

Keywords: molybdenum, sunflower, rhizobox, nutrient solution