Different expression of an S-adenosylmethionine synthetase gene in transgenic tobacco callus modifies alkaloid biosynthesis

Transformed callus cultures of Nicotiana tabacum were generated in which the SAM-1 gene from Arabidopsis thaliana encoding S-adenosylmethionine synthetase (SAM-S), under the control of the 35S promoter, had been integrated. The presence of the SAM-1 gene was detected in all tested transformants and the SAM-S activity correlated with the accumulation of SAM in the tobacco callus cultures. Three distinct phenotypic classes were identified among the transgenic cell lines in relation to growth of the cells, structure of the calli, and level of SAM. Transgene silencing was observed in several cultivated transgenic calli and this phenomenon was correlated directly with a low level of SAM-1 mRNA accompanied by a decrease of the SAM-S activity. The transgenic calli overexpressing the SAM-1 gene accumulated a high SAM level. The modifications in SAM-S activity were reflected in the pattern of secondary products present in the different cell lines, thereby demonstrating that the flux through the biosynthetic pathway of a plant secondary product can be modified by means of genetic engineering.     

Use of 15N reverse gradient two-dimensional nuclear magnetic resonance spectroscopy to follow metabolic activity in Nicotiana plumbaginifolia cell-suspension cultures

Nitrogen metabolism was monitored in suspension cultured cells of Nicotiana plumbaginifolia Viv. using nuclear magnetic resonance (NMR) spectroscopy following the feeding of (¹⁵NH₄)₂SO₄ and K¹⁵NO₃. By using two-dimensional ¹⁵N-¹H NMR with heteronuclear single-quantum-coherence spectroscopy and heteronuclear multiple-bond-coherence spectroscopy sequences, an enhanced resolution of the incorporation of ¹⁵N label into a range of compounds could be detected. Thus, in addition to the amino acids normally observed in one-dimensional ¹⁵N NMR (glutamine, aspartate, alanine), several other amino acids could be resolved, notably serine, glycine and proline. Furthermore, it was found that the peak normally assigned to the non-protein amino-acid γ-aminobutyric acid in the one-dimensional ¹⁵N NMR spectrum was resolved into a several components. A peak of N-acetylated compounds was resolved, probably composed of the intermediates in arginine biosynthesis, N-acetylglutamate and N-acetylornithine and, possibly, the intermediate of putrescine degradation into γ-aminobutyric acid, N-acetylputrescine. The occurrence of ¹⁵N-label in agmatine and the low detection of labelled putrescine indicate that crucial intermediates of the pathway from glutamate to polyamines and/or the tobacco alkaloids could be monitored. For the first time, labelling of the peptide glutathione and of the nucleotide uridine could be seen. Received: 29 March 1999 / Accepted: 15 July 1999     

Global patterns in species richness of pelagic seabirds: the Procellariiformes

Quantitative information on large scale spatial patterns of biodiversity remains poor, especially for pelagic systems. In this paper the regional diversity of procellariiforms is mapped worldwide at the species level. These seabirds do not display a conventional latitudinal gradient of decreasing species richness towards high latitudes, but rather are most speciose between 37° and 59°S in all ocean basins. Based on data for foraging ranges, areas with the highest species richness and the most species with smaller range sizes are all found in the vicinity of New Zealand and its sub-Antarctic islands. In contrast, data for breeding ranges show islands in the southern Indian and Atlantic oceans to have the highest number of breeding species, while these islands and New Zealand have the most species with smaller range sizes. No northern hemisphere regions are amongst the top ten grid cells for foraging and breeding species richness, although Hawaii has the highest species richness of procellariilforms north of the equator. Northern Baja California. Madeira, the Canary islands, and the west coast of South America are all important sites of narrow endemism in the northern hemisphere. High species richness and narrow endemism coincide with areas of significant longline fishing activity in the southern hemisphere. Near-minimum sets based on one and three representations demonstrate that if all procellariiform species are to be retained, large areas of the ocean and almost all breeding sites require conservation.     

The anatomy of the interspecific abundance–range size relationship for the British avifauna: I. Spatial patterns

Data from the British Trust for Ornithology Common Birds Census and two atlases of breeding birds were used to examine the form of the interspecific abundance–range size relationship for the British avifauna. The relationship is positive for both farmland and woodland habitats and over two different periods, with some evidence of curvilinearity, using either proportion of occupied sites or numbers of occupied 10 × 10 km squares as measures of range size, and mean density at occupied sites as a measure of abundance. A log-linear plot gives the highest correlation. The relationship is stronger if based on maximum local densities than if based on average densities, but there is no relationship using minimum local densities. Relationships based on abundances at individual sites are uniformly positive for all sites, although the relationships for many sites also show evidence of curvilinearity, especially when range size is measured as the proportion of occupied sites. Species show significant concordance in their rank abundances across sites. We discuss some implications of these results.     

Effects of urbanisation on disease prevalence and age structure in blackbird Turdus merula populations

Despite increasing interest in urban ecology most attention has focussed on describing changes in assemblage composition and structure along urbanisation gradients, whilst relatively little research has focussed on the mechanisms behind these changes. Ecological theory predicts that alterations in biotic interactions are particularly likely to arise, especially with regard to disease risk. Here, we report on differences in prevalence of avian malaria and tick infection and intensity in 11 paired urban and rural blackbird Turdus merula populations from across the western Palearctic. We find large and consistent reductions in tick prevalence and intensity in urban areas. There are also large reductions in the prevalence of avian malaria in many, but not all, urban areas. The proportion of first year birds in urban populations is significantly lower than that in rural ones, and across the more natural rural sites southerly populations contain fewer first years than northern ones. These patterns are expected to arise if survival rates are higher in urban areas, and are negatively correlated with latitude.     

Assessing the potential for Grey Squirrels Sciurus carolinensis to compete with birds at supplementary feeding stations

Supplementary feeding of birds, particularly in urban areas, is often associated with increased population size and fecundity. In the UK, the non‐native Grey Squirrel Sciurus carolinensis is common in rural and urban habitats. It exploits supplementary feeders and may induce interference competition by excluding birds, but empirical evidence of this is unavailable. Using controlled model presentation experiments, we demonstrate that Grey Squirrels could reduce bird use of supplementary feeders and induce interference competition. Total bird resource use was reduced by 98% and most species exhibited similar sensitivities. The likelihood and magnitude of interference competition will depend on how rapidly displaced birds find alternative food sources; it will be greatest where there are high Grey Squirrel densities and few supplementary feeders. Other studies suggest that supplementary feeding increases Grey Squirrel numbers, and the species is also predicted to expand its non‐native range across most of Europe. Our data indicate that Grey Squirrels may eventually alter the net effect of supplementary feeding on bird populations across the European continent; increased use of squirrel‐proof feeders may help to minimize such effects.     

S-nitrosothiols increases cystic fibrosis transmembrane regulator expression and maturation in the cell surface

S-nitrosothiols (SNOs) are endogenous signaling molecules with a broad spectrum of beneficial airway effects. SNOs are normally present in the airway, but levels tend to be low in cystic fibrosis (CF) patients. We and others have demonstrated that S-nitrosoglutathione (GSNO) increases the expression, maturation, and function of wild-type and mutant F508del cystic fibrosis transmembrane conductance regulator (CFTR) in human bronchial airway epithelial (HBAE) cells. We hypothesized that membrane permeable SNOs, such as S-nitrosoglutathione diethyl ester (GNODE) and S-nitroso-N-acetyl cysteine (SNOAC) may be more efficient in increasing the maturation of CFTR. HBAE cells expressing F508del CFTR were exposed to GNODE and SNOAC. The effects of these SNOs on the expression and maturation of F508del CFTR were determined by cell surface biotinylation and Western blot analysis. We also found for the first time that GNODE and SNOAC were effective at increasing CFTR maturation at the cell surface. Furthermore, we found that cells maintained at low temperature increased cell surface stability of F508del CFTR whereas the combination of low temperature and SNO treatment significantly extended the half-life of CFTR. Finally, we showed that SNO decreased the internalization rate of F508del CFTR in HBAE cells. We anticipate identifying the novel mechanisms, optimal SNOs, and lowest effective doses which could benefit cystic fibrosis patients.     

BiP Binding to the ER-Stress Sensor Ire1 Tunes the Homeostatic Behavior of the Unfolded Protein Response

The unfolded protein response (UPR) is an intracellular signaling pathway that counteracts variable stresses that impair protein folding in the endoplasmic reticulum (ER). As such, the UPR is thought to be a homeostat that finely tunes ER protein folding capacity and ER abundance according to need. The mechanism by which the ER stress sensor Ire1 is activated by unfolded proteins and the role that the ER chaperone protein BiP plays in Ire1 regulation have remained unclear. Here we show that the UPR matches its output to the magnitude of the stress by regulating the duration of Ire1 signaling. BiP binding to Ire1 serves to desensitize Ire1 to low levels of stress and promotes its deactivation when favorable folding conditions are restored to the ER. We propose that, mechanistically, BiP achieves these functions by sequestering inactive Ire1 molecules, thereby providing a barrier to oligomerization and activation, and a stabilizing interaction that facilitates de-oligomerization and deactivation. Thus BiP binding to or release from Ire1 is not instrumental for switching the UPR on and off as previously posed. By contrast, BiP provides a buffer for inactive Ire1 molecules that ensures an appropriate response to restore protein folding homeostasis to the ER by modulating the sensitivity and dynamics of Ire1 activity.