Accumulation of organic and inorganic solutes in the subantarctic cruciferous species Pringlea antiscorbutica in response to saline and cold stresses

Pringlea antiscorbutica R. Br., a subantarctic endemic cruciferous species, is endangered in its natural sites by several ecological changes. This species is tolerant to salinity and a permanent cold temperature on Kerguelen and Crozet Islands. We attempted the investigation of regulating mechanisms of osmotic adjustment in this species. ¹³C NMR analyses of water-soluble compounds from leaves collected from the field revealed glucose and proline to be the main accumulated organic solutes. Colorimetric determinations in these samples showed that proline and soluble carbohydrates were present at remarkably high levels. When young plants were cultivated in growth chambers they showed a good resistance to cold and medium resistance to saline conditions. High levels of soluble carbohydrates were present in all situations. Proline was accumulated in response to a saline and a cold treatment. The quantitative variations of the pool of proline in response to saline treatments were rapid and important. The adaptive value of these responses of organic solutes in the tolerance of Pringlea antiscorbutica to various stresses is discussed. Received: 16 June 1997 / Accepted: 5 May 1998     

Comparative Genometrics (CG): a database dedicated to biometric comparisons of whole genomes

The ever increasing rate at which whole genome sequences are becoming accessible to the scientific community has created an urgent need for tools enabling comparison of chromosomes of different species. We have applied biometric methods to available chromosome sequences and posted the results on our Comparative Genometrics (CG) web site. By genometrics, a term coined by Elston and Wilson [Genet. Epidemiol. (1990), 7, 17–19], we understand a biometric analysis of chromosomes. During the initial phase, our web site displays, for all completely sequenced prokaryotic genomes, three genometric analyses: the DNA walk [Lobry (1999) Microbiology Today, 26, 164–165] and two complementary representations, i.e. the cumulative GC- and TA-skew analyses, capable of identifying, at the level of whole genomes, features inherent to chromosome organization and functioning. It appears that the latter features are taxon-specific. Although primarily focused on prokaryotic chromosomes, the CG web site contains genometric information on paradigm plasmids, phages, viruses and eukaryotic organelles. Relevant data and methods can be readily used by the scientific community for further analyses as well as for tutorial purposes. Our data posted at the CG web site are freely available on the World Wide Web at http://www.unil.ch/comparativegenometrics.     

Resistance induction and herbivore virulence in the interaction between Myzus persicae (Sulzer) and a major aphid resistance gene (Rm2) from peach

In gene-for-gene host–enemy interactions, monogenic plant resistance results from pathogen recognition that initiates the induction of plant defense responses. Schematically, as the result of the on/off process of recognition, phenotypic variability in enemy virulence is expected to be qualitative, with either a failure or a success of host colonization. We focussed on a major gene from peach conferring avoidance resistance against the green peach aphid Myzus persicae. Measurements of herbivore density and time-dependent aspects of resistance induction were examined, as well as variability in the aphid’s ability to exploit the resistant host. Varying densities of infestation did not provoke differences in the aphid’s tendency to leave a plant, and a single aphid was sufficient to elicit a response. Similarly, the duration of infestation did not affect the aphid response. A brief aphid feeding time of 3 h triggered induced resistance, which became effective between 24 and 48 h after the initial attack. Induced resistance decayed over time in the absence of additional infestation. Thirty aphid genotypes collected from natural populations were tested in the laboratory. No clone could colonize the resistant host, suggesting that all of them triggered the induction of effective plant defense responses. However, we detected significant quantitative variation among clones in the tendency of aphids to leave plants. These results improve our understanding of induced resistance as a dynamic phenomenon and suggest that the potential for aphids to adapt to a major plant resistance gene may depend on factors other than the mere capacity to evade recognition.     

Mycobacterium tuberculosis Exploits Asparagine to Assimilate Nitrogen and Resist Acid Stress during Infection

Mycobacterium tuberculosis is an intracellular pathogen. Within macrophages, M. tuberculosis thrives in a specialized membrane-bound vacuole, the phagosome, whose pH is slightly acidic, and where access to nutrients is limited. Understanding how the bacillus extracts and incorporates nutrients from its host may help develop novel strategies to combat tuberculosis. Here we show that M. tuberculosis employs the asparagine transporter AnsP2 and the secreted asparaginase AnsA to assimilate nitrogen and resist acid stress through asparagine hydrolysis and ammonia release. While the role of AnsP2 is partially spared by yet to be identified transporter(s), that of AnsA is crucial in both phagosome acidification arrest and intracellular replication, as an M. tuberculosis mutant lacking this asparaginase is ultimately attenuated in macrophages and in mice. Our study provides yet another example of the intimate link between physiology and virulence in the tubercle bacillus, and identifies a novel pathway to be targeted for therapeutic purposes.     

Synthesis and evaluation of new omega-borono-alpha-amino acids as rat liver arginase inhibitors

Recent studies have demonstrated that arginase plays important roles in pathologies such as asthma or erectile dysfunctions. We have synthesized new omega-borono-alpha-amino acids that are analogues of the previously known arginase inhibitors S-(2-boronoethyl)-l-cysteine (BEC) and 2-amino-6-boronohexanoic acid (ABH) and evaluated them as inhibitors of purified rat liver arginase (RLA). In addition to the distance between the B(OH)(2) and the alpha-amino acid functions, the position of the sulfur atom in the side chain also appears as a key determinant for the interaction with the active site of RLA. Furthermore, substitution of the alkyl side chain of BEC by methyl groups and conformational restriction of ABH by incorporation of its side chain in a phenyl ring led to inactive compounds. These results suggest that subtle interactions govern the affinity of inhibitors for the active site of RLA.     

Anti-retroviral and cytostatic activity of 2',3'-dideoxyribonucleoside 3'-disulfides

Herein, we report the synthesis, antiviral and cytostatic effects of nucleosides bearing a 3'-disulfide function as prodrugs of potentially active 3'-mercaptonucleotides. The lack of the anti-HIV effects in mutant CEM/TK-cells for most of the thymidine disulfides suggests that a phosphorylation step involving thymidine kinase is necessary for the eventual antiviral activity of the thymidine nucleosides. The comparable anti-HIV activities of most of the disulfides and their rapid reduction in CEM cell extracts imply an inhibitory effect of the 2',3'-dideoxy-3'-mercaptothymidine 5'-triphosphate metabolite. The cytostatic effects of the disulfides in CEM/0 and Molt4/C8 cells appeared to be strongly dependent on the nature of the non-nucleosidic disulfide moiety and were decreased in preserving the anti-retroviral activity.     

Impairment of SLC17A8 encoding vesicular glutamate transporter-3, VGLUT3, underlies nonsyndromic deafness DFNA25 and inner hair cell dysfunction in null mice

Autosomal-dominant sensorineural hearing loss is genetically heterogeneous, with a phenotype closely resembling presbycusis, the most common sensory defect associated with aging in humans. We have identified SLC17A8, which encodes the vesicular glutamate transporter-3 (VGLUT3), as the gene responsible for DFNA25, an autosomal-dominant form of progressive, high-frequency nonsyndromic deafness. In two unrelated families, a heterozygous missense mutation, c.632C→T (p.A211V), was found to segregate with DFNA25 deafness and was not present in 267 controls. Linkage-disequilibrium analysis suggested that the families have a distant common ancestor. The A211 residue is conserved in VGLUT3 across species and in all human VGLUT subtypes (VGLUT1-3), suggesting an important functional role. In the cochlea, VGLUT3 accumulates glutamate in the synaptic vesicles of the sensory inner hair cells (IHCs) before releasing it onto receptors of auditory-nerve terminals. Null mice with a targeted deletion of Slc17a8 exon 2 lacked auditory-nerve responses to acoustic stimuli, although auditory brainstem responses could be elicited by electrical stimuli, and robust otoacoustic emissions were recorded. Ca²⁺-triggered synaptic-vesicle turnover was normal in IHCs of Slc17a8 null mice when probed by membrane capacitance measurements at 2 weeks of age. Later, the number of afferent synapses, spiral ganglion neurons, and lateral efferent endings below sensory IHCs declined. Ribbon synapses remaining by 3 months of age had a normal ultrastructural appearance. We conclude that deafness in Slc17a8-deficient mice is due to a specific defect of vesicular glutamate uptake and release and that VGLUT3 is essential for auditory coding at the IHC synapse.     

COST Action CM1201 “Biomimetic Radical Chemistry”: free radical chemistry successfully meets many disciplines

Abstract

The COST Action CM1201 “Biomimetic Radical Chemistry” has been active since December 2012 for 4 years, developing research topics organized into four working groups: WG1 – Radical Enzymes, WG2 – Models of DNA damage and consequences, WG3 – Membrane stress, signalling and defenses, and WG4 – Bio-inspired synthetic strategies. International collaborations have been established among the participating 80 research groups with brilliant interdisciplinary achievements. Free radical research with a biomimetic approach has been realized in the COST Action and are summarized in this overview by the four WG leaders.     

Long-term acclimatization of Scenedesmus bicellularis to high-frequency intermittent lighting (100 Hz). I. Growth, photosynthesis and photosystem II activity

Responses of the green microalga, Scenedesmus bicellularis tohigh-frequency intermittent lighting (II., 100 Hz) were assessedafter a 4 week acclimatization. Effects of IL on growth, photosynthesisand photosystem II (PSII) activity were studied at limitingand saturating irradiances, and compared to those of continuouslight (CL) of the same instantaneous and daily irradiances.Even after a 4 week acclimatization period, the photosyntheticcapacity (P_max), the photosynthetic efficiency () and the photosyntheticactivity at growth irradiance, either expressed on a per cellor a chlorophyll a basis, showed little difference, neitherdid the index of light adaptation (I_k) or PSII activity. Incontrast, growth was lower under IL at saturating irradiance.Results are discussed considering the non-linearity of the relationshipbetween growth or photosynthesis and irradiance.