RNA editing affects messenger RNAs and transfer RNAs in plant mitochondria by site-specific exchange of cytidine and uridine bases in both seed and nonseed plants. Distribution of the phenomenon among bryophytes has been unclear since RNA editing has been detected in some but not all liverworts and mosses. A more detailed understanding of RNA editing in plants required extended data sets for taxa and sequences investigated. Toward this aim an internal region of the mitochondrial nad5 gene (1104 nt) was analyzed in a large collection of bryophytes and green algae (Charles). The genomic nad5 sequences predict editing in 30 mosses, 2 hornworts, and 7 simple thalloid and leafy liverworts (Jungermanniidae). No editing is, however, required in seven species of the complex thalloid liverworts (Marchantiidae) and the algae. RNA editing among the Jungermanniidae, on the other hand, reaches frequencies of up to 6% of codons being modified. Predictability of RNA editing from the genomic sequences was confirmed by cDNA analysis in the mosses Schistostega pennata and Rhodobryum roseum, the hornworts Anthoceros husnotii and A. punctatus, and the liverworts Metzgeria conjugata and Moerckia flotoviana. All C-to-U nucleotide exchanges predicted to reestablish conserved codons were confirmed. Editing in the hornworts includes the removal of genomic stop codons by frequent reverse U-to-C edits. Expectedly, no RNA editing events were identified by cDNA analysis in the marchantiid liverworts Ricciocarpos natans, Corsinia coriandra, and Lunularia cruciata. The findings are discussed in relation to models on the phylogeny of land plants.

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Autocatalytic activity of some group II introns has been demonstrated in vitro, but helper functions such as the yeast MRS2 protein are essential for splicing in vivo. In our search for such helper factors in plants, we pursued the cloning of two Arabidopsis thaliana homologues, atmrs2-1 and atmrs2-2. Atmrs2-1, but not atmrs2-2, complements the yeast deletion mutant of mrs2, and this is congruent with the prediction of two adjacent transmembrane stretches in AtMRS2-1 and yeast MRS2 but not in AtMRS2-2. This complementation depends on fusion of the native yeast mitochondrial import sequence to atmrs2-1. A differing, non-mitochondrial, cellular targeting in Arabidopsis is supported by the analysis of green fluorescent protein fusion constructs after transient transformation into plant protoplasts. Further members of what now appears to be a family of 10 mrs2 homologues are identified in the Arabidopsis genome. Similarity searches with the PSI-BLAST algorithm in the protein database fail to identify homologues of this novel gene family in any eukaryotes other than yeasts, but do identify its distant relatedness to the corA group of bacterial magnesium transporters. In line with this observation, intramitochondrial magnesium concentrations are indeed restored to wild-type levels in the yeast mutant on complementation with atmrs2-1.

Summary Autocatalytic activity of some group II introns has been demonstrated in vitro, but helper functions such as the yeast MRS2 protein are essential for splicing in vivo. In our search for such helper factors in plants, we pursued the cloning of two Arabidopsis thaliana homologues, atmrs2‐1 and atmrs2‐2. Atmrs2‐1, but not atmrs2‐2, complements the yeast deletion mutant of mrs2, and this is congruent with the prediction of two adjacent transmembrane stretches in AtMRS2‐1 and yeast MRS2 but not in AtMRS2‐2. This complementation depends on fusion of the native yeast mitochondrial import sequence to atmrs2‐1. A differing, non‐mitochondrial, cellular targeting in Arabidopsis is supported by the analysis of green fluorescent protein fusion constructs after transient transformation into plant protoplasts. Further members of what now appears to be a family of 10 mrs2 homologues are identified in the Arabidopsis genome. Similarity searches with the psi‐blast algorithm in the protein database fail to identify homologues of this novel gene family in any eukaryotes other than yeasts, but do identify its distant relatedness to the corA group of bacterial magnesium transporters. In line with this observation, intramitochondrial magnesium concentrations are indeed restored to wild‐type levels in the yeast mutant on complementation with atmrs2‐1.

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Thermal sprayed coatings are used in various applications often dedicated to corrosion and wear protection.Poresand other coating imperfections reduce corrosion and wear resistance and/or necessitate higher coating thicknesses. To improve the quality of thermal sprayed coatings, various post-treatment processes can be used. Characterisation of the efficiency of sealing was studied by metallographic examination andcomparative investigation of the corrosion and wear behaviour of the thermal sprayed coatings used with and without sealing and also by measuring the insulation resistance of the coating system. The results differ among the sealants. It is possible to remove the sealants from the coatings by mechanical treatment. Corrosion tests of the sealants demonstrate their efficiency in closing the interconnected pores and, consequently, preventing corrosion.

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