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COOK C. M.; LANARAS T.; ROUBELAKIS-ANGELAKIS K. A. 《Journal of experimental botany》1988,39(9):1185-1198
Photosynthesis by four species of Rhodophyta: Ceramium rubrum,Ceramium tenuissimum, Gelidium crinale and Pterocladia capillaceawas optimal at 25 to 30?C and at pH 8.0 to 8.5. The measuredrates of photosynthesis exceeded the rate which could be supportedby the carbon dioxide arising from the dehydration of bicarbonatein the medium, from 2.7- to 10.9-fold at pH 8.0 and from 9-to 33.4-fold at pH 9.0, in the absence of measurable extracellularcarbonic anhydrase activity. Assays for malic enzyme and pyruvate,orthophosphate dikinase were negative, indicating that bicarbonateions are taken up by a transport system rather than by an accessorycarbon fixation pathway. When the algae were allowed to photosynthesizein an unbuffered system a DCMU (3-[3', 4'-dichlorophenyl]-1,1-dimethylurea)-sensitive alkalization of the medium was observed.This alkalization was shown to have a 1:1 stoichiometry withphotosynthetic carbon fixation. Alkalization of the medium occurredfrom 3.4 to 5.8 times the theoretical rate of supply of hydroxylions arising from the dehydration of bicarbonate. The data areconsistent with the operation of a bicarbonate transport systemin these macroalgae, in which electrical neutrality and pH balanceare maintained by hydroxyl ion efflux. A difference observedbetween the time-course of alkalization and oxygen evolutionsuggests that the transport of the two ions is not compulsorilycoupled. Key words: Bicarbonate transport, alkalization of the medium, Rhodophyta 相似文献
34.
Comparison of the behaviour of slugs before and during trailfollowing shows that there is no change in their rates of locomotionbut that there are decreases in measures of tentacle activity(distance moved and the frequency of substrate contacts) duringtrail following. Bilateral amputation of tentacles has the generaleffect of slowing the speed of locomotion whether trail followingor not, and preventing the decrease in tentacle activity duringtrail following. Amputation of the anterior tentacles results in a decrease inthe accuracy with which trails are followed. Amputation of theposterior tentacles on the other hand, results in a decreasein the frequency with which slugs turned onto trails. Removalof all the tentacles prevents trail following. It is concludedthat the posterior tentacles are concerned with the detectionand identification of trails which are subsequently followedand that the anterior tentacles normally control the behaviourof the slug on the trail. (Received 22 May 1984; 相似文献
35.
The load required to break shells of the snail Littor-aria pallescens(Philippi) (Gastropoda: Littorinidae) has been established.Mass increases more than proportionally with size. Size forsize, relatively heavy shells are thicker than relatively lightones, and the thicker shells are stronger. Three samples fromdifferent localities differ significantly in strength. Littorariapallescens is polymorphic for shell colour. It is shown thatin two of the three samples, both from Papua New Guinea, individualsof the dark morph are significantly heavier and stronger thanthose of the yellow morph, while there is no difference betweenmorphs in the third sample, from Thailand. In the sample withthe most robust shells the dark individuals are stronger, massfor mass, than yellows. Thus, colour morph is sometimes, butnot always, associated with differences in shell characteristicswhich are likely to affect fitness. Where there is a difference,the dark morph is estimated to be on average about 22% strongerthan the yellow morph. The difference between morphs is smallcompared with the large variation in shell characters associatedwith size. (Received 20 May 1992; accepted 22 June 1992) 相似文献
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Three bacterial strains have been isolated that differ in their ability to degrade polyethylene glycols (PEGs). Strains R and O showed a marked preference for growth on the low and high molecular weight PEGs, respectively, while strain Z utilized mono-ethylene glycol only. The partial degradation of PEG 200 by strains R and O was studied in some detail and the results suggested that those components of the mixture that were not utilized were converted into acidic derivatives which accumulated in the medium. 相似文献
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BENJAMIN J. COOK J. MARK THOMPSON WAYNE D. SHELTON 《Invertebrate reproduction & development.》2013,57(6):351-362
The oviduct of the pink bollworm is innervated by an intrinsic neural network arising from 4 nerves from the terminal ganglion. The nerve tracts in this network often contained elliptical swellings, each with a central nucleus. A distinct surface topography was evident in the muscular sheath of the common and lateral oviduct. A very thin muscular envelope consisting of an inner band of circular fibers and an outer layer of longitudinal fibers was also found in the ovarioles. Although conventional A and I bands were recognized, the z-disk was composed of an irregular and loose meshwork, suggesting that the visceral muscles of the reproductive tract possess super-contracting properties. Even when the oviduct and the ovarioles were isolated from the central nervous system, an endogenous rhythmic activity was evident. Two types of spontaneous excitatory postsynaptic potentials were detected in the oviduct. The type most frequently observed had a complex of multiple spikes with a duration of 18–32 msec. The other type had a saw-tooth shape and a duration of 80–160 msec. Spontaneous action potentials with a plateau-type configuration and a duration of 280–320 msec were also observed. After the removal of the terminal ganglion, endogenous electrical activity distinct from the events just described was found in the midand upper common oviduct. Such discharges seem to originate from the intrinsic neural network and had durations similar to those found for neurosecretory cells. 相似文献
38.
S. LUYSSAERT I. INGLIMA M. JUNG A. D. RICHARDSON M. REICHSTEIN D. PAPALE S. L. PIAO E. ‐D. SCHULZE L. WINGATE G. MATTEUCCI L. ARAGAO M. AUBINET C. BEER C. BERNHOFER K. G. BLACK D. BONAL J. ‐M. BONNEFOND J. CHAMBERS P. CIAIS B. COOK K. J. DAVIS A. J. DOLMAN B. GIELEN M. GOULDEN J. GRACE A. GRANIER A. GRELLE T. GRIFFIS T. GRÜNWALD G. GUIDOLOTTI P. J. HANSON R. HARDING D. Y. HOLLINGER L. R. HUTYRA P. KOLARI B. KRUIJT W. KUTSCH F. LAGERGREN T. LAURILA B. E. LAW G. LE MAIRE A. LINDROTH D. LOUSTAU Y. MALHI J. MATEUS M. MIGLIAVACCA L. MISSON L. MONTAGNANI J. MONCRIEFF E. MOORS J. W. MUNGER E. NIKINMAA S. V. OLLINGER G. PITA C. REBMANN O. ROUPSARD N. SAIGUSA M. J. SANZ G. SEUFERT C. SIERRA M. ‐L. SMITH J. TANG R. VALENTINI T. VESALA I. A. JANSSENS 《Global Change Biology》2007,13(12):2509-2537
Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome‐specific carbon budgets; to re‐examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 °C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome‐specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non‐CO2 carbon fluxes are not presently being adequately accounted for. 相似文献
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Significance of nucleotide sequence alignments: a method for random sequence permutation that preserves dinucleotide and codon usage 总被引:10,自引:0,他引:10
The similarity of two nucleotide sequences is often expressed in terms of
evolutionary distance, a measure of the amount of change needed to
transform one sequence into the other. Given two sequences with a small
distance between them, can their similarity be explained by their base
composition alone? The nucleotide order of these sequences contributes to
their similarity if the distance is much smaller than their average
permutation distance, which is obtained by calculating the distances for
many random permutations of these sequences. To determine whether their
similarity can be explained by their dinucleotide and codon usage, random
sequences must be chosen from the set of permuted sequences that preserve
dinucleotide and codon usage. The problem of choosing random dinucleotide
and codon-preserving permutations can be expressed in the language of graph
theory as the problem of generating random Eulerian walks on a directed
multigraph. An efficient algorithm for generating such walks is described.
This algorithm can be used to choose random sequence permutations that
preserve (1) dinucleotide usage, (2) dinucleotide and trinucleotide usage,
or (3) dinucleotide and codon usage. For example, the similarity of two
60-nucleotide DNA segments from the human beta-1 interferon gene
(nucleotides 196-255 and 499-558) is not just the result of their nonrandom
dinucleotide and codon usage.
相似文献