Livestock settlement affects shrub abundance via plant functional diversity but not species richness in arid environments

Plant Ecology - Recent theoretical and empirical studies have assumed that livestock grazing acts as a biotic filter favouring plant species with functional traits that confer resistance to...     

Potential of the Bacillus thuringiensis Toxin Reservoir for the Control of Lobesia botrana (Lepidoptera: Tortricidae), a Major Pest of Grape Plants

The potential of Bacillus thuringiensis Cry proteins to control the grape pest Lobesia botrana was explored by testing first-instar larvae with Cry proteins belonging to the Cry1, Cry2, and Cry9 groups selected for their documented activities against Lepidoptera. Cry9Ca, a toxin from B. thuringiensis, was the protein most toxic to L. botrana larvae, followed in decreasing order by Cry2Ab, Cry1Ab, Cry2Aa, and Cry1Ia7, with 50% lethal concentration values of 0.09, 0.1, 1.4, 3.2, and 8.5 μg/ml of diet, respectively. In contrast, Cry1Fa and Cry1JA were not active at the assayed concentration (100 μg/ml). In vitro binding and competition experiments showed that none of the toxins tested (Cry1Ia, Cry2Aa, Cry2Ab, and Cry9C) shared binding sites with Cry1Ab. We conclude that either Cry1Ia or Cry9C could be used in combination with Cry1Ab to control this pest, either as the active components of B. thuringiensis sprays or expressed together in transgenic plants.     

Uptake,demand and internal cycling of nitrogen in saplings of Mediterranean<Emphasis Type="Italic"> Quercus</Emphasis> species

Nitrogen uptake, nitrogen demand and internal nitrogen cycling were studied to address the question of the importance of nutrient storage in Quercus species with contrasting leaf longevities. We carried out this study at the whole-plant level with young trees (2-4 years old) of three Mediterranean Quercus species: the evergreen Q. ilex, the marcescent/evergreen Q. faginea, and the deciduous Q. pyrenaica. Seasonal dynamics of nitrogen in all compartments of the plant were followed for 3 years. Nitrogen losses were measured through litter production, herbivory and fine root shedding. Nitrogen uptake was estimated using increments of nitrogen plant content plus accumulative nitrogen losses. Nitrogen uptake was limited to a few months during late winter and spring. Before budbreak, acquired nitrogen was stored in old-leaf cohorts of evergreen and woody compartments. After budbreak, Quercus species relied first on soil uptake and second on nitrogen retranslocation to supply new growth requirements. However, in most cases we found a high asynchrony between nitrogen demand by growing tissues and soil supply, which determined a strong nitrogen retranslocation up to 88.4% of the nitrogen demand throughout leaf expansion. Except for the first year after planting, the above- and underground woody fractions provided more nitrogen to the new tissues than the old leaf cohorts. Differences in the benefit of nitrogen withdrawn from senescent and old leaves were not found between species. We conclude that sink/source interaction strength was determined by differences between nitrogen demand and uptake, regulating internal nutrient cycling at the whole plant level.     

Nitric oxide promotes strong cytotoxicity of phenolic compounds against Escherichia coli: the influence of antioxidant defenses

The induction of mutagenic and cytotoxic effects by simple phenolics, including catechol (CAT), 3,4-dihydroxyphenylacetic acid (DOPAC), hydroquinone (HQ), and 2,5-dihydroxyphenylacetic (homogentisic) acid (HGA), appears to occur through an oxidative mechanism based on the ability of these compounds to undergo autoxidation, leading to quinone formation with the production of reactive oxygen species. This is supported by the detection of such adverse effects in plate assays using Escherichia coli tester strains deficient in the OxyR function, but not in OxyR(+) strains. The OxyR protein is a redox-sensitive regulator of genes encoding antioxidant enzymes including catalase and alkyl hydroperoxide reductase, which would eliminate hydrogen peroxide. Methyl-substituted phenolics such as 4-methylcatechol (MCAT) and methylhydroquinone (MHQ) produced, in addition to oxidative toxicity, marked cytotoxic effects against OxyR(+) cells, thus revealing a mechanism of toxicity not mediated by hydrogen peroxide that could involve quinones and quinone methides arising from MCAT and MHQ oxidation. Quinone compounds could also be responsible for the enhanced cytotoxicity of certain phenolics when combined with a nitric oxide (NO(*)) donor such as diethylamine/NO (DEA/NO). Phenolics scavenge NO(*) and, in turn, NO(*) oxidizes phenolics to form their quinone derivatives. In OxyR(+) cells, where the oxidative toxicity is inhibited, DEA/NO promoted exceptional increases in the cytotoxicity of CAT and 3,4-dihydroxycinnamic (caffeic) acid (CAF), which both exhibited very low oxidative cytotoxicity, as well as in that of MCAT, HQ, and MHQ. In contrast, DEA/NO failed to promote toxicity by DOPAC and HGA, probably due to their ability to undergo oxidative polymerization, leading to the formation of melanins. Spectroscopic studies demonstrated quinone generation from the oxidation of CAF, HQ, and MHQ by DEA/NO. The o-quinone derived from CAF was rather unstable and decomposed during its isolation. For the generation of toxic quinones, e.g., to be used as therapeutic agents producing antitumor or antibacterial effects, the isolation step could be avoided with the method proposed. It combines quinone precursors, i.e. phenolic compounds, with an oxidant such as NO(*).     

Echinoid synergizes with the Notch signaling pathway in Drosophila mesothorax bristle patterning

echinoid (ed) encodes an immunoglobulin domain-containing cell adhesion molecule that negatively regulates the Egfr signaling pathway during Drosophila photoreceptor development. We show a novel function of Ed, i.e. the restriction of the number of notum bristles that arise from a proneural cluster. Thus, loss-of-function conditions for ed give rise to the development of extra macrochaetae near the extant ones and increase the density of microchaetae. Analysis of ed mosaics indicates that extra sensory organ precursors (SOPs) arise from proneural clusters of achaete-scute expression in a cell-autonomous way. ed embryos also exhibit a neurogenic phenotype. These phenotypes suggest a functional relation between ed and the Notch (N) pathway. Indeed, loss-of-function of ed reduces the expression of the N pathway effector E(spl)m8 in proneural clusters. Moreover, combinations of moderate loss-of-function conditions for ed and for different components of the N pathway show clear synergistic interactions manifested as strong neurogenic bristle phenotypes. We conclude that Ed is not essential for, but it facilitates, N signaling. It is known that the N and Egfr pathways act antagonistically in bristle development. Consistently, we find that Ed also antagonizes the bristle-promoting activity of the Egfr pathway, either by the enhancement of N signalling or, similar to the eye, by a more direct action on the Egfr pathway.     

Arthritogenicity ofYersinia enterocolitica O:8 in Hamsters: Analysis of the immune response

An animal model, hamster, was used for the study ofYersinia-induced arthritis. The development of arthritis, estimated by measuring the inflammation on hind paws after infection, was correlated with the kinetics of the immune response. Hostological and immunofluorescence (IFI) studies and serum antibody measurements were performed. Two inflammatory peaks were observed: an acute one on day 11 post-infection (p.i) and a chronic one on days 26–35 p.i. Joint cultures were positive until day 14 p.i. IFI was used to demonstrate the deposit of bacterial antigens in the joint. A persistent response of cellular extract-specific IgG antibodies was observed until day 94. Lipopolysaccharide-specific IgG was statistically significant on day 26 p.i. Antibodies against bands 66 and 54 were observed by immunoblotting. Polyclonal activation was detected during reactive arthritis. It is shown thatY. enterocolitica is arthritogenic in hamsters, immune mechanisms participating in the development of this disease.     

Efficient and sensitive assay for T-DNA-dependent transient gene expression

We describe here a very sensitive and reproducible method to detect the efficiency ofAgrobacterium-mediated T-DNA transfer. This method is based on a quantitative assay of β-glucuronidase activity produced in the plant cell upon transfer of T-DNA carrying a specialuidA gene construct. Analysis of the transfer efficiency of a transfer-proficient bacterium compared with that of the same bacterium diluted at different ratios with a transfer-defective bacterium shows a high sensitivity of the β-glucuronidase activity in the plant. Five orders of magnitude in T-DNA transfer efficiency can be covered when the activity is measured combining the fluorimetric MUG assay (for high activity) and the histochemical X-Gluc assay (very sensitive for low activity).     

Generalist diurnal pollination provides greater fitness in a plant with nocturnal pollination syndrome: assessing the effects of a Silene – Hadena interaction

Nursery pollination in Caryophyllaceae species by Hadena and Perizoma moths has been extensively described in the last few decades. Evidence across multiple pairs of species shows that such pollination systems constitute relatively specialized interactions, shifting between parasitism and mutualism depending on the presence of effective co‐pollinators. In this work, we describe a new specific Silene–Hadena interaction, the Silene ciliata–Hadena consparcatoides system. Although S. ciliata presents a typical nocturnal pollination syndrome, diurnal flower visitors have also been recorded, which motivated us to evaluate the costs and benefits of this nursery moth pollination to the plant. We experimentally induced two pollination regimes at non‐overlapping day‐night periods in a natural population of S. ciliata, and compared their effects on plant reproductive success from flower to seedling stages. Flower scent composition of S. ciliata and antennal responses of H. consparcatoides to this scent were recorded to evaluate the specificity of olfactory signals in this interaction system. In accordance with its nocturnal pollination syndrome, S. ciliata emitted a greater amount of flower scent compounds during the night. Some of the predominant scent compounds, such as benzaldehyde, benzyl acetate and methyl salicylate elicited signals in the antennae of H. consparcatoides. Diurnal pollination produced more fruits per flower than nocturnal pollination, but the latter produced higher brood size resulting in similar overall fecundity. However, seeds generated from diurnal pollination were heavier and germinated better. We conclude that despite its nocturnal pollination syndrome, S. ciliata achieved similar reproductive success and higher offspring vigour under the diurnal pollinator regime. Although H. consparcatoides is specialized in S. ciliata, its shortage or absence would not jeopardize the reproductive success of its host plant. On the contrary, the seed predation exerted by this nursery pollinator shifts the interaction towards parasitism.     

Seasonal variation of arbuscular mycorrhizal fungi in temperate grasslands along a wide hydrologic gradient

We studied seasonal variation in population attributes of arbuscular mycorrhizal (AM) fungi over 2 years in four sites of temperate grasslands of the Argentinean Flooding Pampas. The sites represent a wide range of soil conditions, hydrologic gradients, and floristic composition. Lotus glaber, a perennial herbaceous legume naturalised in the Flooding Pampas, was dominant at the four plant community sites. Its roots were highly colonised by AM fungi. Temporal variations in spore density, spore type, AM root colonisation, floristic composition and soil chemical characteristics occurred in each site and were different among sites. The duration of flooding had no effect on spore density but depressed AM root colonisation. Eleven different types of spores were recognized and four were identified. Two species dominated at the four sites: Glomus fasciculatum and Glomus intraradices. Spore density was highest in summer (dry season) and lowest in winter (wet season) with intermediate values in autumn and spring. Colonisation of L. glaber roots was highest in summer or spring and lowest in winter or autumn. The relative density of G. fasciculatum and G. intraradices versus Glomus sp. and Acaulospora sp. had distinctive seasonal peaks. These seasonal peaks occurred at all four sites, suggesting differences among AM fungus species with respect to the seasonality of sporulation. Spore density and AM root colonisation when measured at any one time were poorly related to each other. However, spore density was significantly correlated with root colonisation 3 months before, suggesting that high colonisation in one season precedes high sporulation in the next season.