Effect of ammonium on nitrate utilization by roots of dwarf bean

The effect of exogenous NH₄⁺ on NO₃⁻ uptake and in vivo NO₃⁻ reductase activity (NRA) in roots of Phaseolus vulgaris L. cv Witte Krombek was studied before, during, and after the apparent induction of root NRA and NO₃⁻ uptake. Pretreatment with NH₄Cl (0.15-50 millimolar) affected neither the time pattern nor the steady state rate of NO₃⁻ uptake.

When NH₄⁺ was given at the start of NO₃⁻ nutrition, the time pattern of NO₃⁻ uptake was the same as in plants receiving no NH₄⁺. After 6 hours, however, the NO₃⁻ uptake rate (NUR) and root NRA were inhibited by NH₄⁺ to a maximum of 45% and 60%, respectively.

The response of the NUR of NO₃⁻-induced plants depended on the NH₄Cl concentration. Below 1 millimolar NH₄⁺, the NUR declined immediately and some restoration occurred in the second hour. In the third hour, the NUR became constant. In contrast, NH₄⁺ at 2 millimolar and above caused a rapid and transient stimulation of NO₃⁻ uptake, followed again by a decrease in the first, a recovery in the second, and a steady state in the third hour. Maximal inhibition of steady state NUR was 50%. With NO₃⁻-induced plants, root NRA responded less and more slowly to NH₄⁺ than did NUR.

Methionine sulfoximine and azaserine, inhibitors of glutamine synthetase and glutamate synthase, respectively, relieved the NH₄⁺ inhibition of the NUR of NO₃⁻-induced plants. We conclude that repression of the NUR by NH₄⁺ depends on NH₄⁺ assimilation. The repression by NH₄⁺ was least at the lowest and highest NH₄⁺ levels tested (0.04 and 25 millimolar).

     

Effect of amino compounds on nitrate utilization by roots of dwarf bean

Amino compounds (1 mM, pH 5) were given prior to, together with, or after the addition of nitrate to study their effect on nitrate uptake and in vivo nitrate reductase activity (NRA) in roots of Phaseolus vulgaris. The effect of amino compounds varied with the amino species, the nitrate status of the plant (induced vs uninduced) and the aspect of nitrate utilization. Cysteine inhibited the nitrate uptake rate and root NRA under all conditions tested. NRA in uninduced roots was stimulated by tryptophan, and arginine inhibited NRA under all conditions tested. Uptake was inhibited by aspartate and glutamate and stimulated by leucine when these amino compounds were given prior to or after completion of the apparent induction of nitrate uptake. In the presence of β-alanine and tryptophan, induction of uptake was accelerated.     

Fate of nitrate during initial nitrate utilization by nitrogen-depleted dwarf bean

The fate of nitrate and nitrogen-15 was followed during the apparent induction phase (6h) for nitrate uptake by N-depleted dwarf bean (Phaseolus vulgaris L. ev. Witte Krombek). Experiments were done with intact plants and with detached root systems. Qualitatively and quantitatively, xylem exudation from detached roots was a bad estimate of the export of NO^?₃ or NO^?₃-¹⁵N from roots of intact plants. In vivo nitrate reductase activity (NRA) agreed well with in situ reduction, calculated as the difference between uptake and accumulation in whole plants, provided NRA was assayed with merely endogenous nitrate as substrate (‘actual’ NRA). The majority (75%) of the entering nitrate remained unmetabolized. Both nitrate reduction and nitrate accumulation occurred predominantly in the root system. Some (< 25%) of the root-reduced nitrate-N was translocated to the shoot. Nitrate uptake occurred against the concentration gradient between medium and root cells, and probably against the gradient of the electro-chemical potential of nitrate. Part of the energy expended for NO^?₃ absorption came from the tops, since decapitation and ringing at the stem base restricted nitrate uptake.     

Role of sugars in nitrate utilization by roots of dwarf bean

Nitrate uptake and in vivo, nitrate reductase activity (NRA) in roots of Phaseolus vulgaris, L. cv. Witte Krombek were measured in nitrogen-depleted plants of varying sugar status, Variation in sugar status was achieved at the start of nitrate nutrition by excision, ringing, darkness or administration of sugars to the root medium. The shape of the apparent induction pattern of nitrate uptake was not influenced by the sugar status of the absorbing tissue. When measured after 6 h of nitrate nutrition (0.1 mol m^?3), steady state nitrate uptake and root NRA were in the order intact>dark>ringed>excised. Exogenous sucrose restored NRA in excised roots to the level of intact plants. The nitrate uptake rate of excised roots, however, was not fully restored by sucrose (0.03–300 mol m^?3). When plants were decapitated after an 18 h NO₃^? pretreatment, the net uptake rate declined gradually to become negative after three hours. This decline was slowed down by exogenous fructose, whilst glucose rapidly (sometimes within 5 min) stimulated NG^?₃ uptake. Presumably due to a difference in NO₃^? due to a difference in NO₃^? uptake, the NRA of excised roots was also higher in the presence of glucose than in the presence of fructose after 6 h of nitrate nutrition. The sugar-stimulation of, oxygen consumption as well as the release of ¹⁴CO₂ from freshly absorbed (U-¹⁴C) sugar was the same for glucose and fructose. Therefore, we propose a glucose-specific effect on NO₃^? uptake that is due to the presence of glucose rather than to its utilization in root respiration. A differential glucose-fructose effect on nitrate reductase activity independent of the effect on NO₃^? uptake was not indicated. A constant level of NRA occurred in roots of NO₃^? induced plants. Removal of nutrient nitrate from these plants caused an exponential NRA decay with an approximate half-life of 12 h in intact plants and 5.5 h in excised roots. The latter value was also found in roots that were excised in the presence of nitrate, indicating that the sugar status primarily determines the apparent rate of nitrate reductase decay in excised roots.     

Utilization of nitrite and nitrate by dwarf bean

The uptake and conversion of NO ₂ ^- and the effect of NO ₂ ^- on the uptake and reduction of NO ₃ ^- were examined in N-depleted Phaseolus vulgaris L. Nitrite uptake at 0.1 mmol dm^-3 was against an electrochemical gradient and became constant after one or two initial phases. Steadystate uptake declined with increasing ambient NO ₂ ^- concentration (0–0.7 mmol dm^-3). In this concentration range root oxygen consumption was unaffected by NO ₂ ^- , indicating that the decrease of NO ₂ ^- uptake was not related to respiration. After 6 h NO ₂ ^- supply, about one-third of the absorbed NO ₂ ^- had accumulated, mainly in the root system. Oxidation of NO ₂ ^- to NO ₃ ^- was not observed. The apparent induction period for NO ₃ ^- uptake was about 6 h in control plants and 3.5 h in plants that were pretreated for 18 h with NO ₂ ^- . In contrast, the time course of NO ₂ ^- uptake was unaffected by pretreatment with NO ₃ ^- . Steadystate NO ₃ ^- uptake was less affected by NO ₂ ^- than was steady-state NO ₂ ^- uptake by NO ₃ ^- . Nitrate reductase activity (NRA) in leaves and roots was induced by both NO ₃ ^- and NO ₂ ^- . In roots, induction with NO ₂ ^- was faster than with NO ₃ ^- , but there was no difference in NRA after 5 h. Nitrite inhibited NRA in the roots of NO ₃ ^- -induced plants and thus seems to stimulate the induction, but not the activity of induced nitrate reductase. In view of the observed differences in time course and mutual competition, a common uptake mechanism for NO ₂ ^- and NO ₃ ^- seems unlikely. Expression of the NO ₂ ^- effect on the induction of NO ₃ ^- uptake required more time than the induction itself. We therefore conclude that NO ₂ ^- is not the physiological inducer of NO ₃ ^- uptake.Abbreviations NR(A) nitrate reductase (activity) - BM basal medium     

Effect of ammonium and ferricyanide on nitrate utilization by Chlorella vulgaris

It has been shown previously that added ammonium salts cause a cessation of nitrate utilization in some Chlorella species. It has also been shown that Chlorella vulgaris can form an inactivated nitrate reductase which is an HCN complex. In the present study, a comparison has been made of the rate of nitrate utilization and the rate of nitrate reductase inactivation in Chlorella vulgaris in response to the addition of ammonium salts and light-dark changes. The rate of formation of HCN-inactivated enzyme is too slow to account for the prompt inhibition of nitrate utilization caused by adding ammonium. In contrast, when nitrate utilization is inhibited by addition of ferricyanide to intact cells, the HCN-inactivated enzyme is promptly formed in vivo, and might account for the inhibition of nitrate utilization, though inhibition of nitrate uptake can not be excluded.     

Effect of exogenous and endogenous nitric oxide on biofilm formation by Lactobacillus plantarum

Biofilms are a widespread form of occurrence of microorganisms in nature, and understanding the mechanism of regulation of their formation is of unquestionable practical significance for medicine and biotechnology. In the present work, the effect of nitric oxide (NO) on biofilm formation by Lactobacillus plantarum was investigated and the micromolar concentrations of exogenous NO were shown to have a negative effect on this process due to its toxic effect on the cells. However, the decrease in the level of endogenous NO in bacteria in the presence of a nitric oxide scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) impaired the characteristics of the forming biofilms, as was evident from the decrease in their size.     

Effect of estradiol on splenic repopulation by endogenous and exogenous hemopoietic cells in irradiated mice

Estradiol treatment of irradiated mice during repopulation of their spleens by endogenous hemopoietic cells reduced the number of myelocytic colonies and increased the numbers of erythropoietic and undifferentiated colonies. The inhibitory effects of the hormone on myelopoiesis were not dependent on stimulation of erythropoiesis, since they occurred in the absence of erythropoiesis in mice made polycythemic by hypertransfusion. Treatment of bone marrow donors with estradiol reduced the ability of their marrow cells to form spleen colonies, particularly reducing the proportion of myelopoietic colonies relative to the total number of colonies of all types. Conversely erythropoietic colonies, though reduced in absolute number, were increased in relative number. Such treatment also decreased the volume and cell content of the marrow cavity through stimulation of endosteal bone formation. Estradiol treatment of lethally irradiated recipient mice did not detectably alter the total numbers or types of hemopoietic spleen colonies formed in these animals from transplanted marrow cells; however, without estradiol treatment, myelopoietic colonies were so few and erythropoietic colonies so numerous that the effects of the hormones may have been undetectable by the methods employed. The sex of the donor or recipient mouse did not affect the numbers or types of colonies formed, suggesting that endogenous levels of estradiol were too low to exert effects dectectable by the methods used. However, since our mice were only 8 weeks old, the data do not exclude the possibility that older female mice, with higher levels of estradiol, would have differed from males in relative numbers of myelopoietic as compared with erythropoietic colonies.     

矮生菜豆品种比较试验

从生育期、植物性状、产量等方面对6个矮生菜豆品种进行比较试验。结果表明,德国矮菜豆和日本佳美四季豆具有较高推广价值。     

Changes in concentration of endogenous growth inhibitors during growth recovery of dwarf pea seedlings

In order to clarify the role of endogenous growth inhibitors A-2α and A-2β in a dwarf pea plant, red light (emission peak 657 nm) treated, 9-d-old seedlings of dwarf pea (Pisum sativum L. cv. Progress No. 9) were transferred to darkness, and the resulting changes in growth rate and concentrations of A-2α and A-2β were monitored. The growth rate of the epicotyls increased, and the concentration of the inhibitors in the epicotyls decreased, according to sigmoidal time courses. The relationship between the logarithms of the concentration of the inhibitors and the corresponding growth rate was linear. These results suggest that A-2α and A-2β, may play an important role in the growth recovery process of the dwarf pea cultivar after termination of red light irradiation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of nitrate nutrition on iron utilization by an Fe-efficient and an Fe-inefficient soybean cultivar

Summary The effects of increasing amount of nitrate nitrogen on the growth, dry matter production, ionic balance and the appearance of iron chlorosis in two soybean cultivars were studied. More nitrogen increased the dry matter production of the Fe-efficient cultivar Hawkeye and decreased that of the Fe-inefficient cultivar T-203. The plants of Hawkeye showed no iron deficiency symptoms whereas all the plants of the Fe-inefficient cultivar T-203 developed Fe deficiency after about one week following emergence. The degree of chlorosis in the cultivar T-203 was more pronounced as the amount of nitrate applied increased.Deceased     

Effect of nitrate and ammonium concentration on nitrate reductase activity in five species of mycorrhizal fungi

The nitrate reducing capacity of pure cultures of Cenococcum geophilum (Sow.) Ferd. & Winge, Paxillus involutes (Batsch: Fr.) Fr. (strains 1 and 2), Piloderma croceum Erikss. & Hjortst., Suillus variegatus (Fr.) O. Kuntze (strains 1 and 2) and an ectendomycorrhizal (E-strain) fungus was measured using an in vivo nitrate reductase (EC 1.6.6.3) assay. Differences between species and strains were established. The nitrate concentration of the culture medium influenced the nitrate reductase activities of the E-strain fungus and one strain of S. variegatus. The nitrate reductase activity of certain species and strains was a function of nitrate concentration. Addition of ammonium to the growth medium did not have any significant effect on the in vivo or in vitro nitrate reductase activity. The in vivo nitrate reductase activity in the mycelia of C. geophilum and the E-strain fungus decreased during 28 day growth in modified Melin-Norkrans medium. For mycelia of Paxillus involutus, Piloderma croceum and S. variegatus grown on agar the in vitro assays showed higher nitrate reductase activity than the in vivo assays.