Effect of taurine supplementation on hepatic metabolism and alleviation of cadmium toxicity and bioaccumulation in a marine teleost,red sea bream, <Emphasis Type="Italic">Pagrus major</Emphasis>

This study was performed to unravel the mechanism of the beneficial action of taurine on marine teleost fish, red sea bream (Pagrus major), by analyzing the hepatic metabolism. Moreover, the ameliorative effects of the nutrient against cadmium toxicity and bioaccumulation were further evaluated. The fish were fed a diet containing 0 % (TAU0 %), 0.5 % (TAU0.5 %), or 5.0 % (TAU5.0 %) taurine for 40–55 days (d) and subjected to cadmium acute toxicity and bioaccumulation tests. Taurine deficiency in feed severely affected growth and the hepatic metabolic profiles of the fish, including a remarkable increase in myo-inositol, aspartate, and ß-alanine in the TAU0 % group, which indicates a complementary physiological response to taurine deficiency. For the acute toxicity test, fish were fed the test diets for 55 d and were then exposed to different dose of cadmium ranging from 0 to 5.6 mg/L for 96 h. Fish fed taurine had a higher tolerance to cadmium than those not fed taurine. For the bioaccumulation test, fish were fed the test diets for 40 d and then were chronically exposed to 0.2 mg/L of cadmium for 28 d followed by depuration for 21 d. Cadmium concentrations in the liver and muscle of fish fed TAU5.0 % were significantly lower than those of fish fed TAU0 % for the first 7 d of exposure and the first 7 d of elimination. Our findings suggest a possible mechanism for the beneficial role played by taurine and that the inclusion of taurine in fish aquaculture feed may reduce cadmium contamination of fish intended for human consumption.     

Underestimation of chromium and zirconium in soils by hydrofluoric acid digestion and inductively coupled plasma-mass spectrometry

The concentrations of chromium (Cr) and zirconium (Zr) in 503 soil samples collected from 78 site in Japan were determined by using two utterly different methods. The first was the relatively widely used inductively coupled plasma-mass spectrometry (ICP-MS) combined with digestion with hydrofluoric acid (HF) and perchloric acid (HClO₄). The second was a non-destructive polarizing energy dispersive X-ray fluorescence spectrometric method (EDXRF) using pressed powder pellets. The Cr concentrations obtained by EDXRF were higher than those obtained by ICP-MS in ~75% of the samples. The EDXRF/ICP-MS ratios ranged from 0.48 to 9.65, and the geometric mean was 1.23. A typical example having big a difference in Cr content between the two methods was found in seven samples taken from a podzolic soil developed on sand dunes in northern Hokkaido. This sampling site is around 20 km from the northern edge of a serpentinite area that extends from north to south, forming the backbone mountain range of Hokkaido. The Cr concentrations obtained by ICP-MS for the seven samples were 27.9–52.2 mg kg^?1, similar to the average for all the samples, whereas those obtained by EDXRF were 101–460 mg kg^?1, falling within the range between the third quartile and the maximum for all the samples. It would be difficult to predict these results from the analytical data of other elements because the samples were high in silica (SiO₂) and low in magnesia (MgO), and did not show any characteristics typical of soils derived from serpentinite. X-ray adsorption near-edge structure (XANES) showed that Zr occurred as zircon (ZrSiO₄) in soils. The differences between the two methods were greater for Zr than for Cr. Zirconium concentrations obtained by EDXRF were higher than those by ICP-MS for all samples except three. The difference between the two methods was more pronounced in soils derived from granite that is widespread in western Japan. The EDXRF/ICP-MS ratios for seven soil samples from different horizons at a single sampling site ranged from 4.82 to 6.94 and were generally higher at the A horizon (Apg and Ag) and decreased with depth. Our results indicate that there is a high possibility of underestimation of Cr and Zr contents in soils for a considerable number of samples if determined with ICP-MS, and it could also overlook some important chemical characteristics of soils.     

Mode of transmission and morphological structures of two <Emphasis Type="Italic">Eremothecium</Emphasis> species between <Emphasis Type="Italic">Riptortus pedestris</Emphasis> and soybean

Eremothecium ashbyi and E. coryli were present in the maxillary and mandibular stylet pouches of the contaminated heads of the true bug Riptortus pedestris collected during a field survey, 2007. Ascospores of E. ashbyi and E. coryli were taken up in the stylet pouch when R. pedestris fed on soybean seeds infected with the respective fungus. In the case of E. ashbyi, the ascospores had subsequently germinated and were recognized as large masses of mycelia in the stylet pouch. In contrast, masses of E. coryli including buds of irregular size and shape were recognized about 3 days after. These results proved that these yeasts are taken up and become lodged in the stylet pouch when the insect feeds on infected host plants. In stylet sheaths stained with erythrosine, E. ashbyi was found as fragments of mycelia and E. coryli was found as small buds. These observations yield evidence to confirm that E. ashbyi and E. coryli are transmitted as fragments of mycelia and as small buds, respectively, after the insect has fed on infected host plants.     

Toxicity of chlorothalonil to marine organisms

We evaluated the acute toxicity of the antifouling biocide 2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile (chlorothalonil, TPN) to an alga (Skeletonema costatum), crustacea (Tigriopus japonicus, kuruma prawn Marsupenaeus japonicus), and a teleost fish (red sea bream Pagrus major) commonly found in the coastal waters of Japan. We also performed acute toxicity and early-life-stage tests for TPN using mummichog Fundulus heteroclitus and used the results to predict the chronic toxicity of TPN to red sea bream. The acute toxicity values of TPN (based on measured concentrations) for S.?costatum, T.?japonicus, M.?japonicus, red sea bream, and mummichog were 0.95, 16, 290, 35, and 61???g/l, respectively. The early-life-stage test with mummichog embryos revealed that hatchability and growth were the most sensitive indicators, and the lowest- and no-observed-effect concentrations, based on the measured concentrations, were 32 and 11???g/l, respectively. We estimated the chronic toxicity value for red sea bream to be 11???g/l based on these toxicity values. Considering the current measured concentrations of TPN in coastal waters of Japan, its environmental impact would appear to be limited.     

Enzymatic solubilization of collagen in the skin of diamond squid Thysanoteuthis rhombus: application of a fungal acid protease

Enzymatic solubilization of collagen from the skin tissue of diamond squid Thysanoteuthis rhombus, an underutilized resource in Japan, was attempted using an acid protease from the fungus Rhizopus niveus. This novel approach was compared with the conventional method using porcine pepsin. Both proteases were able to solubilize most of the skin collagen (>90 % of the total collagen) by performing the treatment in 0.5 M acetic acid at 4 °C for 72 h and at an enzyme/substrate ratio (w/w) of 1/10. The SDS-PAGE patterns of the solubilized collagen preparations were quite similar to each other, and two types of collagen (major and minor collagens) were purified from each preparation by cation-exchange column chromatography. These collagen types from the porcine pepsin-solubilized collagen showed similar features to those from the Rhizopus acid protease-solubilized collagen. These results suggest that the Rhizopus acid protease, a protease of non-animal origin, is applicable for solubilizing collagen in the skin of diamond squid.     

Competition as a predisposing factor of crown dieback in a secondary forest of <Emphasis Type="Italic">Betula maximowicziana</Emphasis> in Hokkaido,northern Japan

We analyzed the probability that Betula maximowicziana Regel (monarch birch) would suffer crown dieback (crown-dieback probability) and the basal area growth rate (GB), which was found to be a predisposing stress factor making birch trees susceptible to crown dieback. First, we analyzed the relationship between the probability that birch trees would suffer from crown dieback in 1999 and GB from a period prior to the occurrence of crown dieback (1985–1987), using a data set of repeated measurements on 217 trees. Logistic regression analysis revealed that monarch birch had a larger crown-dieback probability when GB was low in the preceding period. Hence, there were predisposing stress factors that reduced GB and continued to affect trees for at least a decade. Next, we analyzed GB in the same period in relation to symmetrical and asymmetrical competition between trees and found that GB was reduced by symmetrical competition, suggesting that this was one of the predisposing factors for crown dieback. Based on these results, we used selected models for crown-dieback probability and GB to calculate crown-dieback probabilities for individuals with different initial basal areas and experiencing different intensities of symmetrical competition. The predicted crown-dieback probability decreased with decreasing symmetrical competition between trees. We discuss a possible process of crown dieback to death for monarch birch and the use of thinning as a method to reduce the risk of crown dieback.     

Litter of an alien tree, <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis>, inhibits seed germination and initial growth of a native tree on the Ogasawara Islands (subtropical oceanic islands)

We investigated the effects of the accumulation of litter of an alien tree, Casuarina equisetifolia, on the initial establishment of Schima mertensiana, a tree native to the Ogasawara (Bonin) Islands, in the northwestern Pacific Ocean, in field and greenhouse experiments. The field experiment compared emergence of seedlings in forests dominated by C. equisetifolia with those in native forests, with and without litter removal. The greenhouse experiment compared seedling germination and biomass among 12 treatments that included two soil types (collected from the C. equisetifolia and native forests), two litter types (C. equisetifolia and native litter), and three amounts of litter (5, 15, or 45 g/pot). Significantly fewer S. mertensiana seedlings emerged at sites dominated by C. equisetifolia than at sites of native species in the field experiment. Litter removal tended to increase seedling emergence. Fewer and smaller S. mertensiana seedlings germinated with greater litter cover regardless of soil type or litter type in the greenhouse experiment. Our results demonstrate that C. equisetifolia litter suppresses germination and initial growth of S. mertensiana, and that the main cause of the suppression is the greater amount of litter accumulated under C. equisetifolia forest floor rather than factors such as the nature of the soil or litter between native and alien species.