QTL analysis of resistance to sharka disease in the apricot (Prunus armeniaca L.) ‘Polonais’ × ‘Stark Early Orange’ F1 progeny

Different hypotheses on the genetic control of the resistance to the plum pox virus (PPV) have been reported in apricot, but there was a lack of agreement about the number of loci involved. In recent years, apricot genetic maps have been constructed from progenies derived from ‘Stark Early Orange’ or ‘Goldrich’, two main sources of resistance, three of these including the mapping of the PPV resistance loci. As the location of the locus was not precisely established, we mapped the PPV resistance loci using interval mapping (IM), composite interval mapping (CIM), and the Kruskal–Wallis non-parametric test in the F₁ progeny derived from a cross between the susceptible cv. ‘Polonais’ and ’Stark Early Orange’. Four genomic regions were identified as being involved in PPV resistance. One of these mapped to the upper region of linkage group 1 of ‘Stark Early Orange’, and accounted for 56% of the phenotypic variation. Its location was similar to the one previously identified in ‘Goldrich’ and Prunus davidiana. In addition, a gene strongly associated to these major quantitative trait loci (QTL) was found to be related to PPV infection. Two putative QTLs were detected on linkage groups 3 of ‘Polonais’ and 5 of both ‘Polonais’ and ‘Stark Early Orange’ with both parametric and non-parametric methods at logarithm of odds (LOD) scores slightly above the detection threshold. The last QTL was only detected in the early stage of the infection. PPV resistance is, thus, controlled by a major dominant factor located on linkage group 1. The hypothesis of recessive factors with lower effect is discussed.     

Soil CO2 efflux in a mixed pine-oak forest in Valsaín (central Spain)

Soil-surface CO2 efflux and its spatial and temporal variation were investigated in a southern Mediterranean, mixed pine-oak forest ecosystem on the northern slopes of the Sierra de Guadarrama in Spain from February 2006 to July 2006. Measurements of soil CO2 efflux, soil temperatures, and moisture were conducted in nine 1963-m2 sampling plots distributed in a gradient around the ecotone between Pinus sylvestris L. and Quercus pyrenaica Lam. forest stands. Total soil organic matter, Walkey-Black C, particulate organic matter, organic matter fraction below 53 microm, total soil nitrogen content, total soil organic carbon content, and pH were also measured under three representative mature oak, pine, and mixed pine-oak forest stands. Soil respiration showed a typical seasonal pattern with minimums in winter and summer, and maximums in spring, more pronounced in oak and oak-pine stands. Soil respiration values were highest in pine stands during winter and in oak stands during spring and summer. Soil respiration was highly correlated with soil temperatures in oak and pine-oak stands when soil moisture was above a drought threshold of 15%. Below this threshold value, soil moisture was a good predictor of soil respiration in pine stands. Greater soil organic matter, particulate organic matter, Walkey-Black C, total organic C, and total N content in pine compared to oak sites potentially contributed to the greater total soil CO2 efflux in these stands during the winter. Furthermore, opposing trends in the organic matter fraction below 53 microm and soil respiration between plots suggest that in oak stands, the C forms are less affected by possible changes in use. The effects of soil properties on soil respiration were masked by differences in soil temperature and moisture during the rest of the year. Understanding the spatial and temporal variation even within small geographic areas is essential to assess C budgets at ecosystem level accurately. Thus, this study bears important implications for the study of large-scale ecosystem dynamics, particularly in response to climatic change.     

Modulation of K+ translocation by AKT1 and AtHAK5 in Arabidopsis plants

Root cells take up K⁺ from the soil solution, and a fraction of the absorbed K⁺ is translocated to the shoot after being loaded into xylem vessels. K⁺ uptake and translocation are spatially separated processes. K⁺ uptake occurs in the cortex and epidermis whereas K⁺ translocation starts at the stele. Both uptake and translocation processes are expected to be linked, but the connection between them is not well characterized. Here, we studied K⁺ uptake and translocation using Rb⁺ as a tracer in wild‐type Arabidopsis thaliana and in T‐DNA insertion mutants in the K⁺ uptake or translocation systems. The relative amount of translocated Rb⁺ to the shoot was positively correlated with net Rb⁺ uptake rates, and the akt1 athak5 T‐DNA mutant plants were more efficient in their allocation of Rb⁺ to shoots. Moreover, a mutation of SKOR and a reduced plant transpiration prevented the full upregulation of AtHAK5 gene expression and Rb⁺ uptake in K⁺‐starved plants. Lastly, Rb⁺ was found to be retrieved from root xylem vessels, with AKT1 playing a significant role in K⁺‐sufficient plants. Overall, our results suggest that K⁺ uptake and translocation are tightly coordinated via signals that regulate the expression of K⁺ transport systems.     

Toxic Metals and Trace Elements in Artisanal Honeys from the Canary Islands

Honey is a natural product made by honey bees from the nectar of flowers or secretions produced by other living plant parts. The metal content of the honeys is related to the levels of metals in the environment. Due to the importance of honey in the human diet and the increase of environmental pollution, it is necessary to determine the content of metals in honey to evaluate the toxicological risk derived from its consumption. The objective of this study was to determine the content of 20 metals (Al, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Pb, Sr, V, and Zn) in different samples of artisanal honey from the Canary Islands (Spain) in order to evaluate the dietary intake derived from the consumption of these honeys. A total of 161 samples of different types of Canary honey were analyzed by ICP-OES (inductively coupled plasma–optical emission spectrometry). K (825 mg/kg) was the macroelement found in highest concentration, while B (4.25 mg/kg) was the trace element with the highest mean concentration. Al (3.33 mg/kg) was the most abundant toxic metal, followed by Pb (0.040 mg/kg) and Cd (0.002 mg/kg). A mean consumption of 25 g/day of honey mainly contributes to the recommended daily intake of Cu (1.34% adults) and K (0.67% adults). As regards the toxic metals, the contribution percentage to the TDI (tolerable daily intake) of Pb at 2.92% for adults is noteworthy. However, the consumption of honey does not imply a high intake of metals and, therefore, does pose a risk to the health of adult men and women.

     

The Old World sparrows (genus Passer) phylogeography and their relative abundance of nuclear mtDNA pseudogenes

The phylogenetic relationships of genus Passer (Old World sparrows) have been studied with species covering their complete world living range. Mitochondrial (mt) cyt b genes and pseudogenes have been analyzed, the latter being strikingly abundant in genus Passer compared with other studied songbirds. The significance of these Passer pseudogenes is presently unclear. The mechanisms by which mt cyt b genes become pseudogenes after nuclear translocation are discussed together with their mode of evolution, i.e., transition/transversion mitochondrial ratio is decreased in the nucleus, as is the constraint for variability at the three codon positions. However, the skewed base composition according to codon position (in 1^st position the percentage is very similar for the four bases, in 2^nd position there are fewer percentage of A and G and more percentage of T, and in 3^rd codon position fewer percentage of G and T and is very rich in A and C) is maintained in the translocated nuclear pseudogenes. Different nuclear internal mechanisms and/or selective pressures must exist for explaining this nuclear/mitochondrial differential DNA base evolutive variability. Also, the phylogenetic usefulness of pseudogenes for defining relationships between closely related lineages is stressed. The analyses suggest that the primitive genus Passer species comes from Africa, the Cape sparrow being the oldest: P. hispaniolensis italiae is more likely conspecific to P. domesticus than to P. hispaniolensis. Also, Passer species are not included within weavers or Estrildinae or Emberizinae, as previously suggested. European and American Emberizinae sparrows are closely related to each other and seem to be the earliest species that radiated among the studied songbirds (all in the Miocene Epoch). Received: 29 November 2000 / Accepted: 22 March 2001     

Genetic variation of Citrus tristeza virus isolates from California and Spain: evidence for mixed infections and recombination

We examined the population structure and genetic variation of four genomic regions within and between 30 Citrus tristeza virus (CTV) isolates from Spain and California. Our analyses showed that most isolates contained a population of sequence variants, with one being predominant. Four isolates showed two major sequence variants in some genomic regions. The two major variants of three of these isolates showed very low nucleotide identity to each other but were very similar to those of other isolates, suggesting the possibility of mixed infections with two divergent isolates. Incongruencies of phylogenetic relationships in the different genomic regions and statistical analyses suggested that the genomes of some CTV sequence variants originated by recombination events between diverged sequence variants. No correlation was observed between geographic origin and nucleotide distance, and thus from a genetic view, the Spanish and Californian isolates analyzed here could be considered members of the same population.     

Molybdopterin guanine dinucleotide cofactor in Synechococcus sp. nitrate reductase: identification of mobA and isolation of a putative moeB gene

Cathepsin B and other lysosomal cysteine proteinases are synthesized as inactive zymogens, which are converted to their mature forms by other proteases or by autocatalytic processing. Procathepsin B autoactivation was shown in vitro at pH 4.5 to be a bimolecular process with K(s) and k(cat) values of 2.1+/-0.9 microM and 0.12+/-0.02 s(-1)6.0. However, in the presence of 0.5 microg/ml of dextran sulfate, relatively rapid processing is observed even at pH 6.5 (t(1/2) approximately 90 min), suggesting that glycosaminoglycans are involved in in vivo processing of lysosomal cysteine proteases.     

Immunohistochemical evidence of the presence of aromatase P450 in the rat hypophysis

In order to analyze whether aromatase is present in the hypophysis of adult rats, we have performed an immunohistochemical study in young adult male and female rats. Our study has revealed that the hypophysis of adult rats contains aromatase, although marked differences are found between the sexes. The hypophyses of male rats have cells immunoreactive for the enzyme, 34.40% of these hypophyseal cells showing reaction. By contrast, cells from female rats show very little reaction, only 0.84% of them being reactive. No significant differences in the percentage of immunoreactive cells between one phase and another are observed during the estrous cycle. Our results point to the immunohistochemical expression of aromatase in the hypophysis of adult rats and at the same time suggest that its expression is sex-dependent. The enzyme may therefore be involved in the regulation of adenohypophyseal cytology by androgens.