Isolation of Catenated Forms of R Factor DNA from Minicells

STUDIES^1–6 of the molecular nature of antibiotic resistance (R) factors in Escherichia coli have shown that several of them consist of covalently closed molecules of circular DNA. Use was made of this property in the separation of the R factor from chromosomal DNA of E. coli, which has a similar nucleotide-base composition. In selecting for covalently circular R factor DNA molecules, however, the procedures used in these earlier experiments-caesium chloride-ethidium bromide centrifuga-tion⁷ and bulk nitrocellulose adsorption²—necessarily selected against isolation of other (non-circular) forms of R factor DNA that might have been present.     

Comparison of Two Techniques for Surveying Headwater Stream Amphibians

Abstract: We compared rubble-rousing versus light-touch stream amphibian survey techniques in multiple 1-m plots across 10 streams in southwest Washington, USA. Specifically, we wanted to determine if light-touch surveys provide unbiased estimates of abundance (i.e., provide counts correlated with rubble-rousing counts) and which method would provide more cost-effective presence or absence information. Rubble-rousing, a common technique for surveying stream-associated amphibians in the Pacific Northwest, took 12 times as long as light-touch to apply. Abundance estimates and standard errors for rubble-rousing were consistently higher than those for light-touch for all life stages for the coastal tailed frog (Ascaphus truei) and Columbia torrent salamander (Rhyacotriton kezeri). Except for eggs, light-touch detected all life stages found during rubble-rousing. For frogs, only some rubble-rousing abundance estimates, mostly involving second-year larvae, were highly correlated with their light-touch counterparts, whereas for salamanders, similar comparisons generated high correlations across most life stages. Correlations between methods were consistently greater for salamanders than for frogs. However the smaller tailed frog sample sizes and the cryptozoic nature of some life stages may have contributed to this pattern. Depending on the degree to which researchers can tolerate false-negative error rates, light-touch may prove less costly than rubble-rousing for detecting species presence. For the cost of obtaining one rubble-rousing sample, many light-touch samples can be used across a range of habitats for detecting species patchily distributed.     

Analysis of cytosolic and plastidic serine acetyltransferase mutants and subcellular metabolite distributions suggests interplay of the cellular compartments for cysteine biosynthesis in Arabidopsis

In plants, the enzymes for cysteine synthesis serine acetyltransferase (SAT) and O-acetylserine-(thiol)-lyase (OASTL) are present in the cytosol, plastids and mitochondria. However, it is still not clearly resolved to what extent the different compartments are involved in cysteine biosynthesis and how compartmentation influences the regulation of this biosynthetic pathway. To address these questions, we analysed Arabidopsis thaliana T-DNA insertion mutants for cytosolic and plastidic SAT isoforms. In addition, the subcellular distribution of enzyme activities and metabolite concentrations implicated in cysteine and glutathione biosynthesis were revealed by non-aqueous fractionation (NAF). We demonstrate that cytosolic SERAT1.1 and plastidic SERAT2.1 do not contribute to cysteine biosynthesis to a major extent, but may function to overcome transport limitations of O-acetylserine (OAS) from mitochondria. Substantiated by predominantly cytosolic cysteine pools, considerable amounts of sulphide and presence of OAS in the cytosol, our results suggest that the cytosol is the principal site for cysteine biosynthesis. Subcellular metabolite analysis further indicated efficient transport of cysteine, γ -glutamylcysteine and glutathione between the compartments. With respect to regulation of cysteine biosynthesis, estimation of subcellular OAS and sulphide concentrations established that OAS is limiting for cysteine biosynthesis and that SAT is mainly present bound in the cysteine–synthase complex.     

Characterization of di‐, tri‐ and tetranucleotide microsatellite markers with perfect repeats for Trypanosoma brucei and related species

Trypanosoma brucei, a unicellular parasite causing human sleeping sickness and animal nagana, has a great impact on the socioeconomic environment of sub‐Saharan Africa. The dynamics of the parasite are still poorly understood. We have characterized 14 polymorphic di‐, tri‐ and tetranucleotide microsatellite loci with perfect repeats (only one motif) exhibiting between five and 16 alleles in T. brucei isolates from all over Africa and from all described subspecies. The microsatellites will be useful in addressing population genetic questions in T. brucei to better understand the population structure and spread of this important parasite.     

Temperature effects on forest herbs assessed by warming and transplant experiments along a latitudinal gradient

Slow‐colonizing forest understorey plants are probably not able to rapidly adjust their distribution range following large‐scale climate change. Therefore, the acclimation potential to climate change within their actual occupied habitats will likely be key for their short‐ and long‐term persistence. We combined transplant experiments along a latitudinal gradient with open‐top chambers to assess the effects of temperature on phenology, growth and reproductive performance of multiple populations of slow‐colonizing understorey plants, using the spring flowering geophytic forb Anemone nemorosa and the early summer flowering grass Milium effusum as study species. In both species, emergence time and start of flowering clearly advanced with increasing temperatures. Vegetative growth (plant height, aboveground biomass) and reproductive success (seed mass, seed germination and germinable seed output) of A. nemorosa benefited from higher temperatures. Climate warming may thus increase future competitive ability and colonization rates of this species. Apart from the effects on phenology, growth and reproductive performance of M. effusum generally decreased when transplanted southwards (e.g., plant size and number of individuals decreased towards the south) and was probably more limited by light availability in the south. Specific leaf area of both species increased when transplanted southwards, but decreased with open‐top chamber installation in A. nemorosa. In general, individuals of both species transplanted at the home site performed best, suggesting local adaptation. We conclude that contrasting understorey plants may display divergent plasticity in response to changing temperatures which may alter future understorey community dynamics.     

European phenological response to climate change matches the warming pattern

Global climate change impacts can already be tracked in many physical and biological systems; in particular, terrestrial ecosystems provide a consistent picture of observed changes. One of the preferred indicators is phenology, the science of natural recurring events, as their recorded dates provide a high-temporal resolution of ongoing changes. Thus, numerous analyses have demonstrated an earlier onset of spring events for mid and higher latitudes and a lengthening of the growing season. However, published single-site or single-species studies are particularly open to suspicion of being biased towards predominantly reporting climate change-induced impacts. No comprehensive study or meta-analysis has so far examined the possible lack of evidence for changes or shifts at sites where no temperature change is observed. We used an enormous systematic phenological network data set of more than 125 000 observational series of 542 plant and 19 animal species in 21 European countries (1971–2000). Our results showed that 78% of all leafing, flowering and fruiting records advanced (30% significantly) and only 3% were significantly delayed, whereas the signal of leaf colouring/fall is ambiguous. We conclude that previously published results of phenological changes were not biased by reporting or publication predisposition: the average advance of spring/summer was 2.5 days decade⁻¹ in Europe. Our analysis of 254 mean national time series undoubtedly demonstrates that species' phenology is responsive to temperature of the preceding months (mean advance of spring/summer by 2.5 days°C⁻¹, delay of leaf colouring and fall by 1.0 day°C⁻¹). The pattern of observed change in spring efficiently matches measured national warming across 19 European countries (correlation coefficient r =−0.69, P <0.001).     

Stream characteristics and their implications for the protection of riparian fens and meadows

1. Running waters, including associated riparian areas, are embraced by international legal frameworks outlining targets for the preservation, protection and improvement of the quality of the environment. Interactions between stream and river processes and riparian habitats have not received much attention in the management of stream ecosystems, and integrated measures that consider both the ecological status of streams and rivers (sensu EU Water Framework Directive, WFD) and the conservation status of riparian habitats and species (sensu EU Habitats Directive, HD) are rare. 2. Here, we analysed the influence of stream size, morphology and chemical water characteristics for the distribution of water‐dependent terrestrial habitat types, i.e. alkaline fens, periodically inundated meadows and meadows in riparian areas in Denmark using an extensive data set covering a total of 254 stream reaches. A species‐based classification model was used to translate species lists into a standardised interpretation of habitat types protected by the HD in Denmark. 3. No size dependency was found regarding the distribution of fen and meadow vegetation. Instead, the distribution of fen and meadow vegetation was strongly affected by the morphology of the streams. Alkaline fens, periodically inundated meadows and meadows occurred six, five and four times, respectively, less frequently along channelised compared with natural stream reaches. Our results indicate that stream channelisation strongly interfered with the natural hydrology of riparian areas, affecting conditions needed to sustain protected fen and meadow communities. 4. We also found that water chemistry strongly influenced the occurrence of fen and meadow vegetation in riparian areas. The probability of finding fen and meadow vegetation was reduced when total phosphorus (TP) concentration exceeded 40–50 μg P L^?1, whereas meadow vegetation responded less strongly to TP. 5. Our findings highlight the importance of restoring hydrology of riparian areas to improve conditions for fen and meadow vegetation, but also that the water chemistry should be considered when measures that increase hydrological connectivity result in an increase in the probability of flooding.     

Seedling Growth and Storage Characteristics of Seeder and Resprouter Species of Mediterranean-type Ecosystems of S. W. Australia

Juvenile (2–4 years old) plants of a taxonomically diverserange of dicotyledonous species were examined following recruitmentfrom seed in recently burnt habitats in S.W. Australia. Obligateseeder species (those succumbing to fire) had on average, analmost threefold greater total plant d. wt and more than a fourfoldgreater shoot: root d. wt ratio than comparably-aged, cohabiting,resprouter species (those capable of surviving fire). Starchwas generally much more concentrated in root dry matter of resproutersthan seeders, and both categories exhibited greater starch storagecapacity in roots than shoots. Members of the Myrtaccae wereexceptional in not showing a greater root starch reserve inresprouter than in seeder species. and in carrying as high,or higher, starch levels in shoots as in roots. Anatomical investigationson roots provided instances of zero starch storage, storage,only in rays or in cortex, in rays and in xylem parenchyma,in rays and in cortex, or in all three locations. High starchratings of resprouter roots related mostly to higher starchgrain packing density at storage sites, but in certain instancesthese also reflected proportionally greater areas of tissuespecifically devoted to storage. Dry matter of shoots of bothseeders and resprouters generally contained higher levels ofN, P, K, Ca and Mg than that of roots, but there was no significantevidence of elements being more concentrated in resproutersthan in seeders. Fire response, seedlings, resprouter, obligate seeder, shoot: root ratio, starch storage, mineral nutrition     

The Starch Statolith Hypothesis and the Interaction of Amyloplasts and Endoplasmic Reticulum in Root Geotropism

Roots of cress (Lepidium sativum L, ) seedlings continuouslystimulated at an angle of 135°—root tips pointingobliquely upwards—develop a larger final geotropic curvaturethan roots stimulated at 45° or 90°. This well-knownbehaviour has previously been interpreted as support for thestarch statolith hypothesis. In the present experiments two groups of cress and lettuce (Lactucasativa L.) seedlings were used: (a) the control group in whichthe roots were allowed to curve without adjustment of the stimulationangle, and (b) the test group in which the roots were readjustedat different time intervals to the original stimulation angle.They were stimulated continuously at 45°, 90°, or 135°and the development of root curvatures was followed over a periodof 5–8 h. Initially (1–2 h) the rate of curvature was approximatelythe same for 135° and 90° control and tested cress andlettuce roots. Thereafter the test roots stimulated at 135°followed a linear curvature pattern. Seedlings stimulated at45° and 90° did not show the same linearity in curvaturedevelopment in the test group. The rates of curvature in thetest group were generally higher than in the control group atangles less than 135°. Cress seedlings were examined by light and electron microscopyin order to follow the movement of the cell organelles in thestatocytes. In the statocytes of roots of test seedlings thestarch statoliths were located in the position attained beforethe first readjustment of the stimulation angle. In the statocytesof control roots the starch statoliths followed the curvatureof the root tip sliding along the cell walls and attaining therest position as in normally orientated roots. The behaviour of control and readjusted roots is interpretedas a result of interaction between starch statoliths and endoplasmicreticulum membranes.