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1.
Summary Theoretical studies on the optimal numbers of components in mixtures (for example multiclonal varieties or mixtures of lines) have been performed according to phenotypic yield stability (measured by the parameter variance). For each component i, i = 1, 2,..., n, a parameter ui with 0 ui 1 has been introduced reflecting the different survival and yielding ability of the components. For the stochastic analysis the mean of each ui is denoted by u 1 and its variance by i 2 For the character total yield the phenotypic variance V can be explicitly expressed dependent on 1) the number n of components in the mixture, 2) the mean of the i 2 3) the variance of the i 2 4) the ratio and 5) the ratio i 2 /2 where denotes the mean of the u i and u 2 is the variance of the u j. According to the dependence of the phenotypic stability on these factors some conclusions can be easily derived from this V-formula. Furthermore, two different approaches for a calculation of necessary or optimal numbers of components using the phenotypic variance V are discussed: A. Determination of optimal numbers in the sense that a continued increase of the number of components brings about no further significant effect according to stability. B. A reduction of b % of the number of components but nevertheless an unchanged stability can be realized by an increase of the mean of the u i by 1% (with and u 2 assumed to be unchanged). Numerical results on n (from A) and 1 (from B) are given. Computing the coefficient of variation v for the character total yield and solving for the number n of components one obtains an explicit expression for n dependent on v and the factors 2.-5. mentioned above. In the special case of equal variances, i 2 = o 2 for each i, the number n depends on v, x = (0/)2 and y = (u/)2. Detailed numerical results for n = n (v, x, y) are given. For x 1 and y 1 one obtains n = 9, 20 and 79 for v = 0.30, 0.20 and 0.10, respectively while for x 1 and arbitrary y-values the results are n = 11, 24 and 95.This publication is an extended version of a lecture given at the 1984-EUCARPIA meeting (Section Biometrics in Plant Breeding) in Stuttgart-Hohenheim (Federal Republic of Germany)  相似文献   

2.
Summary A simple viscoelastic film model is presented, which predicts a breakdown electric potential having a dependence on the electric pulse length which approximates the available experimental data for the electric breakdown of lipid bilayers and cell membranes (summarized in the reviews of U. Zimmermann and J. Vienken, 1982,J. Membrane Biol. 67:165 and U. Zimmermann, 1982,Biochim. Biophys. Acta 694:227). The basic result is a formula for the time of membrane breakdown (up to the formation of pores): =(/C)/( m 2 0 2 U 4/24Gh 3+T 2/Gh–1), where is a proportionality coefficient approximately equal to ln(h/20),h being the membrane thickness and 0 the amplitude of the initial membrane surface shape fluctuation ( is usually of the order of unity), represents the membrane shear viscosity,G the membranes shear elasticity modules, m the membrane relative permittivity, 0=8.85×10–12 Fm,U the electric potential across the membrane, the membrane surface tension andT the membrane tension. This formula predicts a critical potentialU c ;U c =(24Gh 3/ m 2 0 2 )1/4 (for = andT=0). It is proposed that the time course of the electric field-induced membrane breakdown can be divided into three stages: (i) growth of the membrane surface fluctuations, (ii) molecular rearrangements leading to membrane discontinuities, and (iii) expansion of the pores, resulting in the mechanical breakdown of the membrane.  相似文献   

3.
Clostridium sporogenes MD1 grew rapidly with peptides and amino acids as an energy source at pH 6.7. However, the proton motive force (p) was only –25 mV, and protonophores did not inhibit growth. When extracellular pH was decreased with HCl, the chemical gradient of protons (ZpH) and the electrical membrane potential () increased. The p was –125 mV at pH 4.7, even though growth was not observed. At pH 6.7, glucose addition did not cause an increase in growth rate, but increased to –70 mV. Protein synthesis inhibitors also significantly increased . Non-growing, arginine-energized cells had a of –80 mV at pH 6.7 or pH 4.7, but was not detected if the F1F0 ATPase was inhibited. Arginine-energized cells initiated growth if other amino acids were added at pH 6.7, and and ATP declined. At pH 4.7, ATP production remained high. However, growth could not be initiated, and neither nor the intracellular ATP concentration declined. Based on these results, it appears that C. sporogenes MD1 does not need a large p to grow, and p appears to serve as a mechanism of ATP dissipation or energy spilling.Mandatory disclaimer: Proprietary or brand names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product, and exclusion of others that may be suitable.  相似文献   

4.
Summary Olfactory receptor neurons enzymatically dissociated from channel catfish olfactory epithelium were depolarized transiently following dialysis of IP3 or cAMP (added to the patch pipette) into the cytoplasm. Voltage and current responses to IP3 were blocked by ruthenium red, a blocker of an IP3-gated Ca2+-release channel in sarcoplasmic reticulum. In contrast, the responses to cAMP were not blocked by extracellularly applied ruthenium red, nor by l-cis-diltiazem or amiloride and two of its derivatives. The current elicited by cytoplasmic IP3 in neurons under voltage clamp displayed a voltage dependence different from that of the cAMP response which showed marked outward rectification. A sustained depolarization was caused by increased cytoplasmic IP3 or cAMP when the buffering capacity for Ca2+ of the pipette solution was increased, when extracellular Ca2+ was removed or after addition of 20–200 nm charibdotoxin to the bathing solution, indicating that the repolarization was caused by an increase in [Ca i ] that opened Ca2+-activated K+ channels. The results suggest that different conductances modulated by either IP3 or cAMP are involved in mediating olfactory transduction in catfish olfactory receptor neurons and that Ca2+-activated K+ channels contribute to the termination of the IP3 and cAMP responses.Abbreviations ATP adenosine 5-triphosphate - BAPTA (bis-(o-aminophenoxy)-ethane-N-N-N-N)-tetraacetic acid - cAMP adenosine cyclic 3,5-monophosphate - cGMP guanosine cyclic 3,5-monophosphate - CTX charybdotoxin - DCB 3,4-dichlorobenzamil - EDTA ethylenediaminetetraacetic acid - EGTA ethylenglycol-bis-(b-aminoethyl)-N-N-N-N-tetraacetic acid - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - IP3 inositol-1,4,5-triphosphate - NMDG N-methyl-d-glucamine We would like to thank the Tanabe Seiyaku Co., Ltd., for their gift of l-cis-diltiazem. This work was supported by National Institutes of Health grants DC00566 and BRSG S07RR05825.  相似文献   

5.
Jia  Yinsuo  Gray  V.M. 《Photosynthetica》2003,41(4):605-610
We determined for Vicia faba L the influence of nitrogen uptake and accumulation on the values of photon saturated net photosynthetic rate (P Nmax), quantum yield efficiency (), intercellular CO2 concentration (C i), and carboxylation efficiency (C e). As leaf nitrogen content (NL) increased, the converged onto a maximum asymptotic value of 0.0664±0.0049 mol(CO2) mol(quantum)–1. Also, as NL increased the C i value fell to an asymptotic minimum of 115.80±1.59 mol mol–1, and C e converged onto a maximum asymptotic value of 1.645±0.054 mol(CO2) m–2 s–1 Pa–1 and declined to zero at a NL-intercept equal to 0.596±0.096 g(N) m–2. fell to zero for an NL-intercept of 0.660±0.052 g(N) m–2. As NL increased, the value of P Nmax converged onto a maximum asymptotic value of 33.400±2.563 mol(CO2) m–2 s–1. P N fell to zero for an NL-intercept of 0.710±0.035 g(N) m–2. Under variable daily meteorological conditions the values for NL, specific leaf area (L), root mass fraction (Rf), P Nmax, and remained constant for a given N supply. A monotonic decline in the steady-state value of Rf occurred with increasing N supply. L increased with increasing N supply or with increasing NL.  相似文献   

6.
Synopsis Arsenic persists in Chautauqua Lake, New York waters 13 years after cessation of herbicide (sodium arsenite) application and continues to cycle within the lake. Arsenic concentrations in lake water ranged from 22.4–114.81 g l–1, = 49.0 ag l–1. Well water samples generally contained less than 10 g l–1 arsenic. Arsenic concentrations in lake water exceeded U.S. Public Health Service recommended maximum concentrations (10 g l–1) and many samples exceeded the maximum permissible limit (50 g l–1). Fish accumulated arsenic from water but did not magnify it. Fish to water arsenic ratios ranged from 0.4–41.6. Black crappie (Pomoxis nigromaculatus) contained the highest arsenic concentrations (0.14–2.04 g g–1 ), X = 0.7 g g–1) while perch (Perca flavescens), muskellunge (Esox masquinongy) and largemouth bass (Micropterus salmoides) contained the lowest concentrations (0.02–0.13 g g–1). Arsenic concentrations in fish do not appear to pose a health hazard for human consumers.  相似文献   

7.
This study reports the analysis of K+ channel activity in bovine periaxolemmal-myelin and white matter-derived clathrin-coated vesicles. Channel activity was evaluated by the fusion of membrane vesicles with phospholipid bilayers formed across a patch-clamp pipette. In periaxolemmal myelin spontaneous K+ channels were observed with amplitudes of 25–30, 45–55, and 80–100 pS, all of which exhibited mean open-times of 1–2 msec. The open state probability of the 50 pS channel in periaxolemmal-myelin was increased by 6-methyldihydro-pyran-2-one. Periaxolemmal-myelin K+ channel activity was regulated by Ca2+. Little or no change in activity was observed when Ca2+ was added to thecis side of the bilayer. Addition of 10 M total Ca2+ also resulted in little change in K+ channel activity. However, at 80 M total Ca2+ all K+ channel activity was suppressed along with the activation of a 100 pS Cl channel. The K+ channel activity in periaxolemmal myelin was also regulated through a G-protein. Addition of GTPS to thetrans side of the bilayer resulted in a restriction of activity to the 45–50 pS channel which was present at all holding potentials. Endocytic coated vesicles, form in part through G-protein mediated events; white matter coated vesicles were analyzed for G proteins and for K+ channel activity. These vesicles, which previous studies had shown are derived from periaxolemmal domains, were found to be enriched in the subunits of G0, Gs, and Gi and the low molecular weight G protein,ras. As with periaxolemmal-myelin treated with GTPS, the vesicle membrane exhibited only the 50 pS channel. The channel was active at all holding potentials and had open times of 1–6 msec. Addition of GTPS to the bilayer fused with vesicle membrane appeared to suppress this channel activity at low voltages yet induced a hyperactive state at holding potentials of 45 mV or greater. The vesicle 50 pS K+ channel was also activated by the 6-methyl-dihydropyron-2-one (20 M).Abbreviations CNPase 2–3 cyclic nucleotide phosphohydrolase - EDTA ethylenediamine N,N,N,N-tetraacetic acid - G-protein GTP(guanosine triphosphate) binding protein - GTPS guanosine 5-O-(3-thiotriphosphate) - MAG myelin associated glycoprotein - Na+ K+ ATPase, Na+ and K+ stimulated adenosine triphosphatase - PLP myelin proteolipid protein Special issue dedicated to Dr. Majorie B. Lees.  相似文献   

8.
The structure of theEscherichia coli ATP synthase has been studied by electron microscopy and a model developed in which the and subunits of the F1 part are arranged hexagonally (in top view) alternating with one another and surrounding a central cavity of around 35 Å at its widest point. The and subunits are interdigitated in side view for around 60 Å of the 90 Å length of the molecule. The F1 narrows and has three-fold symmetry at the end furthest from the F0 part. The F1 is linked to F0 by a stalk approximately 45 Å long and 25–30 Å in diameter. The F0 part is mostly buried in the lipid bilayer. The subunit provides a domain that extends into the central cavity of the F1 part. The and subunits are in a different conformation when ATP+Mg2+ are present in catalytic sites than when ATP+EDTA are present. This is consistent with these two small subunits switching conformations as a function of whether or not phosphate is bound to the enzyme at the position of the phosphate of ATP. We suggest that this switching is the key to the coupling of catalytic site events with proton translocation in the F0 part of the complex.  相似文献   

9.
Atriplex gmelini plants were regenerated via organogensis from hypocotyl explants. Callus lines were induced from the hypocotyl explants on Linsmaier and Skoog (LS) medium supplemented with 1 M benzyladenine and 5 M -naphthaleneacetic acid in the dark. Shoots were regenerated from the callus lines on LS medium supplemented with 20 M thidiazuron and 0.1 M -naphthaleneacetic acid under a high-intensity light condition (450 mol m–2 s–1). The regenerated shoots were rooted on LS medium without growth regulators to obtain fully developed plants. We succeeded in transforming Atriplex gmelini from callus lines using Agrobacterium tumefaciens.  相似文献   

10.
Summary By use of well characterized antisera in the peroxidase-antiperoxidase method, we were able to demonstrateMSH andMSH immunoreactive cells and nerve fibres within the nervous system of adults and larvae ofLocusta migratoria and 3-, 5- and 8-day-old adultSarcophaga bullata. In neither of these insect species, any immunoreaction was obtained with a 3MSH-antiserum. Double immuno-histochemical stainings revealed thatMSH-like andMSH-like substances are located in different cells. These cells show no immunoreactivity to a number of antisera against other POMC-derivatives (anti-lipotropin, anti-endorphin, anti-ACTH1–24); thus they appear to containMSH- orMSH-like material in a specific way. The function of the immunologically detected peptides remains to be demonstrated. The distribution of the immunoreactive material suggests that, like in amphibians and other lower vertebrates, the synthesis or release of melanotropins might be under the influence of external stimuli. The present observations support the recently developed concept that even some of the smallest neuropeptides, the melanotropins, have been highly conserved during a long period of evolution.  相似文献   

11.
Summary The surface tension and foaminess of (a) unlimited, (b) substrate limited, and (c) oxygen transfer limited growth media of Hansenula polymorpha were measured using methanol, ethanol or glucose as a substrate.The time dependence of can be described by the Avrami-Überreiter relationship: log (2.3 log V)=n log t+log b, where V = (Oeq/(teq, and O, t and eq are at tM=0, tM=t and tM (equilibrium value).The constants n and b are functions of the fermentation time tF as long as the growth is unlimited but they are constant in the state of limited growth. With glucose substrate, the foaminess can be presented as a definite function of the time, tDG, which is necessary to attain eq. With alcohol as a substrate no definite (tDG) function was found.Symbols b constant in Eq. (1) - n constant in Eq. (1) - S substrate concentration - T temperature - tM time h (measured from the beginning of the determination of the surface tension ) - tF cultivation time h (measured from the time of inoculation) - tDG time (min) necessary to attain the equilibrium surface tension ) - X dry biomass concentration (gl–1) - V (Oeq)/(teq) - VS equilibrium volume of the foam (cm3) - VG volumetric gas flow rate during the estimation of (cm3 s–1) - vvm volumetric gas flow rate with regard to the volume of the medium (min–1) - wSG superficial gas velocity (cm s–1) - m maximum specific growth rate (h–1) - VS/VG foaminess (s) - surface tension, mMm–1 (milli Newton m–1) - O at tM=0 - eq equilibrium surface tension ( at tM) - t at tM=t - HP probes from Hansenula polymorpha cultivation - NLG non limited growth - OTLG oxygen transfer limited growth - SLG substrate limited growth  相似文献   

12.
The rate of CO2- and p-benzoquione-dependent photosynthetic O2 evolution by Anabaena variabilis cells remained unaltered and the rate of O2 uptake observed after switching off the light (endogenous respiration) was enhanced by a factor of 6–8 when the O2 concentration was increased from 200 to 400 M. Photosystem-I-linked O2 uptake and respiration of the cells incubated with ascorbate and N,N,NN-tetramethyl-p-phenylenediamine was not appreciable influenced by the O2 concentration. 2-Iodo-6-isopropyl-3-methyl-2,4,4-trinitrodiphenyl ether, blocking electron transfer at the plastoquinone level, suppressed O2 evolution and had no influence on endogenous respiration. 2-n-Heptyl-4-hydroxyquinoline-N-oxide, an inhibitor of electron transfer between photosystems II and I, as well as the cytochrome-oxidase inhibitors N 3 - , CN- and NH2OH, caused a 35–50% retardation of endogenous respiration and blocked photosynthetic O2 evolution. The molar ratio of cytochromes b6, f, c-553, aa3 and photosystem-I reaction centers in the isolated membranes equalled approx. 2:1:2:0.7:2. It is inferred that endogenous respiration of A. variabilis cells is inhibited by the light-induced electron flow through both photosystems at the level of the plastoquinone-plastocyanin-oxidoreductase complex.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DNP-INT 2-iodo-6-isopropyl-3-methyl-2,4,4-trinitrodiphenyl ether - Hepes 4-(2-hydroxyethyl)-1-piperazine ethansulfonic acid - TMPD N,N,NN-tetramethyl-p-phenylenediamine  相似文献   

13.
Stable carbon (13C) and nitrogen (15N) isotopes were used to elucidate primary food sources and trophic relationships of organisms in Khung Krabaen Bay and adjacent offshore waters. The three separate sampling sites were mangroves, inner bay and offshore. The 13C values of mangrove leaves were –28.2 to –29.4, seagrass –10.5, macroalgae –14.9 to –18.2, plankton –20.0 to –21.8, benthic detritus –15.1 to –26.3, invertebrates –16.5 to –26.0, and fishes –13.4 to –26.3. The 15N values of mangrove leaves were 4.3 to 5.7, seagrass 4.3, macroalgae 2.2 to 4.4, plankton 5.7 to 6.4 , benthic detritus 5.1 to 5.3, invertebrates 7.2 to 12.2 , and fishes 6.3 to 15.9. The primary producers had distinct 13C values. The 13C values of animals collected from mangroves were more negative than those of animals collected far from shore. The primary carbon sources that support food webs clearly depended on location. The contribution of mangroves to food webs was confined only to mangroves, but a mixture of macroalgae and plankton was a major carbon source for organisms in the inner bay area. Offshore organisms clearly derived their carbon through the planktonic food web. The 15N values of consumers were enriched by 3–4 relative to their diets. The 15N data suggests that some of aquatic animals had capacity to change their feeding habits according to places and availability of foods and as a result, individuals of the same species could be assigned to different trophic levels at different places.  相似文献   

14.
The influence of some macronutrients, especially NH4NO3 and KNO3, on root development of microcuttings from 3 apple scion cultivars is discussed. A reduction of the level of NH4NO3 in the medium from full strength to 1/4 strength significantly increased the percentage rooting of Gala and Royal Gala, but not Jonagold. Further reduction of NH4NO3 level from 1/4 strength to zero significantly reduced the percentage of rooting in Gala but not Royal Gala. Jonagold rooted best at zero concentration NH4NO3. Without NH4NO3, rooting percentages were as high as 100% for all 3 cultivars when KNO3 was provided at full strength. The results show that adventitious roots can be induced on apple scion cultivars by media manipulation.  相似文献   

15.
Summary A system of nonlinear differential equations describing a resource-population system is analyzed in terms of the existence and characteristics of its equilibrium states.It is proved that, under the condition that k< (necessary condition for the population being able to grow under optimal conditions), it is a necessary and sufficient condition for the system to have a steady state that the resource input rate to the system be constant.When the resource input rate is a constant different from zero, the system has only one equilibrium point, at M 0=/0/k, A 0=–(/0/k)ln(1–k/), and this equilibrium point is always stable. In other words, the system population-resource will always reach the steady state, either monotonically (node) or by damped oscillations (focus), from any arbitrary initial condition in the positive quadrant.When the resource input rate is equal to zero, the system has an infinite number of equilibrium points at M 0=0, A 0=constant. All these equilibrium points are unstable in the sense that any slight increase in M will move the system away from the equilibrium states, except for the point M 0=0, A 0=0, which is the only stable equilibrium point, to which the system will tend. This stable equilibrium point corresponds to the condition of complete annihilation of both resource and population.Finally, it is proved that the system does not have limit cycles in the positive quadrant and is therefore incapable of self-oscillations.This work was partially supported by a Ford Foundation fellowship and various Cornell University fellowships.  相似文献   

16.
A large number of surface charge density () and surface potential (o) estimations have been based on 1) titrations of the fluorescence of 9-aminoacridine released from the diffuse double layer adjacent to negatively charged membrane surfaces by non-adsorbing monovalent and divalent cations, and 2) calculations using experimental data from the titration curves and the Gouy-Chapman theory of the diffuse double layer. In this paper we discuss the different simplifying approximations employed in the earlier calculations and recommend modified formulas for the calculations. The latter have been derived without any simplifying approximation concerning the ionic (electrolyte) composition of the titration assays. We also show that depends, to some extent, on the concentrations of buffer and vesicles in the assays and present experimental evidence that decamethonium (decane-1,10-bis-trimethylammonium), a bulky organic divalent cation, can be satisfactorily used for the estimation of under well-defined conditions, despite its putative interaction with membranes.Abbreviations 9-AA 9-aminoacridine - (DeM)2+ decamethonium - (DiM)2+ dimethonium - EDTA ethylenediaminetetraacetic acid - EGTA ethylene glyol-bis(-aminoethyl ether) N,N,N,N-tetraacetic acid - (HeM)2+ hexamethonium - MES 2-(N-morpholino) ethanesulfonic acid - MOPS 4-morpholinopropanesulfonic acid - PM plasma membrane - Tris tris(hydroxymethyl)aminomethane - surface charge density - o surface potential Correspondence to: A. Bérczi  相似文献   

17.
The goal of this research was to investigate if culturing in high sucrose (5%) liquid media during multiplication phase (stage II) would enhance endogenous sugar levels and dry matter sufficiently to allow storage of in vitro plants in sugar free media without adversely affecting post-storage recovery. Hosta tokudama Newberry Gold (NBG) and Hosta Striptease were cultured in Murashige and Skoog (MS) media containing 5% sucrose during stage II and transferred to rooting phase (stage III) in MS medium without (0%) sucrose or with 3% sucrose for 4weeks. At the end of stage III, cultures were stored, with the remaining media, at 10°C with 5molm–2s–1 photosynthetic photon flux (PPF) from cool white fluorescent lamps for 7 or 14weeks with or without a 2-week dark period prior to removal from storage. In both cultivars, stage III plants cultured in 3% sucrose media had higher soluble sugar levels and greater shoot and root biomass than those cultured in 0% sucrose media. Shoot and root soluble sugars decreased during storage. Shoot growth ceased during storage in both media. Root dry matter continued to increase in plants stored in 3% sucrose media but did not change in 0% sucrose media. Plants cultured in 3% sucrose media had less leaf chlorosis and less mortality after 7 or 14weeks of low temperature storage than the plantlets from sugar free media. Extending the storage period from 7 to 14weeks or introduction of 2-week dark period at the end of storage did not affect leaf chlorosis or plant mortality during acclimatization. Post-storage growth varied with the cultivar. Benefit of having sucrose in storage media was to develop a strong root system that aided the acclimatization and post-storage growth following 7 or 14week storage. Sucrose loading by culturing plants in liquid media containing 5% sucrose did not allow storage in sugar free media without adversely affecting post-storage growth in both cultivars.  相似文献   

18.
The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (13C) were used as tracers. Values of 13C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO2.The percentage of carbon derived from C4 macrophytes for bacterially produced CO2 was the highest, on average 89%. The average 13C value of CO2 from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO2 of 3 by bacterial respiration, 13C value was –15.5, near C4 macrophyte 13C value (–13.1).The average value of total DOC 13C was –26.8 ± 2.4. The percentage of C4 macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C3 plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C4 macrophytes to the consumers.  相似文献   

19.
    
Summary As has been shown previously, RNA polymerase subunit ts-mutation rpoC1 results in an overproduction of RNA polymerase subunits at nonpermissive temperature. The mutant enzyme shows low activity in vitro and a sedimentation coefficient 9S which is characteristic of immature core polymerase. In this paper we describe a mutation designated opr1 which suppresses RNA polymerase subunit overproduction. The mutation was found among Ts+ revertants of the Ts double mutant carrying a rpoC1 mutation and a rif-r rpo B251 mutation. Opr1 is closely linked to the original rpo mutations and shows complete trans-dominance. Although opr1 seems to affect RNA polymerase, it does not suppress the accumulation of immature 9S RNA polymerase and does not restore the activity of the RpoC1 mutant enzyme. This and other results of a comparison of strains carrying different combinations of rpoC1, rpoB251 and opr1 mutations suggest that neither inhibition of total RNA and protein synthesis, nor the low RNA polymerase activity in vitro, nor the apparent defects in enzyme maturation, nor the enzyme degradation observed at 42°C are responsible for the overproduction in RpoC1 strains.  相似文献   

20.
Tate  Amanda W.  Hershey  Anne E. 《Hydrobiologia》2003,499(1-3):13-23
Carbon and nitrogen stable isotopic data from the primary producers in mangrove ecosystems are needed to investigate trophic links and biogeochemical cycling. Compared with other mangrove species (e.g. Rhizophora mangle) very few measurements have been conducted on the white mangrove, Laguncularia racemosa. The carbon and nitrogen stable isotopic and elemental compositions of L. racemosa were analyzed and compared from Florida and Belize. 13C values of L. racemosa from Florida (mean = –26.4) were slightly higher than those from Twin Cays, Belize (mean = -27.4), which may be due to higher salinity in some parts of the Florida site. There was no difference between the 15N values from L. racemosa from these two sites (Florida mean = 0.6; Belize mean = 0.3), which are indicative of nitrogen derived from nitrogen fixation in a planktonic marine system. However, higher 15N values from L. racemosa at Man of War Cay in Belize (11.4 and 12.3), which is fertilized by roosting marine birds (14.0), illustrate that L. racemosa can sensitively reflect alternative nitrogen sources. Although the isotopic data could not distinguish between Avicennia germinans, R. mangle and L. racemosa in Belize the L. racemosa had considerably higher C/N ratios (46.5 – 116.1) compared with the Florida samples (42.2 – 76.0) or the other mangrove species. Unlike some previous findings from R. mangle, substrate characteristics (e.g. salinity, NH4 +, and H2S) were not related to the isotopic or elemental composition of L. racemosa. 13C, 15N and C/N were analyzed for ecosystem components from L. racemosa habitats at Twin Cays, including other plants (e.g. R. mangle, A. germinans and seagrass), detritus, microbial mats and sediments. Results from mass-balance calculations show that mangrove detritus composes very little of the sediment, which is principally composed of microbial biomass (80 – 90%). Detritus at some sites is also influenced by sources other than that from L. racemosa, including seagrass leaves.  相似文献   

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