Identification of high levels of phytochelatins, glutathione and cadmium in the phloem sap of Brassica napus. A role for thiol-peptides in the long-distance transport of cadmium and the effect of cadmium on iron translocation

Phytochelatins (PCs) are glutathione-derived peptides that function in heavy metal detoxification in plants and certain fungi. Recent research in Arabidopsis has shown that PCs undergo long-distance transport between roots and shoots. However, it remains unknown which tissues or vascular systems, xylem or phloem, mediate PC translocation and whether PC transport contributes to physiologically relevant long-distance transport of cadmium (Cd) between shoots and roots. To address these questions, xylem and phloem sap were obtained from Brassica napus to quantitatively analyze which thiol species are present in response to Cd exposure. High levels of PCs were identified in the phloem sap within 24 h of Cd exposure using combined mass spectrometry and fluorescence HPLC analyses. Unexpectedly, the concentration of Cd was more than four-fold higher in phloem sap compared to xylem sap. Cadmium exposure dramatically decreased iron levels in xylem and phloem sap whereas other essential heavy metals such as zinc and manganese remained unchanged. Data suggest that Cd inhibits vascular loading of iron but not nicotianamine. The high ratios [PCs]/[Cd] and [glutathione]/[Cd] in the phloem sap suggest that PCs and glutathione (GSH) can function as long-distance carriers of Cd. In contrast, only traces of PCs were detected in xylem sap. Our results suggest that, in addition to directional xylem Cd transport, the phloem is a major vascular system for long-distance source to sink transport of Cd as PC–Cd and glutathione–Cd complexes

Insights into the structure, function and evolution of the radical-SAM 23S rRNA methyltransferase Cfr that confers antibiotic resistance in bacteria

The Cfr methyltransferase confers combined resistance to five classes of antibiotics that bind to the peptidyl tranferase center of bacterial ribosomes by catalyzing methylation of the C-8 position of 23S rRNA nucleotide A2503. The same nucleotide is targeted by the housekeeping methyltransferase RlmN that methylates the C-2 position. Database searches with the Cfr sequence have revealed a large group of closely related sequences from all domains of life that contain the conserved CX3CX2C motif characteristic of radical S-adenosyl-l-methionine (SAM) enzymes. Phylogenetic analysis of the Cfr/RlmN family suggests that the RlmN subfamily is likely the ancestral form, whereas the Cfr subfamily arose via duplication and horizontal gene transfer. A structural model of Cfr has been calculated and used as a guide for alanine mutagenesis studies that corroborate the model-based predictions of a 4Fe–4S cluster, a SAM molecule coordinated to the iron–sulfur cluster (SAM1) and a SAM molecule that is the putative methyl group donor (SAM2). All mutations at predicted functional sites affect Cfr activity significantly as assayed by antibiotic susceptibility testing and primer extension analysis. The investigation has identified essential amino acids and Cfr variants with altered reaction mechanisms and represents a first step towards understanding the structural basis of Cfr activity

The Bowen–Conradi syndrome protein Nep1 (Emg1) has a dual role in eukaryotic ribosome biogenesis, as an essential assembly factor and in the methylation of Ψ1191 in yeast 18S rRNA

The Nep1 (Emg1) SPOUT-class methyltransferase is an essential ribosome assembly factor and the human Bowen–Conradi syndrome (BCS) is caused by a specific Nep1D86G mutation. We recently showed in vitro that Methanocaldococcus jannaschii Nep1 is a sequence-specific pseudouridine-N1-methyltransferase. Here, we show that in yeast the in vivo target site for Nep1-catalyzed methylation is located within loop 35 of the 18S rRNA that contains the unique hypermodification of U1191 to 1-methyl-3-(3-amino-3-carboxypropyl)-pseudouri-dine (m1acp3Ψ). Specific 14C-methionine labelling of 18S rRNA in yeast mutants showed that Nep1 is not required for acp-modification but suggested a function in Ψ1191 methylation. ESI MS analysis of acp-modified Ψ-nucleosides in a Δnep1-mutant showed that Nep1 catalyzes the Ψ1191 methylation in vivo. Remarkably, the restored growth of a nep1-1ts mutant upon addition of S-adenosylmethionine was even observed after preventing U1191 methylation in a Δsnr35 mutant. This strongly suggests a dual Nep1 function, as Ψ1191-methyltransferase and ribosome assembly factor. Interestingly, the Nep1 methyltransferase activity is not affected upon introduction of the BCS mutation. Instead, the mutated protein shows enhanced dimerization propensity and increased affinity for its RNA-target in vitro. Furthermore, the BCS mutation prevents nucleolar accumulation of Nep1, which could be the reason for reduced growth in yeast and the Bowen-Conradi syndrome

Narażenia cieplne i elektrodynamiczne wyłączników różnicowoprądowych przy ich dobezpieczaniu wyłącznikami nadprądowymi instalacyjnymi

Residual current operated circuit breakers without integral overcurrent protection should be back-up protected. As back-up protection devices, overcurrent circuit breakers are used. The maximum let-through energy and let-through current of the overcurrent devices were evaluated under laboratory conditions. The thermal and electrodynamic risk of residual current devices was analyzed.Powszechnie stosowane wyłączniki różnicowoprądowe bez wbudowanego zabezpieczenia nadprądowego wymagają dobezpieczenia. Jako urządzenia dobezpieczające stosuje się m.in. wyłączniki nadprądowe instalacyjne. W artykule autorzy przedstawili wyniki badań prądów ograniczonych i całek Joule’a wyłączania tych wyłączników oraz omówili zagrożenia, które mogą wystąpić przy dobezpieczaniu wyłączników różnicowoprądowych wyłącznikami nadprądowymi instalacyjnymi

Narażenia cieplne i elektrodynamiczne wyłączników różnicowoprądowych przy ich dobezpieczaniu wyłącznikami nadprądowymi instalacyjnymi

Residual current operated circuit breakers without integral overcurrent protection should be back-up protected. As back-up protection devices, overcurrent circuit breakers are used. The maximum let-through energy and let-through current of the overcurrent devices were evaluated under laboratory conditions. The thermal and electrodynamic risk of residual current devices was analyzed.Powszechnie stosowane wyłączniki różnicowoprądowe bez wbudowanego zabezpieczenia nadprądowego wymagają dobezpieczenia. Jako urządzenia dobezpieczające stosuje się m.in. wyłączniki nadprądowe instalacyjne. W artykule autorzy przedstawili wyniki badań prądów ograniczonych i całek Joule’a wyłączania tych wyłączników oraz omówili zagrożenia, które mogą wystąpić przy dobezpieczaniu wyłączników różnicowoprądowych wyłącznikami nadprądowymi instalacyjnymi

Thermal and electrodynamics risk of residual current devices in case of back-up protection by overcurrent circuit breakers

Powszechnie stosowane wyłączniki różnicowoprądowe bez wbudowanego zabezpieczenia nadprądowego wymagają dobezpieczenia. Jako urządzenia dobezpieczające stosuje się m.in. wyłączniki nadprądowe instalacyjne. W artykule przedstawiono wyniki badań prądów ograniczonych i całek Joule’a wyłączania tych wyłączników oraz omówiono zagrożenia, które mogą wystąpić przy dobezpieczaniu wyłączników różnicowoprądowych wyłącznikami nadprądowymi instalacyjnymi.Residual current operated circuit-breakers without integral overcurrent protection should be back-up protected. As backup protection devices the overcurrent circuit breakers are used. The maximum let-through energy and let-through current of the overcurrent devices were evaluated under laboratory condition. Thermal and electrodynamics risk of residual current devices was analyzed