LAUSR

Abstract Barley (Hordeum vulgare L.) is an important crop for cereal research. In this study, two barley genotypes the wild-type (Steptoe) and the mutant (Az12) were used. An experiment was conducted using 15N-tracing method to NADH-specific nitrate reductase (NR)-deficient mutant seedling of barley. The N-depleted seedlings were exposed to a nutrient solution containing nitrate and nitrite, and were labeled with 15N for 38 h under (14 L/10D) cycles. The two genotypes utilized 15NO3− and accumulated it as reduced 15N, predominately in the shoots. However, nitrate reduction in the Az12 shoots was 9% lower than that in the Steptoe shoots at 38 h. As a result, in the Az12, nitrate accumulation in shoots was 78% higher than that in the Steptoe. Accumulation of reduced 15N in the Az12 roots was nearly similar to that of the Steptoe roots, but 8% lower in the Az12 shoots than in the Steptoe shoots at the end of the experiment. Also for both genotypes, root contribution increased during L/D cycles and decreased during the subsequent light cycle. Upward transport of reduced 15N via the xylem in the Az12 was nearly two times higher than that in Steptoe during the second light period (24–38 h). In both genotypes, xylem transport of reduced 15N was far exceeded the downward phloem transport. AbbreviationsAnl accumulation of reduced 15N from 15NO3− in non-labeled roots of split rootsAr accumulation in roots of reduced 15N from 15NO3−As accumulation in shoots of reduced 15N from 15NO3−Rr 15NO3− reduction in rootsRs 15NO3− reduction in shootsTp translocation to root of shoot reduced 15N from 15NO3− in phloemTx translocation to shoot of root-reduced 15N from 15NO3− in xylemFW fresh weight