Relationship of Nitrate Reductase Activity to Grain Protein Production in Wheat¹

Abstract

Studies were conducted with field grown wheat (Triticum aestivum L.) with and without supplemental nitrogen to determine if nitrate reductase activity could be correlated with water soluble leaf protein, grain and grain protein (% and total) production. Nitrate reductase activity, nitrate, and water soluble leaf protein were determined at intervals throughout the life cycle of ‘Ponca’ and ‘Monon’ hard and soft red winter wheats, respectively. The major conclusions are, (a) nitrate content of the tissue was a major factor in controlling the level of enzyme activity; (b) nitrate reductase activity was related, though not numerically, to leaf protein content; (c) induction of nitrate reductase on a field scale, was achieved by supplemental nitrogen; (d) increased enzyme activity from supplemental nitrogen treatments was associated with increases in gram protein (% or total); (e) a significant correlation was found between the spring seasonal total of nitrate reductase activity (units of nitrogen reduced per hectare) and grain protein (kg/h) for both varieties; (f) this correlation is valid only for a specified genotype as Ponca required a higher level of enzyme activity to accumulate a unit of grain protein than Monon and (g) this observation suggests that Monon is more efficient in transporting reduced nitrogen from the vegetation to the grain than Ponca. Thirty‐two hard and soft red winter wheat varieties grown in a field nursery with low nitrogen fertility were evaluated for nitrate reductase activity; nitrate and water soluble leaf protein, grain and grain protein (kg/h) production. Average values of enzyme activity obtained from three fall and three spring samplings showed little variation among genotypes and no correlation with grain or grain protein production. However, selection of 16 of the varieties exhibiting highest nitrate reductase activity on November 12, when nitrate was in adequate supply, would have included 9 of the 13 varieties which ultimately produced significantly higher grain protein (kg/h).

Use of Protein in Extraction and Stabilization of Nitrate Reductase

“…In olders leaves of oats and corn, normal extraction and in vitro assay (6) may have underestimated nitrate-reducing capacity by as much as 15-fold. Because measurements of nitrate reductase activity have been used as an index in selecting desirable stocks in plant breeding programs, it is essential that enzyme activity be stabilized in all extracts for genotypic comparisons (7,8,10), or for comparisons of enzyme activity with total accumulation of reduced nitrogen in plant parts (2,4,5). Hence, we report in- vestigations of the instability phenomenon in corn, oats, and tobacco, and development of a procedure for stabilizing nitrate reductase activity after extraction.…”

Aspects of Nitrogen Metabolism in the Rice Seedling

“…A positive relationship has been observed in some upland cereal crops between leaf nitrate reductase activity and grain protein production (1,5). No such relationship was noted among four rices that differed in grain protein content for 1-month-old seedlings transplanted and grown under flooded conditions to maturity (24).…”

Assimilation and Remobilization of Nitrogen and Carbohydrates in Oats, Especially as Related to Groat Protein Concentration

“…Fructosans, which were low at anthesis, declined to maturity. Net losses of N from leaf and culm tissue between anthesis and maturity accounted for 27 (Croy and Hageman 1970;Eilrich and Hageman 1973) and corn Q,ea mays L.) (Deckard et al 1973). A high-protein wheat cultivar had higher acid protease activity in the leaves after flowering than did a low-protein cultivar (Rao and Croy 1972 (Cruz et al 1970: Cagampang et al 1971) and rate of amino acid incorporation (Cruz et al 1970) Total-N was determined as described by Peterson and Chesters (1964) Rao and Croy (1972).…”