共查询到20条相似文献,搜索用时 31 毫秒
1.
Seedings of Vicia faba were grown for four weeks at two different light intensities (55 and 105 watts per square meter) in a saline (50 millimolar NaCl) and nonsaline nutrient solution. NaCl salinity depressed growth and restricted protein formation, CO 2 assimilation, and especially the incorporation of photosynthates into the lipid fraction. Conversion of photosynthates in leaves was much more affected by salinity than was photosynthate turnover in roots. The detrimental effect of NaCl salinity on growth, protein formation, and CO 2 assimilation was greater under low than under high light conditions. Plants of the high light intensity treatment were more capable of excluding Na + and Cl − and accumulating nutrient cation species (Ca 2+, K +, Mg 2+) than plants grown under low light intensity. It is suggested that the improved ionic status provided better conditions for protein synthesis, CO 2 assimilation, and especially for the conversion of photosynthates into lipids. 相似文献
2.
The effect of Ca2+ on NO3- assimilation in young barley (Hordeum vulgare L. var CM 72) seedlings in the presence and absence of NaCl was studied. Calcium increased the activity of the NO3- transporter under saline conditions, but had little effect under nonsaline conditions. Calcium decreased the induction period for the NO3- transporter under both saline and nonsaline conditions but had little effect on its apparent Km for NO3- both in the presence and absence of NaCl. The enhancement of NO3- transport by Ca2+ under saline conditions was dependent on the presence of Ca2+ in the uptake solution along with the salt, since Ca2+ had no effect when supplied before or after salinity stress. Although Mn2+ and Mg2+ enhanced NO3- uptake under saline conditions, neither was as effective as Ca2+. In longer studies, increasing the Ca2+ concentration in saline nutrient solutions resulted in increases in NO3- assimilation and seedling growth. 相似文献
3.
The effect of NaCl and Na 2SO 4 salinity on NO 3− assimilation in young barley ( Hordeum vulgare L. var Numar) seedlings was studied. The induction of the NO 3− transporter was affected very little; the major effect of the salts was on its activity. Both Cl − and SO 42− salts severely inhibited uptake of NO 3−. When compared on the basis of osmolality of the uptake solutions, Cl − salts were more inhibitory (15-30%) than SO 42− salts. At equal concentrations, SO 42− salts inhibited NO 3− uptake 30 to 40% more than did Cl − salts. The absolute concentrations of each ion seemed more important as inhibitors of NO 3− uptake than did the osmolality of the uptake solutions. Both K + and Na + salts inhibited NO 3− uptake similarly; hence, the process seemed more sensitive to anionic salinity than to cationic salinity. Unlike NO3− uptake, NO3− reduction was not affected by salinity in short-term studies (12 hours). The rate of reduction of endogenous NO3− in leaves of seedlings grown on NaCl for 8 days decreased only 25%. Nitrate reductase activity in the salt-treated leaves also decreased 20% but its activity, determined either in vitro or by the `anaerobic' in vivo assay, was always greater than the actual in situ rate of NO3− reduction. When salts were added to the assay medium, the in vitro enzymic activity was severely inhibited; whereas the anaerobic in vivo nitrate reductase activity was affected only slightly. These results indicate that in situ nitrate reductase activity is protected from salt injury. The susceptibility to injury of the NO3− transporter, rather than that of the NO3− reduction system, may be a critical factor to plant survival during salt stress. 相似文献
4.
Soybeans ( Glycine max L. Merr., cv Kingsoy) were grown on media containing NO 3− or urea. The enrichments of shoots in K +, NO 3−, and total reduced N (N r), relative to that in Ca 2+, were compared to the ratios K +/Ca 2+,NO 3−/Ca 2+, and N r/Ca 2+ in the xylem saps, to estimate the cycling of K +, and N r. The net production of carboxylates (R −) was estimated from the difference between the sums of the main cations and inorganic anions. The estimate for shoots was compared to the theoretical production of R − associated with NO 3− assimilation in these organs, and the difference was attributed to export of R − to roots. The net exchange rates of H + and OH − between the medium and roots were monitored. The shoots were the site of more than 90% of total NO 3− reduction, and N r was cycling through the plants at a high rate. Alkalinization of the medium by NO 3−-fed plants was interrupted by stem girdling, and not restored by glucose addition to the medium. It was concluded that the majority of the base excreted in NO 3− medium originated from R − produced in the shoots, and transported to the roots together with K +. As expected, cycling of K + and reduced N was favoured by NO 3− nutrition as compared to urea nutrition. 相似文献
5.
The absorption and assimilation patterns of 15NO 3− supplied as the Ca 2+ and Mg 2+ salts to intact ryegrass ( Lolium perenne) seedlings were compared. No statistically significant effect of ambient cation on the amounts of 15NO 3− absorbed was observed in the initial six hours, but during the subsequent six hours, absorption from Ca( 15NO 3) 2 exceeded that from Mg ( 15NO 3) 2. 相似文献
6.
Tomato plants ( Lycopersicon esculentum L. var. Ailsa Craig) were grown in water culture in nutrient solution in a series of 10 increasing levels of nitrate nutrition. Using whole plant data derived from analytical and yield data of individual plant parts, the fate of anion charge arising from increased NO 3 assimilation was followed in its distribution between organic anion accumulation in the plant and OH − efflux into the nutrient solution as calculated by excess anion over cation uptake. With increasing NO 3 nutrition the bulk of the anion charge appeared as organic anion accumulation in the plants. OH − efflux at a maximum accounted for only 20% of the anion charge shift. The major organic anion accumulated in response to nitrate assimilation was malate. The increase in organic anion accumulation was paralleled by an increase in cation concentration (K +, Ca 2+, Mg 2+, Na +). Total inorganic anion levels (NO 3−, SO 42−, H 2PO 4−, Cl −) were relatively constant. The effect of increasing NO 3 nutrition in stimulating organic anion accumulation was much more pronounced in the tops than in the roots. 相似文献
7.
The nature of the injury and recovery of nitrate uptake (net uptake) from NaCl stress in young barley ( Hordeum vulgare L, var CM 72) seedlings was investigated. Nitrate uptake was inhibited rapidly by NaCl, within 1 minute after exposure to 200 millimolar NaCl. The duration of exposure to saline conditions determined the time of recovery of NO 3− uptake from NaCl stress. Recovery was dependent on the presence of NO 3− and was inhibited by cycloheximide, 6-methylpurine, and cerulenin, respective inhibitors of protein, RNA, and sterol/fatty acid synthesis. These inhibitors also prevented the induction of the NO 3− uptake system in uninduced seedlings. Uninduced seedlings exhibited endogenous NO 3− transport activity that appeared to be constitutive. This constitutive activity was also inhibited by NaCl. Recovery of constitutive NO 3− uptake did not require the presence of NO 3−. 相似文献
8.
Mass spectrometric analysis shows that assimilation of inorganic nitrogen (NH 4+, NO 2−, NO 3−) by N-limited cells of Selenastrum minutum (Naeg.) Collins results in a stimulation of tricarboxylic acid cycle (TCA cycle) CO 2 release in both the light and dark. In a previous study we have shown that TCA cycle reductant generated during NH 4+ assimilation is oxidized via the cytochrome electron transport chain, resulting in an increase in respiratory O 2 consumption during photosynthesis (HG Weger, DG Birch, IR Elrifi, DH Turpin [1988] Plant Physiol 86: 688-692). NO 3− and NO 2− assimilation resulted in a larger stimulation of TCA cycle CO 2 release than did NH 4+, but a much smaller stimulation of mitochondrial O 2 consumption. NH 4+ assimilation was the same in the light and dark and insensitive to DCMU, but was 82% inhibited by anaerobiosis in both the light and dark. NO 3− and NO 2− assimilation rates were maximal in the light, but assimilation could proceed at substantial rates in the light in the presence of DCMU and in the dark. Unlike NH 4+, NO 3− and NO 2− assimilation were relatively insensitive to anaerobiosis. These results indicated that operation of the mitochondrial electron transport chain was not required to maintain TCA cycle activity during NO 3− and NO 2− assimilation, suggesting an alternative sink for TCA cycle generated reductant. Evaluation of changes in gross O 2 consumption during NO 3− and NO 2− assimilation suggest that TCA cycle reductant was exported to the chloroplast during photosynthesis and used to support NO 3− and NO 2− reduction. 相似文献
9.
Effects of Na application on the capacity of NO 3− assimilation were studied in Na-deficient Amaranthus tricolor L. cv Tricolor plants. On day 30 after germination, Na-deficient A. tricolor plants received either 0.5 millimolar NaCl or KCl. The level of nitrate reductase activity doubled within 24 hours by the addition of Na and the enhanced level was maintained thereafter. When the plants were exposed to 2 millimolar 15NO 3−, total 15N taken up by the plants was greater in the Na-treated plants than in the K-treated plants within 24 hours of the Na treatment. Incorporation of 15N into the 80% ethanol-insoluble nitrogen fraction of the Na-treated plants in the light period was about 260% of those of the K-treated plants indicating greater capacity of NO 3− assimilation in the Na-treated plants. From these results, it was demonstrated that Na application to the Na-deficient A. tricolor plants promoted NO 3− reduction and its subsequent assimilation into protein, resulting in growth enhancement. 相似文献
10.
Peanut is one of the calciphilous plants. Calcium (Ca) serves as a ubiquitous central hub in a large number of signaling pathways. The effect of exogenous calcium nitrate [Ca(NO 3) 2] (6 mM) on the dissipation of excess excitation energy in the photosystem II (PSII) antenna, especially on the level of D1 protein and the xanthophyll cycle in peanut plants under heat (40°C) and high irradiance (HI) (1 200 µmol m −2 s −1) stress were investigated. Compared with the control plants [cultivated in 0 mM Ca(NO 3) 2 medium], the maximal photochemical efficiency of PSII (Fv/Fm) in Ca 2+-treated plants showed a slighter decrease after 5 h of stress, accompanied by higher non-photochemical quenching (NPQ), higher expression of antioxidative genes and less reactive oxygen species (ROS) accumulation. Meanwhile, higher content of D1 protein and higher ratio of (A+Z)/(V+A+Z) were also detected in Ca 2+-treated plants under such stress. These results showed that Ca 2+ could help protect the peanut photosynthetic system from severe photoinhibition under heat and HI stress by accelerating the repair of D1 protein and improving the de-epoxidation ratio of the xanthophyll cycle. Furthermore, EGTA (a chelant of Ca ion), LaCl 3 (a blocker of Ca 2+ channel in cytoplasmic membrane), and CPZ [a calmodulin (CaM) antagonist] were used to analyze the effects of Ca 2+/CaM on the variation of (A+Z)/(V+A+Z) (%) and the expression of violaxanthin de-epoxidase (VDE). The results indicated that CaM, an important component of the Ca 2+ signal transduction pathway, mediated the expression of the VDE gene in the presence of Ca to improve the xanthophyll cycle. 相似文献
11.
When assayed in the presence of azide, NO 3− was shown to be a specific inhibitor of a proton-translocating ATPase present in corn ( Zea mays L. cv WF9 × M017) root microsomal membranes. The distribution of the NO 3−-sensitive ATPase on sucrose gradients and its general characteristics are similar to those previously reported for the anion-stimulated H +-ATPase of corn roots believed to be of tonoplast origin. An ATPase inhibited by 20 μ m vanadate and insensitive to molybdate was also identified in corn root microsomal membranes which could be largely separated from the NO 3−-sensitive ATPase on sucrose gradients and is believed to be of plasma membrane origin. Inasmuch as both ATPase most likely catalyze the efflux of H + from the cytoplasm, our objective was to characterize and compare the properties of both ATPases under identical experimental conditions. The vanadate-sensitive ATPase was stimulated by cations (K + > NH 4+ > Rb + > Cs + > Li + > Na + > choline +) whereas the NO 3−-sensitive ATPase was stimulated by anions (Cl − > Br − > C 2H 3O 2− > SO 42− > I − > HCO 3− > SCN −). Both ATPases required divalent cations. However, the order of preference for the NO 3−-sensitive ATPase (Mn 2+ > Mg 2+ > Co 2+ > Ca 2+ > Zn 2+) differed from that of the vanadate-sensitive ATPase (Co 2+ > Mg 2+ > Mn 2+ > Zn 2+ > Ca 2+). The vanadate-sensitive ATPase required higher concentrations of Mg:ATP for full activity than did the NO 3−-sensitive ATPase. The kinetics for Mg:ATP were complex for the vanadate-sensitive ATPase, indicating positive cooperativity, but were simple for the NO 3−-sensitive ATPase. Both ATPases exhibited similar temperature and pH optima (pH 6.5). The NO 3−-sensitive ATPase was stimulated by gramicidin and was associated with NO 3−-inhibitable H + transport measured as quenching of quinacrine fluorescence. It was insensitive to molybdate, azide, and vanadate, but exhibited slight sensitivity to ethyl-3-(3-dimethylaminopropyl carbodiimide) and mersalyl. Overall, these results indicate several properties which distinguish these two ATPases and suggest that under defined conditions NO 3−-sensitive ATPase activity may be used as a quantitative marker for those membranes identified tentatively as tonoplast in mixed or nonpurified membrane fractions. We feel that NO 3− sensitivity is a better criterion by which to identify this ATPase than either Cl − stimulation or H + transport because it is less ambiguous. It is also useful in identifying the enzyme following solubilization. 相似文献
12.
We examined nitrate-dependent Fe 2+ oxidation mediated by anaerobic ammonium oxidation (anammox) bacteria. Enrichment cultures of “ Candidatus Brocadia sinica” anaerobically oxidized Fe 2+ and reduced NO 3− to nitrogen gas at rates of 3.7 ± 0.2 and 1.3 ± 0.1 (mean ± standard deviation [SD]) nmol mg protein −1 min −1, respectively (37°C and pH 7.3). This nitrate reduction rate is an order of magnitude lower than the anammox activity of “ Ca. Brocadia sinica” (10 to 75 nmol NH 4+ mg protein −1 min −1). A 15N tracer experiment demonstrated that coupling of nitrate-dependent Fe 2+ oxidation and the anammox reaction was responsible for producing nitrogen gas from NO 3− by “ Ca. Brocadia sinica.” The activities of nitrate-dependent Fe 2+ oxidation were dependent on temperature and pH, and the highest activities were seen at temperatures of 30 to 45°C and pHs ranging from 5.9 to 9.8. The mean half-saturation constant for NO 3− ± SD of “ Ca. Brocadia sinica” was determined to be 51 ± 21 μM. Nitrate-dependent Fe 2+ oxidation was further demonstrated by another anammox bacterium, “ Candidatus Scalindua sp.,” whose rates of Fe 2+ oxidation and NO 3− reduction were 4.7 ± 0.59 and 1.45 ± 0.05 nmol mg protein −1 min −1, respectively (20°C and pH 7.3). Co-occurrence of nitrate-dependent Fe 2+ oxidation and the anammox reaction decreased the molar ratios of consumed NO 2− to consumed NH 4+ (ΔNO 2−/ΔNH 4+) and produced NO 3− to consumed NH 4+ (ΔNO 3−/ΔNH 4+). These reactions are preferable to the application of anammox processes for wastewater treatment. 相似文献
13.
Shamouti orange ( Citrus sinensis L. Osbeck) salt-tolerant cells were grown under low water potential conditions induced by polyethylene glycol (PEG), NaCl, and CaCl 2. On the basis of equal osmotic potentials, PEG was the least inhibitory, NaCl next, and CaCl 2 the most inhibitory. The relation between growth capacity and ion content can be summarized as follows. (a) Internal K + concentration was a major factor which changed in the presence of PEG, NaCl, and CaCl 2 and probably played a key role in determining growth capacity. (b) Internal concentrations of Na +, Ca 2+, or Cl − could not be directly correlated with growth. (C) Internal Mg 2+ concentration could be significant only in the presence of high external Ca 2+ concentrations. (d) The contribution of nitrate and phosphate to the internal osmoticum was negligible. The ratio of external (Ca 2+)/(Na +) 2 concentration is crucial for growth. Ratios above 0.5 × 10 −4 per millimolar gave maximal protection from adverse effects of NaCl. Growth capacity was found to be determined by the combination of (Ca 2+)/(Na +) 2 ratio and the absolute external concentration of NaCl. However, a correlation between internal K + concentration and growth capacity seemed independent of external NaCl concentration. 相似文献
14.
Ricinus communis was used to test the Ben Zioni-Dijkshoorn hypothesis that NO 3 uptake by roots can be regulated by NO 3 assimilation in the shoot. The rate of the anion charge from assimilated NO 3− (and SO 42−) was followed in its distribution between organic acid anion accumulation and HCO 3− efflux into the nutrient solution. In plants adequately supplied with NO 3−, HCO 3− efflux accounted for between 56 and 63% of the anion charge. When the plants were subjected to a low NO 3 regime HCO 3− excretion accounted for only 23% of the charge. A comparison of mature plants growing for a 10-day period at the two levels of NO 3 nutrition revealed that the uptake of NO 3− at the higher level was increased 3-fold, whereas K uptake was unaltered. To trace ion movement within the plant, the ionic constituents of xylem and phloem sap were determined. In xylem sap these constituents were found to be predominantly K +, Ca 2+, and NO 3−, whereas in the phloem sap they were mainly K + and organic acid anions. Results have been obtained which may be interpreted as providing direct evidence of NO 3 uptake by roots regulated by NO 3 reduction in the tops, the process being facilitated by the recirculation of K + in the plant. 相似文献
15.
We examined nitrate assimilation and root gas fluxes in a wild-type barley ( Hordeum vulgare L. cv Steptoe), a mutant ( nar1a) deficient in NADH nitrate reductase, and a mutant ( nar1a; nar7w) deficient in both NADH and NAD(P)H nitrate reductases. Estimates of in vivo nitrate assimilation from excised roots and whole plants indicated that the nar1a mutation influences assimilation only in the shoot and that exposure to NO 3− induced shoot nitrate reduction more slowly than root nitrate reduction in all three genotypes. When plants that had been deprived of nitrogen for several days were exposed to ammonium, root carbon dioxide evolution and oxygen consumption increased markedly, but respiratory quotient—the ratio of carbon dioxide evolved to oxygen consumed—did not change. A shift from ammonium to nitrate nutrition stimulated root carbon dioxide evolution slightly and inhibited oxygen consumption in the wild type and nar1a mutant, but had negligible effects on root gas fluxes in the nar1a; nar7w mutant. These results indicate that, under NH 4+ nutrition, 14% of root carbon catabolism is coupled to NH 4+ absorption and assimilation and that, under NO 3− nutrition, 5% of root carbon catabolism is coupled to NO 3− absorption, 15% to NO 3− assimilation, and 3% to NH 4+ assimilation. The additional energy requirements of NO 3− assimilation appear to diminish root mitochondrial electron transport. Thus, the energy requirements of NH 4+ and NO 3− absorption and assimilation constitute a significant portion of root respiration. 相似文献
16.
The regulation of NO 3− assimilation by xylem flux of NO 3− was studied in illuminated excised leaves of soybean ( Glycine max L. Merr. cv Kingsoy). The supply of exogenous NO 3− at various concentrations via the transpiration stream indicated that the xylem flux of NO 3− was generally rate-limiting for NO 3− reduction. However, NO 3− assimilation rate was maintained within narrow limits as compared with the variations of the xylem flux of NO 3−. This was due to considerable remobilization and assimilation of previously stored endogenous NO 3− at low exogenous NO 3− delivery, and limitation of NO 3− reduction at high xylem flux of NO 3−, leading to a significant accumulation of exogenous NO 3−. The supply of 15NO 3− to the leaves via the xylem confirmed the labile nature of the NO 3− storage pool, since its half-time for exchange was close to 10 hours under steady state conditions. When the xylem flux of 15NO 3− increased, the proportion of the available NO 3− which was reduced decreased similarly from nearly 100% to less than 50% for both endogenous 14NO 3− and exogenous 15NO 3−. This supports the hypothesis that the assimilatory system does not distinguish between endogenous and exogenous NO 3− and that the limitation of NO 3− reduction affected equally the utilization of NO 3− from both sources. It is proposed that, in the soybean leaf, the NO 3− storage pool is particularly involved in the short-term control of NO 3− reduction. The dynamics of this pool results in a buffering of NO 3− reduction against the variations of the exogenous NO 3− delivery. 相似文献
17.
Tributyltin in the concentration range 1–4μ m failed to stimulate Ca 2+ transport by Lucilia flight-muscle mitochondria in a medium containing KCl and respiratory substrate but devoid of P i, despite its promotion of a rapid Cl −/OH − exchange. When 2m m-P i was present, concentrations of tributyltin greater than 1μ m inhibited the initial rate of Ca 2+ transport and induced efflux of the ion from the mitochondria in Cl −- or NO 3−-containing media. Lower concentrations had little effect. Oligomycin added at up to 10μg/mg of mitochondrial protein had no effect on Ca 2+ transport. By contrast, approx. 0.3μ m-tributyltin completely inhibited respiration supported by α-glycerophosphate in either the presence or absence of added ADP. The data suggest that tributyltin can inhibit Ca 2+ transport in Lucilia flight-muscle mitochondria other than by facilitating a Cl −/OH − exchange or producing an oligomycin-like effect. 相似文献
18.
Week-old wheat seedlings absorbed at least 40% NO 3− from NaNO 3 when preloaded with K + than when preloaded with Na + or Ca 2+. Cultures of Triticum vulgare L. cv. Arthur were grown for 5 days on 0.2 m m CaSO 4, pretreated for 48 hours with either 1 m m CaSO 4, K 2SO 4, or Na 2SO 4, and then transferred to 1 m m NaNO 3. All solutions contained 0.2 m m CaSO 4. Shoots of K +-preloaded plants accumulated three times more NO 3− than shoots of the other two treatments. Initially, the K +-preloaded plants contained 10-fold more malate than either Na +- or Ca 2+-preloaded seedlings. During the 48-hour treatment with NaNO 3, malate in both roots and shoots of the K +-preloaded seedlings decreased. Seedlings preloaded with K + reduced 25% more NO 3− than those preloaded with either Na + or Ca 2+. These experiments indicate that K + enhanced NO 3− uptake and reduction even though the absorption of K + and NO 3− were separated in time. Xylem exudate of K +-pretreated plants contained roughly equivalent concentrations of K + and NO 3−, but exudate from Na + and Ca 2+-pretreated plants contained two to four times more NO 3− than K +. Therefore K + is not an obligatory counterion for NO 3− transport in xylem. 相似文献
19.
The effects of several photosynthetic inhibitors and uncouplers of oxidative phosphorylation on NO 3− and NO 2− assimilation were studied using detached barley ( Hordeum vulgare L. cv Numar) leaves in which only endogenous NO 3− or NO 2− were available for reduction. Uncouplers of oxidative phosphorylation greatly increased NO 3− reduction in both light and darkness, while photosynthetic inhibitors did not. The NO2− concentration in the control leaves was very low in both light and darkness; 98% or more of the NO2− formed from NO3− was further assimilated in control leaves. More NO2− accumulated in the leaves in light and darkness in the presence of photosynthetic inhibitors. Of this NO2−, 94% or more was further assimilated. It appears that metabolites, either external or internal to the chloroplast, capable of reducing NADP (which, in turn, could reduce ferredoxin via NADP reductase) might support NO2− reduction in darkness and light when photosynthetic electron flow is inhibited by photosynthetic inhibitors. Nitrite assimilation was much more sensitive to uncouplers in darkness than in light: in darkness, 74% or more of NO2− formed from NO3− was further assimilated, whereas in light, 95% or more of the NO2− was further assimilated. 相似文献
20.
Using 13NO 3−, effects of various NO 3− pretreatments upon NO 3− influx were studied in intact roots of barley ( Hordeum vulgare L. cv Klondike). Prior exposure of roots to NO 3− increased NO 3− influx and net NO 3− uptake. This `induction' of NO 3− uptake was dependent both on time and external NO 3− concentration ([NO 3−]). During induction influx was positively correlated with root [NO 3−]. In the postinduction period, however, NO 3− influx declined as root [NO 3−] increased. It is suggested that induction and negative feedback regulation are independent processes: Induction appears to depend upon some critical cytoplasmic [NO 3−]; removal of external NO 3− caused a reduction of 13NO 3− influx even though mean root [NO 3−] remained high. It is proposed that cytoplasmic [NO 3−] is depleted rapidly under these conditions resulting in `deinduction' of the NO 3− transport system. Beyond 50 micromoles per gram [NO 3−], 13NO 3− influx was negatively correlated with root [NO 3−]. However, it is unclear whether root [NO 3−] per se or some product(s) of NO 3− assimilation are responsible for the negative feedback effects. 相似文献
|