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1.
The effects of nitrogen applied at increasing levels of 0, 4, 8, 16 and 32 mM N (KNO3 or NH4Cl) were studied in faba bean (Vicia faba) nodulated byRhizobium leguminosarum bv.viceae RCR lool. Nitrogenase activity was higher at 4 and 8 mM N than the zero N treatment (control), but 16 and 32 mM N significantly reduced the efficiency of nodule functions. Nitrate reductase activities (NRA) of leaves, stems, roots, nodules and nodule fractions (bacteroid and cytosol) were increased with rising the NO3 ? or NH4 + levels. NRA decreased in the order of nodules>leaves>stems>roots. Cytosolic NR was markedly higher than that recorded in the bacteroid fractions. Nitrate levels were linearly correlated to NRA of nodules. Accumulation of NO2 ? within nodules suggests that NO2 ? inhibits nodule’s activity after feeding plants with NO3 ? or NH4 +. 相似文献
2.
The utilization and translocation of nitrogen was investigated in exponentially growing, nitrogen-limited Pisum sativum L. cv. Marma. The plants were given N daily at exponentially increasing, although suboptimal, relative nitrogen addition rates (RN) calculated to yield a relative increment in N of 0.06 day?1 and 0.12 day?1. After 10 days of NO?3 additions (26 days after sowing), the relative growth rate more or less equaled RN. Uptake of NO?3 was several-fold higher than the N requirement for the growth rate set by RN. The daily addition of NO?3 was taken up after 7 to 8 h, resulting in a cyclic behaviour in the NO?3 utilization. During the phase of net NO?3 influx, the filling phase (0 to 8 h), in vitro nitrate reductase activity (NR activity) and intracellular levels of soluble N in the root increased. In the phase of no net influx of NO?3 the depletion phase (8 to 24 h), the plants were entirely dependent on stored N. During this phase both in vitro NR activity and intracellular levels of soluble N decreased. Also the calculated actual rate of NO?3 reduction was high in the filling phase, while it was close to zero in the depletion phase. The pattern of these fluctuations indicates that the regulation of NO?3 utilization involves an interplay between transmembrane fluxes of NO?3, the cytosolic NO?3 concentration and NR activity. Cyclic fluctuations in N-containing compounds were also found in the xylem. Nitrogen was mainly transported as amino acids. The pattern of NO?3 transport in the xylem and the fluctuations in the shoot of in vitro NR activity indicate that a reasoning similar to that for the regulation of NO?3 assimilation in the root also applies for the shoot. The results also indicate a substantial supply of amino acids to the xylem through recirculation from the shoot. 相似文献
3.
Effects of sodium on mineral nutrition in rose plants 总被引:2,自引:0,他引:2
The effects of sodium (Na+) ion concentration on shoot elongation, uptake of ammonium (NH4+) and nitrate (NO3?) and the activities of nitrate reductase (NR) and glutamine synthetase (GS) were studied in rose plants (Rosa hybrida cv. “Lambada”). The results showed that shoot elongation was negatively correlated with sodium concentration, although no external symptoms of toxicity were observed. Nitrate uptake decreased at high sodium levels, specifically at 30 meq litre4 of sodium. As flower development was normal under high saline conditions, this could suggest that nitrogen was being mobilised from shoot and leaf reserves. Ammonium uptake was not affected by any of the salt treatments applied probably because it diffuses through the cell membrane at low concentrations. Nitrate reductase activity was reduced by 50% at 30 meq litre 1 compared with control treatment, probably due to a decrease in the free nitrate related to nitrate uptake pattern. None of the salt treatments used affected total leaf GS activity (both chloroplastic and cytosolic isoforms) or leaf NPK mineral contents. Nitrate reductase activity in leaves increased at 10 meq litre?1 of sodium and GS activity in roots (cytosolic isoform only) followed the same pattern as NR. It is suggested that the activation of both enzymes at low salt level could be attributed to the beneficial effect of increased sulphur in the nutrient solutions. 相似文献
4.
Enhancement of Nitrate Reductase Activity by Benzyladenine in Agrostemma githago 总被引:4,自引:8,他引:4
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Nitrate reductase activity in excised embryos of Agrostemma githago increases in response to both NO3− and cytokinins. We asked the question whether cytokinins affected nitrate reductase activity directly or through NO3−, either by amplifying the effect of low endogenous NO3− levels, or by making NO3− available for induction from a metabolically inactive compartment. Nitrate reductase activity was enhanced on the average by 50% after 1 hour of benzyladenine treatment. In some experiments, the cytokinin response was detectable as early as 30 minutes after addition of benzyladenine. Nitrate reductase activity increased linearly for 4 hours and began to decay 13 hours after start of the hormone treatment. When embryos were incubated in solutions containing mixtures of NO3− and benzyladenine, additive responses were obtained. The effects of NO3− and benzyladenine were counteracted by abscisic acid. The increase in nitrate reductase activity was inhibited at lower abscisic acid concentrations in embryos which were induced with NO3−, as compared to embryos treated with benzyladenine. Casein hydrolysate inhibited the development of nitrate reductase activity. The response to NO3− was more susceptible to inhibition by casein hydrolysate than the response to the hormone. When NO3− and benzyladenine were withdrawn from the medium after maximal enhancement of nitrate reductase activity, the level of the enzyme decreased rapidly. Nitrate reductase activity increasd again as a result of a second treatment with benzyladenine but not with NO3−. At the time of the second exposure to benzyladenine, no NO3− was detectable in extracts of Agrostemma embryos. This is taken as evidence that cytokinins enhance nitrate reductase activity directly and not through induction by NO3−. 相似文献
5.
The response of the tubers to NO3– was studied in comparison to the other organs of Solanum tuberosum var. Sava, with special focus on: (a) whether tubers are capable of primary N assimilation; (b) whether N assimilation is stimulated by NO3–; and (c) whether primary N assimilation in tubers is important for tuber growth. NO3– reduction via nitrate reductase (NR; EC 1.6.6.1) and NH4+ assimilation via glutamine synthetase (GS; EC 6.3.1.2) occurred predominantly in the shoots, but up to 20% was contributed by the tubers under low‐NO3– conditions. NR activation was highest in tubers (up to 90%) and declined in all organs with increasing NO3– supply. NR and GS activity responded with a decline in tubers and roots as opposed to an increase in the shoots. This corresponded to relative organ growth: growth of tubers and roots was stimulated relative to that of shoots at a limiting NO3– supply. Absolute growth of all organs was stimulated by NO3–, whereas tuber number declined. The concentration of N compounds increased with NO3– supply in all organs: NO3– increased most dramatically in the shoots (81‐fold), free amino acids most markedly in the tubers (three‐fold). The amount of patatin and of the 22 kDa protein complex in the tuber reached a minimum when the amount of Rubisco in the shoot reached maximum as a response to NO3– supply. Tuber sucrose and starch increased by 40%, whereas glucose and fructose declined two‐fold as plant N status increased. It is concluded that tubers are potentially N autotroph organs with capacity for de novo synthesis of amino acids. Primary N assimilation in tubers, however, declines with increasing NO3– supply and is not of major importance for tuber growth. 相似文献
6.
The physiological consequences for NO3– utilization by the plant of underexpression and overexpression of nitrate reductase (NR) were investigated in nine transformants of Nicotiana tabacum and Nicotiana plumbaginifolia. The in vitro NR activities (NRAs) in both roots and leaves of low- and high-NR tobacco transformants ranged from 5–10% to 150–200%, respectively, of those measured in wild-type plants. The level of NR expression markedly affected the NO3– reduction efficiency in detached leaves and intact plants. In both species, 15NO3– reduction ranged from 15–45% of 15NO3– uptake in the low-NR plants, to 40–80% in the wild-type, and up to 95% in high-NR plants. In the high-NR genotypes, however, total 15NO3– assimilation was not significantly increased when compared with that in wild-type plants, because the higher 15NO3– reduction efficiency was offset by lower 15NO3– uptake by the roots. The inhibition of NO3– uptake appeared to be the result of negative feedback regulation of NO3– influx, and is interpreted as an adjustment of NO3– uptake to prevent excessive amino acid synthesis. In genotypes underexpressing NR, the low 15NO3– reduction efficiency also was generally associated with a decrease in net 15NO3– uptake as compared with the wild type. Thus, underexpression of NR resulted in an inhibition of reduced 15N synthesis in the plant, although the effect was much less pronounced than that expected from the very low NRAs. The restricted NO3– uptake in low-NR plants emphasizes the point that the products of NO3– assimilation are not the only factors responsible for down-regulation of the NO3– uptake system. 相似文献
7.
Ammonium can stimulate nitrate and nitrite reductase in the absence of nitrate in Clematis vitalba 总被引:3,自引:1,他引:3
R. A. Bungard A. Wingler J. D. Morton M. Andrews M. C. Press & J. D. Scholes 《Plant, cell & environment》1999,22(7):859-866
Nitrogen assimilation was studied in the deciduous, perennial climber Clematis vitalba. When solely supplied with NO3– in a hydroponic system, growth and N-assimilation characteristics were similar to those reported for a range of other species. When solely supplied with NH4+, however, nitrate reductase (NR) activity dramatically increased in shoot tissue, and particularly leaf tissue, to up to three times the maximum level achieved in NO3– supplied plants. NO3– was not detected in plant material that had been solely supplied with NH4+, there was no NO3– contamination of the hydroponic system, and the NH4+-induced activity did not occur in tobacco or barley grown under similar conditions. Western Blot analysis revealed that the induction of NR activity, either by NO3– or NH4+, was matched by NR and nitrite reductase protein synthesis, but this was not the case for the ammonium assimilation enzyme glutamine synthetase. Exposure of leaf disks to N revealed that NO3– assimilation was induced in leaves directly by NO3– and NH4+ but not glutamine. Our results suggest that the NH4+-induced potential for NO3– assimilation occurs when externally sourced NH4+ is assimilated in the absence of any NO3– assimilation. These data show that the potential for nitrate assimilation in C. vitalba is induced by a nitrogenous compound in the absence of its substrate and suggest that NO3– assimilation in C. vitalba may have a significant role beyond the supply of reduced N for growth. 相似文献
8.
Radish (Raphanus sativus L.) seedlings pretreated with different hormones viz. kinetin, gibberellic acid and abscisic acid were subjected to different
N-forms. The seedlings were treated with different concentrations of KNO3, NH4Cl and NH4NO3 and the changes in nitrate reductase activity were seen in light and dark conditions in the cotyledons. Nitrate reductase
activity was affected differently by hormone application. Nitrate increased and ammonia decreased nitrate reductase activity;
in both light and dark-grown seedlings KNO3 induced more in vitro nitrate reductase activity. NH
4
+
when combined with NO
3
−
, however, could level up to some extent, with KNO3 in light, except in kinetin. A transient response of induction of NR activity was evident with decreased levels after a certain
specific ambient N-concentration, despite the presence of high N in the medium. However, the pattern of transition varied
with the hormones applied. Further, hormones are found to affect induction of different isoforms of nitrate reductase by NH
4
+
and NO
3
−
. NH
4
+
induced isoform was prominently promoted by kinetin treatment in dark. The data documents a particular kind of interaction
between controlling factors (light, N-source and phytohormones) which affect nitrate reductase levels. 相似文献
9.
Nitrate reductase (NR) activity and nutrient (N, P) recycling in the ciliatesColpoda steinii andStylonychia sp. and two unidentified flagellates (I and II), isolated from Lake Kinneret, have been studied. When grown on a bacterium
also isolated from the lake, all species, except flagellate I, exhibited NR activity. Activity was higher in the presence
of nitrate than in its absence, and in the case ofC. steinii showed a dependence on initial ambient NO3 concentrations in the cultures. NR activity was inversely proportional to body size, suggesting that the larger protozoan
species have decreased specific metabolic rates. A net increase in ammonium concentrations and a decrease in orthophosphate
levels was observed, but both phenomena were much less sensitive to ambient NO3 concentrations than NR activity. Similar trends in NR activity and NH4 production were also observed whenC. steinii was grown on the picocyanobacteriumSynechococcus sp. Our results suggest that NH4 excretion is the outcome of N remineralization from the food supply but is also partially due to dissimilatory nitrate reduction.
These data imply that protozoa may have an important role in nutrient recycling in Lake Kinneret and that some species could
use NO3 respiration in anoxic regions of the water column.
Offprint requests to: O. Hadas. 相似文献
10.
Limitations on Leaf Nitrate Reductase Activity during Flowering and Podfill in Soybean 总被引:1,自引:1,他引:0
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The objective of this study was to identify factors which limit leaf nitrate reductase (NR) activity as decline occurs during flowering and beginning seed development in soybean (Glycine max [L.] Merr. cv Clark). Level of NR enzyme activity, level of reductant, and availability of NO3− as substrate were evaluated for field-grown soybean from flowering through leaf senescence. Timing of reproductive development was altered within one genotype by (a) exposure of Clark to an artificially short photoperiod to hasten flowering and podfill, and (b) the use of an early flowering isoline. Nitrogen (N) was soil-applied to selected plots at 500 kilograms per hectare as an additional variable. Stem NO3− concentration and in vivo leaf NR activity were significantly correlated (R2 = 0.69 with nitrate in the assay medium and 0.74 without nitrate in the medium at P = 0.001) across six combinations of reproductive and soil N-treatment. The supply of NO3− from the root to the leaf tissue was the primary limitation to leaf NR activity during flowering and podfill. Levels of NR enzyme and reductant were not limiting to leaf NR activity during this period. 相似文献
11.
Effect of chlorate, nitrogen source, and light on chlorate toxicity and nitrate reductase activity in soybean leaves 总被引:1,自引:0,他引:1
James E. Harper 《Physiologia plantarum》1981,53(4):505-510
Growth chamber studies were conducted to assess the relationship between nitrate reductase (NR) activity and development of chlorate (KClO3) toxicity symptoms in leaflets of soybeans [Glycine max (L.) Merr.]. Fourteen day-old soybean seedlings, grown in NO3 - or urea-nutrient solutions, were exposed to various KClO3 concentrations (0 to 2.0 mM) and light levels (100, 67, 33 and 0% of full light which was 750 μE m?2s?1) for 24 h. Visual KClO3 toxicity symptoms were noted and NR activity was measured. Toxicity symptoms (interveinal chlorosis) were evident within 24 h following addition of 0.5 mM KClO3 to the nutrient solution, regardless of N nutrition, and symptom severity increased with increased KClO3 concentration (up to 2.0 mM). Leaflet NR activity was lower following 24 h KClO3 treatments at concentrations of 0.5 mM and higher, indicating that ClO3 - or some reduction product of ClO3 - likely ClO2 - was detrimental to enzyme functionality. The light study supported involvement of NR activity in KClO3 toxicity in that comparison of control and KClO3 treated plants exposed to decreased light levels revealed a decrease in NR activity of control plants parallel to a decrease in severity of KClO3 toxicity symptoms of treated plants. Urea-grown plants, which have an apparent constitutive NR enzyme, were used to verify that the KClO3 toxicity symptoms were not simply N starvation symptoms due to competition of ClO3 - and NO3 - for uptake and reduction. In vivo NR assays also ruled out that ClO3 - was decreasing NR activity through competition with NO3 - for reduction sites. The close relationship between KClO3 toxicity symptoms and NR activity, in response to light treatments, suggested that KClO3 toxicity symptoms were associated with reduction of ClO3 - to ClO2 - by the NR enzyme. However, the possibility that a more direct photochemical reaction occurred in the presence of KClO3 to produce the toxicity symptoms could not be ruled out. 相似文献
12.
Renata Matraszek 《Acta Physiologiae Plantarum》2008,30(3):361-370
The author studied the effect of different nickel concentrations (0, 0.4, 40 and 80 μM Ni) on the nitrate reductase (NR) activity
of New Zealand spinach (Tetragonia expansa Murr.) and lettuce (Lactuca sativa L. cv. Justyna) plants supplied with different nitrogen forms (NO3
−–N, NH4
+–N, NH4NO3). A low concentration of Ni (0.4 μM) did not cause statistically significant changes of the nitrate reductase activity in
lettuce plants supplied with nitrate nitrogen (NO3
−–N) or mixed (NH4NO3) nitrogen form, but in New Zealand spinach leaves the enzyme activity decreased and increased, respectively. The introduction
of 0.4 μM Ni in the medium containing ammonium ions as a sole source of nitrogen resulted in significantly increased NR activity
in lettuce roots, and did not cause statistically significant changes of the enzyme activity in New Zealand spinach plants.
At a high nickel level (Ni 40 or 80 μM), a significant decrease in the NR activity was observed in New Zealand spinach plants
treated with nitrate or mixed nitrogen form, but it was much more marked in leaves than in roots. An exception was lack of
significant changes of the enzyme activity in spinach leaves when plants were treated with 40 μM Ni and supplied with mixed
nitrogen form, which resulted in the stronger reduction of the enzyme activity in roots than in leaves. The statistically
significant drop in the NR activity was recorded in the aboveground parts of nickel-stressed lettuce plants supplied with
NO3
−–N or NH4NO3. At the same time, there were no statistically significant changes recorded in lettuce roots, except for the drop of the
enzyme activity in the roots of NO3
−-fed plants grown in the nutrient solution containing 80 μM Ni. An addition of high nickel doses to the nutrient solution
contained ammonium nitrogen (NH4
+–N) did not affect the NR activity in New Zealand spinach plants and caused a high increase of this enzyme in lettuce organs,
especially in roots. It should be stressed that, independently of nickel dose in New Zealand spinach plants supplied with
ammonium form, NR activity in roots was dramatically higher than that in leaves. Moreover, in New Zealand spinach plants treated
with NH4
+–N the enzyme activity in roots was even higher than in those supplied with NO3
−–N. 相似文献
13.
Growth and nitrate reductase activity were measured in Paul's Scarlet rose cell suspensions, cultured in media purified from molybdenum and containing nitrate or urea as sole nitrogen source with or without added Mo. Urea could replace nitrate to yield 80% of the fresh weight in nitrate medium. Nitrate reductase activities were compared by in vivo and in vitro assays. The latter varied due to inactivation during extraction. Compared with activities in cells in complete NO3
- medium, activity in NO3
--Mo cells was reduced to 30% and, in urea-grown cells, to trace amounts. Increases in nitrate reductase activity were found when NO3
- alone was added to NO3
- or urea+Mo cultures. In NO3
--Mo cultures, Mo alone or with NO3
- caused a similar increase in activity, whereas urea-Mo cultures required both NO3
- and Mo for enzyme induction.Abbreviations FAD
flavin adenine dinucleotide
- Mo
molybdenum
- NADH
reduced nicotinamide adenine dinucleotide
- NO3
-+Mo
standard MX1 culture medium
- NO3
--Mo
MX1 medium purified of Mo and used for continuous subculture with nitrate
- NR
nitrate reductase
- PSR
Paul's Scarlet rose
- PVP
polyvinylpyrrolidone
- U
urea
- U+Mo
MX1 medium containing urea instead of nitrate
- U-Mo
MX1 medium containing urea instead of nitrate and also purified of Mo 相似文献
14.
Nitrate Reductase Activity in Shoots and Roots of Maize Seedlings as Affected by the Form of Nitrogen Nutrition and the pH of the Nutrient Solution 总被引:5,自引:1,他引:4
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The effect of nitrogen form (NH4-N, NH4-N + NO3−, NO3−) on nitrate reductase activity in roots and shoots of maize (Zea mays L. cv INRA 508) seedlings was studied. Nitrate reductase activity in leaves was consistent with the well known fact that NO3− increases, and NH4+ and amide-N decrease, nitrate reductase activity. Nitrate reductase activity in the roots, however, could not be explained by the root content of NO3−, NH4-N, and amide-N. In roots, nitrate reductase activity in vitro was correlated with the rate of nitrate reduction in vivo. Inasmuch as nitrate reduction results in the production of OH− and stimulates the synthesis of organic anions, it was postulated that nitrate reductase activity of roots is stimulated by the released OH− or by the synthesized organic anions rather than by nitrate itself. Addition of HCO3− to nutrient solution of maize seedlings resulted in a significant increase of the nitrate reductase activity in the roots. As HCO3−, like OH−, increases pH and promotes the synthesis of organic anions, this provides circumstantial evidence that alkaline conditions and/or organic anions have a more direct impact on nitrate reductase activity than do NO3−, NH4-N, and amide-N. 相似文献
15.
Pattern and extent to which the main shoot of rice (Oryza sativa L.) cv. Pusa 33 assimilates NO3- when grown under lowland conditions was determined in a field study. The in vivo NR (nitrate reductase) activity is low as compared to the value in other cereals grown under aerobic soil conditions. The leaf blades had higher NR activity (g fr. wt.)-1 than the sheaths and stem. Calculation of total NO3- (mol) reduced in the main shoot, obtained by integrating the in vivo NR assay values per plant part and per day over the duration for which the various plant parts on the main shoot remained metabolically active, showed that out of the total reduced N at harvest, 16.6% was assimilated via the enzyme nitrate reductase. In the leaf sheaths and stem the NO3- was reduced to slightly over 50% of the total NO3- that was reduced in the main shoot. The rest of the amount was reduced in the leaf blades. 相似文献
16.
Nitrate reductase (NR) in maize (Zea mays cv W64A × W182E) roots has been stabilized in vitro by the addition of chymostatin to extraction buffer. Contrary to previous observations, levels of NR were higher in the mature root than in root tip sections when chymostatin was included in the extraction buffer. Two forms of NR were identified, an NADH monospecific NR found mainly in the 1cm root tip and an NAD(P)H bispecific NR found predominantly in mature regions of the root. During the first 10 days of seedling growth, NR activity in the root ranged from 50 to 80% of the activities found in the leaf (a maximum of 2.4 micromoles NO−2 produced per hour per gram fresh weight was measured at 4 days). 相似文献
17.
The effects of nitrogen source NO3− or NH4+ on nitrogen metabolism during the first 2 weeks of germination of the rice seedling (Oryza sativa L., var. IR22) grown in nutrient solution containing 40 μg/ml N were studied. Total, soluble protein, and free amino N levels were higher in the NH4+-grown seedling, particularly during the 1st week of germination. Asparagine accounted for most of the difference in free amino acid level, in both the root and the shoot. Nitrate and nitrite reductase activities were present mainly in the shoot and were higher in the NO3−-grown seedling, whereas the activity of glutamate dehydrogenase and glutamine synthetase in the root tended to be lower than that of the NH4+-grown seedling during the 1st week of germination. Glycolate oxidase and catalase activities were present mainly in the shoot. Maximum activity of the above five enzymes occurred 7 to 10 days after germination. Differences in the zymograms of nitrate reductase, glutamate dehydrogenase, and catalase were mainly between shoot and root and not from N source. Nitrite reductase bands were observed only in plants grown in plants grown in NO3−. 相似文献
18.
T. C. POKHRIYAL M. S. SACHDEV H. L. GROVER R. P. ARORA Y. P. ABROL 《Physiologia plantarum》1980,48(3):477-481
A field experiment on wheat (Triticum aestivum L.) ev. Shera grown at 120 kg N ha?1 was conducted. Half of the dose of fertilizer N was applied at the pre-sowing stage and the other half when the seedlings were one month old. The leaf blades were examined for their NO3? content and NO3? assimilatory activity at various stages of growth and development. Soil nitrate level at 50 cm depth was determined throughout the wheat growing season in terms of cencentration (μg/ml) and total amount (kg ha?1). The upper leaf blades were examined for their capacity to assimilate NO3?. Highly significant correlation between NR (nitrate reductase) activity and NO3? content in the leaf blades. NR activity and soil NO3?, and between soil NO3? and leaf blade NO3? was observed. Findings on low soil NO3? status during the reproductive phase and the capacity of the upper leaf blades to assimilate additional amounts of NO3?, point to the need for developing a programme of soil fertilizer application whereby all the leaf blades can utilize the NO3? optimally and thus result in greater N harvest. 相似文献
19.
Begoña Blasco Juan J. Rios Luis M. Cervilla Eva Sánchez-Rodríguez María M. Rubio-Wilhelmi Miguel A. Rosales Juan M. Ruiz Luis Romero 《Journal of Plant Growth Regulation》2010,29(4):477-486
Iodine is vital to human health, and iodine biofortification programs help improve human intake through plant consumption.
There is no research on whether iodine biofortification influences basic plant physiological processes. Because nitrogen (N)
uptake, utilization, and accumulation are determining factors in crop yield, the aim of this work was to establish the effect
of the application of different doses (20, 40, and 80 μM) and forms of iodine (iodate [IO3
−] vs. Iodide [I−]) on N metabolism and photorespiration. For this study we analyzed shoot biomass and the activities of nitrate reductase
(NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), aspartate aminotransferase (AAT), glutamate
dehydrogenase (GDH), glycolate oxidase (GO), glutamate:glyoxylate aminotransferase (GGAT), serine:glyoxylate aminotransferase
(SGAT), hydroxypyruvate reductase (HR) and catalase (CAT), nitrate (NO3
−), ammonium (NH4
+), organic and total N, amino acids, proteins, serine (ser), malate, and α-ketoglutaric acid in edible lettuce leaves. Application
of I− at doses of at least 40 μM reduced the foliar concentration of NO3
− with no decrease in biomass production, which may improve the nutritional quality of lettuce plants. In contrast, the application
of 80 μM of I− is phytotoxic for lettuce plants, reducing the biomass, foliar concentration of organic N and NO3
−, and NR and GDH activities. HR activity is significantly inhibited with all doses of I−; the least inhibition was at 80 μM. This may involve a decrease in the incorporation of carbonated skeletons from photorespiration
into the Calvin cycle, which may be partially associated with the biomass decrease. Finally, the application of IO3
− increases biomass production, stimulates NO3
− reduction and NH4
+ incorporation (GS/GOGAT), and optimizes the photorespiratory process. Hence, this appears to be the most appropriate form
of iodine from an agronomic standpoint. 相似文献
20.
Nitrate reductase activity in gibberellic acid and kinetin treated mustard (Brassica juncea Coss. cv. T-59 ‘Varuna’) seedlings, grown in the presence or absence of light and/or NO3 was investigated. While both light and NO3, alone could induce NR activity, their combination showed additive effects. Kinetin treatment significantly promoted both
light- and NO3- induced NR activities, assayed by either in vivo or in vitro techniques, whereas, gibberellic acid was almost ineffective. In the absence of both light and NO3, however, phytohormones alone could not induce NR activity. Both light-induced and NO3 induced NR fractions had a pH optima of 7.5, preferred NADH as an electron donor (NADH: NADPH ratio 2.5) and Km values for NO3 was 0.2 mM. Actinomycin D, cycloheximide and tungstate were equally effective in suppressing the development of NR activity
after exposure to light or NO3. These results indicate that two independent NR fractions operate, with apparently identical properties but separate control
mechanisms. 相似文献