Seasonal variation of domoic acid in a bivalve Spondylus versicolor in association with that in plankton samples in Nha Phu Bay,Khanh Hoa,Vietnam

Previously we reported that a significant level of domoic acid, a causative toxin for amnesic shellfish poisoning, was detected in bivalves belonging to a genus Spondylus from various tropical Asian countries. These findings indicate that causative plankton species for domoic acid widely distribute in these areas. In the present study, we monitored seasonal change of domoic acid level of Spondylus versicolor in association with that of plankton samples in Nha Phu Bay, Khanh Hoa, Vietnam from December 2004 to October 2005. The toxicity of S. versicolor showed distinct seasonal variation. During the period when domoic acid level of S. versicolor was increasing, a significant level of domoic acid was detected in the plankton samples, showing the correlation between these two parameters. These findings show that plankton causative for domoic acid occurred in the bay, and S. versicolor accumulate domoic acid during a bloom of the toxic plankton by food web transfer.     

Natural abundance of 15N in nitrate,ureides, and amino acids from plant tissues

The natural ¹⁵N abundances (δ¹⁵N values) were measured for nitrate and free and bound amino acids from the leaves of field-grown spinach (Spinacia oleracea L.) and komatsuna (Brassica campestris L.), as well as ureides and free and bound amino acids in the leaves and roots of hydroponically grown soybean (Glycine max L.) totally depending on dinitrogen. Nitrate from the spinach and komatsuna leaves and ureides from leaves and roots of soybean showed higher δ¹⁵N values than the total tissue N and N in free or bound amino acid fractions. The δ¹⁵N values of individual free and bound amino acids, determined by GC/C/MS using their acetylpropyl derivatives, were similar in leaf tissues except for proline but varied in soybean root tissues. The order of ¹⁵N enrichment was similar in the four samples: aspartic acid > glutamic acid > threonine, proline, valine > glycine + alanine +serine, γ-amino butyric acid, and phenylalanine.     

Frequent occurrence of the tetrodotoxin-bearing horseshoe crab <Emphasis Type="Italic">Carcinoscorpius rotundicauda</Emphasis> in Vietnam

Tetrodotoxin (TTX) was detected by HPLC and LC-MS/MS in specimens of the horseshoe crab Carcinoscorpius rotundicauda collected from Tan Hai village, Vung Tau province, Vietnam, where cases of poisoning due to the consumption of horseshoe crab have frequently been reported. The soft tissue from 10 out of the 12 specimens analyzed showed considerable levels of TTX, making them unsafe for human consumption (81.2 ± 50.3 MU/g). Paralytic shellfish poisoning (PSP) toxins were also detected in all of the specimens, but the levels were low. These findings show that the frequency of occurrence of C. rotundicauda specimens with a high level of TTX is significantly high, and that the TTX is responsible for the food poisonings caused by the consumption of C. rotundicauda in this area.     

Occurrence of domoic acid in tropical bivalves

Domoic acid was found in bivalves belonging to the genus Spondylus collected randomly from the Philippines, Vietnam, Thailand and Ishigaki Island, Japan. This is the first report of domoic acid accumulating in bivalves from tropical waters. Large differences in domoic acid levels were observed among the Spondylus specimens collected from different areas. The Spondylus specimens from the Philippines and Vietnam showed higher levels of domoic acid whereas the level in Spondylus spp. from Thailand and Japan was low. The highest level of domoic acid—more than four times the safe consumption level of 20 μg/g whole tissue—was found in a specimen from the Philippines. On the other hand, bivalves other than Spondylus collected from the same area at the same time in the Philippines showed very low levels of domoic acid, showing that bivalves belonging to the genus Spondylus accumulate specifically high levels of domoic acid. These results suggest the wide distribution of causative phytoplankton in tropical waters.     

Inhibition of nitrogen uptake by rice after wheat straw application determined by tracer NH4 +-15N

This experiment was carried out to determine whether the delay in rice growth associated with wheat straw application, especially at the early stage, was due to the acceleration of N assimilation or N uptake inhibition.

Tracer ¹⁵N was used for rice plants cultivated in pots. After 24 h of tracer application the plants and soils were sampled for analysis. Seventeen days after transplanting, N uptake of rice decreased and the amount of unavailable tracer remaining in soil increased by wheat straw application. At the booting stage, 6 d before heading, N uptake was larger and the amount of remaining tracer was lower in the plots in which wheat straw was applied than in the control.

It was obvious that the decrease of N uptake by wheat straw application was caused by N uptake inhibition and not by N starvation for a period of time at the early stage. The inhibition was removed at the booting stage.     

"日本书院"的研究现状与课题

分析了“日本书院”的教育特征,无科举制度下的社会学习,是为了教育,认为藩校、乡校、塾、诗子屋等近代化教育前人机构为书院,简素书院即为现代书院教育,并概述了日本近代化后的书院教育。