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The difference in N metabolism between NAD(P)H-specific NR-deficient mutant and wild-type barley (Hordeum vulgare L.)

Abdel-Latif, Salwa A., Abou-Zeid, Hanan M.
Journal of plant nutrition 2019 v.42 no.17 pp. 2029-2042
Hordeum vulgare, NAD (coenzyme), barley, genotype, metabolism, mutants, nitrate reductase, nitrate reduction, nitrates, nitrites, nitrogen, nutrient solutions, phloem, photophase, roots, seedlings, shoots, stable isotopes, xylem
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. AbbreviationsAnlaccumulation of reduced ¹⁵N from ¹⁵NO₃⁻ in non-labeled roots of split roots Araccumulation in roots of reduced ¹⁵N from ¹⁵NO₃⁻ Asaccumulation in shoots of reduced ¹⁵N from ¹⁵NO₃⁻ Rr¹⁵NO₃⁻ reduction in roots Rs¹⁵NO₃⁻ reduction in shoots Tptranslocation to root of shoot reduced ¹⁵N from ¹⁵NO₃⁻ in phloem Txtranslocation to shoot of root-reduced ¹⁵N from ¹⁵NO₃⁻ in xylem FWfresh weight