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1.
The faviid corals, Favites chinensis and Goniastrea aspera are widely distributed in the Indo-Pacific region. Both corals are hermaphroditic broadcast spawners, but G. aspera is also known to brood planula larvae in Okinawa. This study investigated the temporal settlement patterns of planula larvae of the scleractinian corals F. chinensis and G. aspera that developed from spawned gametes, and planula release and settlement of brooded larvae of G. aspera from Okinawa, Japan. Some of the broadcast-spawned larvae of F. chinensis and G. aspera had very short pre-competency periods of 1–2 and 2–3 days after spawning, and relatively long maximum settlement-competency periods of 56–63 and 63–70 days after spawning, respectively. These pre-competency periods are among the shortest reported for larvae of broadcast spawning coral species, and appear to be negatively correlated with seawater temperature. F. chinensis larvae tended to settle rapidly with 34–39% of larvae settling in the first week after spawning, while broadcast-spawned G. aspera larvae had a slower settlement pattern with 11–15% of larvae settling in the first week after spawning. Brooded larvae of G. aspera settled more rapidly, with settlement rates of 27–31% within the first 24 h and 45–65% within the first week after the start of the experiment. The production of planula larvae with rapid settlement capabilities may enable F. chinensis and G. aspera to establish and maintain populations in shallow reef sites at Okinawa. The release of the brooded planulae for up to 2 months may explain why G. aspera is locally more dominant on shallow reefs in Okinawa than F. chinensis. On a broader scale, the longer settlement competency periods of some of the broadcast-spawned larvae of these species increase their potential for longer-distance dispersal and may partly explain the wide biogeographic distribution of these species in the Indo-Pacific region. 相似文献
2.
The location of the endogenous inhibitor protein ( IF1) in the rotor/stator architecture of the bovine mitochondrial ATP synthase was studied by reversible cross-linking with dithiobis(succinimidylpropionate) in soluble F1I and intact F1F0I complexes of submitochondrial particles. Reducing two-dimensional electrophoresis, Western blotting, and fluorescent cysteine labeling showed formation of –IF1, IF1–IF1, –IF1, and –IF1 cross-linkages in soluble F1I and in native F1F0I complexes. Cross-linking blocked the release of IF1 from its inhibitory site and therefore the activation of F1I and F1F0I complexes in a dithiothreitol-sensitive process. These results show that the endogenous IF1 is at a distance 12 Å,to and subunits of the central rotor of the native mitochondrial ATP synthase. This finding strongly suggests that, without excluding the classical assumption that IF1 inhibits conformational changes of the catalytic subunits, the inhibitory mechanism of IF1 may involve the interference with rotation of the central stalk. 相似文献
3.
Charles M. Schron 《The Journal of membrane biology》1991,120(2):192-200
Summary In jejunal brush-border membrane vesicles, an outwardly directed OH– gradient (in>out) stimulates DIDS-sensitive, saturable folate (F) uptake (Schron, C.M. 1985.J. Clin. Invest.
76:2030–2033), suggesting carrier-mediated folate: OH– exchange (or phenomenologically indistinguishable H+: folate cotransport). In the present study, the precise role of pH in the transport process was elucidated by examining F uptake at varying pH. For pH gradients of identical magnitude, F uptake (0.1 M) was greater at lower (pHint/pHext: 5.5/4.5) compared with higher (6.5/5.5) pH ranges. In the absence of a pH gradient, internal Ftrans stimulated DIDS-sensitive3H-folate uptake only at pH6.0. Since stepwise increments ininternal pH (4.57.5; pHext=4.5) stimulated F uptake, an inhibitory effect of higherinternal pH was excluded. In contrast, with increasing external pH (4.356.5; pHint=7.8), a 50-fold decrement in F uptake was observed (H+
K
m
=12.8±1.2 M). Hill plots of these data suggest involvement of at least one H+ (OH–) at low pH (monovalent F– predominates) and at least 2 H+ (OH–) at high pH (divalent F–2 predominates). Since an inside-negative electrical potential did not affect F uptake at either pHext 4.55 or 5.8, transport of F– and F–2 is electroneutral. Kinetic parameters for F– and F–2 were calculated from uptake data at pHext 4.55 and 5.0. Comparison of predictedvs. experimentally determined kinetic parameters at pHext5.8 (K
m
=1.33vs. 1.70 M;V
max=123.8vs. 58.0 pmol/mg prot min) suggest that increasing external pH lowers theV
max, but does not affect theK
m
for carrier-mediated F transport. These data are consistent with similarK
i
'
s for sulfasalazine (competitive inhibitor) at pHext 5.35 and 5.8 (64.7 and 58.5 M, respectively). In summary, the jejunal F carrier mediates electroneutral transport of mono- and divalent F and is sensitive to external pH with a H+
K
m
(or OH– lC50) corresponding to pH 4.89. External pH effects theV
max, but not theK
m
for carriermediated F uptake suggesting a reaction mechanism involving a ternary complex between the outward-facing conformation of the carrier and the transported ions (F and either OH– or H+),rather than competitive binding that is mutually exclusive. 相似文献
4.
Rhizobium trifolii, R. leguminosarum, andR. hedysarum, grownex planta under anoxic conditions in a chemically defined medium, evolve N2O from NO3
–, NO2
–, and (NH4)2NO3. The amount of nitrous oxide formed after 96 hours is about 0.2M×mg–1 cells d.w. Large availability of organic matter enhances the production of N2O from nitrate by free-livingR. trifolii in peat/sand mixtures. Denitrification of the above species andR. meliloti was detected also in planta. Nitrous oxide production increases almost linearly from 10–45M×mg–1 nodules d.w. when nitrogen-fixing plants are exposed to increasing concentrations of nitrate (1–12M). 相似文献
5.
L. Matsson 《Journal of biological physics》2002,28(4):673-699
A nonstationary interaction, that controls DNA replication and the cell cycle, is derived from a manybody physics model in a chemically open T cell. The model predicts a long range force F()=-(/2) (1-)(2-) between the pre-replication complexes (pre-RCs) bound by DNA, =/N being the relative displacement of preRCs, the number of pre-RCs, N the threshold for initiation, and the compressibility modulus in thelattice of pre-RCs which behaves like an elastically braced string. Initiation of DNA replication is induced by a switch of sign of F(), from attraction (-)and assembly in the G
1 phase (0 < < N), to repulsion (+) and partialdisassembly in the S phase (N < < 2N), with release of licensing factors from the pre-RCs, thus explaining prevention of re-replication. Replication is terminated by a switch of sign of F at = 2N, when all primed replicons are duplicated once, and F(0)=0 corresponds to a resting cell in absence of driving force at = 0. The switch of sign of force at = N also explains the dynamic instability in growing microtubules (MTs), as well as switch in the interleukin-2 (IL2) interaction with its receptor in late G
1, at the restriction point. Shape, slope and scale of the response curves derived agree well with experimental data from dividing T cells and polymerizing MTs, the variable length of which is due to anonlinear dependence of the growth amplitude on the initial concentrations of tubulin dimers and guanosine-tri-phosphate (GTP). 相似文献
6.
Vanna Chigorno Marina Pitto Gloria Cardace Domenico Acquotti Günther Kirschner Sandro Sonnino Riccardo Ghidoni Guido Tettamanti 《Glycoconjugate journal》1985,2(3-4):279-291
The preparation of a GM1-ganglioside (GM1) [14C]-labelled in the sialic acid residue is reported. This can be obtained by re-N-acetylation in the presence of [1-14C]-acetic anhydride, of a GM1 derivative de-N-acetylated specifically on the sialic acid residue by alkaline hydrolysis of GM1 with tetramethylammonium hydroxide. The radiolabelled GM1 is utilized to investigate the binding properties and the mode of interaction of GM1 with cultured fibroblasts. Three different forms of association (one serum-removable, one trypsin-removable and one trypsin-stable) have been recognized to occur in a way that depended on cell culture conditions (presence or absence of fetal calf serum), ganglioside concentration (from, 5×10–9 M to 10–4 M) and incubation time (up to 24 h). Some metabolic modifications of GM1 during the period of high cell viability were also investigated.Abbreviations GM1
GM1-ganglioside, II3NeuAc-GgOse4Cer
- FCS
fetal calf serum
- EMEM
Eaglés Minimum Essential Medium with Earlés salts
- PBS
Dulbecco phosphate buffered saline without calcium and magnesium 相似文献
7.
Leif Matsson 《Journal of biological physics》2001,27(4):329-359
A nonstationary interaction that controlsDNA replication and the cell cycle isderived from many-body physics in achemically open T cell. The model predictsa long range force F() =– (/2) (1 – )(2 – )between thepre-replication complexes (pre-RCs) boundby the origins in DNA, = /N being the relativedisplacement of pre-RCs, the number of pre-RCs, Nthe number of replicons to be replicated,and the compressibilitymodulus in the lattice of pre-RCs whichbehaves dynamically like an elasticallybraced string. Initiation of DNAreplication is induced at the threshold = N by a switch ofsign of F'(), fromattraction (–) and assembly in the G
1 phase (0<<N), to repulsion (+) and partialdisassembly in the S phase (N< < 2N), withrelease of licensing factors from pre-RCs,thus explaining prevention ofre-replication. Replication is terminatedby a switch of sign of force at = 2N, from repulsion inS phase back to attraction in G
2, when all primed replicons havebeen duplicated once. F(0) = 0corresponds to a resting cell in theabsence of driving force at = 0. The model thus ensures that the DNAcontent in G
2 cells is exactlytwice that of G
1 cells. The switch of interaction at the R-point, at which N pre-RCs have been assembled, starts the release of Rb protein thus also explaining the shift in the Rb phosphorylation from mitogen-dependent cyclinD to mitogen-independent cyclin E.Shape,slope and scale of the response curvesderived agree well with experimental datafrom dividing T cells and polymerising MTs,the variable length of which is due to anonlinear dependence of the growthamplitude on the initial concentrations oftubulin dimers and guanosine-tri-phosphate(GTP). The model also explains the dynamic instabilityin growing MTs. 相似文献
8.
Marie Hugosson Ghasem Nurani Elzbieta Glaser Lars-Gunnar Franzén 《Plant molecular biology》1995,28(3):525-535
It has previously been shown that presequences of nuclear-encoded chloroplast proteins from the green alga Chlamydomonas reinhardtii contain a region that may form an amphiphilic -helix, a structure characteristic of mitochondrial presequences. We have tested two precursors of chloroplast proteins (the PsaF and PsaK photosystem I subunits) from C. reinhardtii for the ability to be imported into spinach leaf mitochondria in vitro. Both precursors bound to spinach mitochondria. The PsaF protein was converted into a protease-protected form with high efficiency in a membrane potential-dependent manner, indicating that the protein had been imported, whereas the PsaK protein was not protease protected. The protease protection of PsaF was not inhibited by a synthetic peptide derived from the presequence of the N. plumbaginifolia mitochondrial F1 subunit. Furthermore, if the presequence of PsaF was truncated or deleted by in vitro mutagenesis, the protein was still protease-protected with approximately the same efficiency as the full-length precursor. These results indicate that PsaF can be imported by spinach mitochondria in a presequence-independent manner. However, even in the absence of the presequence, this process was membrane potential-dependent. Interestingly, the presequence-truncated PsaF proteins were also protease-protected upon incubation with C. reinhardtii chloroplasts. Our results indicate that the C. reinhardtii chloroplast PsaF protein has peculiar properties and may be imported not only into chloroplasts but also into higher-plant mitochondria. This finding indicates that additional control mechanisms in the cytosol that are independent of the presequence are required to achieve sorting between chloroplasts and mitochondria in vivo.Abbreviations cTP
chloroplast transit peptide
- mTP
mitochondrial targeting peptide
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
- pF1(1,25)
a synthetic peptide derived from the first 25 residues of the Nicotiana plumbaginifolia mitochondrial ATP synthase F1 subunit
- PsaF(2–30) and PsaF(2–61)
mutant proteins lacking regions corresponding to residues 2–30 and 2–61 in the PsaF precursor protein, respectively 相似文献
9.
S. Rospert J. Breitung K. Ma B. Schwörer C. Zirngibl R. K. Thauer D. Linder R. Huber K. O. Stetter 《Archives of microbiology》1991,156(1):49-55
Methanopyrus kandleri belongs to a novel group of abyssal methanogenic archaebacteria that can grow at 110°C on H2 and CO2 and that shows no close phylogenetic relationship to any methanogen known so far. Methyl-coenzyme M reductase, the enzyme catalyzing the methane forming step in the energy metabolism of methanogens, was purified from this hyperthermophile. The yellow protein with an absorption maximum at 425 nm was found to be similar to the methyl-coenzyme M reductase from other methanogenic bacteria in that it was composed each of two -, - and -subunits and that it contained the nickel porphinoid coenzyme F430 as prosthetic group. The purified reductase was inactive. The N-terminal amino acid sequence of the -subunit was determined. A comparison with the N-terminal sequences of the -subunit of methyl-coenzyme M reductases from other methanogenic bacteria revealed a high degree of similarity.Besides methyl-coenzyme M reductase cell extracts of M. kandleri were shown to contain the following enzyme activities involved in methanogenesis from CO2 (apparent Vmax at 65°C): formylmethanofuran dehydrogenase, 0.3 U/mg protein; formyl-methanofuran: tetrahydromethanopterin formyltransferase, 13 U/mg; N
5,N10-methenyltetrahydromethanopterin cyclohydrolase, 14 U/mg; N
5,N10-methylenetetrahydromethanopterin dehydrogenase (H2-forming), 33 U/mg; N
5,N10-methylenetetrahydromethanopterin reductase (coenzyme F420 dependent), 4 U/mg; heterodisulfide reductase, 2 U/mg; coenzyme F420-reducing hydrogenase, 0.01 U/mg; and methylviologen-reducing hydrogenase, 2.5 U/mg. Apparent Km values for these enzymes and the effect of salts on their activities were determined.The coenzyme F420 present in M. kandleri was identified as coenzyme F420-2 with 2 -glutamyl residues.Abbreviations H–S-CoM
coenzyme M
- CH3–S-CoM
methylcoenzyme M
- H–S-HTP
7-mercaptoheptanoylthreonine phosphate
- MFR
methanofuran
- CHO-MFR
formyl-MFR
- H4MPT
tetrahydromethanopterin
- CHO–H4MPT
N
5-formyl-H4MPT
- CH=H4MPT+
N
5,N10-methenyl-H4MPT
- CH2=H4MPT
N
5,N10-methylene-H4MPT
- CH3–H4MPT
N
5-methyl-H4MPT
- F420
coenzyme F420
- 1 U=
1 mol/min 相似文献
10.
Internal pressurization and convective gas flow in emergent wetland plants is a function of the water vapour pressure deficit (WPD) and stomatal conductance (G
s) separating the external atmosphere from the internal aerenchyma. We have compared the effects of WPD and G
s under a range of light intensities on static pressures and convective flows in Phragmites australis, Typha orientalis and Baumea articulata. The capacity of the three species to generate flows per unit leaf area differed, being greatest in P. australisand lowest in B. articulata. In all three species, decreasing light intensity from full sunlight (2200 mol m–2 s–1 photosynthetically active photon flux density (PPFD)) to < 200 and < 10 mol m–2 s–1PPFD caused immediate decreases in photosynthetic assimilation, followed by more gradual decreases in transpiration and G
s. However, internal pressures and flows in the two low light intensities remained similar to values recorded in full sunlight. WPD was more significantly related to pressures and flows in P. australis and T. orientalis than G
s. In B. articulata, pressures increased at low G
s values but flow rates were unaffected, as predicted by earlier models describing pore size effects on pressures and flows. The data suggest that emergent macrophytes can maintain significant internal convection even at low light intensities, and this may be beneficial for nocturnal aeration, particularly in arid climates where the atmospheric humidity at night is low. 相似文献
11.
Colin A. Simpfendorfer Justin Chidlow Rory McAuley Philip Unsworth 《Environmental Biology of Fishes》2000,58(3):335-343
Age and growth of the whiskery shark, Furgaleus macki, from southwestern Australia were examined using vertebral ageing and tag-recapture data. The readability of bands on the vertebral centra varied markedly between individuals. Four readers were used to make band counts, with the most experienced reader having the lowest index of average percent error and the highest level of agreement with final counts. Marginal increment analysis indicated that opaque bands form in January. With parturition occurring from August to October, size data suggests that the first band is probably formed 15–17 months after birth. The age at maturity was estimated to be 4.5 years for males, and 6.5 years for females. The oldest male was 10.5 years, and oldest female was 11.5 years. Von Bertalanffy growth parameters for males were L
=121.5cm fork length, K=0.423 year–1, t
0=–0.472 years, were L
=120.7cm fork length, K=0.369 year–1, t
0=–0.544 years for females, and were L
=118.1cm fork length, K=0.420 year–1, t
0=–0.491 years for combined sexes. Data from a tag recapture study were analysed using a maximum likelihood method to verify the estimates of growth parameters from vertebral ageing. Von Bertalanffy growth parameters from the tag recapture study were L
=128.2cm fork length, K=0.288 year–1, t
0=–0.654 years. The two methods of estimating growth parameters produced similar results, with rapid growth until approximately 5 years of age, after which there was little increase in length. 相似文献
12.
The oxidation of cytochromeb
561 by ATP was measured in submitochondrial particles inhibited by antimycin. The redox potential of the bulk (M phase) was controlled by the ratio of fumarate:succinate, and the oxidation of cytochromeb was calculated and expressed as a change in redox potential (E
h) measured in millivolts. The oxidation of cytochromeb
561 is an energy-driven reaction affected only by the component of the proton motive force. The oxidation (measured in millivolts) is a function of the phosphate potential, reaching a maximal value of 40 mV at GATP<–12 kcal/mole. The maximal measured value of ATP-dependent was 100 mV. Thus only a fraction of the membrane potential effects the redox state of cytochromeb
561. In contrast to the ATP-induced oxidation of cytochromeb
561, cytochromeb
566 is in redox equilibrium with fumarate succinate either in the presence or in the absence of ATP. The selective oxidation ofb
561 is explained within the term of theQ cycle as a reflection of on the electron electrochemical potential. The positive electric potential of theC phase causes cytochromeb
566 to act as oxidant with respect to cytochromeb
561. In the presence of antimycin cytochromeb
561 cannot equilibrate with the quinone and undergoes oxidation, while cytochromeb
566 reequilibrates with the quinone and thus regains redox equilibrium with the fumarate succinate redox buffer.Abbreviations used: ETPH, phosphorylating submitochondrial particles; TMPD,N
1
N
1
NN-tetramethyl-p-phenylenediamine; FCCP, carbonylcyanidep-trifluoromethoxyphenylhydrazone; Mes, 2-(N-morpholino) ethanesulfonic acid. 相似文献
13.
Previous work has shown that the maximum fluorescence yield from PS 2 of Synechococcus PCC 7942 occurs when the cells are at the CO2 compensation point. The addition of inorganic carbon (Ci), as CO2 or HCO3
–, causes a lowering of the fluorescence yield due to both photochemical (qp) and non-photochemical (qN) quenching. In this paper, we characterize the qN that is induced by Ci addition to cells grown at high light intensities (500 mol photons m–2 s–1). The Ci-induced qN was considerably greater in these cells than in cells grown at low light intensities (50 mol photons m–2 s–1), when assayed at a white light (WL) intensity of 250 mol photons m–2 s–1. In high-light grown cells we measured qN values as high as 70%, while in low-light grown cells the qN was about 16%. The qN was relieved when cells regained the CO2 compensation point, when cells were illuminated by supplemental far-red light (FRL) absorbed mainly by PS 1, or when cells were illuminated with increased WL intensities. These characteristics indicate that the qN was not a form of energy quenching (qE). Supplemental FRL illumination caused significant enhancement of photosynthetic O2 evolution that could be correlated with the changes in qp and qN. The increases in qp induced by Ci addition represent increases in the effective quantum yield of PS 2 due to increased levels of oxidized QA. The increase in qN induced by Ci represents a decrease in PS 2 activity related to decreases in the potential quantum yield. The lack of diagnostic changes in the 77 K fluorescence emission spectrum argue against qN being related to classical state transitions, in which the decrease in potential quantum yield of PS 2 is due either to a decrease in absorption cross-section or by increased spill-over of excitation energy to PS 1. Both the Ci-induced qp (t
0.5<0.5 s) and qN (t
0.51.6 s) were rapidly relieved by the addition of DCMU. The two time constants give further support for two separate quenching mechanisms. We have thus characterized a novel form of qN in cyanobacteria, not related to state transitions or energy quenching, which is induced by the addition of Ci to cells at the CO2-compensation point.Abbreviations BTP-
1,3-bis[tris(hydroxymethyl)-methylaminopropane]
- Chl-
chlorophyll
- Ci-
inorganic carbon (CO2+HCO3
–+CO3
2–)
- DCMU-
3-(3,4-dichlorophenyl)-, 1-dimethylurea)
- F-
chlorophyll fluorescence measured at any time in the absence of a saturating flash
- Fo-
chlorophyll fluorescence with only the weak modulated measuring beam on
- FM'-
chlorophyll fluorescence during a saturating flash
- FM-
maximum chlorophyll fluorescence, measured in the presence of WL and FRL at the CO2-compensation point or in the presence of DCMU
- FV-
variable fluorescence (= FM'–F0)
- FRL-
supplemental illumination with far red light
- MB-
modulated measuring beam of the PAM fluorometer
- MV-
methyl viologen
- PAM-
pulse amplitude modulation
- PFD-
incident photon flux density
- PS 1, 2-
Photosystems 1 and 2
- QA-
primary electron-accepting plastoquinione of PS 2
- qN-
non-photochemical quenching of chlorophyll fluorescence
- qp-
photochemical quenching of chlorophyll fluorescence; rubisco-ribulose bisphosphate carboxylase/oxygenase
- SF-
saturating flash (600 ms duration)
- WL-
white light illumination 相似文献
14.
The mangrove cricket Apteronemobius asahinai is endemic to mangrove forest floors in China, Southeast Asia and the Ryukyu archipelago (Amamiohsima, Okinawa, Miyako, Ishigaki and Iriomote Islands) of Japan. We developed six polymorphic microsatellite markers for the mangrove cricket from genomic DNA libraries enriched for CA, GA, AAG and ATG motifs. The M13‐tailed primer method was used in the process of screening of amplification and polymorphism of primers. A total of 64 specimens from two populations (one from Okinawa and the other from Iriomote) were genotyped for allelic diversity. The average number of alleles per locus was 4.67 and 6.67 for Okinawa and Iriomote populations, respectively. A significant genetic differentiation was detected between the two populations (pairwise FST 0.2404). These polymorphic microsatellite loci will be useful in ongoing studies of the population genetic structure of the mangrove cricket including several populations in the Ryukyu archipelago. 相似文献
15.
M. Pasternack B. Rydqvist K. Kaila 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1992,170(4):521-524
Summary The influence of glutamate on the GABA-activated Cl- conductance was studied in the slowly adapting stretch-receptor neuron and dactylopodite opener muscle fibre of the crayfish (Astacus astacus) using a two-microelectrode and a three-microelectrode voltage clamp, respectively. Glutamate (0.5–1.0 mM) had no effect on the GABA-activated conductance in either preparation. This indicates that the availability of the inhibitory channels for activation of GABA is not influenced by glutamate. The present results are in sharp contrast to those obtained by Franke et al. (J Comp Physiol A 159:591–609, 1986) in experiments on excised membrane patches, which suggested that glutamate is capable of both activating and desensitizing inhibitory postsynaptic channels in the crayfish opener muscle fibre.Abbreviations
GABA
-aminobutyric acid
- GGABA and G
GABA
p
GABA-gated conductance and peak conductance
-
HEPES
N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid
-
I
current
-
SRN
stretch-receptor neuron
- Vm and Vl
membrane voltage in two- and three-microelectrode voltage clamp, respectively 相似文献
16.
The dose dependence of the rate of -induced transpositions and consequent dynamics of the MGE 412pattern after -irradiation were investigated in isogenic line 49 in generations F1, F12, F140, and F170. It was shown that the results on dose dependence of transpositions was very similar with the corresponding results of the classic works by Timofeeff-Ressovsky et al.(1935). It is suggested that the transcribed copies of retrotransposon 412cure -radiation-induced double-strand DNA breaks. The phenomenon of prolongation of MGE transposition induction during early generations after treatment was shown. In this period (F1–F12), the maximum transposition rate ( 2 × 10–2events per MGE copy, per haploid genome, per generation) and the maximum number of heterozygous MGE copies were achieved. In the late generations (F140–F170), the reduced induction level ( 10–3) was established. In the population of effective size N
e= 2000 individuals, this corresponds to the state when 1/4N
e, i.e., when the transposition flow prevails over the MGE copy loss by genetic drift. These data together with some indirect evidence argue for the hypothesis that the spontaneous transposition rate is proportional to the average number of heterozygous MGE copies per diploid genome. 相似文献
17.
Nitrogen fixation in perennial forage legumes in the field 总被引:13,自引:0,他引:13
Nitrogen acquisition is one of the most important factors for plant production, and N contribution from biological N2 fixation can reduce the need for industrial N fertilizers. Perennial forages are widespread in temperate and boreal areas, where much of the agriculture is based on livestock production. Due to the symbiosis with N2-fixing rhizobia, perennial forage legumes have great potential to increase sustainability in such grassland farming systems. The present work is a summary of a large number of studies investigating N2 fixation in three perennial forage legumes primarily relating to ungrazed northern temperate/boreal areas. Reported rates of N2 fixation in above-ground plant tissues were in the range of up to 373 kg N ha–1 year–1 in red clover (Trifolium pratense L.), 545 kg N ha–1 year–1 in white clover (T. repens L.) and 350 kg N ha–1 year–1 in alfalfa (Medicago sativa L.). When grown in mixtures with grasses, these species took a large fraction of their nitrogen from N2 fixation (average around 80%), regardless of management, dry matter yield and location. There was a large variation in N2 fixation data and part of this variation was ascribed to differences in plant production between years. Studies with experiments at more than one site showed that also geographic location was an important source of variation. On the other hand, when all data were plotted against latitude, there was no simple correlation. Climatic conditions seem therefore to give as high N2 fixation per ha and year in northern areas (around 60°N) as in areas with a milder climate (around 40°N). Analyzing whole plants or just above-ground plant parts influenced the estimate of N2 fixation, and most reported values were underestimated since roots were not included. Despite large differences in environmental conditions, such as N fertilization and geographic location, N2 fixation (Nfix; kg N per ha and year) was significantly (P<0.001) correlated to legume dry matter yield (DM; kg per ha and year). Very rough, but nevertheless valuable estimations of Nfix in legume/grass mixtures (roots not considered) are given by Nfix = 0.026DM + 7 for T. pratense, Nfix = 0.031DM + 24 for T. repens, and Nfix = 0.021DM + 17 for M. sativa. 相似文献
18.
We have isolated the F0F1-ATP synthase complex from oligomycin-sensitive mitochondria of the green algaChlamydomonas reinhardtii. A pure and active ATP synthase was obtained by eans of sonication, extraction with dodecyl maltoside and ion exchange and gel permeation chromatography in the presence of glycerol, DTT, ATP and-21. The enzyme consists of 14 subunits as judged by SDS-PAGE. A cDNA clone encoding the ATP synthase subunit has been sequenced. The deduced protein sequence contains a presequence of 45 amino acids which is not present in the mature protein. The mature protein is 58–70% identical to corresponding mitochondrial proteins from other organisms. In contrast to the ATP synthase subunit fromC. reinhardtii (Franzen and Falk, Plant Mol Biol 19 (1992) 771–780), the protein does not have a C-terminal extension. However, the N-terminal domain of the mature protein is 15–18 residues longer than in ATP synthase subunits from other organisms. Southern blot analysis indicates that the protein is encoded by a single-copy gene.Abbreviations DM
dodecyl--D-maltoside
- OSCP
oligomycin sensitivity conferring protein
- PMSF
phenyl-methylsulfonylfluoride
- DTT
dithiothreitol
- EDTA
ethylenediaminotetraacetic disodium salt 相似文献
19.
Horst Onken Kai Graszynski Wolfgang Zeiske 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(3):293-301
Summary Single gill lamellae from posterior gills of Chinese crabs (Eriocheir sinensis) were isolated, separated into halves and mounted in a modified Ussing chamber. Area-related short-circuit current (Isc) and conductance (Gtot) of this preparation were measured. Epithelial cells were impaled with microelectrodes through the basolateral membrane and cellular potentials (Vi under open- and Vsc under short-circuit conditions) as well as the voltage divider ratios (Fi, Fo) were determined.With NaCl salines on both sides an outside positive PDte (22±2 mV) and an Isc (-64±13 A·cm-2) with a polarity corresponding to an uptake of negative charges (inward negative) were obtained. Trough-like potential profiles were recorded across the preparation under open- as well as short-circuit conditions (Vo=-101±5 mV, external bath as reference; Vi=-78±2 mV, internal bath as reference; Vsc=-80±2 mV, extracellular space as reference). The voltage divider ratios of the external (apical membrane plus cuticle) and internal (basolateral membrane) barrier were Fo=0.92±0.01 and Fi=0.08±0.01, respectively. To investigate a Cl--related contribution to the above parameters, Na+-free solutions in the external bath (basolateral NaCl-saline) were used. Inward negative Isc under these conditions almost completely depended on external Cl-. Elimination of Cl- in the external bath reversed Isc, and Gtot decreased substantially. Concomitantly, Vsc depolarised and Fo increased. Cl--dependent current and conductance showed saturation kinetics with increasing external [Cl-]. Addition of 20 mmol·1-1 thiocyanate to the external bath had similar, although less pronounced, effects as Cl- substitution. Equally, external SITS (1 mmol·1-1) inhibited the current and, concomitantly, Gtot decreased substantially. Addition of 1 mmol·1-1 acetazolamide to, and omission of NaHCO3 from, the basolateral bath resulted in a decrease of Isc while Gtot remained unchanged. The Cl--channel blocker DPC inhibited Isc almost completely when added to the basolateral saline, whereas Gtot decreased moderately; however, Vsc depolarised without significant change of Fi. Ouabain had no influence on Isc and Gtot. Increasing the basolateral [K+] resulted in a decrease in Isc, while Gtot was not affected. At the same time Vsc largely depolarised and Fi decreased. Addition of the K+-channel blocker Ba++ (5 mmol·1-1) to the basolateral solution resulted in a two-step alteration of the transepithelial (Isc, Gtot) and cellular (Vsc, Fi) parameters. The results are discussed with regard to (i) the mechanisms responsible for active transbranchial Cl- uptake, and (ii) the technical improvement of being able to perform transport studies with crab gill preparations in an Ussing chamber.Abbreviations
DMSO
dimethylsulfoxide
-
DPC
diphenylamine-2-carboxylate
-
F
o, i
voltage divider ratio for external (o) and internal (i) barrier, respectively
-
G
Cl
conductance related to the external [Cl-]
-
G
tot
total tissue conductance
-
I
Cl
short-circuit current related to the external [Cl-]
-
I
sc
short-circuit current
-
PD
te
transepithelial potential difference
-
R
ME
resistance of the microelectrode
-
SITS
4-acetamido-4-isothiocyanato-stilbene-2,2-disulfonic acid
-
V
o, i
open-circuit voltage across the external (o) and internal (i) barrier, respectively
-
V
sc
intracellular potential under short-circuit conditions 相似文献
20.
N. K. Patra R. S. Ram S. P. Chauhan A. K. Singh 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1992,84(3-4):299-302
Summary Nearly 400 individuals at two locations and over a number of years were crossed and subsequently scored for selfing versus outcrossing in eight monohybrid populations of opium poppy (Papaver somniferum). Two different marker loci, petal colour (R/r) and capsule size (B/b) were used to determine the male gametes that had effected fertilizations in F2 recessives (rr and bb). The estimates of the outcrossing parameter were found to vary with year, location and for the marker locus used ( range: 0.0988–0.3704). Study of two dihybrid crosses involving the two loci simultaneously, further confirmed that outcrossing at the R/r locus was significantly greater than that at the B/b locus. The nature of the outcrossing was, in general, nonrandom. Selfmg predominated in this species; however, there was a high frequency of natural outcrossing for generating variations in P. somniferum.CIMAP publication No. 1086 相似文献