Ovule survivorship,brood size,life history,breeding systems,and reproductive success in plants

The percentage of ovules developing into seeds (seed-ovule ratios, S/O ratios) is about 85% in annuals but only approximately 50% in perennials.In both annuals and perennials, these typical S/O ratios occur regardless of the kind of breeding system, although many annuals are normally self-pollinating whereas perennials are virtually all cross-pollinating. The mean number of seeds maturing within individual fruits is defined as brood size, and is correlated with different modes of dispersal and strategies of ovule packging. Annuals also have significantly higher brood sizes (21.7) than perennials (<9.9). Among perennials, woody plants have both lower S/O ratios (32.7%) and brood sizes (3.3) than herbaceous perennials (57.2%, 13.5). S/O ratios appear to be largely determined genetically, whereas resource limitations are perhaps more critical in terms of regulating flower production. Among perennials, increased exposure to predators and pathogens is suggested as the best explanation for theevolution of breeding systems favoring genetic recombination. The maintenance of genetic polymorphisms, however, inevitably increases the frequency of lethal and sub-lethal allelic combinations (and perhaps mutations?), that appear to be responsible for the lower S/O ratios in perennials.     

Mitotic cycle time and DNA content in annual and perennialMicroseridinae (Compositae,Cichoriaceae)

Within eight annual and perennialMicroseridinae species studied, the duration of the mitotic cycle is positively correlated with the nuclear DNA content, cycle time (hrs) = 7.3 + 0.32 × pg DNA/nucleus. Within the generaAgoseris andMicroseris, the annuals have lower DNA contents and more rapid mitotic cycle times than do the perennials. This relationship is predicted by the nucleotypic theory ofBennett. Annual species ofPyrrhopappus have relatively high DNA contents and a proportionately longer mitotic cycle time, but contrary to that expected by the nucleotypic theory as originally proposed have the fastest growth rate and shortest generation time observed in theMicroseridinae. This rapid developmental rate is discussed, nucleotypically, however, by analyzing relationships between DNA content, mitotic cycle time, and cell size.     

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.     

Differential utilization of summer rains by desert plants

Summary Seasonal changes in the hydrogen isotope ratios of xylem waters were measured to determine water sources used for growth in desert plants of southern Utah. While all species used winter-spring recharge precipitation for spring growth, utilization of summer rains was life-form dependent. Annuals and succulent perennials exhibited a complete dependence on summer precipitation. Herbaceous and woody perennial species simultaneously utilized both summer precipitation and remaining winter-spring precipitation, with herbaceous species much more reliant on the summer precipitation component. Several of the woody perennials exhibited no response to summer precipitation. Currently, precipitation in southern Utah is evenly partitioned between winter and summer time periods; however, global circulation models predict that summer precipitation will increase in response to anticipated climate change. Our data indicate that components within the community will differentially responde to the change in precipitation patterns. These results are discussed in relation to impact on competition and possible changes in community structure.     

Cytophotometric estimation of in situ DNA content in several species of Araceae.

A wide variation in the in situ 4C DNA content, ranging from 15.02 pg to 54.09 pg was found in thirteen genera of the family Araceae. The obligate perennial species showed greater 4C DNA values compared with the facultative perennials and annuals. A remarkable heterogeneity in 4C nuclear DNA amounts was noted among obligate perennials. Intraspecific constancy in the amount of 4C DNA was recorded. The nuclear DNA content correlated positively with chromosome size, duration of the mitotic cycle, and annual to perennial growth forms. Despite an extensive variation in DNA content among the aroids investigated, each species was distinctly characterized by its specific nuclear DNA value, indicating its usefulness in taxonomic characterization and comparison of different aroids.     

DNA Content Variation and Its Significance in the Evolution of the Genus Micrasterias (Desmidiales,Streptophyta)

It is now clear that whole genome duplications have occurred in all eukaryotic evolutionary lineages, and that the vast majority of flowering plants have experienced polyploidisation in their evolutionary history. However, study of genome size variation in microalgae lags behind that of higher plants and seaweeds. In this study, we have addressed the question whether microalgal phylogeny is associated with DNA content variation in order to evaluate the evolutionary significance of polyploidy in the model genus Micrasterias. We applied flow-cytometric techniques of DNA quantification to microalgae and mapped the estimated DNA content along the phylogenetic tree. Correlations between DNA content and cell morphometric parameters were also tested using geometric morphometrics. In total, DNA content was successfully determined for 34 strains of the genus Micrasterias. The estimated absolute 2C nuclear DNA amount ranged from 2.1 to 64.7 pg; intraspecific variation being 17.4–30.7 pg in M. truncata and 32.0–64.7 pg in M. rotata. There were significant differences between DNA contents of related species. We found strong correlation between the absolute nuclear DNA content and chromosome numbers and significant positive correlation between the DNA content and both cell size and number of terminal lobes. Moreover, the results showed the importance of cell/life cycle studies for interpretation of DNA content measurements in microalgae.     

Applying DNA C-values to evaluate invasiveness of angiosperms: validity and limitation

DNA C-values might be one of important indices in the evaluation of angiospermous invasiveness. To test this viewpoint, we compared DNA 1C-values and basic genome sizes in 3,676 angiosperms. The results suggest that: (1) the two nuclear values vary greatly among different groups, e.g., significantly higher in herbs than in trees, in monocots than in dicots, in perennials than in non-perennials; (2) the two nuclear values both have significant effects on plant invasiveness, especially in herbs, dicots, monocots, perennials, non-perennials, diploids, polyploids, Compositae, and Poaceae, while not significant in trees and Fabaceae. Similar to weeds, the two values in crops are low, which suggests that crops may commonly hold higher invasive potential; (3) to evaluate the invasiveness of a given species, the information about ploidy level is necessary, and for polyploids, basic genome sizes are more reliable. For the results suggest that the selection favors polyploids in weeds at least partly because of the downsizing of basic genome size along with polyploidization.     

The nuclear DNA content of diploid and triploid Poeciliopsis and other poeciliid fishes with reference to the evolution of unisexual forms

The nuclear DNA content of all diploid poeciliid fishes known to date ranges from 1.30 to 1.92 pg, and is thus lower than the median amount for fishes in general, and teleost fishes in particular (2.0 pg). As is expected, triploid forms of Poecilia and Poeciliopsis have half again as much nuclear DNA as diploid forms. Unisexual forms of the two genera tend to have slightly less nuclear DNA than the amount expected if compared with their gonochoristic progenitors.     

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.     

THE BASE COMPOSITION OF RIBONUCLEIC ACID IN LAMPBRUSH CHROMOSOMES, NUCLEOLI, NUCLEAR SAP, AND CYTOPLASM OF TRITURUS OOCYTES

The base composition of RNA's extracted from chromosomes, nucleoli, nuclear sap, and cytoplasm of Triturus oocytes has been determined by microelectrophoresis. The chromosomal RNA has a content of guanine+cytosine equal to that of DNA, but there is no complementarity in the composition as for DNA. Nuclear sap contains a highly variable RNA with a tendency towards high uracil values. Nucleolar and cytoplasmic RNA's are similar in composition and both are of the guanine-cytosine rich type. The chromosomes and nucleoli contain roughly equivalent amounts of RNA, somewhat less than is present in the nuclear sap. The RNA/DNA ratio of the whole chromosomes is about 10. However, the ratio in the synthetically active regions, the loops, is much higher, since the loops contain all the chromosomal RNA but only a small fraction of the DNA.     

Variation in periodic replication of the chromosome in Escherichia coli B/rTT.

A method using 5-bromouracil photolysis induction with 313 nm radiation was employed to estimate the variation in the period between successive rounds of DNA replication in rapidly growing cultures of Escherichia coli$\text{B}\text{rTT}$ The coefficient of variation of this period was 9.3%, which is significantly less than the corresponding value of about 20% reported for variation in the cell interdivision period. Thus chromosome replication is much more tightly controlled than is cell division. The reduced variability of the DNA replication cycle indicates that the period (D) between termination of a round of DNA replication and cell division and the following period ending in initiation of the next round of DNA replication (B) are riot independent of each other but tend to have compensatory variations. The results suggest that other events in the cell cycle are related more closely to DNA replication rather than to the much less regular event of cell division.     

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.     

Suites of root traits differ between annual and perennial species growing in the field

Here, we tested whether root traits associated with resource acquisition and conservation differed between life histories (annuals, perennials) and families (Fabaceae, Asteraceae and Poaceae). Root topology, morphology, chemistry and mycorrhizal colonization were measured on whole root systems of 18 field-grown herbaceous species grown and harvested in central Argentina. Annuals differed from perennials in several root traits important in resource uptake and conservation. They exhibited higher specific root length (SRL), root nitrogen concentration (RNC) and mycorrhizal colonization but had lower root tissue density (RTD) than perennials. They did not differ in topology or construction cost. These differences were consistent among families. Families differed only in a few root traits known to be strongly associated with certain lineages such as topology and nitrogen concentration. There was a strong parallel between root traits and analogous leaf traits described in the literature for annuals and perennials. Our results suggest the existence at the root level of an acquisitive vs conservative syndrome consistent among families similar to that previously reported for above-ground traits.     

Differential methylation of mitochondrial and nuclear DNA in cultured mouse, hamster and virus-transformed hamster cells. In vivo and in vitro methylation

Information has been lacking as to whether mitochondrial DNA of animal cells is methylated. The methylation patterns of mitochondrial and nuclear DNAs of several mammalian cell lines have therefore been compared by four methods: (1) in vivo transfer of the methyl group from [methyl-³H]methionine; (2) in vivo incorporation of [³²P]orthophosphate and a combination of (1) and (2); (3) in vivo incorporation of [³H]deoxycytidine; (4) in vitro methylation of DNAs with ³H-labeled S-adenosylmethionine as methyl donor and DNA methylase preparations from L cell nuclei. The cell lines were mouse L cells, $\text{BHK21}\text{C13}$, $\text{C13}\text{B4}$ (baby hamster kidney cells transformed by the Bryan strain of Rouse sarcoma virus), and PyY (BHK cells transformed by polyoma virus). DNA bases were separated chromatographically, using 5-methylcytosine, 6-methylaminopurine and, in some cases, 7-methylguanine as markers.Mitochondrial DNA was found to be significantly less methylated than nuclear DNA with respect to 5-methylcytosine in all cell types studied and by all methods used. The relative advantages and disadvantages of each method have been discussed. The level of 5-methylcytosine in mitochondrial DNA as compared with that in nuclear DNA was estimated as one-fourth to one-fourteenth in various cell lines. The estimated 5-methylcytosine content per circular mitochondrial DNA molecule (mol. wt 10 × 10⁶) was about 12 methylcytosine residues for L cells and 24, 30 and 36 methylcytosine residues for BHK, B4 and PyY cells, respectively. Relative to cytosine residues, the estimate was one 5-methylcytosine per 500 cytosine residues of mitochondrial DNA and one 5-methylcytosine per 36 cytosine residues of nuclear DNA from L-cells. The values for methylcytosine of mitochondrial DNA are presumed to be maximal. PyY cells as compared with other cells had the highest methylcytosine content of both mitochondrial and nuclear DNA as estimated by method (3). No methylation of nuclear DNA was observed in confluent L cells.Evidence for the presence of DNA methylase activity associated with mitochondrial fractions was obtained. This activity could be distinguished from other cellular DNA methylase activity by differential response to mercaptoethanol. Radioactivity from ³H-labeled S-adenosylmethionine was found only in 5-methyl-cytosine of DNA.     

Reduction of Chloroplast DNA Content in Solanum nigrum Suspension Cells by Treatment with Chloroplast DNA Synthesis Inhibitors

Suspension cell cultures of Solanum nigrum were grown in the presence of six different chloroplast DNA synthesis inhibitors in order to determine whether the pool size of chloroplast DNA (cpDNA) could be selectively reduced relative to the nuclear DNA content. One of the effects of the inhibitors was a reduction in cell growth and viability. Cell growth (fresh weight) was reduced 50% (in 8 day cultures) by: 100 micromolar bisbenzimide, 8 micromolar ethidium bromide, 0.3 micromolar 5-fluordeoxyuridine (Fudr), 200 micromolar nalidixic acid, 30 micromolar novobiocin, or 10 micrograms per milliliter rifampicin. At these concentrations, three of the inhibitors, ethidium bromide, Fudr, and rifampicin, also substantially reduced the viability of the cultures. Analyses of the chloroplast and nuclear DNA content per gram fresh weight by dot blot hybridizations indicated that the reduction of cpDNA content was greatest at inhibitor concentrations which reduced cell growth by more than 50% but this depended on the culture conditions. For example, the two DNA gyrase inhibitors, nalidixic acid and novobiocin, were more effective in lowering cpDNA content in cultures which were transferred (2 × 4 days) once during the eight day incubation. Because several inhibitors were toxic to cell growth, the DNA content of treated cells was also determined on the basis of cell (protoplasts) number. Analyses of nuclear and cpDNA content per cell for each treatment indicated that only the DNA gyrase inhibitors, nalidixic acid, and novobiocin reduced cpDNA content. Neither inhibitor reduced nuclear DNA content. These results suggest that DNA gyrases participate in cpDNA replication. The selective reduction of cpDNA content in regeneratable cultures may facilitate the generation and selection of cpDNA mutants or transformants from higher plants.     

Different response of cellular DNA content to cardiac hypertrophy in human and rat heart myocytes

1. Rat and human heart myocytes adapt to overload-induced hypertrophy differently. 2. Human myocyte nuclei respond with polyploidization and multinucleation, thus increasing the DNA content per myocyte from 20 to 40 pg. As a result, nuclear DNA content per 10,000 microns3 of cell volume decreases from 12 to 10 pg. 3. In rat hearts with aortic constriction nuclear DNA content remains constant (13 pg), and the DNA content per 10,000 microns3 of myocyte volume falls from 9 to 6 pg. 4. We hypothesize that "dilution" of nuclear DNA in the hypertrophied rat heart myocyte limits the capacity to hypertrophy (much less than 100%). 5. The human heart myocyte, which is able to compensate for dilution of nuclear DNA, may increase in size more than three-fold. 6. The lower limit of DNA content per unit of myocyte volume is 6 pg/10,000 microns3 in both species.     

Cryptosexuality and the genetic diversity paradox in coffee rust, Hemileia vastatrix

Background

Despite the fact that coffee rust was first investigated scientifically more than a century ago, and that the disease is one of the major constraints to coffee production - constantly changing the socio-economic and historical landscape of the crop - critical aspects of the life cycle of the pathogen, Hemileia vastatrix, remain unclear. The asexual urediniospores are regarded as the only functional propagule: theoretically, making H. vastatrix a clonal species. However, the well-documented emergence of new rust pathotypes and the breakdown in genetic resistance of coffee cultivars, present a paradox.

Methods and Results

Here, using computer-assisted DNA image cytometry, following a modified nuclear stoichiometric staining technique with Feulgen, we show that meiosis occurs within the urediniospores. Stages of spore development were categorised based on morphology, from the spore-mother cell through to the germinating spore, and the relative nuclear DNA content was quantified statistically at each stage.

Conclusions

Hidden sexual reproduction disguised within the asexual spore (cryptosexuality) could explain why new physiological races have arisen so often and so quickly in Hemileia vastatrix. This could have considerable implications for coffee breeding strategies and may be a common event in rust fungi, especially in related genera occupying the same basal phylogenetic lineages.     

Leaf flavonoid chemistry and taxonomy of Coreopsis sect. Coreopsis

Seventeen flavonoid glycosides were isolated from the leaves of the nine species of Coreopsis sect. Coreopsis. The compounds include two flavones, four flavonols, a 6-hydroxyflavone, a 6-hydroxyflavonol, two 6-methoxyflavones, a 6-methoxyflavonol and three chalcone-aurone pairs. Chemistry distinguishes all species except C. auriculata and C. intermedia. The mean flavonoid similarity for pair-wise comparison of the four species of annuals (C. basalis, C. nuecensis, C. nuecensoides and C. wrightii) is 0.63 whereas it is 0.66 for the five perennial species (C. auriculata, C. grandiflora, C. intermedia, C. lanceolata, C. pubescens) and 0.54 for comparison of annuals with perennials. This indicates that on the average there is slightly higher flavonoid similarity among species of annuals and among species of perennials than there is between annuals and perennials. Lack of the chalcone-aurone pair coreopsin-sulfurein in perennials is the only consistent chemical difference between annuals and perennials. Leaf flavonoid chemistry supports the hypothesis that C. nuecensis and C. nuecensoides are closely related species but flavonoid data are not concordant with the hypothesis of close relationship between C. basalis and C. wrightii, intermedia, Coreopsis pubescens and C. lanceolata are considered closely related and flavonoid chemistry is concordant with this hypothesis. Coreopsis lanceolata is also viewed as closely allied to C. auriculata, but flavonoids suggest the latter species is more similar to C. intermedia. Coreopsis grandiflora is the only perennial species lacking flavonols and has the fewest number of compounds of any species in the section; chemical data support the view that C. grandiflora is quite distinct from other perennial species of sect. Coreopsis.     

The systematic value of nuclear DNA content for all species of Narcissus L. (Amaryllidaceae)

The taxonomy of all species of Narcissus (Amaryllidaceae), an important horticultural crop, has not been investigated recently. As a new approach, genome size was determined by flow cytometry with propidium iodide from 375 accessions. The somatic nuclear DNA contents (2C) were shown to range from 14 to 38 pg for the diploids. Narcissus assoanus and N. gaditanus are, based on their nuclear DNA content, removed from section Apodanthi and placed in a new section Juncifolii. The different ploidy levels and species involved were entangled for N . “fernandesii” s.l. and a new allotetraploid form is named here. Section Pseudonarcissus was much more heterogeneous in nuclear DNA content than expected. Sixty-five accessions of N. pseudonarcissus possessed, with 23.7 pg, similar amounts of DNA. However, several species from this section were clearly distinctive in nuclear DNA content. It runs from the diploid N. primigenius with 21.7 pg to the also diploid N. nevadensis with 38.2 pg. Also N. abscissus and N. moleroi are with about 26 pg clearly different from N. pseudonarcissus. For the first time, in 11 accessions, hexaploidy was found in N. pseudonarcissus ssp. bicolor. A new section Nevadensis with 30–39 pg of nuclear DNA was split off from the section Pseudonarcissus with now 21–27 pg. A nonoploid N. dubius with 96.3 pg has by far the highest amount of nuclear DNA and can be calculated to have the highest ploidy ever reported in Narcisssus. The total number of Narcissus species was determined as 36, nine more than in Flora Europaea and they were divided up in two subgenera and 11 sections. Flow cytometry is shown to produce easily obtainable and original systematic data that lead to new insights. Genome size or C-value turns out to be one of the most salient features to define the status of the species in the genus Narcissus.