INFLUENCE DE LA FERTILISATION AZOTÉE SUR L’ACTIVITÉ NITRATE RÉDUCTASE ET LA TENEUR EN PROTÉINES DE TROIS VARIÉTÉS D’AVOINE

Abstract

The effect of two application modes of nitrogen fertilization on leaf nitrate reductase activity, leaf nitrate content and grain and straw protein content was studied in three oat cultivars: Lamar, Cascade and Cabot. The enzymatic activity shows the same biological rhythm for the three cultivars, no matter when the nitrogen was applied; the activity was high at the coleoptile stage, reached a maximum at tillering and then decreased until heading. However, Lamar presented a higher maximum activity at tillering when nitrogen fertilizer was applied at sowing. Ammonium nitrate applied twice during growth resulted for all cultivars in a longer period of higher activity and at the same time a decrease of its amplitude. In leaves, the nitrate availability at the site of reduction was different according to fertilization mode: maximum nitrate content did not appear at the same time during plant development; as for nitrate reductase activity Lamar presented a higher maximum when nitrogen was applied at time of sowing. Fertilization at the beginning of stem elongation did not have any effect on leaf nitrate content. The total and soluble protein content in grain and straw in the three cultivars did not show important differences either.Key words: Ammonium nitrate, nitrate reductase activity, nitrate, protein, oat