共查询到20条相似文献,搜索用时 15 毫秒
1.
Kerry L. Griffis-Kyle 《Aquatic Ecology》2007,41(1):119-127
Ephemeral pools, which can have high animal biomass and low dissolved oxygen, may be prone to nitrite accumulation. As such,
it is important to understand how exposure to nitrite might affect development and growth of amphibians that breed in these
ephemeral pools. Wood frog (Rana sylvatica) and eastern tiger salamander (Ambystoma tigrinum tigrinum) embryos and tadpoles and young larvae were exposed to elevated concentrations of nitrite derived from sodium nitrite: 0,
0.3, 0.6, 1.2, 2.1, 4.6, and 6.1 mg l−1 NO2–N. Increasing nitrite exposure slowed embryonic and larval development in both the eastern tiger salamander and the wood
frog, reduced growth in tiger salamander embryos and larvae, and delayed metamorphosis in the wood frog. At concentrations
less than 2 mg l−1 NO2–N nitrite delayed hatching, and at concentrations above 2 mg l−1 time to hatching decreased causing more individuals to hatch at less developed stages. Nitrite also increased asynchrony
in tiger salamander hatching. The sublethal effects of nitrite on amphibian development, growth and hatching could have serious
repercussions on amphibian fitness in ephemeral environments. Potential increases in mortality on field populations caused
by sublethal effects of nitrite are discussed. 相似文献
2.
Microbial conversion of lignocellulose to hydrogen is a fascinating way to provide a renewable energy source. A mesophilic
bacterium strain G1 that had high cellulose degradation and hydrogen production activity (2.38 mmol H2 g−1 cellulose) was isolated from rumen fluid and identified as the Enterococcus gallinarum. Hydrogen production from cellulose by using sequential co-cultures of a cellulosic-hydrolysis bacterium G1 and Ethanoigenens harbinense B49 was investigated. With an initial Avicel concentration of 5 g l−l, the sequential co-culture with G1 and strain Ethanoigenens harbinense B49 produced H2 yield approximately 2.97 mmol H2 g−1 cellulose for the co-culture system. 相似文献
3.
Emilio Maruyama Yoshihisa Hosoi Katsuaki Ishii 《In vitro cellular & developmental biology. Plant》2007,43(1):28-34
Induction of somatic embryogenesis in Pinus armandii var. amamiana, an endemic and endangered species in Japan, was initiated from megagametophytes containing immature zygotic embryos on both
media with and without plant growth regulators. Across nine open-pollinated families initiation frequency ranged from 0 to
20%, with an average of 1.5%. Embryogenic cultures were maintained and proliferated on a medium supplemented with 2,4-dichlorophenoxyacetic
acid (3 μM) and 6-benzylaminopurine (1 μM). Maturation of somatic embryos occurred on medium containing maltose (50 g l−1), activated charcoal (2 g l−1), abscisic acid (100 μM), and polyethylene glycol (100 g l−1). The frequencies of germination and plant conversion of somatic embryos differed among the embryogenic lines from 16 to
51% and from 12 to 40%, respectively. Growth of regenerated somatic plants has been monitored in the field. 相似文献
4.
Maneewan Suwansaard Wanna Choorit Jill H. Zeilstra-Ryalls Poonsuk Prasertsan 《Biotechnology letters》2010,32(11):1667-1671
Rhodopseudomonas palustris TN1 was isolated from Songkhla Lake, Thailand. It phototrophically generates H2 from the predominant volatile fatty acids (VFAs) produced from microbial dark-fermentations of palm oil milling effluent;
yields from 20 mM butyrate, acetate and propionate were 4.7, 2.5, and 1.7 mol H2 mol VFA−1 with light efficiencies of 1.8, 1, and 0.2%, respectively. Optimum conditions were pH 7 and 3000 lux, although production
was reduced by only 33% at 1000 lux. CO2 evolution never exceeded 9 mmol mol VFA−1. 相似文献
5.
Pseudomonas aeruginosa phosphorylcholine phosphatase (PchP) catalyzes the hydrolysis of phosphorylcholine, which is produced by the action of hemolytic
phospholipase C on phosphatidylcholine or sphyngomielin, to generate choline and inorganic phosphate. Among divalent cations,
its activity is dependent on Mg2+ or Zn2+. Mg2+ produced identical activation at pH 5.0 and 7.4, but Zn2+ was an activator at pH 5.0 and became an inhibitor at pH 7.4. At this higher pH, very low concentrations of Zn2+ inhibited enzymatic activity even in the presence of saturating Mg2+ concentrations. Considering experimental and theoretical physicochemical calculations performed by different authors, we
conclude that at pH 5.0, Mg2+ and Zn2+ are hexacoordinated in an octahedral arrangement in the PchP active site. At pH 7.4, Mg2+ conserves the octahedral coordination maintaining enzymatic activity. The inhibition produced by Zn2+ at 7.4 is interpreted as a change from octahedral to tetrahedral coordination geometry which is produced by hydrolysis of
the
[ \textZn 2+ \textL 2 - 1 \textL 20 ( \textH 2 \textO ) 2 ] \left[ {{\text{Zn}}^{ 2+ } {\text{L}}_{ 2}^{ - 1} {\text{L}}_{ 2}^{0} \left( {{\text{H}}_{ 2} {\text{O}}} \right)_{ 2} } \right] complex. 相似文献
6.
Haoran An Hui Zhou Ying Huang Guohong Wang Chunguang Luan Jing Mou Yunbo Luo Yanling Hao 《Molecular biotechnology》2010,45(2):155-160
Lactic acid bacteria (LAB) are generally sensitive to hydrogen peroxide (H2O2), Lactobacillus sakei YSI8 is one of the very few LAB strains able to degrade H2O2 through the action of a heme-dependent catalase. Lactobacillus rhamnosus strains are very important probiotic starter cultures in meat product fermentation, but they are deficient in catalase. In
this study, the effect of heterologous expression of L. sakei catalase gene katA in L. rhamnosus on its oxidative stress resistance was tested. The recombinant L. rhamnosus AS 1.2466 was able to decompose H2O2 and the catalase activity reached 2.85 μmol H2O2/min/108 c.f.u. Furthermore, the expression of the katA gene in L. rhamnosus conferred enhanced oxidative resistance on the host. The survival ratios after short-term H2O2 challenge were increased 600 and 104-fold at exponential and stationary phase, respectively. Further, viable cells were 100-fold higher in long-term aerated cultures.
Simulation experiment demonstrated that both growth and catalase activity of recombinant L. rhamnosus displayed high stability under environmental conditions similar to those encountered during sausage fermentation. 相似文献
7.
A general in vitro cloning system was established for four Helleborus species: H. argutifolius, H. foetidus, H. niger and H. orientalis. The plant material was introduced in vitro from axillary buds. A Murashige and Skoog (MS)—based medium (Murashige and Skoog
1962) was used supplemented with 2% (w/v) sucrose, 2-isopentenyladenine (2-iP) and 6-benzylaminopurine (BA). Multiplication
rates depended on the genotype and varied from 1.3 for H. foetidus till 3.8 for H. niger. The first results showed that the rooting phase could be done ex vitro. Rooting was induced by a drench for one week in
a solution of indole-3-butyric acid (IBA -3 mg l−1) and 1-naphthaleneacetic acid (NAA-1 mg l−1) at 5°C. 相似文献
8.
Raif Musa-Aziz Lihong Jiang Li-Ming Chen Kevin L. Behar Walter F. Boron 《The Journal of membrane biology》2009,228(1):15-31
Others have shown that exposing oocytes to high levels of (10–20 mM) causes a paradoxical fall in intracellular pH (pHi), whereas low levels (e.g., 0.5 mM) cause little pHi change. Here we monitored pHi and extracellular surface pH (pHS) while exposing oocytes to 5 or 0.5 mM NH3/NH4
+. We confirm that 5 mM causes a paradoxical pHi fall (−ΔpHi ≅ 0.2), but also observe an abrupt pHS fall (−ΔpHS ≅ 0.2)—indicative of NH3 influx—followed by a slow decay. Reducing [NH3/NH4
+] to 0.5 mM minimizes pHi changes but maintains pHS changes at a reduced magnitude. Expressing AmtB (bacterial Rh homologue) exaggerates −ΔpHS at both levels. During removal of 0.5 or 5 mM NH3/NH4
+, failure of pHS to markedly overshoot bulk extracellular pH implies little NH3 efflux and, thus, little free cytosolic NH3/NH4
+. A new analysis of the effects of NH3 vs. NH4
+ fluxes on pHS and pHi indicates that (a) NH3 rather than NH4
+ fluxes dominate pHi and pHS changes and (b) oocytes dispose of most incoming NH3. NMR studies of oocytes exposed to 15N-labeled show no significant formation of glutamine but substantial accumulation in what is likely an acid intracellular compartment. In conclusion, parallel measurements of pHi and pHS demonstrate that NH3 flows across the plasma membrane and provide new insights into how a protein molecule in the plasma membrane—AmtB—enhances
the flux of a gas across a biological membrane.
相似文献
Walter F. Boron (Corresponding author)Email: |
9.
l-arabinose isomerase (EC5.3.1.4. AI) mediates the isomerization of d-galactose into d-tagatose as well as the conversion of l-arabinose into l-ribulose. The AI from Lactobacillus plantarum SK-2 was purified to an apparent homogeneity giving a single band on SDS–PAGE with a molecular mass of 59.6 kDa. Optimum
activity was observed at 50°C and pH 7.0. The enzyme was stable at 50°C for 2 h and held between pH 4.5 and 8.5 for 1 h. AI
activity was stimulated by Mn2+, Fe3+, Fe2+, Ca2+ and inhibited by Cu2+, Ag+, Hg2+, Pb2+. d-galactose and l-arabinose as substrates were isomerized with high activity. l-arabitol was the strongest competitive inhibitor of AI. The apparent Michaelis–Menten constant (K
m), for galactose, was 119 mM. The first ten N-terminal amino acids of the enzyme were determined as MLSVPDYEFW, which is identical to L. plantarum (Q88S84). Using the purified AI, 390 mg tagatose could be converted from 1,000 mg galactose in 96 h, and this production
corresponds to a 39% equilibrium. 相似文献
10.
ShuJuan Lai Yun Zhang ShuWen Liu Yong Liang XiuLing Shang Xin Chai TingYi Wen 《中国科学:生命科学英文版》2012,55(4):283-290
l-Serine plays a critical role as a building block for cell growth, and thus it is difficult to achieve the direct fermentation
of l-serine from glucose. In this study, Corynebacterium glutamicum ATCC 13032 was engineered de novo by blocking and attenuating the conversion of l-serine to pyruvate and glycine, releasing the feedback inhibition by l-serine to 3-phosphoglycerate dehydrogenase (PGDH), in combination with the co-expression of 3-phosphoglycerate kinase (PGK)
and feedback-resistant PGDH (PGDHr). The resulting strain, SER-8, exhibited a lower specific growth rate and significant differences in l-serine levels from Phase I to Phase V as determined for fed-batch fermentation. The intracellular l-serine pool reached (14.22±1.41) μmol gCDM
−1, which was higher than glycine pool, contrary to fermentation with the wild-type strain. Furthermore, metabolic flux analysis
demonstrated that the over-expression of PGK directed the flux of the pentose phosphate pathway (PPP) towards the glycolysis
pathway (EMP), and the expression of PGDHr improved the l-serine biosynthesis pathway. In addition, the flux from l-serine to glycine dropped by 24%, indicating that the deletion of the activator GlyR resulted in down-regulation of serine
hydroxymethyltransferase (SHMT) expression. Taken together, our findings imply that l-serine pool management is fundamental for sustaining the viability of C. glutamicum, and improvement of C1 units generation by introducing the glycine cleavage system (GCV) to degrade the excessive glycine is a promising target
for l-serine production in C. glutamicum. 相似文献
11.
E. A. Burenina 《Journal of Evolutionary Biochemistry and Physiology》2010,46(2):153-162
There have been studied the activity and properties of fructose bisphosphatase (FBPase) of Bothriocephalus scorpii parasitizing in pyloric appendages of the goby Myoxocephalus brandti. All subcellular fractions of B. scorpii (12 g/cytosol, 105 g/cytosol, mitochondria, and microsomes) have the FBPase activity. The enzyme has a high affinity to substrate
and needs the presence of bivalent cations (Mg2+ or Mn2+). AMP inhibits the enzyme significantly. Action of various effectors has been studied. The monovalent (Na+, K+, Li+, NH4
+) and bivalent cations (Zn2+ and Cu2+) inhibit the enzyme activity. 相似文献
12.
Anber Hassanein Latifa Hamama Karine Loridon Noëlle Dorion 《Plant cell reports》2009,28(10):1521-1530
Direct genetic transformation of mesophyll protoplasts was studied in Pelargonium × hortorum. Calcein and green-fluorescent protein (GFP) gene were used to set up the process. Electroporation (three electric pulses
from a 33-μF capacitor in a 250-V cm−1 electric field) was more efficient than PEG 6000 for membrane permeation, protoplast survival and cell division. Transient
expression of GFP was detected in 33–36% of electroporated protoplasts after 2 days and further in colonies. A protoplast
suspension conductivity of >1,500 μS cm−1 allowed high colony formation and plant regeneration. Stable transformation was obtained using the plasmid FAJ3000 containing
uidA and nptII genes. When selection (50 mg l−1 kanamycin) was achieved 6 weeks after electroporation, regenerated shoots were able to grow and root on 100 mg l−1 kanamycin. The maximum transformation efficiency was 4.5%, based on the number of colonies producing kanamycin-resistant
rooted plants or 0.7% based on the number of cultured protoplasts. Polymerase chain reaction (PCR) analysis on in vitro micropropagated
plants showed that 18 clones out of 20 contained the nptII gene, while the uidA gene was absent. These results were confirmed after PCR analyses of five glasshouse-acclimatized clones. 相似文献
13.
Little information is known on what the magnitude of nitrogen (N) processed by ectomycorrhizal (ECM) fungal species in the
field. In a common garden experiment performed in a northern California oak woodland, we investigated transfer of nitrogen
applied as 15NH4 or 15NO3 from leaves to ectomycorrhizal roots of three oak species, Quercus agrifolia, Q. douglasii, and Q. garryana. Oak seedlings formed five common ectomycorrhizal morphotypes on root tips. Mycorrhizal tips were more enriched in 15N than fine roots. N transfer was greater to the less common morphotypes than to the more common types. 15N transfer from leaves to roots was greater when , not , was supplied. 15N transfer to roots was greater in seedlings of Q. agrifolia than in Q. douglasii and Q. garryana. Differential N transfer to ectomycorrhizal root tips suggests that ectomycorrhizal morphotypes can influence flows of N
from leaves to roots and that mycorrhizal diversity may influence the total N requirement of plants. 相似文献
14.
D. V. Fedorov S. V. Kovaltzova V. T. Peshekhonov V. G. Korolev 《Russian Journal of Genetics》2010,46(6):659-665
The yeast genes IXR1 and HMO1 encode proteins belonging to the family of chromatin nonhistone proteins, which are able to recognize and bind to irregular
DNA structures. The full deletion of gene IXR1 leads to an increase in cell resistance to the lethal action of UV light, γ-rays, and MMS, increases spontaneous mutagenesis and significantlly decreases the level of UV-induced mutations. It was earlier
demonstrated in our works that the hmo1 mutation renders cells sensitive to the lethal action of cisplatin and virtually does not affect the sensitivity to UV light.
Characteristically, the rates of spontaneous and UV-induced mutagenesis in the mutant are increased. Epistatic analysis of
the double mutation hmo1 ixr1 demonstrated that the interaction of these genes in relation to the lethal effect of cisplatin and UV light, as well as UV-induced
mutagenesis, is additive. This suggests that the products of genes HMO1 and IXR1 participate in different repair pathways. The ixr1 mutation significantly increases the rate of spontaneous mutagenesis mediated by replication errors, whereas mutation hmo1 increases the rate of repair mutagenesis. In wild-type cells, the level of spontaneous mutagenesis was nearly one order of
magnitude lower than that obtained in cells of the double mutant. Consequently, the combined activity of the Hmo1 and the
Ixr1 proteins provides efficient correction of both repair and replication errors. 相似文献
15.
I. M. Andreev N. V. Bulushova I. A. Zalunin G. G. Chestukhina 《Biochemistry. Biokhimii?a》2009,74(10):1096-1103
Effects of entomocidal Cry-type proteins, δ-endotoxins Cry3A and Cry11A produced by Bacillus thuringiensis, on ion permeability of the apical membranes of intestinal epithelium from Tenebrio molitor larvae midgut were studied. Using potential-sensitive dyes safranine O and oxonol VI and δpH indicator acridine orange, it
was shown that placing brush border membrane vesicles (BBMV) (loaded with Mg2+ during their preparation) into a salt-free buffer medium resulted in spontaneous generation of transmembrane electric potential
on the vesicular membrane (negative inside the vesicles) accompanied by acidification of the aqueous phase inside the vesicles.
The generation of transmembrane ion gradients on the vesicular membrane was a result of an electrogenic efflux of Mg2+ from the vesicles as shown by abolishing of the membrane potential by such agents as MgSO4 or CaCl2 in centimolar concentrations, a highly lipophilic cation tetraphenylphosphonium, and some blockers of cell membrane Ca2+-channels in submillimolar concentrations. A passive generation of membrane potential on the vesicular membrane (but positive
inside the vesicles) was also observed upon addition of centimolar concentrations of K2SO4. Addition of δ-endotoxins Cry3A and Cry11A to the vesicle suspension in a salt-free buffer medium or in the same medium supplemented
with centimolar concentrations of K2SO4 exerted a pronounced hyperpolarization of the vesicular membrane. This hyperpolarization was sensitive to the same agents,
which abolished the membrane potential generation in the absence of δ-endotoxin. It is concluded that Cry proteins induced
in BBMV from T. molitor opening pores or ion channels, which were considerably more permeable for alkaline- and alkaline-earth metal cations than
for the accompanying anions. 相似文献
16.
Mature seed-derived embryogenic calli of indica rice (Oryza sativa L. cv. PAU201) were induced on semisolid Murashige and Skoog medium supplemented with 2.5 mg dm−3 2,4-dichlorophenoxyacetic acid + 0.5 mg dm−3 kinetin + 560 mg dm−3 proline + 30 g dm−3 sucrose + 8 g dm−3 agar. Using OsglyII gene, out of 3180 calli bombarded, 32 plants were regenerated on medium containing hygromycin (30 mg dm−3). Histochemical GUS assay of the hygromycin selected calli revealed GUS expression in 50 % calli. Among the regenerants,
46.87 % were GUS positive. PCR analysis confirmed the presence of the transgene of 1 kb in 60 % of independent plants. Further,
these plants have been grown to maturity in glasshouse. In vitro screening for salt tolerance showed increase in fresh mass of OsglyII putative transgenic calli (185.4 mg) as compared to control calli (84.2 mg) on 90 mM NaCl after 15 d. When exposed to 150
mM NaCl, OsglyII putative transgenic plantlets showed normal growth while the non-transgenic control plantlets turned yellow and finally did
not survive. 相似文献
17.
18.
Temperature is a principal environmental factor that directly affects the growth and timing of appearance for crop leaves.
To estimate the leaf number and leaf area of ‘Seoul’ pak-choi plants (Brassica campestns ssp.chinensis), we applied the concept of growing degree-days GDD=(Tavg-Tbase) × days, where Tavg, Tbase and days were the daily average air temperature, base temperature, and days after transplanting, respectively. Leaves that
were beginning to unfold with a leaf area ≥1 cm2 were counted every 2 to 3 d. Linear relationships were found between leaf number and days after transplanting as well as
between leaf number and GDD. The rate of appearance and the number of leaves per GDD were 0.542 leaves d-1 and 0.051 leaves oC-1 d-1, respectively. In contrast, the relationship was non-linear between leaf number and leaf area, with the latter being calculated
as [(128.9+11.6×GDD-0.03×GDD2)/1+(0.051×GDD+3.5) /13.7)-3.9] (cm2oC1 d-1). Using model validation, we found that the estimated leaf number and leaf area showed strong agreement with measured values.
our results demonstrate the usefulness of modeling to estimate total leaf area and growth from hydroponically grown pak-choi
plants. 相似文献
19.
Toxic at low concentrations, phenol is one of the most common organic pollutants in air and water. In this work, phenol biodegradation
was studied in extreme conditions (80°C, pH = 3.2) in a 2.7 l bioreactor with the thermoacidophilic archaeon Sulfolobus solfataricus 98/2. The strain was first acclimatized to phenol on a mixture of glucose (2000 mg l−1) and phenol (94 mg l−1) at a constant dissolved oxygen concentration of 1.5 mg l−1. After a short lag-phase, only glucose was consumed. Phenol degradation then began while glucose was still present in the
reactor. When glucose was exhausted, phenol was used for respiration and then for biomass build-up. After several batch runs
(phenol < 365 mg l−1), specific growth rate (μX) was 0.034 ± 0.001 h−1, specific phenol degradation rate (qP) was 57.5 ± 2 mg g−1 h−1, biomass yield (YX/P) was 52.2 ± 1.1 g mol−1, and oxygen yield factor
( \textY\textX/\textO 2 ) \left( {{\text{Y}}_{{{\text{X}}/{\text{O}}_{ 2} }} } \right) was 9.2 ± 0.2 g mol−1. A carbon recovery close to 100% suggested that phenol was exclusively transformed into biomass (35%) and CO2 (65%). Molar phenol oxidation constant
( \textY\textO 2 /\textP ) \left( {{\text{Y}}_{{{\text{O}}_{ 2} /{\text{P}}}} } \right) was calculated from stoichiometry of phenol oxidation and introducing experimental biomass and CO2 conversion yields on phenol, leading to values varying between 4.78 and 5.22 mol mol−1. Respiratory quotient was about 0.84 mol mol−1, very close to theoretical value (0.87 mol mol−1). Carbon dioxide production, oxygen demand and redox potential, monitored on-line, were good indicators of growth, substrate
consumption and exhaustion, and can therefore be usefully employed for industrial phenol bioremediation in extreme environments. 相似文献
20.
Wen Liu Xuesen Chen Guanjun Liu Qing Liang Tianming He Jianrong Feng 《Plant Cell, Tissue and Organ Culture》2007,88(3):289-299
Embryo rescue technique was used successfully to produce interspecific hybrids by crossing peach (P. persica) as a female parent with apricot (P. armeniaca) and plum (P. salicica). In those crosses that had ‘Yuhualu’ or ‘Zhonghuashoutao’ as female parents, hybrid embryos aborted from the 7th or 8th
week after pollination mainly due to post-pollination incompatibility. An embryo rescue protocol was established to rescue
such embryos and recover hybrid plants. Modified half-strength MS medium containing 4 mg l−1 6-BA and 0.5 mg l−1 IBA produced up to 90% germination in the embryos. Modified MS medium with 1.0 mg l−1 6-BA and 1.0 mg l−1 IBA gave the highest bud induction and multiplication whereas modified MS medium containing 0.5 mg l−1 IAA and 0.2 mg l−1 NAA gave the best rooting percentage. All the hybrids obtained using this embryo rescue technique were verified using simple
sequence repeat (SSR) markers. A series of pollen treatments were carried out to partially overcome pre-pollination incompatibility,
and it was found accidentally that pollen treatment with electrostatic field not only improved pollen germination but also
increased the multiplication coefficient of embryo-induced shoots. 相似文献