Quantification of symplastic continuity as visualised by plasmodesmograms: diagnostic value for phloem-loading pathways

The use of plasmodesmatal frequency to correlate cell-cell symplastic transport capacity remains a contentious problem, as variation in cell shape, accurate determination of interface contact area between cell types, distribution (i.e. whether random or aggregated) and shape (i.e. whether single or branched), and state of permeability may confuse the issue. Additionally, variation in the methods used to determine the frequencies compounds the problem further. Data presented in this paper show that plasmodesmograms offer a means to visualise the potential transport pathway from mesophyll cells to sieve tubes. Furthermore, the results allow an instant appreciation of symplastic continuity or discontinuity and, accordingly, the potential symplastic and-or apoplastic stages involved in the overall loading process.The Foundation for Research Development (FRD, Pretoria, South Africa), and the Rhodes University Council are gratefully acknowledged for their generous financial support. The first author wishes to acknowledge Mr. Barry Hartley for his valued assistance in the preparation of this paper.     

Low CyaA expression and anti-cooperative binding of cAMP to CRP frames the scope of the cognate regulon of Pseudomonas putida

Although the soil bacterium Pseudomonas putida KT2440 bears a bona fide adenylate cyclase gene (cyaA), intracellular concentrations of 3′,5′-cyclic adenosine monophosphate (cAMP) are barely detectable. By using reporter technology and direct quantification of cAMP under various conditions, we show that such low levels of the molecule stem from the stringent regulation of its synthesis, efflux and degradation. Poor production of cAMP was the result of inefficient translation of cyaA mRNA. Moreover, deletion of the cAMP-phosphodiesterase pde gene led to intracellular accumulation of the cyclic nucleotide, exposing an additional cause of cAMP drain in vivo. But even such low levels of the signal sustained activation of promoters dependent on the cAMP-receptor protein (CRP). Genetic and biochemical evidence indicated that the phenomenon ultimately rose from the unusual binding parameters of cAMP to CRP. This included an ultratight cAMP-Crp_{P. putida} affinity (K_D of 45.0 ± 3.4 nM) and an atypical 1:1 effector/dimer stoichiometry that obeyed an infrequent anti-cooperative binding mechanism. It thus seems that keeping the same regulatory parts and their relational logic but changing the interaction parameters enables genetic devices to take over entirely different domains of the functional landscape.     

Different Patterns of Intercellular Transport of Lucifer Yellow in Young and Mature Antheridia of Chara vulgaris L.

Intra- and intercellular movement of the fluorochrome Lucifer Yellow (LY), microinjected into the shield cells of male sex organs, was examined at different stages of spermatogenesis in Chara vulgaris L. Two distinct stage-associated types of probe movement were noted: (I) a fast and uniform spreading of fluorescence within the shield cell injected, followed by centripetal transport of LY into the adjoining manubrium and the capitular cells, and subsequent redistribution into the other manubria and shield cells in young antheridia (up to the stage of 4-cellular filaments), and (II) limited spreading of fluorescence, restricted to the triangle-shaped area of the impaled shield cell in more mature antheridia with multicellular filaments. These results confirm earlier electron microscopic observations on plasmodesmatal connections indicating an intensive solute movement between all cell types in young antheridia of Chara. Developmental changes appearing at later stages, during differentiation of sperm cells, strongly reduce the capacity for intercellular symplasmic transport.     

Multiple mechanisms involved in the large-spectrum therapeutic potential of cannabidiol in psychiatric disorders

Cannabidiol (CBD) is a major phytocannabinoid present in the Cannabis sativa plant. It lacks the psychotomimetic and other psychotropic effects that the main plant compound Δ⁹-tetrahydrocannabinol (THC) being able, on the contrary, to antagonize these effects. This property, together with its safety profile, was an initial stimulus for the investigation of CBD pharmacological properties. It is now clear that CBD has therapeutic potential over a wide range of non-psychiatric and psychiatric disorders such as anxiety, depression and psychosis. Although the pharmacological effects of CBD in different biological systems have been extensively investigated by in vitro studies, the mechanisms responsible for its therapeutic potential are still not clear. Here, we review recent in vivo studies indicating that these mechanisms are not unitary but rather depend on the behavioural response being measured. Acute anxiolytic and antidepressant-like effects seem to rely mainly on facilitation of 5-HT1A-mediated neurotransmission in key brain areas related to defensive responses, including the dorsal periaqueductal grey, bed nucleus of the stria terminalis and medial prefrontal cortex. Other effects, such as anti-compulsive, increased extinction and impaired reconsolidation of aversive memories, and facilitation of adult hippocampal neurogenesis could depend on potentiation of anandamide-mediated neurotransmission. Finally, activation of TRPV1 channels may help us to explain the antipsychotic effect and the bell-shaped dose-response curves commonly observed with CBD. Considering its safety profile and wide range of therapeutic potential, however, further studies are needed to investigate the involvement of other possible mechanisms (e.g. inhibition of adenosine uptake, inverse agonism at CB2 receptor, CB1 receptor antagonism, GPR55 antagonism, PPARγ receptors agonism, intracellular (Ca²⁺) increase, etc.), on CBD behavioural effects.     

Species richness of epiphytic bryophytes: drivers across scales on the edge of the Mediterranean

Spatial variation in species richness is one of the most frequently studied topics on macroecology. However, the relative importance of the factors affecting richness across scales and their influence on some groups of small‐sized organisms, such as bryophytes, remain unclear. We evaluate the relative importance of biogeographic region, climate, topography, forest structure and abundance in shaping epiphytic bryophyte richness at both local (forest) and sample (trunk) scale on the boundary between the Atlantic and Mediterranean regions in NW Spain. For that purpose we used simple, multiple and partial regressions, hierarchical partitioning and partial least squares path analyses. Although climatic variables related to water availability during spring and summer were the most important predictors of bryophyte richness, their effects were moderated by winter temperature. Abundance, in contrast, was mostly related to forest structure. Biogeographic region was not significantly related to richness. Interestingly, forest richness was the best predictor of trunk richness. Our results highlight the importance of seasonal distribution of rainfall and temperatures and support that the richness of bryophyte communities is constrained by mesoscale climatic factors, in particular the interplay between water and energy availability. In contrast, abundance seems to be controlled by habitat characteristics. We also detected a strong top‐down structure between both scales of measurement evidencing a scaling down of the climatic effect: richness at the sample scale is controlled mainly by local richness and local richness is in turn controlled by climate, so mesoscale climatic gradients are indirectly limiting richness at the smallest scale.     

Evaluation of Salmonella 1977 to 1982

Between 1977 and 1982, the National Center of Salmonella of the Institute Pasteur of Tunis has isolated; received and/or identified 1715 Salmonella strains. In typhoid and paratyphoid fevers group Salmonella typhi represent the predominant species with a frequency of 99.6%. In the enteric group, Salmonella wien is the most frequent (50,26%). 11 serotypes appeared in 1982, although 5 serotypes have not been met since 1977.     

Proteomic Analysis of the Action of the Mycobacterium ulcerans Toxin Mycolactone: Targeting Host Cells Cytoskeleton and Collagen

Buruli ulcer (BU) is a neglected tropical disease caused by Mycobacterium ulcerans. The tissue damage characteristic of BU lesions is known to be driven by the secretion of the potent lipidic exotoxin mycolactone. However, the molecular action of mycolactone on host cell biology mediating cytopathogenesis is not fully understood. Here we applied two-dimensional electrophoresis (2-DE) to identify the mechanisms of mycolactone''s cellular action in the L929 mouse fibroblast proteome. This revealed 20 changed spots corresponding to 18 proteins which were clustered mainly into cytoskeleton-related proteins (Dync1i2, Cfl1, Crmp2, Actg1, Stmn1) and collagen biosynthesis enzymes (Plod1, Plod3, P4ha1). In line with cytoskeleton conformational disarrangements that are observed by immunofluorescence, we found several regulators and constituents of both actin- and tubulin-cytoskeleton affected upon exposure to the toxin, providing a novel molecular basis for the effect of mycolactone. Consistent with these cytoskeleton-related alterations, accumulation of autophagosomes as well as an increased protein ubiquitination were observed in mycolactone-treated cells. In vivo analyses in a BU mouse model revealed mycolactone-dependent structural changes in collagen upon infection with M. ulcerans, associated with the reduction of dermal collagen content, which is in line with our proteomic finding of mycolactone-induced down-regulation of several collagen biosynthesis enzymes. Our results unveil the mechanisms of mycolactone-induced molecular cytopathogenesis on exposed host cells, with the toxin compromising cell structure and homeostasis by inducing cytoskeleton alterations, as well as disrupting tissue structure, by impairing the extracellular matrix biosynthesis.