东北地区蒙古栎群落区系成分

根据吴征镒、王荷生区系分析方法, 分析了东北地区蒙古栎群落中２６１ 种维管植物的区系成分, 其中温带成分占４７－４７ ％ , 东亚成分占４２－０２ ％ , 中国特有成分占１０－５１ ％ （ 世界分布不统计在内） 。并分析了种所在属的分布区类型, 温带分布属占９０－３％ 。还分别分析了蒙古栎群落的乔木层、灌木层、草本层以及层间植物的区系成分。     

On the nature of P.P.L.O.

Summary In a number of strains of the three species of P.P.L.O. of human origin coccoid elements have been observed, which are Gram positive or Gram variable and of very small size (<0.5 μ). They are able to grow in pure culture on the surface of nutrient agar in very small colonies. Although they have bacterial characteristics, they could not be identified as known bacteria. Agglutination tests are in favour of a serological relationship between the coccoid elements and P.P.L.O. The suggestion that these elements might be an outside contamination is made unlikely by several observations. The supposition that P.P.L.O.s are L forms of these coccoid elements should be considered further.     

Transposable elements.

Transposable elements comprise a major fraction of eukaryotic genomes. They are studied both because of their intrinsic biological interest and because they can be exploited as valuable research tools. Many interesting papers dealing with various aspects of the biology of these elements have been published during the past year and a number of new elements have been reported. Four areas in which particularly valuable contributions have been made are the mechanisms of transposition, the regulation of transposition, the use of transposable elements as research tools, and the biological function of transposable elements.     

SEM studies on vessels in ferns. 11. Ophioglossum

With scanning electron microscopy (SEM), the nature of metaxylem vessel elements and tracheids was examined in Ophioglossum crotalophomides, 0. pendulum subsp. falcatum , and 0. vulgatum roots and rhizomes. Vessels were identified in all species. End walls of vessel elements, which bear perforations, are like lateral wall pitting of those elements in the secondary wall framework and differ only in absence of pit membranes or presence of pit membrane remnants. Some of the perforations contain pit membrane remnants that have large pores, small porosities, or are threadlike or weblike in structure. Dimorphic perforations were found in some vessel elements of rhizomes of 0. pendulum subsp. falcatum. Tracheids are very likely present in addition to vessels in all three species. The secondary wall framework of both tracheids and vessels is basically scalariform, although deviations in pattern are present. Vessel elements of Ophiglossum are entirely comparable to those of leptosporangiate ferns.     

Origin and nature of vessels in monocotyledons. 5. Araceae subfamily Colocasioideae

Tracheary elements from macerations of roots and stems of one species each of five genera of Araceae subfamily Colocasioideae were studied by means of SEM (scanning electron microscopy). All of the genera have vessel elements not merely in roots, as previously reported for the family as a whole, but also in stems. The vessel elements of stems in all genera other than Syngonium are less specialized than those of roots; stem vessel elements are tracheid-like and have porose pit membrane remnants in perforations. The perforations with pit membrane remnants demonstrate probable early stages in evolution of vessels from tracheids in primary xylem of monocotyledons. The vessel elements with such incipient perforation plates lack differentiation in secondary wall thickenings between perforation plate and lateral wall, and such vessel elements cannot be identified with any reliability by means of light microscopy. The discrepancy in specialization between root and stem vessel elements in genera other than Syngonium is ascribed to probable high conductive rates in roots where soil moisture fluctuates markedly, in contrast with the storage nature of stems, in which selective value for rapid conduction is less. Syngonium stem vessels are considered adapted for rapid conduction because the stems in that genus are scandent. Correlation between vessel element morphology and ecology and habit are supported. Although large porosities in vessel elements facilitate conduction, smaller porosities may merely represent rudimentary pit membrane lysis.     

Nomenclature of transposable elements in prokaryotes.

Transposable elements are defined as specific DNA segments that can repeatedly insert into a few or many sites in a genome. They are classified as simple IS elements, more complex Tn transposons and self-replicating episomes. Definitions and nomenclature rules for these three classes of prokaryotic transposable elements are specified.     

Nomenclature of transposable elements in prokaryotes.

Transposable elements are defined as specific DNA segments that can repeatedly insert into a few or many sites in a genome. They are classified as simple IS elements, more complex Tn transposons, and self-replicating episomes. Definitions and nomenclature rules for these three classes of prokaryotic transposable elements are specified.     

Molecular evolution of P transposable elements in the genus Drosophila. I. The saltans and willistoni species groups

A phylogenetic survey using the polymerase chain reaction (PCR) has identified four major P element subfamilies in the saltans and willistoni species groups of Drosophila. One subfamily, containing about half of the sequences studied, consists of elements that are very similar to the canonical (and active) P element from D. melanogaster. Within this subfamily, nucleotide sequence differentiation among different copies from the same species and among elements from different species is relatively low. This observation suggests that the canonical elements are relatively recent additions to the genome or, less likely, are evolving slowly relative to the other subfamilies. Elements belonging to the three noncanonical lineages are distinct from the canonical elements and from one another. Furthermore, there is considerably more sequence variation, on the average, within the noncanonical subfamilies compared to the canonical elements. Horizontal transfer and the coexistence of multiple, independently evolving element subfamilies in the same genome may explain the distribution of P elements in the saltans and willistoni species groups. Such explanations are not mutually exclusive, and each may be involved to varying degrees in the maintenance of P elements in natural populations of Drosophila.      

A transposon-related palindromic repetitive sequence from C. elegans.

A family of transposon-like sequences in the C. elegans genome is described. This family, termed the Tc6 family, consists mostly of conserved, 1.6 kb elements. Four Tc6 elements or partial elements have been cloned and the DNA sequences of three were determined. One appears to be a complete element of 1603 nucleotides, consisting of a palindrome of 765 nucleotides, with a central, non-palindromic region of 73 nucleotides. Another has an identical structure except for an internal deletion. A third is a partial element terminating at a probable internal restriction site used for cloning. A fourth clone contained portions of the Tc6 sequence juxtaposed to non-Tc6 sequences. All C. elegans strains examined contain 20-30 Tc6 elements. The ends of Tc6 elements are conserved and have sequence similarity to the ends of C. elegans transposons Tc1 and Tc3. The ends of Tc6 elements also have sequence similarity to the heptamer portion of the immunoglobulin and T-cell receptor recombination signal sequence, raising the possibility of wide phylogenetic conservation of the recombination mechanism. Tc6 elements also share sequence motifs with plant-pathogenic viroid RNA's, possibly indicative of a Tc6 RNA replicative phase.     

Genomic organization and chromosomal distribution of rat ID elements.

Identifier (ID) elements are members of a family of short interspersed nuclear elements (SINEs) in rodents. We investigated the genomic organization and chromosomal distribution of the ID elements in the rat, mouse and Chinese hamster. Southern blot hybridization analysis revealed that the ID elements are widespread in the rat genome, but concentrated in the mouse and Chinese hamster genomes, and that the copy of ID elements in the rat is about 5 times and 50 times that in the mouse and Chinese hamster, respectively. FISH analysis showed that the ID elements are predominantly distributed in the R-band regions of rat chromosomes. In mouse and Chinese hamster chromosomes, no specific distribution pattern of the ID elements was found. Furthermore, we found a distinct group of derivative ID elements in the rat, which contain partially repeated ID core domains, by PCR amplification using an ID core sequence. Such derivatives were not found in either the mouse or Chinese hamster. These findings suggest that explosive amplification of the ID elements in the rat has been accompanied by the occurrence of derivative ID elements and a predominant localization to the R-band regions. Similar associations found in the Alu family, one of the human SINEs, allow us to speculate that the rat ID elements and the human Alu family have analogous functions in chromosomal organization.     

Trace elements in agroecosystems and impacts on the environment.

Trace elements mean elements present at low concentrations (mg kg-1 or less) in agroecosystems. Some trace elements, including copper (Cu), zinc (Zn), manganese (Mn), iron (Fe), molybdenum (Mo), and boron (B) are essential to plant growth and are called micronutrients. Except for B, these elements are also heavy metals, and are toxic to plants at high concentrations. Some trace elements, such as cobalt (Co) and selenium (Se), are not essential to plant growth but are required by animals and human beings. Other trace elements such as cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni), mercury (Hg), and arsenic (As) have toxic effects on living organisms and are often considered as contaminants. Trace elements in an agroecosystem are either inherited from soil parent materials or inputs through human activities. Soil contamination with heavy metals and toxic elements due to parent materials or point sources often occurs in a limited area and is easy to identify. Repeated use of metal-enriched chemicals, fertilizers, and organic amendments such as sewage sludge as well as wastewater may cause contamination at a large scale. A good example is the increased concentration of Cu and Zn in soils under long-term production of citrus and other fruit crops. Many chemical processes are involved in the transformation of trace elements in soils, but precipitation-dissolution, adsorption-desorption, and complexation are the most important processes controlling bioavailability and mobility of trace elements in soils. Both deficiency and toxicity of trace elements occur in agroecosystems. Application of trace elements in fertilizers is effective in correcting micronutrient deficiencies for crop production, whereas remediation of soils contaminated with metals is still costly and difficult although phytoremediation appears promising as a cost-effective approach. Soil microorganisms are the first living organisms subjected to the impacts of metal contamination. Being responsive and sensitive, changes in microbial biomass, activity, and community structure as a result of increased metal concentration in soil may be used as indicators of soil contamination or soil environmental quality. Future research needs to focus on the balance of trace elements in an agroecosystem, elaboration of soil chemical and biochemical parameters that can be used to diagnose soil contamination with or deficiency in trace elements, and quantification of trace metal transport from an agroecosystem to the environment.     

Meiosis in triploid Lolium. I. Synaptonemal complex formation and chromosome configurations at metaphase I in aneuploid autotriploid L. multiflorum.

A spreading technique for synaptonemal complexes (SCs) was applied to pollen mother cells of two aneuploid genotypes of autotriploid Lolium multiflorum (2n = 3x + 1 = 22). In the earliest nuclei analyzed the axial elements are in six groups of 3 and one group of 4. Most groups have formed multivalents with from one to five pairing partner exchanges, but there are also groups that have formed bivalents and univalents. Some axial elements have formed triple associations, in one case for the length of the trivalent. Unsynapsed axial elements remain aligned with their homologous SCs into pachytene, but this alignment is abolished as these axes pair heterologously among themselves until the entire axial element complement is synapsed. At metaphase I most chromosomes are associated as trivalents and quadrivalents.     

Trace elements in man.

It is likely that most, if not all, of the elements found to be essential in animals will be shown to be so for man, and the clinical picture produced by deficiency of the elements in the human patient will differ little from that seen in the animal, although this has been established for only five elements (I, Fe, Cu, Co and Zn). However, the link between lack of a given element in the soil and a human patient is far less direct and much more complex than that met with in the animal grazing on deficient pastures, except in isolated primitive communitis. Zn is the most protean of the trace elements and has been chosen to illustrate this in human practice. Excesses of essential elements (both trace and major) give rise to toxic effects and the importance of a proper balance especially of the transitional elements in the human diet is discussed with special reference to Cu, Zn and Fe. Certain non-essential trace elements are individual and community hazards: Cd, Pb and Hg are the principal offenders for humans. Mankind is now largely dependent on grassland products, cereals and livestock with increasing dominance of the former in human nutrition. This has reduced the bioavailability of trace elements so that study of trace metals, especially Zn and Cu, in skeletal and dental remains at human burial and occupation sites should prove useful in assessing the consequences of this striking change in dietary habits.     

Composite rhytidectomy.

Signs of aging in the face reflect the change in position of deep anatomic elements, which are the platysma muscle, cheek fat, and the orbicularis oculi muscle. These changes occur from progressive ptosis of these elements, which continue to keep their intimate relationship with each other throughout the aging process. Conventional face lift procedures disrupt this normal relationship by separating the skin from these elements. All SMAS techniques reposition only the platysma muscle without repositioning the cheek fat and orbicularis muscle. This composite rhytidectomy allows elevation of a composite musculocutaneous flap containing all three elements for repositioning while maintaining their intimate relationship with each other and with the skin. One-hundred and sixty-seven composite rhytidectomies have been done with impressive results and minimal complications.     

Trace elements in the atmosphere.

The distribution and behaviour of particulate trace elements in the atmosphere have been studied by continuous measurements for 5 years at seven non-urban sites in the United Kingdom. Samples have been taken regularly of airborne dust, rainwater and dry deposition: these have been analysed for up to 36 elements. Concentrations of trace elements vary considerably between sites but the relative concentrations are among uniform: this suggests similarity of origin or good atmospheric mixing. By comparing the relative concentrations with those in soil it is possible to differentiate between trace elements that are derived from soil and those that may be attributed to industrial activity. This classification is supported by estimates of the particle sizes in air. The deposition of trace elements can be related to the concentrations presnet in soil and to the annual removal by crops. Retrospective analyses of stored samples from one site describe the history of trace element concentrations in air since 1957. The sea surface is considered as a possible source of atmospheric trace elements.     

土壤微量元素测试及其应用

土壤微量元素测试在其发展历史过程中,不断改进技术,逐渐深入地揭示土壤供给微量元素的能力,对指导施肥和保护生态环境起着积极的作用。现代测试手段发展到广泛采用原子吸收光谱(AA)和电感耦合等离子体发射光谱(ICP),但比色法(光度法)和极谱法不仅设备比较简便,而且新的显色剂、催化系统等方面的研究进展,使其对某些元素的测定灵敏度和准确度超过AA和ICP,从而在微量元素测试技术中仍占据一定地位。土壤溶液抽取技术虽然有所改进,但有效态微量元素仍然主要是选用适当提取剂来提取测定。临界值和分级标准的确定是应用测定值的桥梁。作者曾采用全幅分级标准分级制图,确定缺素面积和需肥区域,再根据土壤含量水平和增产幅度之间的函数关系预测增产效果和投入的经济效益。     

Conservation of ARS elements and chromosomal DNA replication origins on chromosomes III of Saccharomyces cerevisiae and S. carlsbergensis.

DNA replication origins, specified by ARS elements in Saccharomyces cerevisiae, play an essential role in the stable transmission of chromosomes. Little is known about the evolution of ARS elements. We have isolated and characterized ARS elements from a chromosome III recovered from an alloploid Carlsberg brewing yeast that has diverged from its S. cerevisiae homeologue. The positions of seven ARS elements identified in this S. carlsbergensis chromosome are conserved: they are located in intergenic regions flanked by open reading frames homologous to those that flank seven ARS elements of the S. cerevisiae chromosome. The S. carlsbergensis ARS elements were active both in S. cerevisiae and S. monacensis, which has been proposed to be the source of the diverged genome present in brewing yeast. Moreover, their function as chromosomal replication origins correlated strongly with the activity of S. cerevisiae ARS elements, demonstrating the conservation of ARS activity and replication origin function in these two species.     

Interrelationships of selenium with other trace elements.

Biological interactions between selenium and a number of other elements occur that render selenium much less toxic than when it is present alone. These elements are arsenic, mercury, cadmium, and copper. Furthermore, the presence of selenium reduces the toxicity of mercury and cadmium. These are general biological interactions and have been found to occur in a number of animal species under a variety of conditions. It has been shown that the reaction products of selenium with mercury and cadmium are less toxic than an equal amount of selenium fed alone to chicks. The presence of arsenic shifts the excretion of selenium to the bile. There is no conclusive evidence that the presence of other elements reduces the absorption or retention of selenium. It is possible that some of the interactions are caused by the formation of a compound by selenium and other elements which has less affinity for active groups on biologically active compounds.--Hill, C.H. Interrelationships of selenium with other trace elements.     

Composite transposable elements in the Xenopus laevis genome.

Members of two related families of transposable elements, Tx1 and Tx2, were isolated from the genome of Xenopus laevis and characterized. In both families, two versions of the elements were found. The smaller version in each family (Tx1d and Tx2d) consisted largely of two types of 400-base-pair tandem internal repeats. These elements had discrete ends and short inverted terminal repeats characteristic of mobile DNAs that are presumed to move via DNA intermediates, e.g., Drosophila P and maize Ac elements. The longer versions (Tx1c and Tx2c) differed from Tx1d and Tx2d by the presence of a 6.9-kilobase-pair internal segment that included two long open reading frames (ORFs). ORF1 had one cysteine-plus-histidine-rich sequence of the type found in retroviral gag proteins. ORF2 showed more substantial homology to retroviral pol genes and particularly to the analogs of pol found in a subclass of mobile DNAs that are supposed retrotransposons, such as mammalian long interspersed repetitive sequences, Drosophila I factors, silkworm R1 elements, and trypanosome Ingi elements. Thus, the Tx1 elements present a paradox by exhibiting features of two classes of mobile DNAs that are thought to have very different modes of transposition. Two possible resolutions are considered: (i) the composite versions are actually made up of two independent elements, one of the retrotransposon class, which has a high degree of specificity for insertion into a target within the other, P-like element; and (ii) the composite elements are intact, autonomous mobile DNAs, in which the pol-like gene product collaborates with the terminal inverted repeats to cause transposition of the entire unit.