Traffic exposure increases natural 15N and heavy metal concentrations in mosses

Mosses have been used as biomonitors of atmospheric pollution for some years, but few studies have been carried out on the effect of NO_x emissions from traffic on moss tissue N. Eight species of moss (102 samples) growing on walls or roofs next to roads exposed to different traffic densities were collected from urban and rural sites in the UK. The shoots were sampled for total N, their stable isotope ¹⁵N/¹⁴N content (δ¹⁵N) and heavy metal content (Pb, Zn). There was a lack of correlation between tissue total N and traffic exposure, but a very good correlation between traffic exposure and tissue δ¹⁵N. Plants collected near motorways or busy urban roads had δ¹⁵N values ranging between +6 and −1‰, while in rural areas with hardly any traffic these ranged from −2 to −12‰. In a separate survey of mosses, the average δ¹⁵N of shoots from busy roadsides in London was +3.66‰, whereas from samples collected from farm buildings near poultry or cattle pens it was −7.8‰. This indicates that the two main atmospheric N sources, NO_x and NH_x, have different δ¹⁵N signatures, the former tending to be positive and the latter negative. Tissue concentrations of both Pb and Zn show a strong positive correlation with traffic exposure, with Zn in particular being greater than Pb. The results are discussed with regard to the use of moss tissue Zn as a means for monitoring or mapping pollution from vehicles, and of δ¹⁵N as an aid to distinguish between urban (NO_x) and rural (NH_x) forms of N pollution.     

The Torradovirus‐specific RNA2‐ORF1 protein is necessary for plant systemic infection

Tomato apex necrosis virus (ToANV, species Tomato marchitez virus, genus Torradovirus, family Secoviridae) causes a severe tomato disease in Mexico. One distinctive feature of torradoviruses compared with other members of the family Secoviridae is the presence of an additional open reading frame (ORF) in genomic RNA2 (denominated RNA2‐ORF1), located upstream of ORF2. RNA2‐ORF2 encodes a polyprotein that is processed into a putative movement protein and three capsid proteins (CPs). The RNA2‐ORF1 protein has homologues only amongst other torradoviruses and, so far, no function has been associated with it. We used recombinant and mutant ToANV clones to investigate the role of the RNA2‐ORF1 protein in various aspects of the virus infection cycle. The lack of a functional RNA2‐ORF1 resulted in an inability to systemically infect Nicotiana benthamiana and tomato plants, but both positive‐ and negative‐strand RNA1 and RNA2 accumulated locally in agroinfiltrated areas in N. benthamiana plants, indicating that the RNA2‐ORF1 mutants were replication competent. Furthermore, a mutant with a deletion in RNA2‐ORF1 was competent for virion formation and cell‐to‐cell movement in the cells immediately surrounding the initial infection site. However, immunological detection of the ToANV CPs in the agroinfiltrated areas showed that this mutant was not detected in the sieve elements even if the surrounding parenchymatic cells were ToANV positive, suggesting a role for the RNA2‐ORF1 protein in processes occurring prior to phloem uploading, including efficient spread in inoculated leaves.     

Differential proteomics of dehydration and rehydration in bryophytes: evidence towards a common desiccation tolerance mechanism

All bryophytes evolved desiccation tolerance (DT) mechanisms during the invasion of terrestrial habitats by early land plants. Are these DT mechanisms still present in bryophytes that colonize aquatic habitats? The aquatic bryophyte Fontinalis antipyretica Hedw. was subjected to two drying regimes and alterations in protein profiles and sucrose accumulation during dehydration and rehydration were investigated. Results show that during fast dehydration, there is very little variation in protein profiles, and upon rehydration proteins are leaked. On the other hand, slow dehydration induces changes in both dehydration and rehydration protein profiles, being similar to the protein profiles displayed by the terrestrial bryophytes Physcomitrella patens (Hedw.) Bruch and Schimp. and, to what is comparable with Syntrichia ruralis (Hedw.) F. Weber and D. Mohr. During dehydration there was a reduction in proteins associated with photosynthesis and the cytoskeleton, and an associated accumulation of proteins involved in sugar metabolism and plant defence mechanisms. Upon rehydration, protein accumulation patterns return to control values for both photosynthesis and cytoskeleton whereas proteins associated with sugar metabolism and defence proteins remain high. The current results suggest that bryophytes from different ecological adaptations may share common DT mechanisms.     

Alternative oxidase impacts the plant response to biotic stress by influencing the mitochondrial generation of reactive oxygen species

Previously, we showed that inoculation of tobacco with Pseudomonas syringae incompatible pv. maculicola results in a rapid and persistent burst of superoxide (O₂^‐) from mitochondria, no change in amount of mitochondrial alternative oxidase (AOX) and induction of the hypersensitive response (HR). However, inoculation with incompatible pv. phaseolicola resulted in increased AOX, no O₂^‐ burst and no HR. Here, we show that in transgenic plants unable to induce AOX in response to pv. phaseolicola, there is now a strong mitochondrial O₂^‐ burst, similar to that normally seen only with pv. maculicola. This interaction did not however result in a HR. This indicates that AOX amount is a key determinant of the mitochondrial O₂^‐ burst but also that the burst itself is not sufficient to induce the HR. Surprisingly, the O₂^‐ burst normally seen towards pv. maculicola is delayed in plants lacking AOX. This delay is associated with a delayed HR, suggesting that the burst does promote the HR. A O₂^‐ burst can also be induced by the complex III inhibitor antimycin A (AA), but is again delayed in plants lacking AOX. The similar mitochondrial response induced by pv. maculicola and AA suggests that electron transport is a target during HR‐inducing biotic interactions.     

Consequences of grazing on the vertical transmission of a fungal Neotyphodium symbiont in an annual grass population

Symbiosis between cool‐season grasses and vertically transmitted fungal endophytes are common and significantly impact on ecosystem function. This makes the understanding of the underlying mechanisms to symbiotic individuals frequency in local populations much more interesting. Most studies have been focused on the differential fitness between symbiotic and non‐symbiotic counterparts (relative fitness), barely considering other mechanisms. We performed a microcosms experiment to evaluate whether grazing alters the dynamics of the endophyte Neotyphodium occultans in the annual grass Lolium multiflorum by simultaneously modifying the relative fitness and the endophyte efficiency to be transmitted from host plants to seeds. Grazing was simulated by means of clipping and trampling on symbiotic and non‐symbiotic plants growing separately, in soils obtained from paddocks, differing in their agronomic management history (natural grassland vs. ryegrass promotion). Seed production showed a complex pattern as it depended on the symbiotic status of the plants, the level of grazing and the agro‐ecological context. Grazed plants produced three times fewer seeds than ungrazed plants only in microcosms with endophyte‐symbiotic plants in soils from ryegrass promotion. Endophyte benefits on seed production were exclusively observed in ungrazed plants in the same soil. Symbiotic plants produced symbiotic and non‐symbiotic seeds in all the treatments. While the production of non‐symbiotic seeds by these plants was not affected by grazing and the soil, grazing reduced the production of symbiotic seeds in both contexts. Grazing negative effect on the density of fully infected spikes determined a significant increment in the transmission failures which were not modified by agro‐ecological contexts. Therefore, grazing can modulate symbiosis dynamics through reducing seed production and endophyte transmission efficiency. Transmission has been disregarded, but it is a context‐dependent process that could lead to a gradual reduction in the symbiotic plants frequency in a population if the mutualism effectiveness does not outweigh transmission failures.     

Ultrastructural Visualization of Lipids in Trypanosomatids1

An imidazole-buffered osmium tetroxide solution was used to visualize lipids at the ultrastructural level in the following members of the family Trypanosomatidae: Trypanosoma cruzi, T. dionisii, T. vespertilionis, T. rangeli, Crithidia deanei, C. fasciculata, C. oncopelti, and Blastocrithidia culicis. Electron-dense material was seen in various lipid droplets found in all parasites and in the multivesicular structure of members of the sub-genus Schizotrypanum. High contrast of some membranes, mainly those which enclose the mitochondrion, the nucleus, and the endoplasmic reticulum, was observed even in unstained sections. X-ray microanalysis confirmed that the electron density of lipid droplets of B. culicis and membrane-bounded dense granules of C. oncopelti was due to the presence of osmium.     

Myrtlemiris,a new genus and new species of Australian plant bugs (Insecta: Heteroptera: Miridae): systematics,phylogeny and host associations

A new Australian genus of Orthotylinae, Myrtlemiris Cheng, Mututantri & Cassis gen.n. , is described, with nine included species described as new to science (M. agnew sp.n. , M. astartephila sp.n. , M. meanarra sp.n. , M. newmanensis sp.n. , M. rubrocuneatus sp.n. , M. russulatus sp.n. , M. silveirae sp.n. , M. tesselatus sp.n. , M. yalgoo sp.n. ). A phylogenetic analysis based on 39 morphological characters is presented for all Myrtlemiris species and 6 outgroup taxa. This analysis establishes Myrtlemiris as monophyletic, defined by a broad apophysis on the left paramere. A key to species is provided and diagnostic characters are illustrated. Myrtlemiris is endemic to southwest Western Australia. Host plants for Myrtlemiris species are near restricted to the myrtaceous tribe Chamelaucieae.     

Herpetomonas roitmani (Fiorini et al., 1989) N. Comb.: A Trypanosomatid with a Bacterium-like Endosymbiont in the Cytoplasm

The trypanosomatid previously described as Crithidia roitmani is characterized here at the ultrastructural and biochemical levels. The data indicates that the parasite belongs to the Herpetomonas genus, and we therefore suggest the flagellate to be denominated as Herpetomonas roitmani n. comb. Cladistic analysis of isoenzyme data generated by eight different enzymes showed that the parasite presented a distinct banding pattern and could be grouped with some Herpetomonas spp., but not with Crithidia spp., used as reference strains. Accordingly, when the parasites were grown for longer periods in Roitman's defined medium, expontaneous differentiation from promastigotes to opisthomastigotes (typical of the Herpetomonas genus) occurred. Transmission electron microscopy revealed the presence of bacterium-like endosymbionts in the cytoplasm of all evolutive forms of the parasite. All morphological alterations characteristic of endosymbiont-bearing trypanosomatids could be observed.     

Effects of Temperature on Promastigotes of Several Species of Leishmania

ABSTRACT. Six Leishmania species were studied comparatively, in order to determine the influence of temperature "in vitro" on differentiation, infectivily and protein synthesis. Differentiation ocurred in a heterogeneous manner, even in species that produce similar clinical manifestations. Thus, no association could be found between thermosensitivity and disease. The association between expression of proteins and increasing temperatures was analyzed at 34° C by polyacrylamide gel electrophoresis with sodium dodecyl sulphate (SDS-PAGE), using different incubation times, and employing a technique involving metabolic incorporation of [³⁵S]-methionine. Protein synthesis was very similar in all the New World species apart from L. amazonensis , which expressed a protein of approximately 80 kDa when incubated at 34° C for 2 hours. All the tested species had in common the expression of a 70 kDa protein. Differences, however, were observed in relation to the time interval for protein expression. in L. chagasi , synthesis was detected after 30 minutes of incubation at 34° C, while L. braziliensis required 1 hour at the same temperature. The "in vivo" and "in vitro" infectivity of the differentiated forms was also analyzed, but no significant differences were observed.     

Vision and the foraging technique of skimmers (Rynchopidae)

In birds, the position and extent of the region of binocular vision appears to be determined primarily by feeding ecology. Of prime importance is the degree to which vision is used for the precise control of bill position when foraging. Skimmers (Rynchops, Rynchopidae, Charadriiformes) exhibit a unique foraging behaviour and associated structural adaptations. When foraging they fly low and straight over water with the mouth open and the mandible partially submerged. Items that are hit by the lower mandible are grasped by a rapid reflex bill closure. It is believed that this unique ‘skimming’ foraging technique is guided by tactile rather than visual cues. It is predicted therefore that the visual fields of skimmers will have similar topography to those of other tactile feeding birds. We determined retinal visual fields in Black Skimmers Rynchops niger using an ophthalmoscopic reflex technique. Contrary to expectation the visual fields of Black Skimmers are not like those of other tactile feeders. They show high similarity with those of birds that feed by precision‐pecking. The projection of the bill tip when the mouth is closed and when open (as in skimming) falls within the frontal binocular field and there is an extensive blind area above and behind the head. We argue that this visual field topography functions to achieve accurate bill positioning with respect to the water surface when skimming and, because foraging skimmers cannot determine the identity of what they are seizing as they skim, to permit the visual identification of prey items held between the mandibles after they have been taken from the water surface. When skimming, only a small portion of the binocular field, approximately 5° wide and extending 5° above the horizontal, looks in the direction of travel. The small size of this forward‐facing region of binocularity in skimmers suggests that control of locomotion in birds does not necessarily require extensive binocularity in the direction of travel.