Nitrate Decrease with Isotopic Fractionation In Riverside Sediment Column During Infiltration Experiment

This study determined isotopic fractionation of nitrate-nitrogen during denitrification in riparian aquifer sediments by sequential-column experiments at two different water flow rates. The purpose was to discuss the relationships of nitrogen isotopic enrichment factor of denitrification, denitrification rate, and infiltrating condition in sediment. Sandy sediment and groundwater were collected from floodplain in the middle reach of the Tama River where nitrogen isotopic enrichment factor for denitrification had been measured in a result of previous field observation. The denitrification rates and the isotopic enrichment factors of nitrate-nitrogen were estimated at 2.1 mgN dry-kg^?1 day^?1 and ?32.9‰ during the low water flow condition, and at 3.5 mgN dry-kg^?1 day^?1 and ?34.1‰ during the high water flow condition. The calculated water flow rates of the present column experiments were 300–400 times higher than that of the field observation. Because of the fast flow rate, nitrate was expected to continuously pass though active denitrifying sites in the small pore spaces of sediment, and nitrate supply to denitrifers by infiltration flow transport greatly exceeded the supply by diffusion. The observed denitrification rates was proportional to Peclet number as the ratio of solute nitrate transport to the diffusion, and apparent nitrogen isotopic enrichment factors during denitrification of our column experiments were lower than those obtained from the field observation. This study showed that denitrification rate and apparent nitrogen isotopic enrichment factor of denitrification in sediment depended on Peclet number.     

Real-time ultrasonographic evaluation of canine gastric motility in the postprandial state

Gastric motility is affected by several pathological conditions which may induce upper gastrointestinal clinical symptoms. The pathogenesis of canine gastric motility disorders is poorly understood because of methodological limitations. This study aimed at establishing a simple method for evaluating postprandial gastric motility in dogs. Gastric motility was ultrasonographically assessed in 7 healthy beagles using a technique previously described in humans. The motility index (MI), an indicator of gastric antral motility, was calculated by measuring the area of the gastric antrum in both a contracted and relaxed phase and by counting the number of contractions. The MI was measured every 30 min for 3 hr after feeding and compared with gastric emptying as assessed by a (13)C-octanoic acid breath test. The MI at 30 min had the lowest variability in the 7 dogs (mean SD, 9.77 ± 0.42; coefficient of variance, 4.25%), and a significant correlation was observed with gastric emptying coefficient (R(2)=0.8126, P=0.005) and half-emptying time (R(2)=0.654, P=0.027). When atropine was administered, a significant decrease in the MI at 30 min was observed compared with the control (9.77 ± 0.42 vs. 5.19 ± 0.22, P=0.0003). In conclusion, evaluation of the MI at 30 min is suitable for assessing gastric motility and enables us to assess gastric motility simply in a short time. By using this method, further studies for the pathogenesis of canine gastric motility disorders are warranted.     

Potato extract (Potein) suppresses food intake in rats through inhibition of luminal trypsin activity and direct stimulation of cholecystokinin secretion from enteroendocrine cells

Dietary proteins and trypsin inhibitors are known to stimulate the secretion of the satiety hormone cholecystokinin (CCK). A potato extract (Potein) contains 60% carbohydrate and 20% protein including trypsin inhibitory proteins. In this study, we examined whether Potein suppresses food intake in rats and whether it directly stimulates CCK secretion in enteroendocrine cells. In fasted rats, food consumption was measured up to 6 h after the oral administration of Potein or soybean trypsin inhibitor (SBTI). CCK-releasing activities of Potein and SBTI were examined in the murine CCK-producing cell line STC-1. Potein inhibited the trypsin activity in vitro with a potency 20-fold lower than that of SBTI. Oral administration of Potein dose-dependently suppressed food intake for 1-6 h. Potein, but not the SBTI, dose-dependently induced CCK secretion in STC-1 cells. These results suggest that Potein suppresses food intake through the CCK secretion induced by direct stimulation on enteroendocrine cells and through inhibition of luminal trypsin.     

Asparagine test in relation with the nitrogen nutritional status of crop plants I

Extraordinary features of submerged rice soils and its relation to manuring practices has long been the problem of study to increase the average and maximum yield of rice per unit area. Out of these studies many remarkable results have so far been achieved, the mention of which in dentail is not possible in this paper. But in a summarized way it can be easily concluded that during the growth cycle of rice plant nitrogen is most important limiting fertilizer element and its need for the plant is multi-sided. The practical experience of the farmers of Shizuoka prefecture is quite in agreement with this, as they say that in rice-culture fertilizer should be applied at the transplanting time and a little before actual heading. Regarding the late dressing which is called (Hogoe) they have strong belief that it is effective in most of the cases. Taking this into account, in 1933 YAMAMOTO and SUZUKI(18) started to study as to when top dressing be applied with the help of pot experiments, and Were able to conclude that a top dressing of 0.5 g per pot was quite effective. This report is the first to be published on the top-dressing aspect of rice, but it does not seem to be a complete one. A field experiment for such a study was conducted by GOTO(1) in the year 1942. In his experiment, he used ammonium sulphate for top dressing with 3 dates viz. a) Maximum tillering b) Late tillering and c) Panicle formation. He concluded that amm. sulphate as top-dressing is mostly absorbed in the panicle formation stage and is utilized for grain formation. He also stressed the importance of top-dressing at the panicle formation stage.     

The uptake of strontium and cesium by plants from soil with special reference to the unusual cesium uptake by lowland rice and its mechanism

In the previous experiments using strontium-90 and cesium-134, the authors found some differences between lowland and upland rice with respect to their uptake from soil, particularly the unusual high absorption of cesium by lowland rice.     

Nutritional Study of Silicon in Graminaceous Crops (Part 1)

Silicon in crop plants has been studied in various ways, for example, in elucidating its effects on phosphorus and nitrogen uptake by roots, or increase of resistance to diseases and insect pests, Graminaceous crops generally contain much more silicon in them than other families of plants, Remarkable effects of silicon application to plants On their growth appear especially in case they have contained about 5 to 10% of silicon before-hand. When silicon content in plants, on the other hand, is quite low, such as less than 0.5% for dry matter, plants show retardation of their grOwth at both vegetative and reproductive stages. It may be deduced that silicon applied to plants might play a role in different ways in cases where they have already had either considerable or quite small amounts of silicon. While the former case has been studied very much, extreme deficiency of silicon in plants has been investigated very little^1)-8). Experiments reported here were designed for elucidating roles of silicon in its defiCient plants and getting information about the essentiality of silicon for them.     

Nutritional Study of Silicon in Graminaceous Crops (Part 2)

It was reported in the previous paper₁₎ that rice plants showed retardation of their vegetative growth and decrease of degree of seed setting when their silicon content was extremely low. It was concluded from these facts that silicon might most probably be essential for rice. But physiological functions or behaviours of silicon in plants should be clarified in order to solve this problem completely. Uptake and disttibution of silicon in rice plants were first investigated here, especially compared with phosphorus. A possibility of using silicon radioactive isotope (₃₁Si) for this kind of experiment was also investigated. Although tracer techniques have been greatly developed in elucidating behaviours or physiological functions of various elements in plants, radioactive silicon isotopes have been used very little in this field of science because of this very short half lives. Recently Rothbuhr and Scott ²⁾ reported having used radioactive silicon isotope for uptake experiments by plants in Harwell, England. Since a nuclear reactor (JRR-I) in the Japanese Atomic Energy Research Institute started to work in 1959, radioactive isotopes which have rather short half lives have become available for plant experiments in Japan. Methods of preparation of ³¹Si for plant experiments were examined and by using ³¹Si it was studied how silicon was absorbed and translocated by rice and wheat under some particular environmental conditions, and also how the uptake and distribution of it in rice plants were affected by various kinds of metabolic inhibitors.     

Fluctuation in the distribution of low-salinity water in the North Equatorial Current and its effect on the larval transport of the Japanese eel

Surface water in the North Equatorial Current (NEC) is composed of southern low‐salinity water diluted by precipitation to less than 34.2 psu and northern, high‐salinity tropical water greater than 34.8 psu. Analyses of 27‐year historical data, observed in winter and summer along the longitude 137°E by the Japan Meteorological Agency, shows that an obvious salinity front (34.5 psu) generated by the two water masses was usually located around 15°N. However, the salinity front has been moving northward during the past three decades. El Niño/Southern Oscillation (ENSO) affected salinity in the surface layer, while temperature changed in the middle layer. The salinity front sometimes moved southward, mainly south of 5°N, and the movement was well correlated with the southern oscillation index (SOI). Because precipitation at Yap (9.5°N, 138.1°E) fluctuated with SOI, this spike‐like southward movement of the salinity front was probably affected by reduction of low‐salinity water during El Niño in the north‐western Pacific Ocean. However, ENSO only induced such large southward movements of the salinity front when the time lag between the low precipitation and low SOI was short (within four months). This salinity front is quite important for long‐distance migrating fish such as the Japanese eel because the eels spawn just south of the salinity front in the NEC. This behaviour suggests that the movement of the salinity front associated with ENSO may control the success of larval transport from the spawning ground in the NEC to the nursery ground in East Asia. In fact, catch of the Japanese eel larvae in Japan was well correlated with fluctuation of SOI and the location of the salinity front, and lower catch occurred during El Niño. The salinity front has moved from 13°N to 17°N during the past three decades. Considering that conditions of larval transport are worse north of 15°N, we suggest that decadal‐scale linear decrease of glass eel catch during the past three decades also can be explained by the displacement of the salinity front.     

Thermal adaptation of pacific bluefin tuna Thunnus orientalis to temperate waters

ABSTRACT:   Immature Pacific bluefin tuna Thunnus orientalis , tagged with archival tags, were released near Tsushima Island in the East China Sea during the winters of 1995 through 1998. Time-series data for ambient and peritoneal cavity temperatures, recorded every 128 or 256 s for 23 fish recovered, were analyzed. The objective of this study was to clarify the process of development of thermoconservation ability with growth in relation to adaptive mechanisms to cooler temperate waters. According to the results, mean ambient temperatures ranged from 14.9 to 20.7°C, which is almost within the optimum temperature range according to previous reports. Mean peritoneal temperatures were higher than ambient temperatures (19.7–27.3°C), but never reached 35°C, which would induce overheating. Although the mean thermal differences between peritoneal and ambient temperatures increased with body size, the rate of increase decreased with body size. A heat budget model suggests that as the insulation of the body develops, the estimated mean values of internal heat production decrease with body size. This is probably due to the allometric scale effect and explains why the thermal difference does not increase quickly with body size. It is likely that Pacific bluefin tuna inhabit cooler temperate waters in mid-latitude regions to avoid overheating.