From endosperm to triploid plants: a stepwise characterization of the de novo shoot organogenesis and morpho-agronomic aspects of an ornamental passion fruit (Passiflora foetida L.)

Plant Cell, Tissue and Organ Culture (PCTOC) - Somaclonal variation during in vitro culture is often an undesirable phenomenon but may also be a source of genetic variation useful for breeders. The...     

ENDOLITHIC MICROFLORA ARE MAJOR PRIMARY PRODUCERS IN DEAD CARBONATE SUBSTRATES OF HAWAIIAN CORAL REEFS1

To quantify the contribution of endolithic phototrophs to primary production of dead carbonate substrates, experimental blocks of cleaned Porites lobata Dana skeleton were placed at three different sites in Kaneohe Bay, Hawaii: inshore, lagoonal, and oceanic. After 6 months of exposure, experimental blocks were colonized by communities characteristic of their estuarine (inshore, lagoonal) and oceanic (ocean) environments. Blocks were sub-sampled; net photosynthesis (NP) and chl a concentrations of the whole blocks (epi- and endoliths) and scrapped blocks (only endoliths) were quantified. Green turf algae colonized predominantly inshore and lagoonal blocks, while encrusting corallines were the dominant epiliths colonizing oceanic blocks. Four main species of endolithic phototrophs were identified in all blocks: Mastigocoleus testarum Lagerheim, Plectonema terebrans Bornet and Flahault (cyanobacteria), Phaeophila dendroides Crouan and Crouan, and Ostreobium quekettii Bornet and Flahault (Chlorophytes). While epiliths were very different between sites, NP rates and chl a concentration of endoliths did not vary significantly and were positively correlated (191±25 mmol C·m⁻²·day⁻¹ and 590±150 mg chl a·m⁻² of reef, respectively). Assimilation numbers for whole communities, including both epilithic and endolithic communities, were similar to those measured for endolithic communities alone (average of 0.3 g C·g chl a·h⁻¹). Under experimental conditions, the contribution of endolithic phototrophs to community NP rates of blocks ranged from 56% to 81%, and under natural conditions, we estimated that this contribution ranged between 32% and 46%. Thus, we showed that the endolithic phototrophs are one of the major primary producers in dead coral substrates in a wide range of coral reef environments.     

Ascorbate removes key precursors to oxidative damage by cell-free haemoglobin in vitro and in vivo

Haemoglobin initiates free radical chemistry. In particular, the interactions of peroxides with the ferric (met) species of haemoglobin generate two strong oxidants: ferryl iron and a protein-bound free radical. We have studied the endogenous defences to this reactive chemistry in a rabbit model following 20% exchange transfusion with cell-free haemoglobin stabilized in tetrameric form [via cross-linking with bis-(3,5-dibromosalicyl)fumarate]. The transfusate contained 95% oxyhaemoglobin, 5% methaemoglobin and 25 microM free iron. EPR spectroscopy revealed that the free iron in the transfusate was rendered redox inactive by rapid binding to transferrin. Methaemoglobin was reduced to oxyhaemoglobin by a slower process (t(1/2) = 1 h). No globin-bound free radicals were detected in the plasma. These redox defences could be fully attributed to a novel multifunctional role of plasma ascorbate in removing key precursors of oxidative damage. Ascorbate is able to effectively reduce plasma methaemoglobin, ferryl haemoglobin and globin radicals. The ascorbyl free radicals formed are efficiently re-reduced by the erythrocyte membrane-bound reductase (which itself uses intra-erythrocyte ascorbate as an electron donor). As well as relating to the toxicity of haemoglobin-based oxygen carriers, these findings have implications for situations where haem proteins exist outside the protective cell environment, e.g. haemolytic anaemias, subarachnoid haemorrhage, rhabdomyolysis.     

Role of the hindbrain in patterning the otic vesicle: a study of the zebrafish vhnf1 mutant

The vertebrate inner ear develops from an ectodermal placode adjacent to rhombomeres 4 to 6 of the segmented hindbrain. The placode then transforms into a vesicle and becomes regionalised along its anteroposterior, dorsoventral and mediolateral axes. To investigate the role of hindbrain signals in instructing otic vesicle regionalisation, we analysed ear development in zebrafish mutants for vhnf1, a gene expressed in the caudal hindbrain during otic induction and regionalisation. We show that, in vhnf1 homozygous embryos, the patterning of the otic vesicle is affected along both the anteroposterior and dorsoventral axes. First, anterior gene expression domains are either expanded along the whole anteroposterior axis of the vesicle or duplicated in the posterior region. Second, the dorsal domain is severely reduced, and cell groups normally located ventrally are shifted dorsally, sometimes forming a single dorsal patch along the whole AP extent of the otic vesicle. Third, and probably as a consequence, the size and organization of the sensory and neurogenic epithelia are disturbed. These results demonstrate that, in zebrafish, signals from the hindbrain control the patterning of the otic vesicle, not only along the anteroposterior axis, but also, as in amniotes, along the dorsoventral axis. They suggest that, despite the evolution of inner ear structure and function, some of the mechanisms underlying the regionalisation of the otic vesicle in fish and amniotes have been conserved.     

Three new naraoiid species from the Burgess Shale,with a morphometric and phylogenetic reinvestigation of Naraoiidae

Naraoiids are non‐biomineralized euarthropods characterized by the complete fusion of post‐cephalic tergo‐pleurae into a single shield, as well as an extensively ramified digestive tract. Ranging from the early Cambrian to the late Silurian (Pridoli), these arthropods of simple appearance have traditionally been associated with the early diversification of trilobites and their close relatives, but the interrelationships and affinities of naraoiids within Artiopoda remain poorly characterized. Three new species from the Burgess Shale (middle Cambrian, Stage 5) of British Columbia, Canada, are described here: Misszhouia canadensis sp. nov., from Marble Canyon (Kootenay National Park), the first species belonging to the genus Misszhouia outside of China; Naraoia magna sp. nov., from Marble Canyon and also from the Raymond Quarry (Yoho National Park), the largest species of Naraoia described thus far, reaching up to 9 cm in length; and Naraoia arcana sp. nov., from two sublocalities on Mount Stephen (Yoho National Park), defined by its unusual combination of spines. This new material shows that gut morphology is no longer a reliable character to distinguish Misszhouia from Naraoia. We demonstrate that Naraoia and Misszhouia can instead be discriminated morphometrically, based on simple metrics of the dorsal exoskeleton. Our quantitative results also help with inter‐specific discrimination and illustrate possible cases of sexual dimorphism. Phylogenetically, the inclusion of morphometric data adds resolution to our cladogram, although parsimony and likelihood treatments provide somewhat different evolutionary scenarios. In all cases, liwiines are nested within Naraoiidae, resolved as the most derived clade of trilobitomorph arthropods.     

Srf-dependent paracrine signals produced by myofibers control satellite cell-mediated skeletal muscle hypertrophy

Adult skeletal muscles adapt their fiber size to workload. We show that serum response factor (Srf) is required for satellite cell-mediated hypertrophic muscle growth. Deletion of Srf from myofibers and not satellite cells blunts overload-induced hypertrophy, and impairs satellite cell proliferation and recruitment to pre-existing fibers. We reveal a gene network in which Srf within myofibers modulates interleukin-6 and cyclooxygenase-2/interleukin-4 expressions and therefore exerts a paracrine control of satellite cell functions. In Srf-deleted muscles, in vivo overexpression of interleukin-6 is sufficient to restore satellite cell proliferation but not satellite cell fusion and overall growth. In contrast cyclooxygenase-2/interleukin-4 overexpression rescue satellite cell recruitment and muscle growth without affecting satellite cell proliferation, identifying altered fusion as the limiting cellular event. These findings unravel a role for Srf in the translation of mechanical cues applied to myofibers into paracrine signals, which in turn will modulate satellite cell functions and support muscle growth.     

Comparative analysis of expressed genes from cacao meristems infected by Moniliophthora perniciosa

BACKGROUND AND AIMS: Witches' broom disease is caused by the hemibiotrophic basidiomycete Moniliophthora perniciosa, and is one of the most important diseases of cacao in the western hemisphere. Because very little is known about the global process of such disease development, expressed sequence tags (ESTs) were used to identify genes expressed during the Theobroma cacao-Moniliophthora perniciosa interaction. METHODS: Two cDNA libraries corresponding to the resistant (RT) and susceptible (SP) cacao-M. perniciosa interactions were constructed from total RNA, using the DB SMART Creator cDNA library kit (Clontech). Clones were randomly selected, sequenced from the 5' end and analysed using bioinformatics tools including in silico analysis of the differential gene expression. KEY RESULTS: A total of 6884 ESTs were generated from the RT and SP cDNA libraries. These ESTs were composed of 2585 singlets and 341 contigs for a total of 2926 non-redundant sequences. The redundancy of the libraries was low and their specificity high when compared with the few other cacao libraries already published. Sequence analysis allowed the assignment of a putative functional category for 54 % of sequences, whereas approx. 22 % of sequences corresponded to unknown function and approx. 24 % of sequences did not show any significant similarity with other proteins present in the database. Despite the similar overall distribution of the sequences in functional categories between the two libraries, qualitative differences were observed. Genes involved during the defence response to pathogen infection or in programmed cell death were identified, such as pathogenesis related-proteins, trypsin inhibitor or oxalate oxidase, and some of them showed an in silico differential expression between the resistant and the susceptible interactions. CONCLUSIONS: As far as is known this is the first EST resource from the cacao-M. perniciosa interaction and it is believed that it will provide a significant contribution to the understanding of the molecular mechanisms of the resistance and susceptibility of cacao to M. perniciosa, to develop strategies to control witches' broom, and as a source of polymorphism for molecular marker development and marker-assisted selection.