Carbon isotope composition of CH4 from rice paddies in Japan

Carbon isotope ratios (¹³C) for bubble CH₄ in a submerged paddy soil were studied in Yokohama, Japan, throughout a growing period, and its variation was found. Bubble CH₄ collected from other 33 paddy fields in Japan was also measured for its ¹³C and the results agreed with Yokohama. Furthermore, the variation occurred irrespective of the amount and the type of supplied organic substances to the fields (whole rice straw, rice stubble, or compost). The ¹³C value (average value of -55.9 ± 4.24) from these paddy fields was higher than those of the CH₄ emitted from African and North American paddies. The higher value was little affected by their difference in the supplied organic substances. CH₄ oxidation likely occurs for bubble CH₄ in the shallow paddy fields. A rough estimate of the total CH₄ production, using isotope mass balance, showed that 17 to 22% of organic carbon supplied to Japanese paddies transforms to CH₄.     

Enhancement of tissue plasminogen activator production from human normal fibroblast IMR-90 cells by limitation of cell growth

Summary Tissue plasminogen activator (t-PA) production induced by proteose peptone from IMR-90 cells was investigated. Cells monolayered on plastic surfaces had a higher ability to produce t-PA per unit cell compared to those grown tri-dimensionally on ceramic pieces. Furthermore, confluent monolayers of the cells, which suffered contact inhibition and resulted in limited growth, were available for t-PA production. Repeated batch production with microcarriers, on which the cells were almost confluent monolayers similar to those in T-flasks, was performed. Utilization of the cells, which had limited serum in the growth phase, resulted in an increase in production. Moreover, dilution of the basal components of the medium at initiation of the production phase markedly promoted t-PA production. The volumetric productivity was stable for 30 days at 100 IU/cm³ per day. The cells were then mostly retained on microcarriers. Thus, an effective and scalable method of t-PA production by normal fibroblast cells was developed. Offprint requests to: S. Mitsuda     

Stable isotopic structure of aquatic ecosystems

Isotopic, biogeochemical and ecological structure can provide a new dimension for understanding material flows, and the simultaneous function and structure of an ecosystem. Distributions ofδ ¹³C andδ ¹⁵N for biogenic substances in the Nanakita river estuary involving Gamo lagoon in Japan were investigated to construct isotope biogeochemical and ecological structure for assessing fate and transfer of organic matter, and food web structure. The isotopic framework of the ecosystem was successfully described in aδ ¹⁵N–δ ¹³C map. In this estuary the variations of isotope ratios of biogenic substances were clearly explained by the mixing of land-derived organic matter, and marine-derived organic matter. A trophic-level effect of¹⁵N enrichment was clearly observed. Organisms were classified into three groups depending upon the contribution of land-derived organic matter in a food chain. Almost all biota except mollusca in the lagoon depend on organic matter of marine origin. The contributions of both land and marine organic matter were comparable for mollusca in the lagoon.     

A protein essential for recovering oxygen evolution in cholate-treated chloroplasts

A novel method for the reconstitution of oxygen evolution in cholate-extracted spinach thylakoid membranes was established and a protein essential for the reconstitution was purified from cholate extracts. Purification of the protein was accomplished by chromatography on a DEAE-Sephacel column. This protein (M_r 17 000) was reinserted into vesicular membranes reconstituted from cholate-extracted thylakoids in the presence of 25% glycerol to reactivate oxygen evolution.     

Participation of prostaglandin E receptor EP4 subtype in duodenal bicarbonate secretion in rats

We examined, by using a specific PGE receptor subtype EP4 agonist and antagonist, the involvement of EP4 receptors in duodenal HCO(3)(-) secretion induced by PGE(2) and mucosal acidification in rats. Mucosal acidification was achieved by exposing a duodenal loop to 10 mM HCl for 10 min, and various EP agonists were given intravenously 10 min before the acidification. Secretion of HCO(3)(-) was dose-dependently stimulated by AE1-329 (EP4 agonist), the maximal response being equivalent to that induced by sulprostone (EP1/EP3 agonist) or PGE(2). The stimulatory action of AE1-329 and PGE(2) but not sulprostone was attenuated by AE3-208, a specific EP4 antagonist. This antagonist also significantly mitigated the acid-induced HCO(3)(-) secretion. Coadministration of sulprostone and AE1-329 caused a greater secretory response than either agent alone. IBMX potentiated the stimulatory action of both sulprostone and AE1-329, whereas verapamil mitigated the effect of sulprostone but not AE1-329. Chemical ablation of capsaicin-sensitive afferent neurons did not affect the response to any of the EP agonists used. We conclude that EP4 receptors are involved in the duodenal HCO(3)(-) response induced by PGE(2) or acidification in addition to EP3 receptors. The process by which HCO(3)(-) is secreted through these receptors differs regarding second-messenger coupling. Stimulation through EP4 receptors is mediated by cAMP, whereas that through EP3 receptors is regulated by both cAMP and Ca(2+); yet there is cooperation between the actions mediated by these two receptors. The neuronal reflex pathway is not involved in stimulatory actions of these prostanoids.     

Proteasome inhibition induces inclusion bodies associated with intermediate filaments and fragmentation of the Golgi apparatus

The ubiquitin-proteasome system is involved in a variety of biological processes. Inclusion bodies associated with intermediate filaments (IFs) and ubiquitin are observed in various diseases; however, the precise mechanisms of formation and the pathological significance of inclusion bodies have not been fully understood. We examined the effect of proteasome inhibitors on the structure of IF using anti-cytokeratin antibodies or transfection of green fluorescent protein-fused cytokeratin 18 in a hepatoma cell line, Huh7. Intracellular organelles were visualized by immunofluorescent and electron microscopies. Proteasome inhibitors induced IF inclusions associated with ubiquitin. Electron microscopic examination revealed inclusion bodies surrounded by filamentous structures. Autophagic vacuoles and lysosomes were frequently observed, and the organization of the Golgi apparatus was disrupted in these cells. After the removal of the proteasome inhibitors, the IF network and organization of the Golgi apparatus were restored. The IF inclusions could be induced by inhibition of the proteasome function. IF inclusions induced fragmentation of the Golgi apparatus and might inhibit the function of this important station of membrane traffic. The IF inclusions disappeared by restoring proteasome function, and autophagy and lysosomal degradation might be, at least in part, associated with the elimination of inclusion bodies.     

Stable isotope and radiocarbon compositions of methane emitted from tropical rice paddies and swamps in Southern Thailand

Stable isotopes (¹³C, D) and radiocarbon weremeasured in methane bubbles emitted from rice paddies and swamps in southernThailand. Methane emitted from the Thai rice paddies was enriched in¹³C (mean ¹³C; –51.5 ±7.1 and–56.5 ± 4.6 for mineral soil and peat soil paddies,respectively)relative to the reported mean value of methane from temperate rice paddies(– 63 ± 5). Large seasonal variation was observed in¹³C(32) in the rice paddies, whereas variationinD was much more smaller (20), indicating that variation in¹³C is due mainly to changes in methane production pathways.Values of ¹³C were lower in swamps (–66.1 ±5.1)than in rice paddies. The calculated contribution of acetate fermentation from¹³C value was greater in rice paddies (mineral soils:62–81%, peat soils: 57–73%) than in swamps (27–42%). Din methane from Thai rice paddies (–324± 7 (n=46)) isrelativelyhigher than those from 14 stations in Japanese rice paddies ranging from–362 ± 5 (Mito: n=2) to –322 ± 8(Okinawa: n=3), due tohigher D in floodwaters. ¹⁴C content in methane produced fromThai rice paddies (127±1 pMC) show higher ¹⁴Cactivity compared with previous work in paddy fields and those from Thai swamps(110±2 pMC).     

Natural<Superscript>15</Superscript> N Abundance of Plants and Soil N in a Temperate Coniferous Forest

Measurement of nitrogen isotopic composition (¹⁵N) of plants and soil nitrogen might allow the characteristics of N transformation in an ecosystem to be detected. We tested the measurement of ¹⁵N for its ability to provide a picture of N dynamics at the ecosystem level by doing a simple comparison of ¹⁵N between soil N pools and plants, and by using an existing model. ¹⁵N of plants and soil N was measured together with foliar nitrate reductase activity (NRA) and the foliar NO₃^– pool at two sites with different nitrification rates in a temperature forest in Japan. ¹⁵N of plants was similar to that of soil NO₃^– in the high-nitrification site. Because of high foliar NRA and the large foliar NO₃^– pool at this site, we concluded that plant ¹⁵N indicated a great reliance of plants on soil NO₃^– there. However, many ¹⁵N of soil N overlapped each other at the other site, and ¹⁵N could not provide definitive evidence of the N source. The existing model was verified by measured ¹⁵N of soil inorganic N and it explained the variations of plant ¹⁵N between the two sites in the context of relative importance of nitrification, but more information about isotopic fractionations during plant N uptake is required for quantitative discussions about the plant N source. The model applied here can provide a basis to compare ¹⁵N signatures from different ecosystems and to understand N dynamics.     

Fe deficiency induces phosphorylation and translocation of Lhcb1 in barley thylakoid membranes

HvLhcb1 a major light-harvesting chlorophyll a/b-binding protein in barley, is a critical player in sustainable growth under Fe deficiency. Here, we demonstrate that Fe deficiency induces phosphorylation of HvLhcb1 proteins leading to their migration from grana stacks to stroma thylakoid membranes. HvLhcb1 remained phosphorylated even in the dark and apparently independently of state transition, which represents a mechanism for short-term acclimation. Our data suggest that the constitutive phosphorylation-triggered translocation of HvLhcb1 under Fe deficiency contributes to optimization of the excitation balance between photosystem II and photosystem I, the latter of which is a main target of Fe deficiency.     

Involvement of prostaglandin E receptor EP3 subtype in duodenal bicarbonate secretion in rats

We investigated the involvement of prostaglandin E (PGE) receptor subtype EP3 in the regulatory mechanism of duodenal HCO₃⁻ secretion in rats. A proximal duodenal loop or a chambered stomach was perfused with saline, and HCO₃⁻ secretion was measured using a pH-stat method and by adding 2 mM HCl. Mucosal acidification was achieved through 10 min of exposure to 10 mM HCl in the duodenum or 100 mM HCl in the stomach. Various EP agonists or the EP4 antagonist were given i.v., while the EP1 or EP3 antagonist was given s.c. or i.d., respectively. Sulprostone (EP1/EP3 agonists) stimulated duodenal HCO₃⁻ secretion in a dose-dependent manner, and this response was inhibited by AE5-599 (EP3 antagonist) but not AE3-208 (EP4 antagonist). AE1-329 (EP4 agonist) also increased duodenal HCO₃⁻ secretion, and this action was inhibited by AE3-208 but not AE5-599. The response to PGE₂ or acidification in the duodenum was partially attenuated by AE5-599 or AE3-208 alone but completely abolished by the combined administration. Duodenal damage caused by mucosal perfusion with 150 mM HCl for 4 h was worsened by pretreatment with AE5-599 and AE3-208 as well as indomethacin and further aggravated by co-administration of these antagonists. Neither the EP3 nor EP4 antagonist had any effect on the gastric response induced by PGE₂ or acidification. These results clearly demonstrate the involvement of EP3 receptors, in addition to EP4 receptors, in the regulation of duodenal HCO₃⁻ secretion as well as the maintenance of the mucosal integrity of the duodenum against acid injury.