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

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.

Abbreviations
Anl	=	accumulation of reduced 15N from 15NO3− in non-labeled roots of split roots
Ar	=	accumulation in roots of reduced 15N from 15NO3−
As	=	accumulation in shoots of reduced 15N from 15NO3−
Rr	=	15NO3− reduction in roots
Rs	=	15NO3− reduction in shoots
Tp	=	translocation to root of shoot reduced 15N from 15NO3− in phloem
Tx	=	translocation to shoot of root-reduced 15N from 15NO3− in xylem
FW	=	fresh weight

Keywords:

• barley
• light/dark
• mutant
• nitrate reduction
• ¹⁵N incorporation model

Acknowledgments

I am deeply grateful to Professor Dr. Takuji Ohyama and Professor Dr. Kuni Sueyoshi at Department of Applied Biological Chemistry, Faculty of Agriculture, Niigata University, Japan, for their technical assistance and help during the experimental work.

Disclosure statement

No potential conflict of interest was reported by the authors.