Genome size dynamics in Artemisia L. (Asteraceae): following the track of polyploidy.

Polyploidy is a key factor in the evolution of higher plants and plays an important role in the variation of plant genomes, leading to speciation in some cases. During polyploidisation, different balancing processes take place at the genomic level that can promote variation in nuclear DNA content. We estimated genome size using flow cytometry in 84 populations of 67 Artemisia species and one population of Crossostephium chinense. A total of 73 sequences of nrDNA ITS and 3'-ETS were newly generated and analysed, together with previously published sequences, to address the evolution of genome size in a phylogenetic framework. Differences in 2C values were detected among some lineages, as well as an increase of genome size heterogeneity in subgenera whose phylogenetic relationships are still unclear. We confirmed that the increase in 2C values in Artemisia polyploids was not proportional to ploidy level, but 1Cx genome size tended to decrease significantly when high ploidy levels were reached. The results lead us to hypothesise that genome size in polyploids tends to a maximum as it follows saturation behaviour, in agreement with the Michaelis-Menten model. We tested different arithmetic functions with our dataset that corroborated a non-linear relationship of genome size increase in polyploids, allowing us to suggest a theoretical upper limit for the DNA content of this genus.

Discrete design of enzyme kinetic experiments.

The usefulness of discrete designs in enzyme kinetics as an alternative to continuous designs is discussed in this paper, focusing on designs satisfying the D-optimality criterion. This study has been carried out using a program called DODID, specifically devised for this purpose, which is available by request to the authors. The results presented in this paper show that the relative efficiency of the D-optimal discrete designs with respect to the continuous ones increases rapidly when increasing the number of possible values for the control variables. Relative efficiencies higher than 0.98 are achieved when using 20 possible values for each variable. The power of the tools provided by the computational approach of this work is proved by the analysis made on the robustness of different designs for estimating the kinetic parameters when a wrong assumption on the error structure has been made. The robustness of the designs made assuming medium constant error (error variance proportional to the true response) is thus confirmed. A comparative study of several discriminating designs is also presented. The results obtained show that the designs produced by adding the optimal discrete designs corresponding to both candidate models plus the point where the weighted difference between the predicted values is maximum, is a good choice when designing an experiment for discrimination.

Accuracy and precision in the determination of Stokes radii and molecular masses of proteins by gel filtration chromatography.

The accuracy and precision of the estimates of hydrodynamic parameters of globular proteins obtained by inverse regression from gel filtration chromatographic data are discussed. The usefulness of gel filtration chromatography as the basis for a rapid and reliable method for the determination of the Stokes radius and the molecular mass is considered. The discussion is supported by an analysis of the models already proposed in the literature, and is based on the precision of the estimates.