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991.
Summary The presteady-state influxes and effluxes of sodium across frog skin epithelium have been determined as a function of time while all electrophysiological parameters were maintained constant. The fluxes measured were resolved in the fractions which have passed a pathway through the cells and those that have used a paracellular pathway. The procedure is based on the theory that all presteady-state flux ratios have to be equal to the steady-state flux ratio if only one pathway is involved. The flux ratios for the transcellular route were used to calculate the electromotive force of the sodium pump. The calculation hinges on the assumptions (a) that both influx and efflux have to pass through the sodium pump and (b) that single file diffusion of sodium is not taking place anywhere along the path. The validity of both assumptions is discussed. Our calculated values for the electromotive force of the sodium pumpE
Na
a
vary between 146 and 200 mV, which is in agreement with the energy of the ATP/ADP system. There is a distinct indication that, as the electrochemical gradient for sodium opposing the transport is being increased, the emf increases towards an asymptotic value around 200 mV. The relation between the value ofE
Na
a
and the cellular phosphorylation potential for ATP is discussed. 相似文献
992.
Takehisa Oikawa 《Ecological Research》1987,2(3):289-300
By employing a microcomputer model developed in a previous study (Oikawa, 1985), the stability of a tropical rainforest ecosystem
composed of three strata was analyzed in relation to incident light flux density. Surplus production (P
s
), calculated as a function of the leaf area index and light attenuation coefficient, was remarkably affected by the maximum
illuminance at noon (I
0, max).
Simulation experiments for a period of 100 years demonstrated that the upper stratum was able to reach a steady state at about
50 years and thereafter, when a value ofI
0, max
equal to or greater than 80 klux was assigned to the upper stratum, where the higher the value ofI
0, max
, the greater the biomasses and the carbon fluxes at the steady state as a result of enhanced productivity. WhenI
0, max
was assigned a value of 70 klux, on the other hand, this experiment predicted a failure of the upper stratum to maintain
stability due to deficiency of surplus productivity.
Moreover, it was also suggested that excessive luxuriance of the upper stratum due toI
0, max
elevation may have a detrimental effect upon the survival of the middle stratum, since increasingI
0, max
decreases the light energy available for the middle stratum even in absolute terms, resulting in disappearance of this stratum
whenI
0, max
is equal to or greater than 120 klux.
These simulation experiments suggested that a tropical rainforest ecosystem composed of three strata is able to exist within
a narrow range ofI
0, max
between 80 and 110 klux, light conditions which are much higher than the light compensation point for canopy photosynthesis
This article is dedicated to Professor Toshiro Saeki, University of Tokyo, in appreciation of the sincere encouragement he
has given to the author. 相似文献
993.
G. Eriksson I. Ekberg I. Dormling B. Matérn D. von Wettstein 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1978,52(1):3-19
Summary Diallel crosses were made between clones of a French and a Swedish provenance of Picea abies. The former is characterized by a long critical night length for bud-set and a late flushing of the buds; the latter by a short critical night length for bud-set and an early flushing of the buds. The F1 hybrid seedlings and their French and Swedish intraprovenance half-sibs were tested over three growth periods in the phytotron at the College of Forestry, Stockholm. In comparison with intraprovenance half-sibs, the hybrid progenies gave, on average, an intermediate response for the photoperiodic control over budset and for the temperature requirements for bud-flushing. This indicates the prevalence of additive action of multiple factors in the determination of the photoperiodic and temperature response. However, individual interprovenance hybrid progenies revealed a range of responses, and in certain combinations the response of these hybrids and their intraprovenance half-sibs coincided. By selection of suitable parents, interprovenance crosses can be used to produce hybrids with desired photoperiodic characteristics and temperature requirements.With gratitude and appreciation we dedicate this paper to Åke Gustafsson at the occasion of his 70th birthday, April 8, 1978 相似文献
994.
Steady-state fluxes of 86Rb+ (as a tracer for K+) were measured in Chinese hamster ovary cells (CHO-K1) and a mutant (CR1) defective in the regulation of cholesterol biosynthesis; the membrane cholesterol content of this mutant was varied by growing it on a range of cholesterol supplements to lipid-free medium (Sinensky, M. (1978) Proc. Natl. Acad. Sci. U.S. 75, 1247–1249).Analogous to previous findings in ascites tumor cells, 86Rb+ influx in the parent strain was differentiated into a ouabain-inhibitable ‘pump’ flux, furosemide-sensitive, chloride-dependent exchange diffusion, and a residual ‘leak’ flux.On the basis of this flux characterization, 86Rb+ pump and leak fluxes were measured in the mutant as a function of membrane cholesterol content. Pump and leak fluxes, when expressed per ml cell water, were independent of the cholesterol content of the mutant. Moreover, 86Rb+ fluxes in the mutant were equal to those in the parent strain. Our data imply that the flux behavior of K+ in the steady state is independent of the ordering of membrane lipid acyl chains. 相似文献
995.
Pahl Bernier 《Geobios》1979,12(6):839-861
The genus Petrascula has not been reviewed since J. Pia in 1920. At present, seven species are attributed to this genus. Different characteris have been used to define it by the authors. After abundant sampling in the Upper Kimmeridgian or the Southern Jura Mountains, the species-type has been reviewed and divided in two species, the second one named: Petrascula guembeli nov. sp.An other level of Portlandian age, in the same azea, is very rich in Petrascula piaiBachmayer, 1944. This species which has not been observed since that time is here reviewed. Associated with this species, a new one was found and described Petrascula? bugesiaca nov. sp., in spite a doubtful genus attribution.So many different species allow the review and emendation of the genus Petrascula. Then, the other species of the genus: P. globosa (Alth) P. herakiSokac & Nikler, P. illyricaSokac & Nikler, are discussed using the new definition. 相似文献
996.
Jean Gaudant 《Geobios》1977,10(5):671-681
The mythical character of the species «Smerdis glangeaudiPriem is demonstrated, using mainly lithological, anatomical, morphometrical and field arguments. In fact, this species has been described from a composite hypodigm which truly includes two specimens of Dapalis (=Smerdis) macrurus (Ag.) from the neighbourhood of Céreste (Alpes de Haute-Provence) and another one of Dapalis (=Smerdis) minutus (Bl.) from the ancient gypsum quarries of Aix-en-Provence. 相似文献
997.
K. R. Robinson 《Planta》1977,136(2):153-158
The effect of external calcium and sodium ion concentrations on the calcium fluxes on the Pelvetia fastigiata De Toni egg was measured. Decreasing external [Ca2+] greatly increased the permeability of the eggs to Ca2+; at 1 mM external Ca2+ this permeability was 60 times as great as it was at the normal [Ca2+] of 10 mM. Lowering the external [Na+] also increased Ca2+ influx; at 2 mM Na+, the Ca2+ influx was 2–3 times as great as it was at the normal [Na+] if choline was used as a Na+ substitute. Lithium was less effective as a Na+ substitute in increasing Ca2+ influx. The extra Ca2+ influx in low [Na+] seemed to be dependent on internal [Na+]. The Ca2+ efflux increased transiently and then declined in low Na+ media. 相似文献
998.
Photosynthetic characteristics were compared between plants of low altitude (LA) grown at LA (Palampur; 1 300 m) and at high altitude, HA (Kibber; 4 200 m), and plants naturally occurring at different altitudes (Palampur, 1 300 m; Palchan, 2 250 m; and Marhi, 3 250 m). Net photosynthetic rate (P
N) was not significantly different between altitudes. However, the slopes of the curve relating P
N to intercellular CO2 concentration (C
i) were higher in plants at Palchan, Marhi, and Kibber compared to those at Palampur, indicating that plants had higher efficiency of carbon uptake (the initial slope of P
N/C
i curve is an indication) at HA. They had also higher stomatal conductance (g
s), transpiration rate, and lower water use efficiency at HA. g
s was insensitive to photosynthetic photon flux density (PPFD) for plants naturally occurring at Palampur, Palchan, and Marhi, whereas plants from LA grown at Palampur and Kibber responded linearly to increasing PPFD. Insensitivity of g
s to PPFD could be one of the adaptive features allowing wider altitudinal distribution of the plants.This research is supported by the Department of Biotechnology (DBT), Government of India vide grant number BT/PR/502/AGR/08/39/966-VI. 相似文献
999.
Elizabeth?H.?BurrowsEmail author Jill?L.?Bubier Andrew?Mosedale George?W.?Cobb Patrick?M.?Crill 《Biogeochemistry》2005,76(1):21-45
We used five analytical approaches to compare net ecosystem exchange (NEE) of carbon dioxide (CO2) from automated and manual static chambers in a peatland, and found the methods comparable. Once per week we sampled manually
from 10 collars with a closed chamber system using a LiCor 6200 portable photosynthesis system, and simulated four photosynthetically
active radiation (PAR) levels using shrouds. Ten automated chambers sampled CO2 flux every 3 h with a LiCor 6252 infrared gas analyzer. Results of the five comparisons showed (1) NEE measurements made
from May to August, 2001 by the manual and automated chambers had similar ranges: −10.8 to 12.7 μmol CO2 m−2 s−1 and −17.2 to 13.1 μmol CO2 m−2 s−1, respectively. (2) When sorted into four PAR regimes and adjusted for temperature (respiration was measured under different
temperature regimes), mean NEE did not differ significantly between the chambers (p < 0.05). (3) Chambers were not significantly different in regression of ln( − respiration) on temperature. (4) But differences
were found in the PAR vs. NEE relationship with manual chambers providing higher maximum gross photosynthesis estimates (GPmax), and slower uptake of CO2 at low PAR (α) even after temperature adjustment. (5) Due to the high variability in chamber characteristics, we developed an equation
that includes foliar biomass, water table, temperature, and PAR, to more directly compare automated and manual NEE. Comparing
fitted parameters did not identify new differences between the chambers. These complementary chamber techniques offer a unique
opportunity to assess the variability and uncertainty in CO2 flux measurements. 相似文献
1000.
Desvaux M 《FEMS microbiology reviews》2005,29(4):741-764
Clostridium cellulolyticum ATCC 35319 is a non-ruminal mesophilic cellulolytic bacterium originally isolated from decayed grass. As with most truly cellulolytic clostridia, C. cellulolyticum possesses an extracellular multi-enzymatic complex, the cellulosome. The catalytic components of the cellulosome release soluble cello-oligosaccharides from cellulose providing the primary carbon substrates to support bacterial growth. As most cellulolytic bacteria, C. cellulolyticum was initially characterised by limited carbon consumption and subsequent limited growth in comparison to other saccharolytic clostridia. The first metabolic studies performed in batch cultures suggested nutrient(s) limitation and/or by-product(s) inhibition as the reasons for this limited growth. In most recent investigations using chemostat cultures, metabolic flux analysis suggests a self-intoxication of bacterial metabolism resulting from an inefficiently regulated carbon flow. The investigation of C. cellulolyticum physiology with cellobiose, as a model of soluble cellodextrin, and with pure cellulose, as a carbon source more closely related to lignocellulosic compounds, strengthen the idea of a bacterium particularly well adapted, and even restricted, to a cellulolytic lifestyle. The metabolic flux analysis from continuous cultures revealed that (i) in comparison to cellobiose, the cellulose hydrolysis by the cellulosome introduces an extra regulation of entering carbon flow resulting in globally lower metabolic fluxes on cellulose than on cellobiose, (ii) the glucose 1-phosphate/glucose 6-phosphate branch point controls the carbon flow directed towards glycolysis and dissipates carbon excess towards the formation of cellodextrins, glycogen and exopolysaccharides, (iii) the pyruvate/acetyl-CoA metabolic node is essential to the regulation of electronic and energetic fluxes. This in-depth analysis of C. cellulolyticum metabolism has permitted the first attempt to engineer metabolically a cellulolytic microorganism. 相似文献