Location of nucleolar organizers in animal and plant chromosomes by means of an improved N-banding technique

With an improved N-banding technique, the location of nucleolar organizing region was determined in 27 kinds of material including mammals, a marsupial, birds, amphibians, fishes, an insect and plants. In most cases the N-bands were clearly located on certain specific regions of chromosomes, such as the secondary constriction, satellite, centromere, telomere and heterochromatic segment, while in some species they were detected as very minute bodies distributed over many chromosomes. From the available cytological and biochemical data it was suggested that the N-bands represent certain structural non-histone proteins specifically linked to nucleolar organizers in various eukaryotic chromosomes.     

Karyotype and DNA-content evolution in ten species of Crepis (Asteraceae) distributed in Bulgaria

Ten Crepis species from Bulgaria—five perennials (C. viscidula, C. paludosa, C. coryzaefolia, C. bilhynica, C. schochtii) four annuals (C. pulchra, C. sancta, C. setosa, C. zacintha) and one biennial (C. biennis)—were analysed karyologically using haematoxyh staining, Feulgen cytophotometry (scanning densitometry and video-based image analysis), and DNA flow cytometry with propidium iodide. All taxa but the biennial are diploids with descending basic chromosome numbers, x=6, 5, 4, 3. Significant positive correlations were found between nuclear DNA content and karyotype length and nuclear DNA content and karyotypic asymmetry. Together with the results of previous authors our data suggest that evolutionary advancement could be correlated with more symmetrical karyotypes. Negative significant correlations were established between presumably advanced growth habit (from rhizomatous and tap-rooted perennials towards highly specialized annuals) and chromosome number and karyotype length. Nuclear DNA 1C-values on average were higher in perennials than in annuals, but the ranges were overlapping and the differences not significant. Crepis biennis (2n=c. 40, presumably 10x) had the highest DNA quantity, but calculated at its x-level ranked relatively low in the species sample.     

Unequal evolutionary rates between annual and perennial lineages of checker mallows (Sidalcea, Malvaceae): evidence from 18S-26S rDNA internal and external transcribed spacers

Heterogeneous DNA substitution rates were found in the 18S-26S nuclear ribosomal DNA internal transcribed spacer (ITS) and external transcribed spacer (ETS) regions of Sidalcea (Malvaceae), a putatively young genus of annuals and perennials. The majority of comparisons revealed that the annual species had significantly higher molecular evolutionary rates than the perennials, whereas rates were consistently homogenous between obligate annual species. These findings led us to conclude that generation time or possibly another biological factor distinguishing annuals and perennials has influenced rates of molecular evolution in SIDALCEA: The congruence of relative-rate test results across both spacer regions reinforced the association between life history and rate of rDNA evolution across lineages of checker mallows. Evolutionary rate variation within perennials mainly involved three basally divergent lineages. The faster rate in one lineage, Sidalcea stipularis, compared with other perennials may be the result of genetic drift in the only known, small, population. The other two basally divergent lineages had slower evolutionary rates compared with the remaining perennials; possible explanations for these differences include rate-reducing effects of a suffrutescent (rather than herbaceous) habit and seed dormancy.     

Annual and Perennial Grass Growth on Nitrogen-Depleted Decomposed Granite

Decomposed granite (DG) is often difficult to revegetate because of its low nitrogen (N) content and poor physical properties. Use of soluble fertilizers on DG sites increases plant-available N but may encourage invasive annuals to grow rapidly and exclude perennial species. This study evaluates the effect of N availability on two potential DG revegetation species: an invasive, exotic annual grass ( Bromus mollis ) and a native perennial grass ( Elymus glaucus ). Plants in 10-L pots filled with DG were irrigated with all essential elements except N, which was provided in treatments ranging from zero to 1000 μ M NO₃-N. Shoot biomass and root distribution were measured in monocultures and in mixtures of annual and perennial plants, both when the two species were seeded simultaneously and when the perennials were seeded 50 days prior to the annuals. At the higher N treatments, growth of annuals exceeded that of perennials. At solution N concentrations lower then the 50–100 μ M treatments, however, growth of the perennial grasses equaled or exceeded that of the annuals. When seeded simultaneously, both species showed reduced biomass in mixtures to an extent similar to that when each species grew alone. When the perennials were already established, the biomass of annuals was reduced proportionately more than that of perennials, even at the highest N treatment. At low and medium N treatments, root placement of the perennial was deeper than that of the annual. At high N treatments, however, root distribution of both species was similar, and the deep rooting characteristic of the perennial was no longer observed.     

Giemsa C-banded karyotypes and taxonomic relationships of some North AmericanAllium species and their relationship to Old World species (Liliaceae)

The somatic karyotypes of six North AmericanAllium species and the EuropeanA. scorzonerifolium have been investigated using a Giemsa C-banding technique. All species have a chromosome number of 2n = 14. InA. scorzonerifolium and the three North American speciesA. dichlamydeum, A. fibrillum andA. unifolium C-bands are restricted to two pairs of nucleolar chromosomes. Each chromosome has a band proximal to the nucleolar constriction and a positively banded satellite. InA. acuminatum, in addition to the bands associated with the nucleolar constrictions, all chromosomes also have pericentromeric bands.A. cernuum exhibits a distinctive banding style: two chromosome pairs with bands adjacent to the nucleolar constrictions and four pairs with telomeric bands on their short arms. In the karyotype ofA. geyeri neither C-bands nor nucleolar chromosomes were found.—A comparison of the banding styles together with other cytological and morphological characters of these species with old world members ofAllium reveals:A. cernuum closely resembles species within subgenusRhizirideum, whereas the other species studies exhibit many similarities with subgenusMolium. Their sectional grouping and their relationships with Old World species are discussed.     

California perennial grasses are physiologically distinct from both Mediterranean annual and perennial grasses

In the Central Valley of California, native perennial grass species have been largely replaced by Eurasian annual species, while in many parts of the Mediterranean Basin native perennial grasses continue to dominate, even on disturbed or degraded sites. We assessed whether differences in summer rainfall patterns have lead to the development of different plant-water strategies between grasses from these two regions. We compared six measures of plant-water physiology for three guilds of grasses: California perennial grasses, Mediterranean perennial grasses, and Mediterranean annual grasses. Discriminant analysis distinguished between the three guilds; Mediterranean perennial grasses were characterized by a more conservative water-relations physiology than Mediterranean annual grasses, whereas California perennial grasses were in some ways intermediate between the two Mediterranean grass guilds. For individual traits, California perennial grasses were either intermediate or more like Mediterranean annuals than Mediterranean perennials. Our results suggest California perennials are more drought tolerant than Mediterranean annuals but less drought tolerant than Mediterranean perennials, despite the fact that California??s Central Valley has a more intense summer drought than the Mediterranean Basin. These patterns may help explain why Mediterranean annuals, but not Mediterranean perennials, have been more successful invaders of interior California grasslands.     

两种髭蟾的Ag—NORs,C—带及核型的研究

本文叙述和比较了峨眉髭蟾和哀牢髭蟾的核型,C-带和Ag-NORs,结果表明两者有下列相同方面:2n=26(6+7)、除No.3为SM外,其余诸对概为M,次缢痕和Ag-NoRs位于6q,并都表现出异形现象,No.1长臂有长度异形,但所增染色体片断不呈现C-带正染,C-带正染主要是在各对染色体的着丝点区域,另外No.2短臂近着丝区域亦为正染。这些表明二者之间有很大的核带型同源性。但是二者间在核型的某些对应染色体之间,在相对长度(6对)和臂比值(2对)方面有显著性差异,故可推测其机制是相互易位和臂间倒位。另外,哀牢髭蟾未发现与性别相关的异形性染色体。     

中国水龟类的核型与银带带型研究

以血培养细胞为材料,研究了三种水龟的核型与ＮＯＲｓ,结果表明,染色体数均为２ｎ＝５２,核型模式９＋５＋１２,属龟科核型中的原始类型,但眼斑水龟ＮＦ＝７６,而四眼斑水龟和黄喉拟水龟的ＮＦ＝７８。从核型结构看,眼斑水龟与四眼斑水龟相似,而黄喉拟水龟则有较大差别,作者还发现黄喉拟水龟核型的一些重要特征,即其Ａ组Ｎｏ．３和Ｎｏ．６染色体有次缢痕,Ｎ．别,作者还发现黄喉拟水龟核型的一些重要特征,即Ａ组这些是     

Karyotypes,nucleoli, and amphiplasty in hybrids between Hordeum vulgare L. and H. bulbosum L.

Chromosome measurements were carried out in Hordeum vulgare, H. bulbosum, and their diploid, triploid, and tetraploid hybrids. The chromosomes were classified by using relative values, and thus karyotypes were established. For comparison of these karyotypes both relative and absolute values were used. It was concluded that differential amphiplasty occurred, whereas neutral amphiplasty could not be demonstrated. In the hybrids the relative length of the parts of the chromosomes (long arm, short arm, satellite) was not changed in comparison with these lengths in the pure species. The karyotypes of both species had considerable similarities. From comparing the mean absolute genome lengths, it was, however, concluded that in the pure species, as well as in all hybrid types, the chromosomes of H. vulgare were longer than those of H. bulbosum. In the diploid and tetraploid hybrids the mean genome lengths were shorter than those in the pure species and the triploid hybrids. The differential amphiplasty was such that the secondary constriction of chromosome 6 of H. bulbosum, did not show up in the hybrids. This could be related to the suppression of nucleolar formation in the genome of H. bulbosum, because the maximum number of nucleoli in root tip cells equalled the number of satellite chromosomes. Finally it was found that the pattern of nucleolar fusion in diploid and triploid hybrids deviated from the expectation. The results were discussed in relation to chromosomal disturbances that occurred in the hybrid tissues and that resulted in elimination of chromosomes and other effects.     

Perennial polypores as indicators of annual and red-listed polypores

Many polypores are specialized in their requirements for substrate and environment, and they have been suggested to indicate the continuity of coarse woody debris or naturalness of a forest stand. However, the use of polypores as indicators of conservation value is restricted by the temporally limited appearance of annual fruit bodies. We studied whether the species richness of perennial polypores (perennials) can be used to predict the species richness of annual or annual red-listed polypores (annuals). Our data included 1471 separate datasets (sample plots or larger inventoried areas) in different parts of Finland and Russian Karelia, ranging from the southern to northern boreal zone. At the large scale (the whole area) the number of perennials explained about 70% of the variation in the number of annuals, and about 67% in the number of red-listed annuals. A minimum set of 40–60 perennial occurrences gave a reliable estimate on the species richness of annuals, and 60–80 occurrences on the species richness of red-listed annuals. The richness of perennials predicted the richness of annuals and, in particular, richness of red-listed annuals, better than the size of inventoried area. According to our results, perennial polypores can be used as a surrogate for overall polypore species richness in natural and seminatural boreal forests, but the predictive power is weaker in managed forests. In addition, the relationship between the perennial and annual species seems to differ in different vegetation zones, management types and forest types. Due to this variation direct application of the indicator values derived from different vegetation zones and management or forest types are not recommended. Since perennials are easier to identify than annuals, detectable throughout the year, and have much smaller year-to-year variation, their use as an indicator group seems to offer advantages regarding the timing and cost-efficiency of inventories.     

GERMINATION ECOPHYSIOLOGY OF HERBACEOUS PLANT SPECIES IN A TEMPERATE REGION

Germination phenology data have been collected from 75 winter annuals, 49 summer annuals, 28 monocarpic perennials, and 122 polycarpic perennials, and experimental investigations of dormancy breaking and germination requirements have been conducted on 56 winter annuals, 32 summer annuals, 18 monocarpic perennials, and 73 polycarpic perennials. The purpose of these studies was to determine if there are correlations between the dormancy breaking and germination requirements of seeds and the germination phenology, life cycle type, habitat requirements, range of geographical distribution, and phylogenetic relationships of the species. Germination phenology is highly correlated with the responses of seeds to the yearly temperature cycle. Species with winter and summer annual life cycles have predictable germination characteristics, but monocarpic and polycarpic perennials do not. Several dormancy types may be found in a given habitat, and narrowly endemic and widely-distributed species in the same genus may have similar germination characteristics. Within some families there is a tendency for a particular type of seed-temperature response to be very important, but frequently this is related to the predominance of a given life cycle type in the family.     

Host plant predictability and the feeding patterns of monophagous,oligophagous, and polyphagous insect herbivores

Summary Host plant preferences for 34 insect herbivore species are reported. Most polyphagous herbivores feeding on annuals, herbaceous perennials, and woody perennials show distinct preferences for the least abundant plant species among their various host plants. In addition, some populations of widely distributed polyphagous species are much more specialized in their diet than host plant lists alone would suggest. The high level of polyphagy on annuals and herbaceous perennials is suggested to be strongly influenced by the unpredictability of the host plant that is, in turn, controlled by environmental variability. Oligophagous herbivores preferred the least abundant woody perennials on the study sites. Ten of the 22 monophagous herbivores preferred the rarest of all the plant species on the same sites.     

Accumulation of buried seeds and establishment of ruderal therophytic communities in disturbed habitat,central Japan

The establishment and maintenance mechanisms of pioneer communities were investigated in ruderal habitats under two disturbance regimes, frequent and infrequent cutting sites. In the infrequent cutting sites, large perennials dominated through the year and inhibited the invasion of annuals, and the perennial community succeeded to forest stage if the cutting was stopped. In the frequent cutting sites, therophytic communities of winter and summer annuals alternated by season. Fresh seeds of both winter and summer annuals are dormant, but they have different germination times and thus can share the same sites in different seasons. Wind-dispersed biennials and large perennials have nondormant seeds and easily invade the sites; however, they are unable to mature to reproductive phase due to recurrent cuttings. The therophytic species, which can complete their life-cycle in a period between cuttings, accumulate seeds in the soils and are maintained by these buried seeds (seed bank annuals) during recurrent disturbances. The seed bank is compensation for the dispersal inefficiency of seed bank annuals. After abandonment of the frequent cutting sites, the buried seeds of seed bank annuals germinate and become the first-year pioneers. Thus, seed bank annuals are not invasive colonizers but are the remnants of the ruderal weed communities before abandonment.     

Chromosome nucleolus organizer regions of the African green monkey

The silver staining Ag-I for detection of nucleolar organizer regions (NOR) in the African green monkey chromosomes was used. NOR were situated on the secondary constrictions of one pair of homologous marker chromosomes and consisted of two parts. A block of condensed chromatin was seen in the middle of the despiralized portion corresponding to the secondary constriction. The data suggest that the stalks of satellites of chromosomes, rather than satellites themselves, are regions of nucleolar organizer.     

How do steppe plants follow their optimal environmental conditions or persist under suboptimal conditions? The differing strategies of annuals and perennials

For a species to be able to respond to environmental change, it must either succeed in following its optimal environmental conditions or in persisting under suboptimal conditions, but we know very little about what controls these capacities. We parameterized species distribution models (SDMs) for 135 plant species from the Algerian steppes. We interpreted low false‐positive rates as reflecting a high capacity to follow optimal environmental conditions and high false‐negative rates as a high capacity to persist under suboptimal environmental conditions. We also measured functional traits in the field and built a unique plant trait database for the North‐African steppe. For both perennial and annual species, we explored how these two capacities can be explained by species traits and whether relevant trait values reflect species strategies or biases in SDMs. We found low false‐positive rates in species with small seeds, flowers attracting specialist pollinators, and specialized distributions (among annuals and perennials), low root:shoot ratios, wide root‐systems, and large leaves (perennials only) (R² = .52–58). We found high false‐negative rates in species with marginal environmental distribution (among annuals and perennials), small seeds, relatively deep roots, and specialized distributions (annuals) or large leaves, wide root‐systems, and monocarpic life cycle (perennials) (R² = .38 for annuals and 0.65 for perennials). Overall, relevant traits are rarely indicative of the possible biases of SDMs, but rather reflect the species' reproductive strategy, dispersal ability, stress tolerance, and pollination strategies. Our results suggest that wide undirected dispersal in annual species and efficient resource acquisition in perennial species favor both capacities, whereas short life spans in perennial species favor persistence in suboptimal environmental conditions and flowers attracting specialist pollinators in perennial and annual species favor following optimal environmental conditions. Species that neither follow nor persist will be at risk under future environmental change.     

Comparison of Acetyl-CoA carboxylase 1 (Acc-1) gene diversity among different Triticeae genomes

It has widely been documented that life form and mating system have significant influences on genetic diversity. In the tribe Triticeae, several genera contain both annual and perennial species, whereas other genera comprise strictly annual or perennial species. It was suggested that Triticeae annuals have originated from Triticeae perennials. The present study aims to analyze nucleotide diversity of Acc-1 gene among different Triticeae genomes, and attempts to link effects of life history (annuals and perennials) and mating systems. The nucleotide diversity of 364 Acc-1 sequences in Triticeae species was characterized. The highest estimates of nucleotide diversity values (π = 0.01919, θ = 0.03515) were found for the Ns genome among the genomes analyzed. Nucleotide diversities in the D genome and Ns genome of polyploids are higher than those in respective genomes of diploids, while in the St genome of polyploids, it is lower than that in the St genome of diploids. The averaged π value (0.013705) in the genomes of perennials is more than twice of the value (0.00508) in the genomes of annuals. The averaged π value (0.01323) in the genomes of outcrossing species is two-fold of the value (0.005664) in the genomes of selfer. Our results suggested that the evolutionary history and mating system may play an important role in determining nucleotide diversity of Acc-1 gene in each genome.     

The nucleolar chromatin and the secondary constriction

We have traced the nucleolar chromatin from early prophase to the metaphase stage. In prophase this chromatin begins to condense and in metaphase it is fully condensed. In mitotic chromosomes, this chromatin remains surrounded by achromatic materials resembling the fibrillar centre. As such this region of the chromosomes appears as a gap or constriction at the light microscope level. The possible role of this achromatic material in relation to nucleologenesis and satellite association has been discussed.     

Ecological effects of cell-level processes: genome size,functional traits and regional abundance of herbaceous plant species

Background and Aims

Genome size is known to be correlated with a number of phenotypic traits associated with cell sizes and cell-division rates. Genome size was therefore used as a proxy for them in order to assess how common plant traits such as height, specific leaf area and seed size/number predict species regional abundance. In this study it is hypothesized that if there is residual correlation between genome size and abundance after these traits are partialled out, there must be additional ecological effects of cell size and/or cell-division rate.

Methods

Variation in genome size, plant traits and regional abundance were examined in 436 herbaceous species of central European flora, and relationships were sought for among these variables by correlation and path analysis.

Key Results

Species regional abundance was weakly but significantly correlated with genome size; the relationship was stronger for annuals (R² = 0·145) than for perennials (R² = 0·027). In annuals, genome size was linked to abundance via its effect on seed size, which constrains seed number and hence population growth rate. In perennials, it weakly affected (via height and specific leaf area) competitive ability. These relationships did not change qualitatively after phylogenetic correction. In both annuals and perennials there was an unresolved effect of genome size on abundance.

Conclusions

The findings indicate that additional predictors of regional abundance should be sought among variables that are linked to cell size and cell-division rate. Signals of these cell-level processes remain identifiable even at the landscape scale, and show deep differences between perennials and annuals. Plant population biology could thus possibly benefit from more systematic use of indicators of cell-level processes.     

青藏高原东部高山植物的水分利用效率与氮素利用效率研究

对生长在青藏高原东部隶属于23科、49属的71种高山植物(包括多年生和一年生植物)的稳定碳同位素比值、氮含量以及碳/氮比率进行了分析,并以稳定碳同位素比值及碳/氮比率来分别指示植物的水分利用效率和氮素利用效率.结果表明:(1)多年生植物稳定碳同位素比值显著高于一生年植物,而碳/氮比率显著低于一年生植物(P<0.01),氮含量两者无显著性差异.(2)多年生植物和一年生植物的稳定碳同位素比值均与碳/氮比率呈显著负相关(-0.643**和-0.707),而与氮含量均无明显相关性.研究证实,在自然条件下多年生植物的水分利用效率比一年生植物更高,而氮素利用效率却更低;高山植物水分利用效率和氮素利用效率存在明显的权衡",即植物不能同时提高水分利用效率和氮素利用效率,高水分利用效率的代价是降低氮素利用效率,青藏高原不同植物即使在相同环境条件下具有不同适应对策.