Drought stress provokes the down‐regulation of methionine and ethylene biosynthesis pathways in Medicago truncatula roots and nodules

Symbiotic nitrogen fixation is one of the first physiological processes inhibited in legume plants under water‐deficit conditions. Despite the progress made in the last decades, the molecular mechanisms behind this regulation are not fully understood yet. Recent proteomic work carried out in the model legume Medicago truncatula provided the first indications of a possible involvement of nodule methionine (Met) biosynthesis and related pathways in response to water‐deficit conditions. To better understand this involvement, the drought‐induced changes in expression and content of enzymes involved in the biosynthesis of Met, S‐adenosyl‐L‐methionine (SAM) and ethylene in M. truncatula root and nodules were analyzed using targeted approaches. Nitrogen‐fixing plants were subjected to a progressive water deficit and a subsequent recovery period. Besides the physiological characterization of the plants, the content of total sulphur, sulphate and main S‐containing metabolites was measured. Results presented here show that S availability is not a limiting factor in the drought‐induced decline of nitrogen fixation rates in M. truncatula plants and provide evidences for a down‐regulation of the Met and ethylene biosynthesis pathways in roots and nodules in response to water‐deficit conditions.     

Activation of geminivirus V‐sense promoters in roots is restricted to nematode feeding sites

Obligate sedentary endoparasitic nematodes, such as the root‐knot and cyst nematodes, elicit the differentiation of specialized nematode nurse or feeding cells [nematode feeding sites (NFS), giant cells and syncytia, respectively]. During NFS differentiation, marked changes in cell cycle progression occur, partly similar to those induced by some geminiviruses. In this work, we describe the activation of V‐sense promoters from the Maize streak virus (MSV) and Wheat dwarf virus (WDV) in NFS formed by root‐knot and cyst nematodes. Both promoters were transiently active in microinjection experiments. In tobacco and Arabidopsis transgenic lines carrying promoter–β‐glucuronidase fusions, the MSV V‐sense promoter was activated in the vascular tissues of aerial plant parts, primarily leaf and cotyledon phloem tissue and some floral structures. Interestingly, in roots, promoter activation was restricted to syncytia and giant cells tested with four different nematode populations, but undetectable in the rest of the root system. As the activity of the promoter in transgenic rootstocks should be restricted to NFS only, the MSV promoter may have utility in engineering grafted crops for nematode control. Therefore, this study represents a step in the provision of some of the much needed additional data on promoters with restricted activation in NFS useful in biotechnological nematode control strategies.     

Alkalinity generation and sediment CO2 uptake influence establishment of Sparganium angustifolium in softwater lakes

1. Softwater lakes are generally dominated by slow growing, small, isoetid plant species that are adapted to the carbon‐ and nutrient‐limited conditions in these lakes. We investigated the strategy of a fast growing species, Sparganium angustifolium, for occupying softwater lakes. A field survey was carried out in Norwegian carbon‐limited Isoëteto‐Lobelietum softwater lakes to compare abiotic conditions at locations with and without S. angustifolium. In addition, long term abiotic changes (1995–2008) related to the sudden establishment of the species on experimentally limed plots were studied. Based on the results, the carbon acquisition mechanism of S. angustifolium was tested in eco‐physiological laboratory experiments. 2. The redox potential was significantly lower at locations with S. angustifolium (220 ± 2.3) compared to locations without S. angustifolium (338.1 ± 13.9). The lower redox potential was accompanied by significantly higher concentrations of HCO₃^?, CO₂ and Fe²⁺ in the sediment pore water, indicating in‐lake alkalinity generation due to higher iron reduction rates in the generally iron‐rich sediments. In addition, the lower redox potential was accompanied by a higher nutrient availability (NH₄⁺ and PO₄^3?) in the sediment pore water. Since there were no differences in water quality between the lakes, the ability of S. angustifolium to grow in softwater lakes very likely depends upon the higher dissolved inorganic carbon (DIC) and nutrient concentrations present in the sediment pore water. 3. Results from the liming experiment revealed that appearance of S. angustifolium on limed plots was related to the dissolution of Ca and Mg carbonates and development of a lower redox potential in the sediment. These processes were accompanied by a sustained increase in the availability of DIC in the sediment pore water. 4. The eco‐physiological experiments indicated that S. angustifolium can increase in biomass and produce floating leaves at a relatively high DIC availability in the root medium. In addition, it appeared that S. angustifolium can take up CO₂ by the roots. As far as we know, the ability to use sediment CO₂ has only been described as an adaptation typical for isoetid plant species. Use of the relatively large sediment CO₂ pools present in these sediment types (>1000 μmol L^?1) to enable development of long floating leaves for additional uptake of atmospheric CO₂ is a very different strategy to colonise softwater lakes as compared to isoetid plant species.     

Can the variability of mitochondrial DNA distinguish between commensal and feral populations of the house mouse?

The dynamics and variability of mitochondrial DNA (mtDNA) were compared in one commensal and one feral population of the house mouse ( Mus domesticus ) in Israel. The rate of turnover was high in both populations (the average proportion of new or discontinuing mice per trapping session was about 50%), as was the level of heterogeneity of mtDNA: using six restriction enzymes, 18 mice from the commensal population had eight different haplotypes (the degree of heterogeneity, h , was 0.802), and 412 mice from the feral population had 16 ( h = 0.894). These results suggest that neither population was composed of rigid breeding units made up of relatives, but that in the commensal population the few neighbouring resident mice that had the same mtDNA haplotype may have been siblings.     

Changes Induced by Salinity to the Anatomy and Morphology of Excised Pea Roots in Culture

Excised pea roots were grown in culture in the absence or presenceof NaCl. Salinity induced anatomical and morphological changesin the roots, some of which could be observed after only 24h in culture. Roots became constricted just above the apex,the region above the constriction thickened and the root tipcurved through 90°. Cellular differentiation began nearerthe apex, cortical and epidermal cells shortened and mitoticactivity in the pericycle increased as a result of exposureto salinity. Some of the changes resemble those induced by ethylene,but ethylene probably was not the cause of the response to salinity.Root cultures seem to be a suitable model for studying the effectof salinity in plant roots. Pisum sativum cv. Alaska, salinity, roots, cortex, root culture, pericycle, growth and differentiation     

A direct search approach to characterize the sex pheromone composition giving maximal male response

ABSTRACT. Response of male moths to sex pheromones differs markedly depending on blend composition. Natural selection can therefore be expected to favour males responding maximally to the blend produced by most females in the population. Thus it is relevant to quantify male response by the blend to which the males of a population respond maximally.
To do this, wind tunnel experiments were carried out where males were observed while responding to blends of synthetic compounds emitted from rubber septa. By stepwise improvement it was shown that the blend to which Yponomeuta cagnagellus responds maximally comprises (Z)11-tetradecenyl acetate (Z11-14Ac), ( E )11-tetradecenyl acetate (E11-14Ac), (Z)11-tetradecenol (Z11-140H), and tetradecyl acetate (14Ac) in the ratio 100(=50μg):1.5:20:45.
The innovate aspects of the method used to obtain this result, are the use of a direct search approach as an integral part of the experimental procedure and the use of a summary variable to characterize male response. These aspects are discussed using the data on the response of Y. cagnagellus males.     

Use of computed tomography as a non‐invasive method for diagnosing cephenemyiosis in roe deer (Capreolus capreolus)

This study was conducted to assess the reliability of computed tomography (CT) for diagnosing bot fly infestations by Cephenemyia stimulator (Clark) (Diptera: Oestridae) in roe deer (Capreolus capreolus L.) (Artiodactyla: Cervidae). For this purpose, the heads of 30 animals were analysed, firstly by CT and then by necropsy, which was used as the reference standard method. The prevalence values obtained by both methods were identical; the prevalence of infestation was 40.0% overall, and was higher in males (45.5%) than in females (25.0%). These results highlight the usefulness of CT as an alternative or non‐invasive method for diagnosing cephenemyiosis in live‐captured roe deer and in hunting trophies or museum collections that cannot be destroyed or damaged.     

Effect of host diet and adult parasitoid diet on egg load dynamics and egg size of braconid parasitoids attacking Anastrepha ludens

The quantity and quality of host nutrients can affect fitness‐related traits in hymenopteran parasitoids, including oogenesis. The present study tested the prediction that a high host quality will influence oogenesis‐related traits positively in synovigenic parasitoids, and that a high‐quality adult parasitoid diet can positively affect the same parameters, potentially compensating for development on low‐quality hosts. Four braconid parasitoid species with contrasting life histories are reared on a low‐quality diet [Anastrepha ludens Loew (Diptera: Tephritidae) larvae reared on mango] or a high‐quality (artificial) diet. Adult parasitoids are provided with a high‐quality (honey ad libitum), moderate‐quality (honey every other day) or low‐quality (guava pulp) diet. Generalist species that encounter high variation in host quality naturally are predicted to be more flexible in dealing with nutrient shortfalls than specialist species. By contrast to the predictions, low‐quality hosts yield parasitoids with higher egg loads in two species: Opius hirtus Fisher and Diachasmimorpha longicaudata Ashmead. However, as predicted, a high‐quality adult diet exerts a positive effect on egg load (Utetes anastrephae Viereck), egg size (Doryctobracon crawfordi Viereck) and egg maturation rate (D. longicaudata, O. hirtus and U. anastrephae). The generalist D. longicaudata varies in egg load and maturation rate depending on host quality and adult diet, respectively. Evidence of the combined effect of both factors on parasitoid fertility is presented for the specialist O. hirtus. The theoretical and practical implications of these findings are discussed.     

New hosts for the mite Ornithonyssus bursa in Argentina

The mite Ornithonyssus bursa (Berlese) (Mesostigmata: Macronyssidae) is considered a poultry pest causing important infestations in chickens and it is considered a potential vector of arbovirus. Despite being considered a common parasite in wild birds, there is scarce published information about its potential hosts and effects on them. Here we present new bird hosts for O. bursa, assess the presence of Alphavirus, Flavivirus and Bunyavirus in mites from three host species, and discuss its potential impact on wild bird populations. We found O. bursa infecting five raptor and six passerine wild bird species. For nine of these species, this is the first record of infection by O. bursa. Although all analysed mites were negative for the examined arboviruses, the small sample size of mites does not allow further conclusions at the present moment. Because of the general nature of this ectoparasite, its presence in migratory long dispersal and endangered bird species, and the seropositivity for arboviruses in some of the species studied here, we consider it critical to assess the role of O. bursa and other ectoparasites as vectors and reservoirs of pathogens and as potential deleterious agents in wild bird populations.