共查询到20条相似文献,搜索用时 15 毫秒
1.
Ellis L. Yochelson 《Pal?ontologische Zeitschrift》2002,76(2):297-304
Dentalium antiquum is one of two moderately well-known Devonian “scaphopods” in the German literature. Examination of the type material and
a few specimens in other institutions indicates more individual variability than is to be expected in species of the molluscan
class Scaphopoda. The species is transferred with question toColeolus
Hall, a fossil presumed to be a calcareous “worm” tube.
相似文献
2.
It has been anticipated that new, much more sensitive, next generation sequencing (NGS) techniques, using massively parallel
sequencing, will likely provide radical insights into the genetics of multifactorial diseases. While NGS has been used initially
to analyze individual human genomes, and has revealed considerable differences between healthy individuals, we have used NGS
to examine genetic variation within individuals, by sequencing tissues “in depth”, i.e., oversequencing many thousands of
times. Initial studies have revealed intra-tissue genetic heterogeneity, in the form of multiple variants of a single gene
that exist as distinct “majority and “minority” variants. This highly specialized form of somatic mosaicism has been found
within both cancer and normal tissues. If such genetic variation within individual tissues is widespread, it will need to
be considered as a significant factor in the ontogeny of many multifactorial diseases, including cancer. The discovery of
majority and minority gene variants and the resulting somatic cell heterogeneity in both normal and diseased tissues suggests
that selection, as opposed to mutation, might be the critical event in disease ontogeny. We, therefore, are proposing a hypothesis
to explain multifactorial disease ontogeny in which pre-existing multiple somatic gene variants, which may arise at a very
early stage of tissue development, are eventually selected due to changes in tissue microenvironments. 相似文献
3.
Szucs P Skinner JS Karsai I Cuesta-Marcos A Haggard KG Corey AE Chen TH Hayes PM 《Molecular genetics and genomics : MGG》2007,277(3):249-261
The epistatic interaction of alleles at the VRN-H1 and VRN-H2 loci determines vernalization sensitivity in barley. To validate the current molecular model for the two-locus epistasis,
we crossed homozygous vernalization-insensitive plants harboring a predicted “winter type” allele at either VRN-H1 (Dicktoo) or VRN-H2 (Oregon Wolfe Barley Dominant), or at both VRN-H (Calicuchima-sib) loci and measured the flowering time of unvernalized F2 progeny under long-day photoperiod. We assessed whether the spring growth habit of Calicuchima-sib is an exception to the
two-locus epistatic model or contains novel “spring” alleles at VRN-H1 (HvBM5A) and/or VRN-H2 (ZCCT-H) by determining allele sequence variants at these loci and their effects relative to growth habit. We found that (a) progeny
with predicted “winter type” alleles at both VRN-H1 and VRN-H2 alleles exhibited an extremely delayed flowering (i.e. vernalization-sensitive) phenotype in two out of the three F2 populations, (b) sequence flanking the vernalization critical region of HvBM5A intron 1 likely influences degree of vernalization sensitivity, (c) a winter habit is retained when ZCCT-Ha has been deleted, and (d) the ZCCT-H genes have higher levels of allelic polymorphism than other winterhardiness regulatory genes. Our results validate the model
explaining the epistatic interaction of VRN-H2 and VRN-H1 under long-day conditions, demonstrate recovery of vernalization-sensitive progeny from crosses of vernalization-insensitive
genotypes, show that intron length variation in VRN-H1 may account for a continuum of vernalization sensitivity, and provide molecular markers that are accurate predictors of “winter
vs spring type” alleles at the VRN-H loci. 相似文献
4.
Citrus is an important fruit crop as regards accumulation of carotenoids. In plant carotenoid biosynthesis, phytoene synthase gene
(Psy) plays a key role in catalyzing the head-to-head condensation of geranylgeranyl diphosphate molecules to produce colorless
phytoene. In the present paper, we reported the phytoene contents determination and characterization of Psy during fruit ripening of “Washington” navel orange and its red-fleshed mutant “Cara Cara”. Results showed that phytoene was
exclusively accumulated in peel and pulp of “Cara Cara”. Although phytoene was observed accumulating with fruit ripening of
“Cara Cara”, the contents in pulp were 10 times higher than those in peel. The isolated two Psy cDNAs were both 1520 bp in full length, containing 436 deduced amino acid residues, with a different amino acid at 412th.
Genomic hybridization results showed that one or two copies might be present in “Cara Cara” and “Washington” genomes. During
“Cara Cara” and “Washington” fruit coloration, expression of Psy was observed to be up-regulated, as revealed by tissue specific profiles in the flavedo, albedo, segment membrane and juice
sacs. However, Psy expression in albedo of “Cara Cara” was higher than that in “Washington”, as evidenced by phytoene accumulation in the peel. 相似文献
5.
Charles S. Vairappan 《Journal of applied phycology》2006,18(3-5):611-617
Common problems faced in farming of the red algal genus Kappaphycus/Eucheuma are “ice-ice disease” and the occurrence of epiphytes. Considerable work has been documented on “ice-ice disease” and it's mode of infection but limited information is available on the emergence of epiphytes. The present study addresses the phenomenon of epiphyte infection, its prevalence in commercially cultivated red alga, Kappaphycus alvarezii, and their variability associated with seasonality. Cultured seaweed became susceptible to epiphytes in the dry seasons (1) between March – June and (2) September – November. Findings revealed Neosiphonia savatieri (Hariot) M. S. Kim et I. K. Lee, as the dominant infecting epiphyte, representing up to 80–85% of the epiphyte present during peak seasons. Besides N. savatieri, Neosiphonia apiculata, Ceramium sp., Acanthophora sp. and Centroceras sp. were observed in smaller quantities. SEM (Scanning Electron Microscope) micrographs revealed the epiphyte's attachment to the host. Further histological study showed the extent of penetration of epiphytes into the host's cortex tissues and condition of its surrounding tissues. The outbreak of epiphytic filamentous red algae also correlated with drastic changes in seawater temperature and salinity during March– June and September – November. 相似文献
6.
A new partial skeleton of the Cretaceous “symmetrodontan” mammal Zhangheotherium quinquecuspedens from the Yixian Formation of Liaoning, China has shed light on the dental and skeletal features of this taxon. The new fossil
is a juvenile individual of late growth stage, preserved with interesting features of the premolar replacement. This fossil
also provides new information on the vertebral column, the pelvis, the hindlimb and pes. Zhangheotherium has a typical diphyodont replacement of its premolars that is characterized by an alternating pattern (p1 → p3 → p2). This
alternating replacement of premolars is a derived condition shared by Dryolestes, Slaughteria, and some basal eutherians, and differs from the plesiomorphic sequential replacement of anterior postcanines in eutricondontans,
in most multituberculates and in stem mammaliaforms. The calcaneus and astragalus in the ankle joint of Zhangheotherium lack superposition. This shows that the trechnotherian clade, of which Zhangheotherium is a basal taxon, has retained the primitive condition of mammaliaforms in which the astragalus is in juxtaposition with
the calcaneus. Coupled with recent evidence from the earliest metatherians and eutherians, this suggests that the superposition
of astragalus and calcaneus evolved in parallel in metatherians and eutherians. 相似文献
7.
V. V. Anistratenko 《Biology Bulletin》2010,37(2):130-137
The phenomenon of “switching” of the early ontogeny type (nonpelagic versus pelagic) is considered in the context of the presence
of alternative modes of early ontogeny in recent and fossil gastropod mollusks. Possible environmental inducing mechanisms
(decrease in salinity and/or water temperature), as well as the role of this phenomenon in the evolution of Gastropoda, are
discussed. The concept of a “mesopoikilohaline” zone is introduced; it is interpreted as a biologically important barrier
of salinity (presumably about 13–15‰) which plays the key role in suppression of the free-living larval stage during the process
of gradual water freshening. The change in strategy of early ontogeny is interpreted as a regulator of the adaptation process
and, to some extent, as a speciation mode in Mollusca. 相似文献
8.
Brian J. Switek 《Evolution》2010,3(3):468-476
On May 19, 2009, an international team of scientists claimed to have found one of our early primate ancestors. Dubbed Darwinius masillae, the 47 million-year-old primate was presented as “the link” that bridged a gap between early primates and our anthropoid
progenitors through a major media campaign, yet details about the way the fossil was acquired, the role media companies played
in the presentation of the fossil, and disagreements about the fossil’s interpretation generated a controversy in which scientists,
journalists, and science bloggers all played important roles. These debates were reinvigorated in the fall of 2009 when an
independent team of researchers described a related fossil primate named Afradapis longicristatus, the study of which suggested that Darwinius was much further removed from our ancestry than had been initially proposed. The discussion of these fossils will no doubt
continue, but the “Darwinius debates” of 2009 are significant in that they precipitated a long-awaited analysis of early primate relationships, illustrated
the benefits and pitfalls of “going broad” with new discoveries, and exhibited how science blogs can work with traditional
media outlets to counter exaggerated claims. 相似文献
9.
M. K. Zhemchuzhnikov A. N. Knyazev 《Journal of Evolutionary Biochemistry and Physiology》2011,47(6):565-570
Data are presented about the development of reproductive and defense behavior of noncopulated female crickets Gryllus argentinus Sauss. in the beginning of the imaginal ontogeny. The character of interaction of females with “virtual” males (the “supporting
ball” method-“trackball”) was studied. The forms of female motor reactions to models of intraspecies male sound signals-the
calling and aggressive songs-are described and analyzed. The character of the development of female acoustic behavior is described
as judged by change in the forms of motor reactions in the course of the imaginal ontogeny. It is shown that immediately after
the imaginal molt the reproductive behavior is not formed yet but it matures gradually within a few days. At the early stages
of the imaginal ontogeny passive defense behavior is found to be most clearly expressed. 相似文献
10.
Summary The Middle Eocene lake sediments of the Eckfeld maar are situated on the southwestern margin of the Tertiary High-Eifel volcanic
field (Germany) and are well known for excellently preserved fossil remains. During a driling campaign in 1996 six well sections
were cored at three different locations. Three cores (E1/96, E2/96 and E3/96) penetrated deposition of the central lake facies,
which is dominated by laminated organic-rich pelites within the uppermost 40 m.
It is the aim of this paper to present a brief survey over the main types of stratification observed within the organic-rich
portions of the Eckfeld lake sediments. Based on the varying distribution of mineral and organic matter three sediment sequences
are distinguished representing different phases of lake development. The “minerogenic laminites” represent the purely clastic
mineral sedimentation in a lake, which was surrounded during this early phase by a tephra rim barren of vegetation. The gradual
overgrowth of the tephra rim by vegetation is reflected by the predominance of land plant detritus in the sediments of the
“transtion beds”, though the siliciclastic input is still significant. In contrast, the succeeding sequence of the “biogenic
laminites” is characterised by the frequent occurrence of centric diatoms (mainly of the planktonic speciesAulacoseira cf.granulata) and Chlorophyceae (mainlyBotryococcus andTetraedron) documenting the increase in autochthonous organic sedimentation in a meromictic lake. 相似文献
11.
Rimoldi S Papis E Bernardini G Prati M Gornati R 《Molecular and cellular biochemistry》2007,301(1-2):143-153
GD3, a minor ganglioside in most normal tissues, is involved in important biological events and its expression could increase
in pathological conditions. Organism integrity requires a tight balance between the anabolic and catabolic processes, thus
it is important to control the intracellular expression of those “key” enzymes, which act at the “branching point” of ganglioside
metabolism; one of these is the GD3-synthase (ST8Sia I). In this paper, we report the sequences of two ST8Sia I mRNAs found
in Xenopus laevis and their genomic organization; the canonical form resulted constituted of 5 exons and 4 introns, while the “short” mRNA
lacks of the exon 2. The expression of the two ST8Sia I mRNAs during embryo development and their tissue distribution in adult
animals showed the single or simultaneous presence of the two forms. Experiments of in vitro expression and evaluation of
enzymatic activity of the two hypothetical proteins turned out to be ST8Sia I. In the end, considering the growing interest
toward the specie Xenopus tropicalis, due to its diploid genome that render it more suitable for genetic studies, we also cloned X. tropicalis ST8Sia I.
Accession numbers: AY272057, AY272056 相似文献
12.
Elaphoglossum amygdalifolium holds a critical phylogenetic position as sister to the remaining ca. 600 extant species of Elaphoglossum and may provide important insight into the evolution of epiphytism in this clade of ferns. Here, we present the first examination
of growth habit and gametophyte morphology for this species. We show that the cordate to elongate-cordate gametophytes occur
up to 0.5 m above the ground on the base of tree trunks. Unlike the gametophytes of all other studied species of Elaphoglossum, rhizoids are absent along the thallus margin and the hairs present on the margin lack whitish waxy caps; both differences
are pleisiomorphic for the genus. Sporelings of E. amygdalifolium produce a single long root that grows straight into the soil where it branches profusely. Mature sporophytes have long-creeping
rhizomes that climb to heights of at least 3 m and produce two types of roots: “feeding roots” that reach the ground and “clasping
roots” that anchor the sporophyte to its host plant. Our observations reveal that E. amygdalifolium is a primary hemiepiphyte, the first example of this growth habit to be documented in Elaphoglossum. Results of an ancestral state reconstruction of growth habit in bolbitidoid ferns show that both primary hemiepiphytism
and holoepiphytism are equally likely to be the ancestral character state for Elaphoglossum. 相似文献
13.
In his considerations of “organs of extreme perfection,” Charles Darwin described the evidence that would be necessary to
support the evolutionary origin of the eye, namely, demonstration of the existence of “numerous gradations” from the most
primitive eye to the most perfect one, where each such tiny change had provided a survival advantage (however slight) to the
organism possessing the subtly altered form. In this paper, we discuss evidence indicating that the vertebrate eye did indeed
evolve through numerous subtle changes. The great majority of the gradual transitions that did occur have not been preserved
to the present time, either in the fossil record or in extant species; yet clear evidence of their occurrence remains. We
discuss the remarkable “eye” of the hagfish, which has features intermediate between a simple light detector and an image-forming
camera-like eye and which may represent a step in the evolution of our eye that can now be studied by modern methods. We also
describe the important clues to the evolutionary origin of the vertebrate eye that can be found by studying the embryological
development of our own eye, by examining the molecular genetic record preserved in our own genes and in the genes of other
vertebrates, and through consideration of the imperfections (or evolutionary “scars”) in the construction of our eye. Taking
these findings together, it is possible to discuss in some detail how the vertebrate eye evolved. 相似文献
14.
Abdel Gaffar Elhag Said Toshio Murashige 《In vitro cellular & developmental biology. Plant》1979,15(8):593-602
Summary Initial trials with tomato-root cultures disclosed the desirability of employing a gently agitated liquid medium containing
iron in the chelated form. For the normal cultivars “Ace” and “Tropic”, subcultures were best achieved by utilizing sectors
that possessed one or more newly emerged laterals. Continuous cultures of a nonlateral-forming tomato mutant, “Diageotropica”,
and of citron were accomplished by subculturing tips of the elongating primary roots. The tomato roots were cultured in White's
medium with the Fe2(SO4)3 replaced by 0.03 mM NaFeEDTA. Sustained growth of citron-root tips necessitated the use of a medium containing Murashige
and Skoog salts, 7.5% sucrose, 100 mg per I each of citric acid and thiamine HCl, and 5000 mg per li-inositol. The success with citron-root cultures was extendable to all cultivars ofC. medica L., but not to otherCitrus species relatives. Both citron and “Diageotropica” root cultures manifested undiminished elongation through repeated subcultures;
but neither produced laterals in response to any cultural treatments.
Research was supported in part by National Science Foundation Grant OIP75-10390 and Elvenia J. Slosson Fellowship in Ornamental
Horticulture. 相似文献
15.
In recent years, marine scientists have become increasingly alarmed over the decline of live coral cover throughout the Caribbean
and tropical western Atlantic region. The Holocene and Pleistocene fossil record of coral reefs from this region potentially
provides a wealth of long-term ecologic information with which to assess the historical record of changes in shallow water
coral reef communities. Before fossil data can be applied to the modern reef system, critical problems involving fossil preservation
must be addressed. Moreover, it must be demonstrated that the classic reef coral zonation patterns described in the early
days of coral reef ecology, and upon which “healthy” versus “unhealthy” reefs are determined, are themselves representative
of reefs that existed prior to any human influence. To address these issues, we have conducted systematic censuses of life
and death assemblages on modern “healthy” patch reefs in the Florida reef tract that conform to the classic Caribbean model
of reef coral zonation, and a patch reef in the Bahamas that is currently undergoing a transition in coral dominance that
is part of a greater Caribbean-wide phenomenon. Results were compared to censuses of ancient reef assemblages preserved in
Pleistocene limestones in close proximity to each modern reef. We have determined that the Pleistocene fossil record of coral
reefs may be used to calibrate an ecological baseline with which to compare modern reef assemblages, and suggest that the
current and rapid decline of Acropora cervicornis observed on a Bahamian patch reef may be a unique event that contrasts with the long-term persistence of this taxon during
Pleistocene and Holocene time.
Accepted: 19 May 1998 相似文献
16.
The effects (and interaction) of two solution concentrations of Mg (50, 500, μM) and two of K (250, 4250 μM) on the growth of micropropagated plants of “F. 12/1” and “Colt” were investigated using a flowing solution culture system.
Magnesium inflow and growth of “Colt” and “F. 12/1” were inhibited to a similar extent by an increased concentration of K
in the nutrient solution. However, the consequences of this inhibition were different. Reduced inflow of Mg in “F. 12/1” caused
Mg deficiency symptoms at high and low concentrations of K, whereas this only occurred with a combination of high K concentration
and low Mg concentration in “Colt”. The distribution of dry matter within the plant was significant in determining susceptibility
to Mg deficiency. Since “F. 12/1” has a smaller root:shoot ratio than Colt it is unable to sustain the same concentration
of Mg in leaves as “Colt” irrespective of external K concentration. The molar ratio of K:Mg in soil solutions should remain
<8.5:1 in order to ensure maximum growth of “F. 12/1” and “Colt”.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
Insect octopamine receptors: a new classification scheme based on studies of cloned Drosophila G-protein coupled receptors 总被引:1,自引:0,他引:1
Summary Insect octopamine receptors are G-protein coupled receptors. They can be coupled to second messenger pathways to mediate either increases or decreases in intracellular cyclic AMP levels or the generation of intracellular calcium signals. Insect octopamine receptors were originally classified on the basis of second messenger changes induced in a variety of intact tissue preparations. Such a classification system is problematic if more than one receptor subtype is present in the same tissue preparation. Recent progress on the cloning and characterization in heterologous cell systems of octopamine receptors from Drosophila and other insects is reviewed. A new classification system for insect octopamine receptors into “α-adrenergic-like octopamine receptors (OctαRs)”, “β-adrenergic-like octopamine receptors (OctβRs)” and “octopamine/tyramine (or tyraminergic) receptors” is proposed based on their similarities in structure and in signalling properties with vertebrate adrenergic receptors. In future studies on the molecular basis of octopamine signalling in individual tissues it will be essential to identify the relative expression levels of the different classes of octopamine receptor present. In addition, it will be essential to identify if co-expression of such receptors in the same cells results in the formation of oligomeric receptors with specific emergent pharmacological and signalling properties. 相似文献
18.
A breakthrough in transgenic Arabidopsis thaliana research was the development of the floral dip transformation protocol, a simple and reliable method of obtaining transformants,
T1 transgenic lines, at high efficiency while avoiding the use of tissue culture. However, the traditional protocol (a “sterile”
method) of obtaining T2 transgenic lines has not evolved along with improvements in transformation technology as it continues to be laborious and
time-consuming. In this study, we report on the development of an improved protocol (a “nonsterile” method) for selecting
and growing A. thaliana transformants (T2 transgenic lines) resistant to kanamycin under nonsterile conditions. This protocol involves the use of a simple yet specialized
device that will aid in solium selection of T2 transgenic lines that can be rapidly grown in a hydroponic system. The “nonsterile” method reduces labor and time involved
as compared to the “sterile” method; moreover, it is easy to set up and maintain. This method may also be applicable to other
selecting agents, and perhaps to other plants. 相似文献
19.
Dessislava Todorova Irina Vaseva-Gemisheva Petar Petrov Ekaterina Stoynova-Bakalova Vera Alexieva Emanuil Karanov Aileen Smith Michael Hall 《Acta Physiologiae Plantarum》2006,28(6):613-617
The specific activity of cytokinin oxidase/dehydrogenase (EC 1.5.99.12) (CKX) was determined in leaves of wild type (wt) and ethylene-insensitive mutant (eti5) of Arabidopsis thaliana (L.) Heynh plants. Comparative studies showed that this mutation has lower basal CKX activity than wt. Application of 4PU-30 (N1-(2-chloro-4-pyridyl)-N2-phenylurea) resulted in decreased CKX activity in both wt and mutant plants. The treatment increased leaf blade thickness and the volume of chlorophyll-containing cells per unit leaf
area in wt but these changes were not observed in the eti5 mutant. The reduction in chlorophyll “a” and “b”, as well as in carotenoids content in the treated wt tissues resulting from altered leaf morphology was not detected in eti5 plants. 相似文献
20.
“Hairy root” systems, obtained by transforming plant tissues with the “natural genetic engineer” Agrobacterium rhizogenes, have been known for more than three decades. To date, hairy root cultures have been obtained from more than 100 plant species,
including several endangered medicinal plants, affording opportunities to produce important phytochemicals and proteins in
eco-friendly conditions. Diverse strategies can be applied to improve the yields of desired metabolites and to produce recombinant
proteins. Furthermore, recent advances in bioreactor design and construction allow hairy root-based technologies to be scaled
up while maintaining their biosynthetic potential. This review highlights recent progress in the field and outlines future
prospects for exploiting the potential utility of hairy root cultures as “chemical factories” for producing bioactive substances. 相似文献