Vein cavitation and stomatal behaviour of sunflower (Helianthus annuus) leaves under water limitation

The impact of leaf vein cavitation and embolism on stomatal response and leaf hydraulic conductance was studied in potted plants of sunflower subjected to water limitation. Plant dehydration was achieved either by cutting well‐watered plants near their base and leaving them dehydrating in air or by depriving intact plants of irrigation. The vein cavitation threshold (Ψ_CAV) was estimated in terms of ultrasound acoustic emissions (UAE) from the leaf blade versus leaf water potential (Ψ_L). This was found to be the same (Ψ_CAV ≈ ?0.6 MPa) for leaves of both cut and intact plants where stomata began to close in coincidence with starting vein cavitation. Vein embolism was detected by infiltrating leaves at different Ψ_L with 0.7 mM fluorescein and measuring the percentage fluorescent area as percentage of total leaf surface area. A distinct loss of vein functionality (up to 50%) was found to occur in leaves at progressively decreasing Ψ_L, starting when leaves reached Ψ_CAV. A linear positive relationship with high statistical significance was found to exist between g_L and percentage leaf fluorescent area, thus indicating that stomata were sensitive to vein embolism. The hydraulic conductance (K_L) of the leaf was affected by leaf dehydration less than expected (K_L decreased by about 20% between near full turgor and Ψ_L = ?1.3 MPa). When the extravascular leaf compartment was excluded either by killing cells by immersing leaves in 70% ethanol or by cutting the main leaf venous system through to allow flow to bypass it, K_L turned out to increase 5.5 times, thus suggesting that the high dominance of the hydraulic resistance of the extravascular leaf compartment over the total leaf resistance might buffer or mask possibly large local changes in K_L inducing stomatal closure.     

Occurrence and patterns of antibiotic resistance in vertebrates off the Northeastern United States coast

The prevalence of antibiotic-resistant bacteria in the marine environment is a growing concern, but the degree to which marine mammals, seabirds and fish harbor these organisms is not well documented. This project sought to identify the occurrence and patterns of antibiotic resistance in bacteria isolated from vertebrates of coastal waters in the northeastern United States. Four hundred and seventy-two isolates of clinical interest were tested for resistance to a suite of 16 antibiotics. Fifty-eight percent were resistant to at least one antibiotic, while 43% were resistant to multiple antibiotics. A multiple antibiotic resistance index value ≥0.2 was observed in 38% of the resistant pathogens, suggesting exposure of the animals to bacteria from significantly contaminated sites. Groups of antibiotics were identified for which bacterial resistance commonly co-occurred. Antibiotic resistance was more widespread in bacteria isolated from seabirds than marine mammals, and was more widespread in stranded or bycaught marine mammals than live marine mammals. Structuring of resistance patterns based on sample type (live/stranded/bycaught) but not animal group (mammal/bird/fish) was observed. These data indicate that antibiotic resistance is widespread in marine vertebrates, and they may be important reservoirs of antibiotic-resistant bacteria in the marine environment.     

Mouse endometrial stromal cells produce basement-membrane components

During mouse pregnancy, uterine stromal cells transform into morphologically distinct decidual cells under the influence of the implanting embryo and a proper hormonal environment. Mechanical stimulation of hormonally primed uterine stromal cells leads to the same morphologic alterations. The decidualization of stromal cells is characterized by the accumulation of pericellular basement-membrane material. Decidualized stromal cells of pregnancy differ in this respect from stromal cells obtained from nonpregnant uteri, which are not associated with any significant amounts of basement-membrane components. Mouse decidual cells isolated from 6- to 7-day pregnant uteri explanted in vitro continue to synthesize basement-membrane-like extracellular matrix. Using immunohistochemistry and metabolic labeling followed by immunoprecipitation, SDS-PAGE, and fluorography, it was shown that the decidual cells synthesize laminin, entactin, fibronectin, type-IV collagen, and heparan sulfate proteoglycan. Stromal cells isolated from nonpregnant uteri and explanted in vitro produced the same basement-membrane components. Apparently, these cells were stimulated by the procedure used during isolation and explanation to undergo pseudodecidualization. We thus showed that stromal cells from pregnant and nonpregnant mouse uteri synthesize significant amounts of basement-membrane components in vitro, and hence could serve as a good model for the study of normal basement-membrane components.     

Mosaic pbpX genes of major clones of penicillin-resistant Streptococcus pneumoniae have evolved from pbpX genes of a penicillin-sensitive Streptococcus oralis

Penicillin-resistant clinical isolates of Streptococcus pneumoniae contain mosaic penicillin-binding protein (PBP) genes that encode PBPs with decreased affinity for β-lactam antibiotics. The mosaic blocks are believed to be the result of gene transfer of homologous PBP genes from related penicillin-resistant species. We have now identified a gene homologous to the pneumococcal PBP2x gene (pbpX) in a penicillin-sensitive Streptococcus oralis isolate M3 from South Africa that diverged by almost 20% from pbpX of penicillin-sensitive pneumococci, and a central sequence block of a mosaic pbpX gene of Streptococcus mitis strain NCTC 10712. In contrast, it differed by only 2-4% of the 1 to 1.5 kb mosaic block in pbpX genes of three genetically unrelated penicillin-resistant S. pneumoniae isolates, two of them representing clones of serotype 6B and 23F, which are prevalent in Spain and are also already found in other countries. With low concentrations of cefotaxime, transformants of the sensitive S. pneumoniae R6 strain could be selected containing pbpX genes from either S. mitis NCTC 10712 or S. oralis M3, demonstrating that genetic exchange can already occur between β-lactam-sensitive species. These data are in agreement with the assumption that PBPs as penicillin-resistance determinants have evolved by the accumulation of point mutations in genes of sensitive commensal species.     

Prenatal ethanol exposure persistently impairs NMDA receptor-dependent activation of extracellular signal-regulated kinase in the mouse dentate gyrus

The dentate gyrus (DG) is the central input region to the hippocampus and is known to play an important role in learning and memory. Previous studies have shown that prenatal alcohol is associated with hippocampal-dependent learning deficits and a decreased ability to elicit long-term potentiation (LTP) in the DG in adult animals. Given that activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling cascade by NMDA receptors is required for various forms of learning and memory, as well as LTP, in hippocampal regions, including the DG, we hypothesized that fetal alcohol-exposed adult animals would have deficits in hippocampal NMDA receptor-dependent ERK1/2 activation. We used immunoblotting and immunohistochemistry techniques to detect NMDA-stimulated ERK1/2 activation in acute hippocampal slices prepared from adult fetal alcohol-exposed mice. We present the first evidence linking prenatal alcohol exposure to deficits in NMDA receptor-dependent ERK1/2 activation specifically in the DG of adult offspring. This deficit may account for the LTP deficits previously observed in the DG, as well as the life-long cognitive deficits, associated with prenatal alcohol exposure.     

Construction and characterization of isogenic O-antigen variants of Salmonella typhi

A 7.5 kb Kpnl-generated fragment, from within the rfb cluster of Salmonella typhimurium LT2 that encodes abequose synthase (the rfbJ gene) which is necessary for O4 antigen synthesis, and flanking sequences, was inserted into a suicide vector. Using allelic exchange techniques, these rfb sequences of S. typhimurium were integrated into the rfb clusters of wild-type Salmonella typhi Vi-positive strain ISP 1820 (i.e. serotype 09,12; Vi⁺ H-d), S. typhi Vi-negative strain H400 (i.e. serotype 09,12; Vi⁻; H-d), and a double aro mutant of S. typhi ISP 1820, strain CVD 906, resulting in the isolation of strains H325, H404 and CVD 906-O4, respectively. Immunoblot analysis of lipopolysaccharide (LPS) purified from H325, H404 and CVD 906-O4 demonstrated that these 8trains express the 04 antigen (an abequose residue) in place of the O9 antigen (a tyvelose residue) in the LPS molecule. Hence, the serotype of H325 is O4,12; Vi⁺; H-d and the serotype of H404 is O4,12; Vi⁻; H-d. DNA hybridization analysis of chromosomal DNA from H325, H404 and CVD 906-O4 confirmed that a precise recombination event within sequences flanking rfbSE of S. typhi (which encodes the enzymes necessary for cytidine diphosphate-tyvelose synthesis) resulted in replacement of rfbSE with rfbJ (which encodes abequose synthase and is necessary for O4 synthesis) of S. typhimurium in strains H325, H404 and CVD 906-O4. The resistance of each strain to the bactericidal effects of guinea-pig serum (GPC) was assessed. Whereas ISP 1820, H325 and H404 exhibit similar resistance patterns in GPC, strain H400 is sensitive to the bactericidal effects of GPC. The results suggest that the development of the O-antigen serotype diversity of Salmonella is probably the result of both sequence divergence and recombination     

Competing Females and Caring Males. Polyandry and Sex-Role Reversal in African Black Coucals, Centropus grillii

Most species of birds show bi‐parental or female‐only care. However, a minority of species is polyandrous and expresses male‐only care. So far, such reversals in sex roles have been demonstrated only in precocial bird species, but there was suggestive evidence that such a mating system may occur in one altricial bird species, the black coucal, Centropus grillii. In a field study in Tanzania we investigated whether black coucals are sex‐role reversed and polyandrous. We found that males were mated to one female, rarely vocalized and provided all parental care from incubation of eggs to feeding of young. In contrast, female black coucals were about 69% heavier and 39% larger than males and polyandrous. They spent a large proportion of time calling from conspicuous perches, defended breeding territories, did not help in provisioning young and had a higher potential reproductive rate than males. We conclude that the black coucal currently represents the only altricial bird species with sole male parental care and a classical polyandrous mating system. High nest predation pressure and small territory sizes due to high food abundance may have been important factors in the evolution of sex‐role reversal and polyandry in this species.     

Inhibition of phototrophically growing Chromatium vinosum D by glycine

Abstract The effect of glycine on phototrophically growing Chromatium vinosum D was investigated in the presence and absence of various amino acids. Inhibition of autotrophic cells was more pronounced than that of heterotrophic cells. Cells of growth-inhibited cultures were misshaped, showing vacuolation and partial protoplast formation. Cells exposed to glycine in the presence of equimolar amounts of either d - or l -alanine did not show any inhibition of growth. Neither serine, leucine, valine, isoleucine nor α-aminoisobutyric acid could counteract the inhibition of growth by glycine. The inhibitory effect of glycine on growth is thus likely to be caused by a competition between glycine and alanine during cell wall synthesis. The possible functions of glycine transport system(s) in the natural habitat of C. vinosum are discussed.     

Vanadate, known to interfere with signal transduction, induces metamorphosis in Hydractinia (Coelenterata; Hydrozoa) and causes profound alterations of the larval and postmetamorphic body pattern

Abstract. Vanadate interferes with the development of planula larvae of the marine hydrozoon Hydractinia echinata . Exposure of embryos (morulae) to vanadate leads to teratomalike and heavily malformed larvae. Thirty h old embryos treated for 18 h develop into larvae signficiantly longer than control larvae. In control larvae cell proliferation detected by BrdU-antiBrdU immuno-histochemistry ceases at the posterior and anterior pole at an age of 72 h but is maintained at a high level in treated larvae. Even in teratomas cell proliferation is at a higher level than in proliferation zones of control animals indicating a deregulation of proliferation in the treated larvae just as in mammalian teratomas. Arginine-phenylalanine-amide (RF-amide) immunopositive nerve cells and fibres are found in 5 day old teratomas. RF-amide immunopositive cells are concentrated in globular structures. The animals overcome the deregulation by extruding these structures. In intact larvae 2–4 m M ort-hovanadate and 25–250 m M metavanadate induced metamorphosis. A majority of the developing polyps displayed an abnormal body pattern often having an elongated hypostome and instead of one whorl, had several tentacle whorls, one upon another. Incomplete polyps with a larval anterior part instead of a basal plate are also observed. Metamorphosis induced by vanadate is promoted by amiloride and inhibited by ouabain. Vanadate also disturbs pattern control in regeneration. Up to 50% of isolated larval tails either regenerate a second mirror-image tail instead of an anterior one or develop tentacles at their anterior part (up to 20%), i.e., exhibited a reversed polarity. Vanadate is assumed to act by influencing signal transducing pathways like the phosphoinositide cycle or tyrosine phosphorylation.     

The role of 4-hydroxyphenylpyruvate dioxygenase in enhancement of solid-phase electron transfer by Shewanella oneidensis MR-1

We hypothesized that Shewanella oneidensis MR-1, a model dissimilatory metal-reducing bacterium, could utilize environmentally relevant concentrations of tyrosine to produce pyomelanin for enhanced Fe(III) oxide reduction. Because homogentisate is an intermediate of the tyrosine degradation pathway, and a precursor of a redox-cycling metabolite, pyomelanin, we evaluated the process of homogentisate production by S. oneidensis MR-1, in order to identify the key steps involved in pyomelanin production. We determined that two enzymes involved in this pathway, 4-hydroxyphenylpyruvate dioxygenase and homogentisate 1,2-dioxygenase are responsible for homogentisate production and oxidation, respectively. We used genetic analysis and physiological characterization of MR-1 strains either deficient in or displaying substantially increased pyomelanin production. The relative significance imparted by pyomelanin on solid-phase electron transfer was also addressed using electrochemical techniques, which allowed us to extend the genetic and physiological findings to biogeochemical cycling of metals. Based on our findings, environmental production of pyomelanin from available organic precursors could contribute to the survival of S. oneidensis MR-1 when dissolved oxygen concentrations become low, by providing an increased capacity for solid-phase metal reduction. This study demonstrates the role of organic precursors and their concentrations in pyomelanin production, solid phase metal reduction and biogeochemical cycling of iron.