The wheat mitochondrial genome contains an ORF showing sequence homology to the gene encoding the subunit 6 of the NADH-ubiquinone oxidoreductase.

A region of the mitochondrial (mt) DNA of wheat was studied because of its homology with other plant mtDNAs. Sequence analysis revealed an open reading frame encoding a polypeptide of 247 amino acids. Comparison of the sequence of the putative polypeptide with the protein sequence data of the Swiss-Prot library reveals homology with subunit 6 of the NADH-ubiquinone complex of mitochondria from Marchantia polymorpha, Podospora anserina, Chlamydomonas reinhardtii and of chloroplasts from M. polymorpha and Oryza sativa. No similarity was detected when compared with the subunit 6 of animal mitochondria, probably due to the rapid evolution of the sequence. A single 1.2 kb transcript appears in northern RNA blots. We found 15 edited sites of which only 13 give amino acid changes. This is the first report of a mt nad6 gene in higher plants.

A trans-splicing model for the expression of the tripartite nad5 gene in wheat and maize mitochondria.

The mitochondrial single-copy gene nad5 of wheat and maize consists of 5 exons located on three widely separated regions of the genome that are independently transcribed. The first region contains exons I and II separated by an atypical group II intron; in the second region is exon III (only 22 bp long), which is flanked upstream by a maturase-related open reading frame (ORF) and exon e of the nad1 gene, and downstream by a previously unidentified ORF (ORF143); in the third region are exons IV and V separated by a group II intron. In maize, this last domain is flanked upstream by the genes rps12, nad3, and tRNA(Ser) and downstream by a chloroplast tRNA(Cys). RNA editing occurs in wheat exons IV and V as C-to-U changes. A detailed analysis of the transcription of the nad5 gene in wheat and maize reveals that the exons are assembled into a 2.4-kb mRNA after two cis-splicing (between exons I and II and exons IV and V) and two trans-splicing events. The trans-splicing process involves the sequences flanking exons II, III, and IV that feature group II introns. A model is proposed for the assembly and maturation of the nad5 transcripts.

An internal part of the chloroplast atpA gene sequence is present in the mitochondrial genome of Triticum aestivum: molecular organisation and evolutionary aspects.

An internal part of the chloroplast atpA gene has been identified in the mitochondrial DNA of Triticum aestivum. It is located near the 18S-5S ribosomal genes and partially contained within a repeated sequence. Comparison of the transferred sequence with the original ct sequence reveals several nucleotide changes and shows that neither 5' nor 3' ends are present in the mt genome. No transcript of this region could be detected by Northern analysis. This sequence is present in mitochondrial genomes of other tetraploid and diploid species of Triticum, also in the vicinity of the 18S-5S ribosomal genes, suggesting a unique transfer event. The date of this event is discussed.

[Effect of gamma radiation on organs and cells of higher plants cultivated in vitro. Dose effect on survival of axillary buds of haploid and diploid Nicotiana sylvestris and Nicotiana tabacum]. / Effet du rayonnement gamma sur les organes et les cellules de plantes supérieures cultivés in vitro. Effet de la dose sur la fréquence de survie de bourgeons axillaires de plantes haploïdes et diploïdes de Nicotiana sylvestris et Nicotiana tabacum.

The Dose/Action relationship between gamma irradiation and bud survival, plotted on log-linear axes, produces a plateau (no decrease in survival) followed by a straight line decrease. The length of the plateau and the slope of the line appear to depend on the degree of ploïdy and the structure of the genome. There could be redondant parts in the genome of Nicotiana sylvestris.