Partial duplication of the large ribosomal RNA sequence in an inverted repeat in circular mitochondrial DNA from Kloeckera africana: Implications for mechanisms of the petite mutation

The 27,100 base-pair circular mitochondrial DNA from the yeast Kloeckera africana has been found to contain an inverted duplication spanning 8600 base-pairs. Sequences hybridizing to transfer RNAs and the large ribosomal RNA are present in the duplication; however, one end of this segment terminates in the large mitochondrial ribosomal RNA sequence so that at least 1000 base-pairs of the gene are not repeated. The large and small mitochondrial ribosomal RNAs have been shown to have lengths of 2700 and 1450 bases, respectively, and genes for these sequences are separated by a minimum of 1300 base-pairs and a maximum of 1750 base-pairs. Consequences of the large inverted duplication to mechanisms of the petite mutation are discussed in terms of previous hypotheses centred on intramolecular recombination in yeast mitochondrial DNA at sequences of homology or partial homology. Despite the long inverted duplication in K. africana mitochondrial DNA, this yeast has one of the lowest frequencies of spontaneous petite mutants amongst petite positive yeasts. One implication of these findings is that in this yeast intra-molecular mitochondrial DNA sequence homology may not be an important factor in the excision process leading to petite formation.     

Role of plant parasitic nematodes and abiotic soil factors in growth heterogeneity of sugarcane on a sandy soil in South Africa

A feature of many sugarcane fields is the patchy growth. This is often thought to be due to physical or chemical differences in the soil. In this paper we investigate the causes of growth heterogeneity of sugarcane on a sandy soil in KwaZulu-Natal, South Africa. To identify the factors that were associated with the good and poor areas, soil texture, pH, organic matter content and a number of soil chemical elements and nematode community data were subjected to principal component analysis (PCA). The numbers of each of the nematode species (Meloidogyne sp., Pratylenchus zeae, Helicotylenchus dihystera, Xiphinema elongatum and Paratrichodorus sp.) were first converted to relative proportions of ectoparasites and endoparasites. The data were collected from the 2nd ratoon crop of a nematicide trial, where half of the plots had been treated with aldicarb in the preceding two crops. Yields of control plots varied from 34.7 to 126.8 t cane ha^–1 and from 85.4 to 138.7 for the treated plots. The yield data were centred and normalised separately for the treated and control plots and the values projected on the trial map to study spatial distribution. Plots with above-average yields, whether treated or untreated, occurred in the lower part of the trial site. The PCA factorial values were also projected onto the map of the trial. According to the first factor of the analysis of the abiotic soil characteristics in the 0–20 cm surface layer, the trial site could be divided into two areas, one on the left and one on the right. PCA of the soil data from the 0–20 and 20–40 cm layers showed that there was little or no difference between the two that might explain the two growth areas. However, analysis of the nematode community distinguished two main areas that largely corresponded to the distribution of the plots of low and high yielding cane. Correlation analysis confirmed the relationship between nematodes and yield. H. dihystera was positively correlated with yield of cane whereas the reverse was true for the Meloidogyne species.     

Contributions of Fe(III) to UV–Vis absorbance in river water: a case study on the Connecticut River and argument for the systematic tandem measurement of Fe(III) and CDOM

Biogeochemistry - Dissolved organic matter (DOM) impacts the structure and function of aquatic ecosystems. DOM absorbs light in the UV and visible (UV–Vis) wavelengths, thus impacting light...     

Genetic characterization of Uruguayan Pampa Rocha pigs with microsatellite markers

In this study, we genetically characterized the Uruguayan pig breed Pampa Rocha. Genetic variability was assessed by analyzing a panel of 25 microsatellite markers from a sample of 39 individuals. Pampa Rocha pigs showed high genetic variability with observed and expected heterozygosities of 0.583 and 0.603, respectively. The mean number of alleles was 5.72. Twenty-four markers were polymorphic, with 95.8% of them in Hardy Weinberg equilibrium. The level of endogamy was low (F_IS = 0.0475). A factorial analysis of correspondence was used to assess the genetic differences between Pampa Rocha and other pig breeds; genetic distances were calculated, and a tree was designed to reflect the distance matrix. Individuals were also allocated into clusters. This analysis showed that the Pampa Rocha breed was separated from the other breeds along the first and second axes. The neighbour-joining tree generated by the genetic distances D_A showed clustering of Pampa Rocha with the Meishan breed. The allocation of individuals to clusters showed a clear separation of Pampa Rocha pigs. These results provide insights into the genetic variability of Pampa Rocha pigs and indicate that this breed is a well-defined genetic entity.