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171.
Cation pretreatment effects on nitrate uptake, xylem exudate, and malate levels in wheat seedlings 总被引:1,自引:1,他引:0
Week-old wheat seedlings absorbed at least 40% NO3− from NaNO3 when preloaded with K+ than when preloaded with Na+ or Ca2+. Cultures of Triticum vulgare L. cv. Arthur were grown for 5 days on 0.2 mm CaSO4, pretreated for 48 hours with either 1 mm CaSO4, K2SO4, or Na2SO4, and then transferred to 1 mm NaNO3. All solutions contained 0.2 mm CaSO4. Shoots of K+-preloaded plants accumulated three times more NO3− than shoots of the other two treatments. Initially, the K+-preloaded plants contained 10-fold more malate than either Na+- or Ca2+-preloaded seedlings. During the 48-hour treatment with NaNO3, malate in both roots and shoots of the K+-preloaded seedlings decreased. Seedlings preloaded with K+ reduced 25% more NO3− than those preloaded with either Na+ or Ca2+. These experiments indicate that K+ enhanced NO3− uptake and reduction even though the absorption of K+ and NO3− were separated in time. Xylem exudate of K+-pretreated plants contained roughly equivalent concentrations of K+ and NO3−, but exudate from Na+ and Ca2+-pretreated plants contained two to four times more NO3− than K+. Therefore K+ is not an obligatory counterion for NO3− transport in xylem. 相似文献
172.
6-Phosphogluconate dehydratase deficiency in pleiotropic carbohydrate-negative mutant strains of Pseudomonas aeruginosa. 下载免费PDF全文
Mutants of Pseudomonas aeruginosa, strain PAO, have been isolated that are unable to grow on mannitol, glucose, gluconate, or 2-ketogluconate, cut that exhibit wild-type growth on pyruvate, lactate, citrate, succinate, or acetate. Although some of these mutants were also unable to grow on glycerol, the mutations formed a single linkage group by quantitative transductional analysis with phage F116 on glucose minimal agar medium. Cell extracts of all mutant strains were either lacking or severely deficient in 6-phosphogluconate dehydratase activity. Glu+ transductants derived from mutant strains that retained the wild-type ability for growth at the expense of glycerol also regained the ability to grow on all C-6 compounds. Although a role for the pentose phosphate pathway in the catabolism of C6 substrates was not found, a functional Entner-Doudoroff pathway appears to be essential for the catabolism of mannitol, glucose, gluconate, and 2-ketogluconate. 相似文献
173.
Simple, Quantitative Assay for Both Xenotropic Murine Leukemia and Ecotropic Feline Leukemia Viruses 总被引:49,自引:28,他引:21
A cat cell line carrying the genome of a murine sarcoma virus developed discrete foci in linear response to infection with feline leukemia virus or xenotropic murine C-type virus. 相似文献
174.
Organic Acids and Ionic Balance in Xylem Exudate of Wheat during Nitrate or Sulfate Absorption 总被引:1,自引:0,他引:1 下载免费PDF全文
Experiments were designed to study the importance of organic acids as counterions for K+ translocation in the xylem during excess cation uptake. A comparison was made of xylem exudate from wheat seedlings treated 72 hours with either 1.0 millimolar KNO3 or 0.5 millimolar K2SO4, both in the presence of 0.2 millimolar CaSO4. Exudation from KNO3 plants had twice the volume and twice the K+ and Ca2+ fluxes or rate of delivery to shoots, as K2SO4 plants. Malate flux was 25% higher in K2SO4 than in KNO3 exudate. Malate was the principal anion accompanying K+ or Ca2+ in K2SO4 treatment, while in the KNO3 treatment, NO3− was the principal anion. The contribution of SO42− was negligible in both treatments. In a second experiment, exudate was collected every 4 hours during the daytime throughout a 72-hour treatment with KNO3. Malate was the only anion present in exudate at first, just after the CaSO4 pretreatment had ended. Malate concentration decreased and NO3− concentration increased with time and these concentrations were negatively correlated. By 62 hours, NO3− represented 80% of exudate anions. K+ and NO3− concentrations in exudate were strongly correlated with K+ and NO3− uptake, respectively. The first 36 hours of absorption from KNO3 solution resembled the continuous absorption of K2SO4, in that malate was the principal counterion for translocation of K+. 相似文献
175.
Mannitol and Fructose Catabolic Pathways of Pseudomonas aeruginosa Carbohydrate-Negative Mutants and Pleiotropic Effects of Certain Enzyme Deficiencies 总被引:18,自引:17,他引:1 下载免费PDF全文
P. V. Phibbs Jr. S. M. McCowen T. W. Feary W. T. Blevins 《Journal of bacteriology》1978,133(2):717-728
Mutant strains of Pseudomonas aeruginosa PAO were isolated on the basis of their inability to utilize mannitol as sole carbon source for growth. Four linkage groups (I through IV) among these mutant strains were resolved by two-factor crosses using the general transducing phage F116, and the strains appeared to contain point mutations as evidenced by ability to give rise to spontaneous revertants with wild phenotype on mannitol minimal agar. Group I strains were affected only in ability to grow on mannitol; all were deficient in inducible mannitol dehydrogenase activity, and all but one were deficient in inducible mannitol transport activity. Fructokinase was induced in group I strains and in wild-type bacteria during growth in the presence of mannitol but not fructose, indicating the presence of a pathway specific for endogenously generated fructose. Cells grown on fructose contained phosphoenolpyruvate:fructose-1-phosphotransferase activity, and mannitol-grown cells contained a lower level of this activity. Group II mutants were deficient in constitutive phosphoglucoisomerase, failed to grow on mannitol, grew very slowly on glycerol and fructose, but grew normally on glucose and gluconate. Group III strains were deficient in both nicotinamide adenine dinucleotide- and nicotinamide adenine dinucleotide phosphate-linked glucose-6-phosphate dehydrogenase activities that reside in a single enzyme species. 6-Phosphogluconate appeared to be the inductive effector for this enzyme, which was not required for aerobic growth on glucose or gluconate. A single mannitol-negative mutant in group IV also failed to grow on glycerol and glucose, but no biochemical lesion was identified. 相似文献
176.
Various species of actinomycetes and cyanobacteria can impart earthy/musty off-flavours to drinking water supplies and to
pond-raised fish and other aquatic food animals. The genetic determinants for production of the most common off-flavour compounds
[geosmin and 2-methylisoborneol (MIB)] have not been extensively studied. An attempt has been rrlade to study the genetics
of production of these compounds was demonstrated by DNA-curing analysis. The effects of two curing agents [ethidium bromide
(EB) and N-methyl-N′-nitro-N-nitrosoguanidine (NTG)] on tha loss of linear plasmid DNA and generation of bald mutants (no
aerial mycelia) inStreptomyces halstedii andStereptomyces violaceusniger which produce geosmin and MIB, respectively, were observed. Production of earthy/musty odour was not eliminated, but was
reduced by 55–95% in the plasmid cured strain. Data suggested that off-flavour production is likely chromosomally-encoded
in theseStreptomyces isolates. 相似文献
177.
Lima bean (Phaseolus lunatus L.) cultivars vary widely in their growth habit and seed size. Preliminary experiments indicated that a large-seeded pole cultivar (King of the Garden) formed many more nodules than a small-seeded bush cultivar (Henderson). The relative importance of seed size and shoot mass in determining nodule number and mass was assessed in five lima bean cultivars differing in seed size and growth habit. Between cultivars, significant positive correlations between initial seed mass, plant weight and nodule number and mass were observed during the first four weeks after planting. Comparisons within cultivars indicated a strong correlation between nodule mass and shoot dry weight. The influence of plant morphology on nodule formation and mass was secondary to the effects of seed and shoot mass. As plants matured, the increase in nodule mass paralleled the increase in plant mass, while nodule number was relatively stable after day 18. These results suggest that the highly regulated process of nodule formation was under the influence of seed derived factors, while the continued accumulation of nodule tissue was related to shoot growth. 相似文献
178.
In individual fura-2 loaded cells of rat pancreatic acini endothelin-1 (ET-1) (10-50 nM) induced sustained oscillations in [Ca2+]i. At higher concentrations a larger, but transient increase in [Ca2+]i was observed, which was largely unaffected by removal of extracellular Ca2+. ET-1 induced the release of Ca2+i from the same store as cholecystokinin (CCK), but with less potency. At concentrations of endothelin which transiently increased Ca2+, ET-1 increased the accumulation of inositol phosphates. Specific binding sites for 125I-endothelin were demonstrated on rat pancreatic acini. A single class of binding sites was identified with an apparent Kd 108 +/- 12 pM and Bmax of 171 +/- 17 fmol/mg for ET-1. The relative potency order for displacing [125I]ET was ET-1 greater than ET-2 greater than ET-3. In contrast to CCK and the non-phorbol ester tumour promoter Thapsigargin (TG) which induce both transient and sustained components of [Ca2+]i elevation, ET-1 failed to increase amylase release over the range 100 pM-1 microM. 相似文献
179.
Boron induces hyperpolarization of sunflower root cell membranes and increases membrane permeability to k 总被引:5,自引:1,他引:4 下载免费PDF全文
Although many studies have alluded to a role for boron (B) in membrane function, there is little evidence for a direct effect of B on the plasmalemma of higher plant cells. These studies were conducted to demonstrate, by electrophysiological techniques, a direct effect of B on the membrane potential (Em) of sunflower (Helianthus annuus [L.], cv Mammoth Grey Stripe) root tip cells and to determine if the response to B occurs rapidly enough to account for the previously observed effects of B on ion uptake. By inserting a glass microelectrode into an individual cell in the root tip, the Em of the cell was determined in basal salt medium (BSM), pH 6.0. The perfusion solution surrounding the root tissue was then changed to BSM + 50 micromolar H3BO3, pH 6.0. The exposure to B induced a significant plasmalemma hyperpolarization in sunflower root cells within 20 minutes. After just 3 minutes of exposure to B, the change in Em was already significantly different from the negligible change in Em observed over time in root cells never exposed to B. Membrane hyperpolarization could be caused by a stimulation of the proton pump or by a change in the conductance of one or more permeable ions. Since B has been shown to affect K+ uptake by plants, the electrophysiological techniques described above were used to determine if B has an effect on membrane permeability to K+, and could thereby lead to an increased diffusion potential. When sunflower root tips were pretreated in 50 micromolar B for 2 hours, cell membranes exhibited a significantly greater depolarization with each 10-fold increase in external [K+] than minus-B cells. Subsequent studies demonstrated that the depolarization due to increased external [K+] was also significantly greater when tissue was exposed to B at the same time as the 10-fold increase in [K+], indicating that the effect of B on K+ permeability was immediate. Analysis of sunflower root tips demonstrated that treatment in 50 micromolar B caused a significantly greater accumulation of K+ after 48 hours. The B-induced increase in K+ uptake may cause a subsequent stimulation of the H+-ATPase (proton pump) and lead to the observed hyperpolarization of root cell membranes. Alternatively, B may stimulate the proton pump, with the subsequent hyperpolarization resulting in an increased driving force for K+ influx. 相似文献
180.
Melanocortinergic control of penile erection 总被引:1,自引:0,他引:1
Melanocortin receptors in the forebrain and spinal cord can be activated by endogenous or synthetic ligands to induce penile erection in rats and human subjects. To better understand how melanocortin circuits play a role in sex behavior, we review the contribution of melanocortin receptors and/or neurons in the hypothalamus, hindbrain, spinal cord and peripheral nerves to erectile function. New information regarding neuropeptides that mediate penile erection has extended our understanding of the central control of sex behavior, and melanocortin agonists may provide alternatives to existing treatment for highly prevalent problems including erectile dysfunction. 相似文献