Effect of water temperature on the feeding activity and the resultant mercury levels in the muscle of cultured bluefin tuna Thunnus orientalis (Temminck and Schlegel)

Tuna muscle often contains high levels of mercury, and fish samples with mercury concentrations ten times higher than the specified safety standards have been reported. Here, we report on the relationship between water temperature and the concentration of mercury in the tail muscle tissue of cultured bluefin tuna Thunnus orientalis. The fish used in this study were cultured at Fisheries Laboratory of Kinki University (Amami Experimental Station, Kagoshima, Japan). One hundred fish weighing 26.2–89.4 kg were selected for analysis between February 2007 and January 2008. Water temperature during rearing ranged from 21 to 29 °C. The total mercury levels were measured using the reduction vaporizing atomic absorption method after acid digestion. Body weight increased approximately 1.5 times that observed in a previous study, despite feeding activity either being the same or less than that observed previously. The average mercury concentration in white muscle was 0.353 mg kg^?1, remaining almost constant and independent of body growth. Unlike previous studies, seasonality was not observed in this study. Based on these findings, water temperatures within a certain range were considered to stabilize feeding activity and increase feeding efficiency. Consequently, water temperature is considered to have a moderating effect on seasonal fluctuations in muscle mercury concentrations in cultured bluefin tuna.     

Effect of food reductones, 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) and hydroxyhydroquinone (HHQ), on lipid peroxidation and type IV and I allergy responses of mouse

The effect of long-term supplementation of food reductones, 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) (2%, w/w), detected in many foodstuffs including soy sauce, and hydroxyhydroquinone (1,2,4-benzenetriol) (HHQ) (1.2%, w/w), detected in coffee, on mouse lipid peroxidation and type IV and I allergy responses was investigated. The effect of supplementation of these reductones combined with NO(2) inhalation (5-6 ppm) was also investigated. Levels of thiobarbituric acid-reactive substances in lung were remarkably increased, and those in kidney and liver were slightly decreased by supplementation of DMHF or HHQ. The degree of 2,4-dinitrochlorobenzene (DNCB)-sensitized lymph node cell proliferation as assessed by lymph node assay was remarkably enhanced by supplementation of DMHF or HHQ. Both the DNCB-sensitized and the trimellitic anhydride-sensitized increases in IgE levels of mice were enhanced to greater extent by supplementation of DMHF or HHQ. In no cases were additive effects of NO(2) inhalation observable. Allergen-sensitized type IV and I allergy responses of mice may be enhanced by supplementation of food reductones, DMHF or HHQ.     

Interspecific differences in the post-settlement survival of <Emphasis Type="Italic">Acropora</Emphasis> corals under a common garden experiment

Extremely low post-settlement survival is one of the largest barriers for artificial rehabilitation of Acropora corals. However, little data have been found for interspecific difference of the post-settlement survival probably because the observation of coral juvenile is difficult in the field. Here, we analyzed the survival of three dominant species of Acropora corals (A. digitifera, A. tenuis, A. yongei), with different colony morphologies and habitat preferences, for 2 years after settlement under the same environmental conditions. The post-settlement survival was significantly higher for A. tenuis than for A. digitifera 3 months after settlement. Two years later, the survival rate of A. tenuis was approximately 15 times higher than A. digitifera. In a separate analysis of three bottle-brush species (A. awi, A. echinata, A. subglabra) and A. tenuis, post-settlement survival was always higher for A. awi than for other two bottle-brush species, suggesting that the initial survival was different among morphologically sister species. Low survival was possibly associated with slow growth rates during the first 7 months. Thus, species selection is important for successful artificial coral rehabilitation, with A. tenuis being the most viable option. Alternatively, new techniques are required to improve post-settlement survival of slow growing coral species.     

Survey of the response of 82 domestic landraces of Zea mays to cucumber mosaic virus (CMV) reveals geographical region‐related resistance to CMV in Japan

Zea mays has been historically imported to Japan via two independent geographical routes: into southern Japan by trading with Europe in the 16th century and into northern Japan by import from North America in the 19th century. Breeding to genetically improve on quality traits and high yields has led to the current domestic landraces in each region. In a survey of 82 domestic landraces, nine out of 38 landraces originating from southern Japan showed complete immunity to cucumber mosaic virus yellow strain (CMV(Y)) without the formation of necrotic local lesions (NLLs). In contrast, three out of 44 landraces originating from northern Japan developed NLLs, but revealed no systemic spread of the virus. Due to the absence of good documentation on NLL formation in Z. mays, the response of domestic landraces Aso‐1 and Aso‐3, originating from Ibaraki in northern Japan, to a challenge with CMV(Y) and CMV(Ma‐1) was further analysed. Aso‐3 only formed NLL in response to CMV(Y) but not to CMV(Ma‐1). Moreover, in CMV(Y)‐inoculated Aso‐3, virus spread was restricted to the primary infection site and the expression of defence‐related genes was up‐regulated, whereas Aso‐1 became systemically infected with either CMV(Y) or CMV(Ma‐1). The response of Aso‐3 to CMV(Y) was inherited as a single dominant trait. Together, these results pointed towards the induction of hypersensitive response (HR)‐mediated resistance to CMV(Y) in Aso‐3. Although HR‐mediated resistance to viruses has been studied mainly in dicots, the pathosystem CMV–Z. mays may provide a model to investigate HR‐mediated resistance to viruses in monocot plants.     

Application of supercooling to long-term storage of fish meat

Fish meat was brought to a supercooled state through slow cooling, and changes in the texture, histology, and protein composition of the meat were investigated. The groups whose storage temperature were lowered by 1.0°C per day (the 1.0°C group) and 0.5°C per day (the 0.5°C group) began to freeze in the vicinity of −3.5 and −5.0°C, respectively. The freezing point depended on the fish species; the lowest freezing point was −8.5°C, for the red sea bream in the 1.0°C group. The breaking strength tended to decrease more slowly in the 1.0°C group, but the collagen fibers collapsed more rapidly in the 1.0°C group. In SDS electrophoresis, a slight change in the banding patterns was observed, but the relationship between this observation and changes in histology and physical properties was unclear. This study shows that it is possible to produce a supercooled state in fish meat, and demonstrates that supercooling is a potential new storage method that lowers the temperature without generating ice crystals.     

Structure-Activity Relationship Study of the Neuritogenic Potential of the Glycan of Starfish Ganglioside LLG-3

LLG-3 is a ganglioside isolated from the starfish Linchia laevigata. To clarify the structure-activity relationship of the glycan of LLG-3 toward rat pheochromocytoma PC12 cells in the presence of nerve growth factor, a series of mono- to tetrasaccharide glycan derivatives were chemically synthesized and evaluated in vitro. The methyl group at C8 of the terminal sialic acid residue was crucial for neuritogenic activity, and the terminal trisaccharide moiety was the minimum active motif. Furthermore, the trisaccharide also stimulated neuritogenesis in human neuroblastoma SH-SY5Y cells via mitogen-activated protein kinase (MAPK) signaling. Phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 was rapidly induced by adding 1 or 10 nM of the trisaccharide. The ratio of phosphorylated ERK to ERK reached a maximum 5 min after stimulation, and then decreased gradually. However, the trisaccharide did not induce significant Akt phosphorylation. These effects were abolished by pretreatment with the MAPK inhibitor U0126, which inhibits enzymes MEK1 and MEK2. In addition, U0126 inhibited the phosphorylation of ERK 1/2 in response to the trisaccharide dose-dependently. Therefore, we concluded that the trisaccharide promotes neurite extension in SH-SY5Y cells via MAPK/ERK signaling, not Akt signaling.     

Management of bakanae and bacterial seedling blight diseases in nurseries by irradiating rice seeds with atmospheric plasma

The control of seedborne rice seedling diseases in the seed beds is important to avoid epidemics in rice nurseries and paddies, which may result in severe yield loss. Recently, irradiation with plasma containing electrons, creating positive or negative ions and neutral species, has been shown to have an antimicrobial effect, probably via generation of reactive oxygen species. This study examines whether two seedborne rice seedling diseases, bakanae disease caused by the fungal pathogen Fusarium fujikuroi, and bacterial seedling blight caused by Burkholderia plantarii, are suppressed by irradiation of infected rice seeds with atmospheric plasma. Seed germination and seedling growth were not inhibited in plasma‐treated healthy seeds. When F. fujikuroi‐infected rice seeds were irradiated with plasma after being immersed in sterile distilled water, bakanae disease severity index and the percentage of plants with symptoms were reduced to 18.1% and 7.8% of non‐irradiated control, respectively, depending on the duration of plasma irradiation. The bacterial seedling blight disease index was also reduced by plasma irradiation in vacuum‐inoculated seeds to 38.6% of the non‐irradiated control, and in infected seeds harvested from spray‐inoculated heads of rice plants to 40.1% of the control. Therefore, plasma irradiation seems to be effective in controlling two independent seedborne rice seedling diseases.     

Involvement of a vascular hypersensitive response in quantitative resistance to Ralstonia solanacearum on tomato rootstock cultivar LS‐89

Ralstonia solanacearum causes bacterial wilt disease in Solanaceae spp. Expression of the Phytophthora inhibitor protease 1 (PIP1) gene, which encodes a papain‐like extracellular cysteine protease, is induced in R. solanacearum‐inoculated stem tissues of quantitatively resistant tomato cultivar LS‐89, but not in susceptible cultivar Ponderosa. Phytophthora inhibitor protease 1 is closely related to Rcr3, which is required for the Cf‐2‐mediated hypersensitive response (HR) to the leaf mould fungus Cladosporium fulvum and manifestation of HR cell death. However, up‐regulation of PIP1 in R. solanacearum‐inoculated LS‐89 stems was not accompanied by visible HR cell death. Nevertheless, upon electron microscopic examination of inoculated stem tissues of resistant cultivar LS‐89, several aggregated materials associated with HR cell death were observed in xylem parenchyma and pith cells surrounding xylem vessels. In addition, the accumulation of electron‐dense substances was observed within the xylem vessel lumen of inoculated stems. Moreover, when the leaves of LS‐89 or Ponderosa were infiltrated with 10⁶ cells mL^?1 R. solanacearum, cell death appeared in LS‐89 at 18 and 24 h after infiltration. The proliferation of bacteria in the infiltrated leaf tissues of LS‐89 was suppressed to approximately 10–30% of that in Ponderosa, and expression of the defence‐related gene PR‐2 and HR marker gene hsr203J was induced in the infiltrated tissues. These results indicated that the response of LS‐89 is a true HR, and induction of vascular HR in xylem parenchyma and pith cells surrounding xylem vessels seems to be associated with quantitative resistance of LS‐89 to R. solanacearum.     

Ceramide aminoethylphosphonate from jumbo flying squid Dosidicus gigas attenuates the toxicity of cyanotoxin microcystin-LR

We have previously established the method for isolation of ceramide aminoethylphosphonate (CAEP) from jumbo flying squid Dosidicus gigas. In this study, we performed a MTT assay to evaluate the safety of CAEP to the cell lines for the application to health food and supplements. The CAEP did not show any cytotoxicity to various HEK293-transfectant cells. Next, we elucidated the positive function of CAEP to the somatic cells. Recently, we have reported that hepatotoxin microcystin-LR was taken up into the hepatocytes mediated by hepatocellular uptake transporters OATP1B1 and OATP1B3, and the cells were induced cytotoxicity subsequently. Cytotoxicity of microcystin-LR to permanently OATP1B3-expressing HEK293-OATP1B3 cells rather than to HEK293-OATP1B1 cells was preferentially attenuated by CAEP in a concentration-dependent manner. In addition, the enzyme activity of serine/threonine phosphatase, which was inhibited by microcystin-LR, was recuperated by co-exposure to CAEP. Furthermore, microcystin-LR-induced cellular protein phosphorylation were disrupted by CAEP exposure. These results suggested that CAEP is a promising remedy and/or preventive medicine for liver damage with microcystin-LR.