Different characteristics of roots in the cadmium-tolerance and Cd-binding complex formation between mono- and dicotyledonous plants

Effects of Cd²⁺ on growth and Cd-binding complex formation in roots were examined with various seedlings of mono- and dicotyledonous plants. Maize, oat, barley and rice exhibited the greater tolerance to Cd²⁺ (100 μM) than did azuki bean, cucumber, lettuce, pea, radish, sesame and tomato (10–30 μM). Azuki bean was the most sensitive to Cd²⁺ (<10 μM). Under these Cd-treatments, cereal roots accumulated Cd²⁺ in the cytoplasmic fractions and transported Cd²⁺ into the same fractions of shoot tissues, to larger extents than did dicotyledonous roots. Cereal roots synthesized a Cd-binding complex containing phytochelatins in the cytoplasmic fractions, depending upon Cd²⁺ concentrations applied (30–100 μM). Such a complex was not detected from the same fractions of dicotyledonous roots treated with Cd²⁺. These results suggest that the Cd-binding complex formation has an important role in the tolerance of cereal roots against Cd²⁺.     

Characterization of a gene responsible for the Na+/H+ antiporter system of alkalophilic Bacillus species strain C-125

An alkali-sensitive mutant, 38154, of the alkalophilic Bacillus sp. strain C-125 could not grow at an alkaline pH. The nucleotide sequence of a 3.7 kb parental DNA fragment that recovers the growth of 38154 at alkaline pH has four open reading frames (ORF1–4). By sub-cloning the fragment, we demonstrated that a 0.25 kb DNA region is responsible for the recovery. Direct sequencing of the mutant's corresponding region revealed a G to A substitution. The mutation resulted in an amino acid substitution from Gly-393 to Arg of the putative 0RF1 product, which was deduced to be an 804-amino-acid polypeptide with a molecular weight of 89 070. The N-terminal part of the putative ORF1 product showed amino acid similarity to those of the chain-5 products of eukaryotic NADH quinine oxidoreductases. Membrane vesicles prepared from 38154 did not show membrane potential (δψ)-driven Na⁺/H⁺ antiporter activity. Antiporter activity was resumed by introducing a parental DNA fragment which recovered the mutant's alkalophily. These results indicate that the mutation in 38154 affects, either directly or indirectly, the electrogenic Na⁺/H⁺ antiporter activity. This is the first report which shows that a gene responsible for the Na⁺/H⁺ anti-porter system is important in the alkalophily of alkalo-philic microorganisms.     

Nucleotide sequence of a rice cDNA similar to a maize NADP-dependent malic enzyme

We have isolated a rice cDNA clone that is homologous to the gene for the maize NADP-dependent malic enzyme (EC 1.1.1.40; NADP-ME). The deduced amino acid sequence coded for by the cDNA indicates a high level of homology to chloroplast type NADP-ME, including a transit peptide with pronounced hydrophobic properties at the amino terminus. Northern blot analysis indicates that the expression of this gene is regulated by external stress such as submergence.     

A Deletion in the Endothelin-B Receptor Gene is Responsible for the Waardenburg Syndrome-Like Phenotypes of WS4 Mice.

The WS4 mouse is an animal model for human Waardenburg syndrome type 4 (WS4), showing pigmentation anomalies, deafness and megacolon, which are caused by defects of neural crest-derived cells. We have previously reported that the gene responsible for the WS4 mouse is an allele of the piebald mutations of the endothelin B receptor gene (Ednrb). In this study, we examined the genomic sequence of the Ednrb gene in WS4 mice and found a 598-bp deletion in the gene. The deleted region contains the entire region of exon 2 and the 5' part of exon 3 and is flanked by inverted repeat sequences which are suggested to trigger the deletion. We concluded that the deletion in the Ednrb gene is the causative mutation for the phenotype of WS4 mice.     

Organization and variation of angiosperm mitochondrial genome

The mitochondrial genomes of angiosperms are the largest mitochondrial genomes so far reported and are highly variable in size among plant species. The comparative analysis of the angiosperm mitochondrial genomes at the nucleotide level has now become feasible for addressing long-standing questions, owing to the publication of five dicot and three monocot genomes. Whereas the identified genes and introns are rather well conserved, intergenic regions are highly variable in sequence, even between two close relatives. Promiscuous DNA and horizontally transferred sequence constitute part of the intergenic regions, but the origin of the majority of these regions is unknown. On the other hand, duplication and extensive rearrangement of preexisting sequences may be one of the explanations for the occurrence of unknown sequences. Functional aspects of the mitochondrial genome, such as RNA editing and expression of unique open reading frames (ORFs), can be changed under certain nuclear genotypes.