Genetic Differentiation of Populations of a Hydrothermal Vent-Endemic Gastropod, Ifremeria nautilei, between the North Fiji Basin and the Manus Basin revealed by Nucleotide Sequences of Mitochondrial DNA

The genetic differentiation of populations of a hydrothermal vent-endemic gastropod, Ifremeria nautilei, between two back-arc basins in the south Western Pacific, namely the Manus Basin and the North Fiji Basin, was analyzed on the basis of nucleotide sequences of the mitochondrial gene for cytochrome oxidase I. The two populations of I. nautilei had no common haplotypes and appeared, therefore, to be isolated from one another. All haplotypes obtained from the North Fiji Basin formed a monophyletic group supported by a high bootstrap probability and the genetic diversity of the population in the North Fiji Basin was much smaller than that of the population in the Manus Basin. The population in the North Fiji Basin might have been founded by relatively recent migrants from the Manus Basin. The present results suggest that the larval dispersal ability of I. nautilei might be lower than that of an undescribed species in the closely related genus Alviniconchay.     

Weather and nodule mediated variations in delta 13C and delta 15N values in field-grown soybean (Glycine max L.) with special interest in the analyses of xylem fluids

The nodulating soybean (Enrei) and its non-nodulating mutant (EN 1282) were grown in outdoor plots for 2 years (1994: extraordinary dry, high temperature, 1995: ordinary year). Carbon and nitrogen accumulation, delta 13C and delta 15N values in plant parts and xylem fluids and delta 15N values in the water-extractable soil N were analysed throughout the growing period. Plant growth in 1994 was rapid during the early growth stages, but no pods were produced. In 1995, plant growth was normal and pods were formed. The delta 13C values of the leaves were less negative in 1994 than in 1995 and the nodulated plants showed less negative delta 13C values than non-nodulated plants in both years. The delta 13C values of the leaves during the vegetative phase were positively correlated to the leaf N concentrations. Leaf N concentrations in their turn were influenced by nodulation and weather conditions and/or soil available N. The delta 15N values in the plants and xylem fluids were lower in the nodulated soybean than in non-nodulated soybean in both years, and estimates of the contribution of N2 fixation in nodulated plants based on plant top delta 15N values were 7-14% in 1994 and 37-63% in 1995. The delta 13C values of xylem fluids did not differ between nodulated and non-nodulated plants. Thus, the expected contribution by phosphopenolpyruvate carboxylase-mediated CO2 fixation in the root nodules to plant C-incorporation could not have been significant.     

Identification of a fmtA-like gene that has similarity to other PBPs and beta-lactamases in Staphylococcus aureus

We identified a gene from Staphylococcus aureus, flp (fmtA-like protein), encoding a protein of 489 amino acid residues with a molecular mass of 56.4 kDa. The deduced amino acid sequence shows similarity to previously characterized penicillin binding proteins (PBPs) and FmtA of S. aureus (one of the factors which affect methicillin resistance). FLP protein has three motifs, which are conserved in PBPs and beta-lactamases, suggesting that it might be associated with cell wall synthesis. Recombinant FLP protein, however, lacks penicillin binding activity, and the inactivation of flp in two methicillin-resistant S. aureus strains did not cause a reduction in the methicillin resistance.     

Relationship between ATP level and respiratory rate in sea urchin embryos

In sea urchin embryos, the rate of respiration, as a result of electron transport through the mitochondrial respiratory chain, was enhanced after hatching without any change in the intrinsic capacity of electron transport in mitochondria. The increase in respiratory rate after hatching was accompanied by an evident decrease in intracellular adenosine triphosphate (ATP) concentration without any change in intracellular levels of adenosine diphosphate (ADP) and adenosine monophosphate (AMP). Adenosine triphosphate is proposed to fortify acceptor control of respiration at high concentrations and to reduce the respiratory rate even in the presence of ADP, the acceptor. The relationships between the respiratory rate and intracellular ATP concentration in embryos were the same as those in mitochondria isolated from embryos, obtained in the presence of ADP at the same concentration as in the embryos. Probably, the respiratory rate is enhanced after hatching because of the decrease in the level of ATP. In embryos kept in a medium containing adenosine, intracellular ATP concentration increased especially after hatching, without any change in the ADP level, and the respiratory rate after hatching was made as low as the rate expected, based on the relationships obtained on isolated mitochondria. The respiratory rate in embryos probably depends on intracellular ATP concentration, irrespective of the developmental stage in early development.     

Isolation and characterization of arsenate-sensitive and resistant mutants of Chlamydomonas reinhardtii

Arsenate-sensitive and resistant mutants of Chlamydomonas reinhardtii were obtained by screening mutants generated by random insertional mutagenesis for growth in the presence of various concentrations of arsenate. The intracellular concentrations of arsenic in the mutants kept in the arsenate-containing medium were determined with an atomic absorption spectrophotometer. The intracellular levels of arsenic in the arsenate-resistant mutants were all lower than that of the parent strain CC425. Some of the arsenate-sensitive mutants, AS1 and AS3, showed obviously higher levels of arsenic than that of CC425, while other sensitive mutant, AS2, did not accumulate arsenic so much. Analysis of the chemical species of arsenic suggested that inorganic arsenic was converted to dimethylarsinic acid (DMAA) in CC425. However, DMAA was hardly detected in AS2. The mechanisms of the resistance to arsenate are discussed on its uptake and detoxification.     

A new method for direct introduction of chemicals into a single sieve tube of intact rice plants

We present a novel method for direct introduction of chemicals into a sieve tube of intact rice plants-namely, the method of micro-introduction using stylet of insect (the MUSI method). Fluorescent dyes were successfully introduced into a sieve tube through a severed stylet of planthopper and the distribution of the dyes was observed.     

Aluminum-induced 1-->3-beta-D-glucan inhibits cell-to-cell trafficking of molecules through plasmodesmata. A new mechanism of aluminum toxicity in plants

Symplastic intercellular transport in plants is achieved by plasmodesmata (PD). These cytoplasmic channels are well known to interconnect plant cells to facilitate intercellular movement of water, nutrients, and signaling molecules including hormones. However, it is not known whether Al may affect this cell-to-cell transport process, which is a critical feature for roots as organs of nutrient/water uptake. We have microinjected the dye lucifer yellow carbohydrazide into peripheral root cells of an Al-sensitive wheat (Triticum aestivum cv Scout 66) either before or after Al treatment and followed the cell-to-cell dye-coupling through PD. Here we show that the Al-induced root growth inhibition is closely associated with the Al-induced blockage of cell-to-cell dye coupling. Immunofluorescence combined with immuno-electron microscopic techniques using monoclonal antibodies against 1-->3-beta-D-glucan (callose) revealed circumstantial evidence that Al-induced callose deposition at PD may responsible for this blockage of symplastic transport. Use of 2-deoxy-D-glucose, a callose synthesis inhibitor, allowed us to demonstrate that a reduction in callose particles correlated well with the improved dye-coupling and reduced root growth inhibition. While assessing the tissue specificity of this Al effect, comparable responses were obtained from the dye-coupling pattern in tobacco (Nicotiana tabacum) mesophyll cells. Analyses of the Al-induced expression of PD-associated proteins, such as calreticulin and unconventional myosin VIII, showed enhanced fluorescence and co-localizations with callose deposits. These results suggest that Al-signal mediated localized alterations to calcium homeostasis may drive callose formation and PD closure. Our data demonstrate that extracellular Al-induced callose deposition at PD could effectively block symplastic transport and communication in higher plants.