Determination Of Growth Rate Research Articles

Bomb-curve radiocarbon measurement of recent biologic tissues and applications to wildlife forensics and stable isotope (paleo)ecology

Above-ground thermonuclear weapons testing from 1952 through 1962 nearly doubled the concentration of radiocarbon ((14)C) in the atmosphere. As a result, organic material formed during or after this period may be radiocarbon-dated using the abrupt rise and steady fall of the atmospheric (14)C concentration known as the bomb-curve. We test the accuracy of accelerator mass spectrometry radiocarbon dating of 29 herbivore and plant tissues collected on known dates between 1905 and 2008 in East Africa. Herbivore samples include teeth, tusks, soft tissue, hair, and horn. Tissues formed after 1955 are dated to within 0.3-1.3 y of formation, depending on the tissue type, whereas tissues older than ca. 1955 have high age uncertainties (>17 y) due to the Suess effect. (14)C dating of tissues has applications to stable isotope (paleo)ecology and wildlife forensics. We use data from 41 additional samples to determine growth rates of tusks, molars, and hair, which improve interpretations of serial stable isotope data for (paleo)ecological studies. (14)C dating can also be used to calculate the time interval represented in periodic histological structures in dental tissues (i.e., perikymata), which in turn may be used as chronometers in fossil teeth. Bomb-curve (14)C dating of confiscated animal tissues (e.g., ivory statues) can be used to determine whether trade of the item is legal, because many Convention of International Trade of Endangered Species restrictions are based on the age of the tissue, and thus can serve as a powerful forensic tool to combat illegal trade in animal parts.

Growth of Juvenile Scup Fed Two Commercial Diets

AbstractJuvenile Scup Stenotomus chrysops 0.35–0.95 g were fed two different commercial diets for 9 weeks to determine growth rates. Diets were hand‐distributed to four replicate groups of 45 fish, four times a day. Survival among all treatments was high (90.0–92.5%), and both diets supported good growth. After five weeks, Scup fed diet 1 were significantly greater in length and weight than fish fed diet 2. These differences remained significant throughout the rest of the study. Specific growth rate (SGR) values were 5.8%/d for fish fed diet 1 and 5.5%/d for diet 2, while feed conversion ratios (FCR) were 1.22 for diet 1 and 1.25 for diet 2. Relative growth rate (RGR) values were diet 1 = 3,689% and diet 2 = 3,077%, and daily weight gain (DWG) values were diet 1 = 0.38 g/d and diet 2 = 0.31 g/d. Scup fed diet 1 had significantly greater final live weight, total length, weight gain, SGR, RGR, and DWG measurements than did fish fed diet 2. Juvenile Scup exhibited high growth rates and low feed conversion ratios when fed the two commercial diets, identifying them as a strong candidate species for commercial aquaculture.

Hundred Years of Environmental Change and Phytoplankton Ecophysiological Variability Archived in Coastal Sediments

Marine protist species have been used for several decades as environmental indicators under the assumption that their ecological requirements have remained more or less stable through time. However, a growing body of evidence suggests that marine protists, including several phytoplankton species, are in fact highly diverse and may quickly respond to changes in the environment. Predicting how future climate will impact phytoplankton populations is important, but this task has been challenged by a lack of time-series of ecophysiological parameters at time-scales relevant for climate studies (i.e. at least decadal). Here, we report on ecophysiological variability in a marine dinoflagellate over a 100-year period of well-documented environmental change, by using the sedimentary archive of living cysts from a Scandinavian fjord (Koljö Fjord, Sweden). During the past century, Koljö Fjord has experienced important changes in salinity linked to the North Atlantic Oscillation (NAO). We revived resting cysts of Pentapharsodinium dalei preserved in the fjord sediments and determined growth rates for 18 strains obtained from 3 sediment core layers at salinity 15 and 30, which represent extreme sea-surface conditions during periods of predominantly negative and positive NAO phases, respectively. Upper pH tolerance limits for growth were also tested. In general, P. dalei grew at a higher rate in salinity 30 than 15 for all layers, but there were significant differences among strains. When accounting for inter-strain variability, cyst age had no effect on growth performance or upper pH tolerance limits for this species, indicating a stable growth response over the 100-year period in spite of environmental fluctuations. Our findings give some support for the use of morphospecies in environmental studies, particularly at decadal to century scales. Furthermore, the high intra-specific variability found down to sediment layers dated as ca. 50 years-old indicates that cyst-beds of P. dalei are repositories of ecophysiological diversity.

Conservative leaf economic traits correlate with fast growth of genotypes of a foundation riparian species near the thermal maximum extent of its geographic range

Summary Plant functional traits involved in carbon and water acquisition are likely to be adaptive across the range of a species if the availability of these resources varies across this range and are limiting to growth or fitness. At the interspecific level, leaf economic traits associated with rapid resource capture are correlated with fast growth rates. However, relationships between leaf traits and growth are poorly understood at the intraspecific level. We examined two hypotheses: (i) leaf traits vary genotypically among Populus fremontii populations from different thermal environments; and (ii) leaf traits are related to growth rate of these P. fremontii populations. We used a common garden at the warm edge of P. fremontii distribution that included individuals transplanted from 11 provenances. Provenances varied in mean annual maximum temperature by 5·9 °C, reflecting a range of expected increases in temperature over the next 80 years. Conservative leaf traits (e.g. low specific leaf area, N content, stomatal conductance, net photosynthetic rate and high leaf water‐use efficiency) were positively related to growth rates of genotypes and populations, a pattern opposite of that widely reported among species in other studies. Provenance temperature explained 75% of the variation in multivariate leaf traits with the warmest provenances having the most conservative traits and highest growth rates. Clinal genetic variation suggests that P. fremontii may be adapted to thermal environments. Leaf area‐to‐sapwood area ratio was positively associated with growth rate, while leaf area‐based net photosynthetic rate was negatively associated with growth rate; these results suggest that hydraulic architecture was more important than leaf‐level photosynthetic rate in determining growth rate. Synthesis. Our results suggest that conservative leaf traits promote rapid growth of P. fremontii genotypes in extremely hot environments. Thus, relationships between leaf economic traits among species do not necessarily apply to the range of variation among genotypes within species. The generality of this pattern should be examined for other species that will be exposed to climate warming. Moreover, our research shows that common garden provenance trials are useful for identifying genotypes best suited to a predicted warmer climate and for improving understanding of the physiological basis for adaptation to warm environments.

Biomass Growth Rate of Trees from Cameroon Based on 14C Analysis and Growth Models

The question of whether the rise in CO2 levels observed during the industrial era has influenced the rates of tree biomass growth represents one of the main unsolved questions in the field of climate change science. In this framework, the African tropical forest represents one of the most important carbon (C) sinks, but detailed knowledge of its response to elevated CO2 is still lacking, especially regarding tree growth rate estimations. A major limitation to determining growth rates in the African tropical region is that many trees lack seasonality in cambial activity determining annual growth rings. In this study, several species of trees characterizing the African tropical forest have been investigated to estimate their biomass growth rate by means of a procedure based on 14C and growth models. A total of 71 subsamples were analyzed for a Entandrophragma cylindricum (sapele) tree, and 38 and 25 wood subsamples for Erythrophleum suaveolens (tali) and Triplochiton scleroxylon (ayous) trees, respectively, using radiocarbon measurements at the Centre for Isotopic Research on Cultural and Environmental Heritage (CIRCE). All measured modern samples were in agreement with the Southern Hemisphere (SH) 14C bomb-spike curve. Observed preliminary results indicate a decrease in the growth rate of the sapele tree (∼350 yr old) in the industrial period compared to the pre-industrial era. Growth rates for trees of the other 2 species were higher than sapele, with ayous being the fastest-growing species.

First Report of Sclerotinia Stem Blight Caused by Sclerotinia trifoliorum on Trifolium ambiguum in Poland.

Kura clover (Trifolium ambiguum M. Bieb.), a rhizomatous, persistent legume native to the Caucasus region, has received recent attention in North America and New Zealand as a pasture and silage crop. It is reported to be resistant to most pathogens affecting other clovers, including Sclerotinia trifoliorum Eriks. (3,4), one of the most destructive pathogens of clovers in northern Europe. Kura clover (cv. KTA202) was established in May 2009 near Mochełek, Poland (53° 13' N, 17° 51' E) on a Luvisol soil. By May 2011, 70% of plants grown in an experimental field (350 m2) had died, and 20% of the remaining plants were yellow and wilted. At crowns and the lower stem regions, wet, brown lesions with delicate white mycelium were observed. Lesion development was followed by death of the entire plant in a few days. By early June, only a few asymptomatic plants per square meter remained in the field. Tissue fragments of 20 symptomatic plants were surface-sterilized with 1% NaOCl for 1 min and plated on potato dextrose agar (PDA). A fungus with morphological characteristics of S. trifoliorum was consistently isolated. DNA isolation from sclerotia was performed with the DNeasy Plant Mini Kit (Qiagen, USA). Amplification and sequencing of the ITS region of rDNA was performed with primers ITS1/ITS4. NCBI Blast analysis of the 542-bp segment showed a 99% homology with most of S. trifoliorum and S. sclerotiorum strains in GenBank (e.g., AY547267.1 and EU082466.1). Sequence of isolate St0211TA was deposited in GenBank (Accession No. JQ743329). To determine growth rate of hyphae, morphology, and dimensions of sclerotia, colonies were grown in three replications on PDA at 20 ± 1°C in the dark. S. trifoliorum (CBS 122377) and S. sclerotiorum from our local collection were used as controls. Mean growth rate of S. trifoliorum isolates (20.5 mm/day) was slower compared to S. sclerotiorum (32.3 mm/day). Sclerotia began to form on delicate and smooth mycelium of S. trifoliorum on the entire surface of the plate in 7 to 8 days. Sclerotial size on day 28 was 2.0 to 9.0 × 2.0 to 7.0 mm (average 4.2 × 3.6 mm). Ultimately, the identification of S. trifoliorum was confirmed on the basis of ascospore morphology. Apothecia grew from sclerotia in wet sand at 12°C after 12 weeks. Asci contained dimorphic ascospores: four larger 13.0 to 16.0 × 6.0 to 9.0 mm (average 14.1 × 7.4 μm) and four smaller 10.0 to 12.0 × 5.4 to 6.0 mm (average 10.6 × 6.0 μm), typical for this species (1). Isolate St0511TA, which most intensively produced apothecia, was deposited in CBS (No. 133234). Koch's postulates were fulfilled by pathogenicity tests carried out on 2-week-old T. ambiguum seedlings grown in pots (6 × 30 plants), sprayed with a mycelial fragment suspension, and incubated at 15°C (2). Brown, wet spots with delicate white mycelium were observed on cotyledons after 3 days. After 5 days, approximately 10% of cotyledons were killed and mycelium appeared on stems and leaves, and after 10 days, 73% of seedlings were dead. S. trifoliorum was reisolated from all symptomatic tissues. To our knowledge, this is the first report of S. trifoliorum stem blight on T. ambiguum in the field.

Effects of a non-native biocontrol weevil, Larinus planus, and other emerging threats on populations of the federally threatened Pitcher’s thistle, Cirsium pitcheri

Larinus planus Frabicius (Curculionidae), is a seed-eating weevil that was inadvertently introduced into the US and was subsequently distributed in the US and Canada for the control of noxious thistle species of rangelands. It has been detected recently in the federally threatened Pitcher’s thistle (Cirsium pitcheri). We assayed weevil damage in a natural population of Pitcher’s thistle at Whitefish Dunes State Park, Door County, WI and quantified the impact on fecundity. We then estimated the impact of this introduced weevil and other emerging threats on two natural, uninvaded populations of Pitcher’s thistle for which we have long-term demographic data for 16yr (Wilderness State Park, Emmet County, MI) and 23yr (Miller High Dunes, Indiana Dunes National Lakeshore, Porter County, IN). We used transition matrices to determine growth rates and project the potential effects of weevil damage, inbreeding, goldfinch predation, and vegetative succession on Pitcher’s thistle population viability. Based on our models, weevil seed predation reduced population growth rate by 10–12%, but this reduction was enough to reduce time to extinction from 24yr to 13yr and 8yr to 5yr in the MI and IN population, respectively. This impact is particularly severe, given most populations of Pitcher’s thistle throughout its range hover near or below replacement. This is the first report of unanticipated ecological impacts from a biocontrol agent on natural populations of Cirsium pitcheri.

Growth Rate, Seed Production, and Assessing the Spatial Risk of Lythrum salicaria using Growing Degree-Days

Purple loosestrife (Lythrum salicaria) is an introduced wetland plant that is of both environmental and economic concern. Although it has been in Prairie Canada for many years, basic biological and spatial data is lacking. In this study we determined growth rates and seed production using season long field data, statistically modelled season long growth, and developed an interpolated growing degree-day (GDD’s) risk surface. We found that stems emerged from perennial root stocks in late May to early June after about 45 GDD’s. On average, stems reached 50 % of their final height at about 338 GDD’s, and final stem heights were reached at about 1007 GDD’s. The mean number of seed capsules produced per stem was 276.4 while the mean number of seeds produced by a seed capsule was 79.4. We found that a three parameter logistic function was a robust predictor of growth (R2 = 0.86). Our interpolated risk surface indicated that GDD’s may be a constraining parameter for the distribution of purple loosestrife in Prairie Canada. The results of this study contribute new biological and spatial data that can be used to support management plans, inform policy, and develop enhanced spatial predictive models.

Cultivation of Chlorella sp. as Biofuel Sources in Palm Oil Mill Effluent (POME)

Renewable energy is essential and vital aspect for development in Indonesia especially less oil reserve for coming 15 years. Biodiesel has received much attention as renewable energy in recent years. One of potential biodiesel is produced from microalgae. Due to high content of nutrients in Palm Oil Mill Effluent (POME), this waste is a potential for nutrient growth for microalgae. Chlorella is one of high potential for biodiesel since it has high lipid content (20-30%). The objective of the research is to determine growth rate and biomass productivity in Chlorella Sp cultured in POME. Chlorella Sp was cultured in 20%, 50%, 70% POME using urea concentration 0.1gr/L (low nitrogen source) and 1gr/l (high nitrogen source) at flask disk, pH 6.8-7.2; aerated using aquarium pump and fluorescence lamp 3000-6000 lux as light. Medium was measured using spectrophotometer Optima Sp-300 OD at 680 wave length in 15 days to calculate specific growth rate. At end of cultivation, Chlorella sp was filtered and measured as dry weight. Result indicated that Chlorella sp at 50% POME 1gr/L urea showed higher specific growth rate (0.066/day). Factor affecting growth rate of microalgae is CNP ratio, POME concentration, and urea concentration.

Cultivation of Chlorella sp. as Biofuel Sources in Palm Oil Mill Effluent (POME)

Renewable energy is essential and vital aspect for development in Indonesia especially less oil reserve for coming 15 years. Biodiesel has received much attention as renewable energy in recent years. One of potential biodiesel is produced from microalgae. Due to high content of nutrients in Palm Oil Mill Effluent (POME), this waste is a potential for nutrient growth for microalgae. Chlorella is one of high potential for biodiesel since it has high lipid content (20-30%). The objective of the research is to determine growth rate and biomass productivity in Chlorella Sp cultured in POME. Chlorella Sp was cultured in 20%, 50%, 70% POME using urea concentration 0.1gr/L (low nitrogen source) and 1gr/l (high nitrogen source) at flask disk, pH 6.8-7.2; aerated using aquarium pump and fluorescence lamp 3000-6000 lux as light. Medium was measured using spectrophotometer Optima Sp-300 OD at 680 wave length in 15 days to calculate specific growth rate. At end of cultivation, Chlorella sp was filtered and measured as dry weight. Result indicated that Chlorella sp at 50% POME 1gr/L urea showed higher specific growth rate (0.066/day). Factor affecting growth rate of microalgae is CNP ratio, POME concentration, and urea concentration.

Unusually high body mass in Virginia meadow voles

We used monthly capture–mark–recapture information to determine growth rates and life spans for 2 populations of meadow voles studied for 28 and 29 months in eastern Virginia in order to learn whether the exceptionally large body masses of some voles were due to rapid growth, long lives, or both. On 1 study grid, 64 males (19%) and 43 nonpregnant females (11%) were 70 g, with the largest male being 89 g. Mostly positive growth rates (averaging 1.1–3.9 g/month) were recorded, even in autumn and winter months, times when meadow voles are losing mass in northern populations, where most studies of body growth have been conducted. Periods of low mean body mass were associated with low population density more than high body mass was associated with high population density. Patterns of body mass dynamics were related more to season than to density in our populations. We concluded that the large body masses we observed in some voles were due more to long field lives than to unusually high rates of body growth.

Geometrical Shape of Micelles Formed by Cationic Dimeric Surfactants Determined with Small-Angle Neutron Scattering

The influence of spacer group on the geometrical shape of micelles formed by quaternary-bis dimeric (Gemini) surfactants C(12)H(25)N(CH(3))(2)(CH(2))(s)N(CH(3))(2)C(12)H(25) (12-s-12) has been investigated with small-angle neutron scattering (SANS). Dimeric surfactants with a short spacer unit (12-3-12 and 12-4-12) are observed to form elongated general ellipsoidal micelles with half axes a < b < c, whereas SANS data demonstrate that 12-s-12 surfactants with 6 ≤ s ≤ 12 form rather small spheroidal micelles rather than strictly spherical micelles. By means of comparing our present SANS results with previously determined growth rates using time-resolved fluorescence quenching, we are able to conclude that micelles formed by 12-6-12, 12-8-12, 12-10-12, and 12-12-12 are shaped as oblate rather than prolate spheroids. As a result, our present investigation suggests a never before reported structural behavior of Gemini surfactant micelles, according to which micelles transform from elongated ellipsoids to nonelongated oblate spheroids as the length of the spacer group is increased. The aggregation number of oblate micelles is observed to monotonously decrease with an increasing length of the surfactant spacer group, mainly as a result of a decreasing minor half axis (a), whereas the major half axis (b) is rather constant with respect to s. We argue that geometrically heterogeneous elongated micelles are formed by dimeric surfactants with a short spacer group mainly as a result of the surface charges becoming less uniformly distributed over the micelle interface. As the length of the spacer group increases, the distance between intramolecular charges become approximately equal to the average distance between charges on the micelle interface, and as a result, rather small oblate spheroidal micelles with a more uniform distribution of surface charges are formed by dimeric 12-s-12 surfactants with 6 ≤ s ≤ 12.

The population biology of penaeid prawns in the Gulf of Suez, Red Sea, Egypt

The prawn fishery in the Gulf of Suez is based on three penaeid species (Penaeus semisulcatus, Melicertus latisulcatus and Marsupenaeus japonicus). The status of the Gulf shrimp fishery was assessed with length frequency distributions from trawl landing data from 1983 to 2008. These data were analysed to determine growth rates, mortality coefficients, biological reference points for fishing mortality from yield per recruit (F max, F 0.1) and maximum spawning potential analysis. The virtual population analysis (VPA) approach was used to obtain point estimates of stock size, recruitment, spawning stock size and fishing mortality rates. Exploitation rates showed a steady state of increase, while the biomass of the three prawn stocks has decreased between 1983 and 2008. This decline is evident from the commercial landings which decreased from 749.4 t in 1983 to 132.9 t in 2008 and in CPUE (catch per unit effort) decreased from 54.7 kg/day to 8.3 kg/day. The size of the spawning stock has decreased by more than 60% of its original size since the beginning of the study period, as has the recruitment number (which decreased from 174 to 35 million recruits for P. semisulcatus, from 275 to 70 million recruits for M. latisulcatus and from 110 to 24 million recruits for M. japonicus). These results indicate that the prawn stocks in the Gulf of Suez are subjected to heavy exploitation and need urgent management regulations. Options for improving and developing the production of prawns in the Gulf of Suez and some implications for fishery management are proposed.

Alternative pathway for atmospheric particles growth

Credible climate change predictions require reliable fundamental scientific knowledge of the underlying processes. Despite extensive observational data accumulated to date, atmospheric aerosols still pose key uncertainties in the understanding of Earth's radiative balance due to direct interaction with radiation and because they modify clouds' properties. Specifically, major gaps exist in the understanding of the physicochemical pathways that lead to aerosol growth in the atmosphere and to changes in their properties while in the atmosphere. Traditionally, the driving forces for particle growth are attributed to condensation of low vapor pressure species following atmospheric oxidation of volatile compounds by gaseous oxidants. The current study presents experimental evidence of an unaccounted-for new photoinduced pathway for particle growth. We show that heterogeneous reactions activated by light can lead to fast uptake of noncondensable Volatile Organic Compounds (VOCs) at the surface of particles when only traces of a photosensitizer are present in the seed aerosol. Under such conditions, size and mass increase; changes in the chemical composition of the aerosol are also observed upon exposure to volatile organic compounds such as terpenes and near-UV irradiation. Experimentally determined growth rate values match field observations, suggesting that this photochemical process can provide a new, unaccounted-for pathway for atmospheric particle growth and should be considered by models.

Short Term Effects of Grazing Sheep on Agroforestry based Pasture

The efficacy of producing sheep by grazing on agroforestry based pasture in relation to growth, breeding traits, and impacts on the pasture were investigated. Sheep were placed on traditional or agroforestry grazing pasture and experiments determined growth rates, organic material and nitrogen concentrations of the soil, forestry utilization, and female breeding traits. There were no significant differences between the growth traits. There was significantly higher organic material from the agroforestry vs. the traditional pasture. The nitrogen content from the agroforestry without sheep was significantly higher compared to the other plots. The percent of understory cover on the agroforestry plot was significantly less compared to a control. There were no significant differences in sexual receptivity or pregnancy rates in the ewes, but the lambing rates of the agroforestry was significantly higher than the traditional pasture.

Mammoth tooth enamel growth rates inferred from stable isotope analysis and histology

Mammoth (Mammuthus sp.) teeth are relatively abundant in Quaternary deposits from Eurasia and North America, and their isotopic compositions can be used to reconstruct past seasonal patterns in precipitation, diet, and migration. Strategies for collecting and interpreting such data, however, are strongly dependent on growth rates, which can vary among species, individuals, and within teeth. In this study, we use histological and isotopic measurements to determine enamel growth rates for a Columbian mammoth (Mammuthus columbi) tooth in two directions. Using histology, the growth rate through the enamel thickness (ET; perpendicular to the height of the tooth) is estimated at 0.8 to 1.5mm/yr. Isotopic sampling through the innermost 0.36mm of the ET recovered less than half a period of variation (i.e., half an inferred year of growth), which is consistent with the histological estimate for ET growth rate. A combination of histological and isotopic measurements suggests that the enamel extension rate (growth in the height of the tooth) is 13–14mm/yr. Knowledge of enamel growth rates should improve the design and interpretation of future isotopic studies of mammoth teeth. The combination of histological and isotopic measurements may also prove useful in determining growth rates for other extinct taxa.

Enhanced production of artemisinin by hairy root cultures of Artemisia dubia

The current research was to enhance the artemisinin concentration in hairy root cultures, produced by transformation of Artemisia dubia with Agrobacterium rhizogenes LBA9402. These cultures were exposed to gibberellic acid and salicylic acid, separately, to determine growth rate and artemisinin production. Gibberellic acid increased the growth rate of hairy roots at its 0.001 mg/L concentration while salicylic acid increased the growth rate at its 0.138 mg/L concentration. Maximum artemisinin concentration that is, 80±3 µg/g of DW was measured at 0.01 mg/L of gibberellic acid which was 91% increase in comparison with control, followed by artemisinin that is, 58±4 µg/g of DW at its 0.001 mg/L concentration that was 38% increase with respect to control. Maximum artemisinin concentration that is, 79±3 µg/g of DW was measured when hairy roots were exposed to 13.8 mg/L of salicylic acid and second highest concentration 73±3 µg/g was obtained at 1.38 mg/L of salicylic acid. The results showed that both substances increased growth rate and artemisinin production. Key words: Agrobacterium rhizogenes, Artemisia dubia, artemisinin, gibberellic acid, salicylic acid, hairy root cultures.

Genetic Basis of Hidden Phenotypic Variation Revealed by Increased Translational Readthrough in Yeast

Eukaryotic release factors 1 and 3, encoded by SUP45 and SUP35, respectively, in Saccharomyces cerevisiae, are required for translation termination. Recent studies have shown that, besides these two key factors, several genetic and epigenetic mechanisms modulate the efficiency of translation termination. These mechanisms, through modifying translation termination fidelity, were shown to affect various cellular processes, such as mRNA degradation, and in some cases could confer a beneficial phenotype to the cell. The most studied example of such a mechanism is [PSI+], the prion conformation of Sup35p, which can have pleiotropic effects on growth that vary among different yeast strains. However, genetic loci underlying such readthrough-dependent, background-specific phenotypes have yet to be identified. Here, we used sup35C653R, a partial loss-of-function allele of the SUP35 previously shown to increase readthrough of stop codons and recapitulate some [PSI+]-dependent phenotypes, to study the genetic basis of phenotypes revealed by increased translational readthrough in two divergent yeast strains: BY4724 (a laboratory strain) and RM11_1a (a wine strain). We first identified growth conditions in which increased readthrough of stop codons by sup35C653R resulted in different growth responses between these two strains. We then used a recently developed linkage mapping technique, extreme QTL mapping (X-QTL), to identify readthrough-dependent loci for the observed growth differences. We further showed that variation in SKY1, an SR protein kinase, underlies a readthrough-dependent locus observed for growth on diamide and hydrogen peroxide. We found that the allelic state of SKY1 interacts with readthrough level and the genetic background to determine growth rate in these two conditions.

Starch in the Arabidopsis plant

AbstractThe genetic and genomic resources available for the model plant Arabidopsis have allowed rapid progress in understanding the pathways of leaf starch synthesis and degradation. The pathway of starch synthesis is generally similar to that in other plants, but Arabidopsis research has permitted new insights into the mechanism of granule initiation. The pathway of starch degradation is very different from the ‘textbook’ version, largely derived from research on germinating cereal grains. The starch granule is attacked by β‐ rather than α‐amylases, and this process is strongly dependent on a cycle of phosphorylation and dephosphorylation of the granule surface. The major product of granule degradation is maltose, which is exported to the cytosol where it is metabolised to hexose phosphate and then to sucrose. Cytosolic maltose metabolism requires a glucanotransferase and a glucosyl acceptor which is believed to be a complex heteroglycan. Plant productivity and yield are highly dependent on leaf starch turnover, and starch metabolism is coordinated with other factors and processes that determine growth rate. Research in Arabidopsis provides an important knowledge base for the study of starch metabolism in other, less tractable species.

Growth Behavior and Kinetics of Self‐Assembled Silica–Carbonate Biomorphs

Upon slow crystallization from silica-containing solutions or gels at elevated pH, alkaline-earth carbonates spontaneously self-assemble into remarkable nanocrystalline ultrastructures. These so-called silica biomorphs exhibit curved morphologies beyond crystallographic symmetry and ordered textures reminiscent of the hierarchical design found in many biominerals. The formation of these fascinating materials is thought to be driven by a dynamic coupling of the components' speciations in solution, which causes concerted autocatalytic mineralization of silica-stabilized nanocrystals over hours. In the present work, we have studied the precipitation kinetics of this unique system by determining growth rates of individual aggregates using video microscopy, and correlated the results with time-dependent data on the concentration of metal ions and pH acquired online during crystallization. In this manner, insight to the evolution of chemical conditions during growth was gained. It is shown that crystallization proceeds linearly with time and is essentially reaction controlled, which fits well in the proposed morphogenetic scenario, and thus, indirectly supports it. Measurements of the silica concentration in solution, combined with analyses of crystal aggregates isolated at distinct stages of morphogenesis, further demonstrate that the fraction of silica coprecipitated with carbonate during active growth is rather small. We discuss our findings with respect to the role of silica in the formation of biomorphs, and moreover, prove that the external silica skins that occasionally sheath the aggregates--previously supposed to be involved in the growth mechanism--originate from secondary precipitation after growth is already terminated.