Contribution of Shoots and Roots to In Vivo Nitrate Reduction in NADH-Specific Nitrate Reductase-Deficient Mutant Seedlings of Barley (Hordeum vulgare L.)(Plant Nutrition)

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Barley (Hordeum vulgare L.) has two nitrate reductase (NR) isozymes, namely NADH-specific NR and NAD(P)H-bispecific NR. To determine the effect of NADH-specific NR deficiency on in vivo nitrate reduction and distribution of reduced N to shoots and roots, the ^<15>N-incorporation model was applied to NADH-specific NR-deficient mutant (Azl2) seedlings of barley. The N-deprived seedlings were treated with a nutrient solution containing 2.3 mM NO_3^- and 0.2 mM NO_2^-, and were labeled with different amounts of ^<15>N for 48 h under continuous illumination. In Azl2, the total in vitro NR activity derived from the NAD(P)H-bispecific NR was only 10% of that of the wild type (cv. Steptoe). In Azl2, the total ^<15>NO_3^- incorporation and translocation of absorbed ^<15>NO_3^- to shoots were about 25% higher than those of Steptoe. Nitrate reduction in the Azl2 roots was 2 times higher than that in Steptoe during the first period (0-24 h) and 1.3 times higher during the second period (24-48 h). However, nitrate reduction in the Azl2 shoots was 10 to 30% lower than that in the Steptoe shoots. As a result, nitrate markedly accumulated in the Azl2 shoots. Accumulation of reduced ^<15>N in the Azl2 roots was 2 times higher than that in the Steptoe roots, but 10% lower in the Azl2 shoots than in the Steptoe shoots at the end of the experiment. Upward transport of reduced ^<15>N via the xylem in Azl2 was nearly 2 times more active than that of Steptoe throughout the experiment. This result suggested that the derepression of the NAD(P)H-NR isozyme in the Azl2 shoots could compensate for the absence of the NADH-NR isozyme. Furthermore, increased levels of root nitrate reduction seemed to make up for the limited nitrate assimilation in the Azl2 shoots.
社団法人日本土壌肥料学会の論文

Contribution of Shoots and Roots to In Vivo Nitrate Reduction in NADH-Specific Nitrate Reductase-Deficient Mutant Seedlings of Barley (Hordeum vulgare L.)(Plant Nutrition)

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