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Abstract

Nitrate reductase was induced in detached leaves of a number of species of Ericaceae by infiltration with KNO3 solution after which enzymatic activity was determined. Considerable activity was found in the leaves of some species and cultivars indicating an inherent capability to synthesize the enzyme in the presence of nitrate. For many members of the ericaceous family, however, the very low level of activity found in the leaves suggests this organ may play little or no part in the reduction of nitrate.

Open Access

the most commonly available form of nitrogen for grasses, has to be reduced to nitrite (NO 2 − ) and then ammonium, which is then incorporated into amino acid biosynthesis ( Wang et al., 2013 ). Nitrate reductase (NaR) is the key enzyme catalyzing the

Open Access

Vaccinium corymbosum, one of the cultivated blueberry species, is not well-adapted to mineral soils, which are generally marked by high pH, the predominance of NO3-N over NH4-N, and limited iron availability. A wild species, V. arboreum, grows naturally on mineral soils, and thus may be better adapted than V. corymbosum. This adaptation may be related to the ability of V. arboreum to assimilate NO3 and/or iron more efficiently than V. corymbosum. Both species were grown in a hydroponic solution containing 5.0 mM N as (NH4)2SO4 or NaNO3, and buffered to pH 5.5. Nitrate reductase (NR) and iron reductase (FeR) activities were measured. NR activity was higher in V. arboreum compared with V. corymbosum when grown with N03-N, while no difference between species was observed when grown under NH4-N. Activity of FeR was higher in V. arboreum compared with V. corymbosum, and higher under NO3-N compared with NH4-N. After 5 months in hydroponics, Fe was removed from one-half of the solutions. The activity of NRA in both species was higher under Fe-sufficient compared with Fe-limited conditions, but in both cases, activity was higher in V. arboreum compared with V. corymbosum. FeR activity continued to be higher in V. arboreum compared with V. corymbosum, and under NO3 compared with NH4-N. Activity decreased in both species under limited Fe conditions, and there were no interactions between species and Fe. These data indicate that V. arboreum possesses higher NR and FeR activities than V. corymbosum, under both Fe-sufficient and Fe-limited conditions. This may play a role in the better adaptability of V arboreum to mineral soil conditions.

Free access

Commercial blueberry production is limited primarily to soils where ammonium, rather than nitrate, is the predominant N form. However, Vaccinium arboreum, a species native to northern Florida, often is found growing in soils where nitrate is the major N form. This species may serve as a breeding source or rootstock for commercial blueberries, expanding the potential soil types that may be used for blueberry cultivation. In our study, in vivo nitrate reductase activity (NRA) was measured in roots and leaves of 2-year-old seedlings of V. arboreum and a commercial cultivar, V. corymbosum `Sharpblue'. Plants were grown hydroponically in sand culture and fertilized with a modified Hoagland's solution containing N as either ammonium, ammonium nitrate, or nitrate. Vaccinium arboreum averaged nitrite at 200, 60, and 20 nmol/g fresh weight per h for nitrate, ammonium nitrate, and ammonium fertilized plants, respectively. `Sharpblue' root NRA was significantly lower, averaging nitrite 50, 38, and 8 nmol/g fresh weight per h for nitrate, ammonium nitrate, and ammonium fertilized plants, respectively. NRA was much lower in leaves than roots of V. arboreum, averaging nitrite at ≈15 nmol nmol/g fresh weight per h across N treatments. No NRA was detected in the leaves of `Sharpblue', regardless of N treatment. These data suggest that V. arboreum may be used as a rootstock or breeding source to expand blueberry production into soil types that are higher in nitrate than the soils typically used for blueberry production.

Free access

Abstract

A tissue infusion method was used to demonstrate nitrate reductase activity in the leaves of Vaccinium corymbosum L. grown with 3 N sources and in 2 pH regimes. Activity was not detectable by the extraction and assay of homogenized leaves of Kalmia latifolia L., Leucothoe catesbaei Gray, Malus sylvestris Mill., Pieris japonica D. Don., and Rhododendron catawbiense Michx. or in the roots of Leucothoe and Zea mays L., but it was detectable in both leaves and roots by the tissue infusion method.

Open Access
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Abstract

Cranberry plants, Vaccinium macrocarpon Ait. cv. Early Black, were grown with NO3-N, NH4-N or NO3-N + NH4-N at a concentration of 50 ppm N. Fresh weight of plants cultured on each Ν treatment was similar. Nitrate Ν was present in roots but not leaves. Ammonium Ν was present in both organs. Nitrate reductase activity was demonstrated in roots but not detected in leaves. Activity was significantly greater in roots of plants grown with NO3-N vs. NO3-N + NH4-N or NH4-N grown roots. Mycorr-hizae were not present in or on the roots and bacteria were eliminated as factors affected NO3 reduction. Results suggested cranberry was able to assimilate the NO3 form of N.

Open Access

Abstract

The activity of nitrate reductase (NR) and glutamine synthetase (GS) was followed during 4 weeks in various tissues of tomato plants (Lycopersicon esculentum Mill. cv. Vedettos) grown in growth chambers under two photosynthetic photon flux (PPF; 125 and 250 μmol·s−1·m−2, high-pressure sodium lamps) conditions for 18 hr and with four N fertilization regimes (5, 10, 15, and 20 meq·liter−1). In roots, NR increased with increased PPF but not with increasing N. Leaf NR activity was stimulated by increased PPF. Leaf NR increased over time in all treatments, but the highest values were obtained at lower N concentrations. Glutamine synthetase was stimulated by both light and N increases; its activity also increased throughout the 4 weeks of treatment. Nitrate reductase activity was highly correlated with the fruit fresh weight : leaf fresh weight ratio. On a mature tomato plant, NR activity was found mainly in leaves opposite developing fruits (sixth and seventh leaves), while GS activity was concentrated in the upper portion of the plant (second and third leaves).

Open Access

Abstract

Rooted cuttings of Chrysanthemum × morifolium Ramat. ‘Gt. #4 Indianapolis White’ were grown in a greenhouse in a sand culture and supplied with either 3.75 or 15.0 mm NO 3 . Changes in dry matter, reduced N and NO 3 of the leaves, stems (plus petioles), roots, and inflorescence and in vivo NO 3 reductase activity (NRA) of leaves were determined at various stages of development. A decrease in the NO 3 supply caused a decrease in the accumulation of plant dry matter, reduced N and NO 3 . Plants receiving 3.75 mm NO 3 remobilized a significant amount of reduced N from vegetative tissues during inflorescence development, suggesting that newly absorbed N was inadequate to supply the flower. At both NO 3 fertilization levels, the NO 3 content of the leaves and stems declined during inflorescence development, suggesting an increased dependence on previously accumulated NO 3 for reduction. The highest NRA of the leaves (3.4 μmoles NO2 gFW−1 hr−1) was associated with early vegetative growth. NRA, however, was detectable throughout plant development. Nitrate reductase activity was greater at 15 mM NO 3 than at 3.75 mM NO 3 during vegetative growth and visible bud stages, but not at later stages of growth.

Open Access
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Abstract

Mature Marsh seedless grapefruit trees on Sour orange stock planted in a loamy soil were subjected to three levels of nitrogen fertilization with and without phosphate or chicken manure added. The details of the experimental plan and tree responses during the five-year experimental period will be described elsewhere. Briefly, the phosphate and manure treatments resulted in a significant increase in yield and in improved fruit quality. As far as the leaf composition is concerned, the phosphate and manure treatments caused an increase in the P and a decrease in the N content of the leaves, thus producing a completely inverse relationship between leaf N concentration and the yield of the corresponding trees. This situation served as an opportunity to test—under orchard. conditions—the validity of NaR (nitrate reductase) assay in leaves as a measure for some “active fraction” of leaf nitrogen and as a parameter for tree productivity. The use of the NaR assay has been suggested for the determination of N requirements of citrus trees (1).

Open Access

Half or whole root systems of micropropagated `Gala' apple (Malus ×domestica Borkh.) plants were subjected to drought stress by regulating the osmotic potential of the nutrient solution using polyethylene glycol (20% w/v) to investigate the effect of root drying on NO3- content and metabolism in roots and leaves and on leaf photosynthesis. No significant difference in predawn leaf water potential was found between half root stress (HRS) and control (CK), while predawn leaf water potential from both was significantly higher than for the whole root stress (WRS) treatment. However, diurnal leaf water potential of HRS was lower than CK and higher than WRS during most of the daytime. Neither HRS nor WRS influenced foliar NO3- concentration, but both significantly reduced NO3- concentration in drought-stressed roots as early as 4 hours after stress treatment started. This reduced NO3- concentration was maintained in HRS and WRS roots to the end of the experiment. However, there were no significant differences in NO3- concerntation between CK roots and unstressed roots of HRS. Similar to the effect on root NO3- concentration, both HRS and WRS reduced nitrate reductase activity in drought-stressed roots. Moreover, leaf net photosynthesis, stomatal conductance and transpiration rate of HRS plants were reduced significantly throughout the experiment when compared with CK plants, but the values were higher than those of WRS plants in the first 7 days of stress treatment though not at later times. Net photosynthesis, stomatal conductance and transpiration rate were correlated to root NO3- concentration. This correlation may simply reflect the fact that water stress affected both NO3- concentration in roots and leaf gas exchange in the same direction.

Free access