No 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).

Field observations have indicated that the winter wheat (Triticum aestivum L.) cv. TAM W‐101 is relatively drought resistant compared with the cv. Sturdy. In a growth chamber experiment, osmotic adjustment and various solutes potentially involved in osmotic adjustment were measured in leaves of TAM W‐101 and Sturdy. Plants were grown in sand culture for 28 days at 20°C with 16 h light per day (=600 μmol m‐2 s‐1). Stress treatments were then imposed by limiting water in pots for 14 days, after which water relations were determined with pressure‐volume curves on leaves of stressed plants following overnight hydration (prestressed), and on hydrated unstresssed plant leaves. Leaf solutes measured were total amino acids, proline, free sugars, and K. Prestressed leaves of both cultivars had significantly lower solute potential at full turgor (Ψfs) and zero turgor (Ψos) than unstressed leaves, indicating osmotic adjustment. But prestressed TAM W‐101 apparently adjusted more, with significantly lower values for Ψfs (−1.61 MPa) and Ψos (−2.44 MPa) compared to prestressed Sturdy (−1.40 and −1.98 MPa, respectively). The relative reduction of dry matter produced in prestressed TAM W‐101 plants did not, however, differ from prestressed Sturdy plants. Water use efficiency (WUE, mg total dry matter/g H2O lost per pot) was significantly lower in TAM W‐101 (2.27) than in Sturdy (2.55) and in prestressed (1.81) than unstressed (2.40) leaves. Tissue elasticity was also lower in TAM W‐101 than Sturdy and lower in prestressed than unstressed leaves. Nonreducing sugars increased from 15 g/kg dry wt in unstressed to 39 g/kg dry wt in prestressed (1.4%) leaves, but reducing sugars did not differ among treatments. Only amino acids, including proline, were greater in prestressed TAM W‐101 than Sturdy leaves. But calculated as ideal osmotica, amino acid concentrations were too low to explain the difference in Ψfs between prestressed cultivars. As the adaptive significance of the cultivar differences in osmotic adjustment, WUE, and tissue elasticity are clarified, selection for these factors to improve wheat drought resistance may be possible.

Sodium nitrate was administered through rumen cannulae to produce NO-3 intoxication in four cows (382 to 445 kg body wt) fed prairie grass hay and a protein-mineral supplement. The cows were fed 0, 1.6 or 3.2 kg of dry rolled corn daily for 10 d prior to sodium nitrate administration. Sodium nitrate administration was followed by a marked increase in intraruminal NO-2 and NH3 and blood NO-2 and methemoglobin. Six of eight cows fed 0 and 1.6 kg of corn were given methylene blue to treat severe methemoglobinemia, while none of the cows fed 3.2 kg corn required such therapy. Feeding of 3.2 kg of corn protected against nitrate poisoning by reducing intraruminal nitrite and blood methemoglobin (P less than .05).

Nitrate reductase was higher in three wheat varieties having "Atlas 66" germ plasm for high grain protein potential than "Triumph 64," a hard red winter wheat (Triticum aesticum L.) with a low grain protein potential. Leaf protease was found to have two pH optima, pH 4 and 7. Protease (pH 4.0) levels were higher for the low protein variety prior to flowering; however, the high protein varieties exhibited higher protease levels after flowering. High nitrate reductase before flowering and high leaf protease activities after flowering appear to be related to high grain protein production.rop physiologists are seeking to obtain biochemical criteria that will be useful to the plant breeders in the