Organic nitrogen content and nitrate and nitrite reductase activities in tritordeum and wheat grown under nitrate or ammonium

Tritordeum is a fertile amphiploid derived from durum wheat (Triticum turgidum L. conv. durum) × a wild barley (Hordeum chilense Roem. et Schultz.). The organic nitrogen content of tritordeum grain (34 mg g-1 DW) was significantly higher than that of its wheat parent (25 mg g-1 DW). Leaf and root nitrogen content became higher in tritordeum than in wheat after four weeks of growth, independently of the nitrogen source (either NO3- or NH4+). Under NO3- nutrition, tritordeum generally exhibited higher levels of nitrate reductase (NR) activity than wheat. Nitrite reductase (NiR) levels were however lower in tritordeum than in its wheat parent. In NH4+-grown plants, both NR and NiR activities progressively decreased in the two species, becoming imperceptible after 3 to 5 weeks of growth. Results indicate that, in addition to a higher rate of NO3- reduction, other physiological factors must be responsible for the greater accumulation of organic nitrogen in tritordeum grain.