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The impact of winter cover crops, specifically wheat (Triticum aestivum L.), red clover (Trifolium pratense L.), and rapeseed (Brassica napus L.) or winter fallow, on community composition of arbuscular mycorrhizal fungi (AMF) in subsequent soybean roots was investigated in a 5-year field trial on andosolic soils in Japan. Soybean roots were sampled at full-flowering and analyzed for AMF communities using a partial LSU rDNA region. Phylogenetic analysis detected 22 AMF phylotypes, including eight Glomus, three Gigaspora, two Scutellospora, three Acaulospora, two Rhizophagus, and one of Funneliformis, Diversispora, Paraglomus, and an unknown glomeromycete in the roots. The 5-year rotation of different winter cover crops or winter fallow did not impact the molecular diversity of AMF communities colonizing the roots of subsequent soybean. In all of the rotations, Glomus and Gigaspora phylotypes were common to soybean roots over the 5-year period. Redundancy analysis (RDA) demonstrated that AMF communities in the roots of subsequent soybean were not significantly different among winter cover crop rotations or fallow. However, AMF communities in soybean roots were clearly influenced by rotation year suggesting that climate or other environmental factors were more important than winter cover cropping system management.

To evaluate the importance of arbuscular mycorrhizal fungi (AMF) to crop production, it is imperative to move beyond the plow layer to include the full soil profile impacted by plant roots. To illustrate this, we investigated the vertical distribution of AMF biomass and community structure within the top 100 cm of soil in soybean (Glycine max (L.) Merr., cv: Enrei) rotational systems cropped to wheat (Triticuma estivum L. cv: Bandowase) or left fallow using fatty acid methyl ester (FAME) biomarkers and molecular analysis, respectively. AMF biomass, as measured by concentration of C16:1cis11, declined during fallow and with increasing soil depth. Greater than 50 % of the stored AMF biomass was found at depths below 35 cm. Phylogenetic analysis revealed 16 AMF phylotypes, including nine Glomus, two Gigaspora, two Scutellospora, and one each of Diversispora, Paraglomus, and an unknown glomeromycete, at different sampling depths in this study. Cluster analysis based on the number and abundance of each AMF phylotype formed two distinct clusters separating wheat from fallow rotations. There was no distinct relationship with soil depth beyond clustering AMF communities above and below 20 cm under wheat. Redundancy analysis (RDA) and hierarchical cluster analysis demonstrated that AMF communities by soil depth within each rotation were not significantly different. However, AMF communities were clearly influenced by crop rotation, where the distribution of specific AMF phylotypes responded to the presence of the wheat crop.

We evaluated Al-tolerance in 44 interspecific lines (32 upland and 12 lowland) developed from the crosses of Oryza sativa and O. glaberrima called New Rice for Africa (NERICA) with 2 O. glaberrima lines and 13 O. sativa varieties under hydroponic culture containing 0.15, 0.3, 0.6, and 1.2 mM Al (+Al) and 0 mM Al (−Al as a control). Ten upland and four lowland NERICA lines showed strong Al-tolerance judging from their higher relative root and shoot dry weights (percentage ratios of dry weights in the Al treatments to the control) than those of the tolerant O. sativa check of IR 53650. Their tolerance was supported by relatively higher root Al accumulation (dark blue color) opposite performance with common knowledge (shown pale blue color) in root using hematoxylin staining compared to the Al-susceptible genotypes identified based on relative root and shoot dry weights in the study. Net Al concentration was higher in roots than in shoots in all +Al conditions for all genotypes; however, a clear difference in the Al concentration among the Al-tolerant, Al-moderately tolerant, and Al-susceptible genotypes was observed in the shoots. Al concentrations in the shoots of the Al-tolerant and Al-moderately tolerant upland and lowland NERICA lines were significantly lower than those of its Al-susceptible counterparts in the groups under 0.6 and 1.2 mM Al conditions, respectively. Differences in root and shoot growth among the Al-tolerant, Al-moderately tolerant, and Al-susceptible NERICA lines were clearer under strong Al toxic conditions (0.6 and 1.2 mM Al) than under weak Al toxic conditions (0.15 and 0.3 mM Al).

Aluminum is a major phytotoxic mineral in the soil at low pH conditions. The effect of aluminum (Al) on root length, flowering time, dry matter production, and grain yield was examined using two tolerant, Pungsan (PS) and Geumgang (GG), and one susceptible, IR36, rice varieties to acid soil. Rice seedlings were subjected to two Al treatments (+Al, 150 μM of Al; −Al, 0 μM of Al) in solution culture, where pH was always adjusted at 3.5. PS and GG showed significantly larger root length than IR36 in +Al at 2 and 8 weeks after the treatment (WAT). Flowering time was delayed 9 days in +Al compared to −Al in GG and PS and 27 days in IR36. Dry matter weight and grain yield of GG and PS were also significantly higher than those of IR36 under +Al. The inhibition of such agronomic traits by Al toxicity was less in Al-tolerant varieties than in a susceptible variety.

Twenty-six upland lines of New Rice for Africa (NERICA) were tested with four Oryza sativa varieties in relation to Fe toxicity tolerance under hydroponic culture containing 1.44 mM Fe (+Fe) and 0 mM Fe (-Fe as a control). Three NERICAs, WAB450-IBP-24-HB (P24), WAB450-IBP-82-1-1 (P82), and WAB450-IBP-163-3-1 (P163) among the 30 lines/varieties tested possessed relatively strong tolerance judging from reduction of root length and dry weight and shoot dry weight in +Fe compared to -Fe and from iron toxicity score (ITS) in +Fe. Only P24, P82, and P163 showed emerged lateral roots from pericycle at the root elongation zone, whereas in the other 23 NERICAs and four O. sativa varieties lateral root was not observed in the root elongation or differentiation zones. Less disruption of cortex on root tissues was observed in P24, P82, and P163 than in WAB450-16-2-BL2-DV2 (BL2-DV2), the most susceptible NERICA identified. P24, P82, and P163 showed significantly lower Fe content in the shoots than BL2-DV2, suggesting that the tolerant NERICAs could have some mechanism to inhibit the absorption of Fe. The emergence of lateral roots from the root elongation zone in the three tolerant NERICAs would be closely associated with reducing Fe absorption into the plants.

The objectives of this study were to determine arbuscular mycorrhizal fungi (AMF) community structure in colonized roots of soybean cultivated from Kanagawa and Hokkaido in Japan and to relate the community structure to environmental conditions, which included soil type, preceding crops, and soil chemical properties. The average number of AMF OTU (operational taxonomic unit) colonizing soybean roots collected from Kanagawa and Hokkaido was 11.2 and 5.8, respectively, a significant difference. Moreover, AMF from the family Gigasporasera was not identified in soybean roots collected from Hokkaido, suggesting that AMF in the family Gigasporasea is absent or rare in the soybean fields of sampled in Hokkaido. We postulate that the soil type, preceding crops or soil chemical properties are not the underlying factor differentiating AMF community structure colonizing in soybean roots between Kanagawa and Hokkaido. Instead we conclude that temperature and phosphate absorption coefficient are the determining factors of AMF OTU in this study.

We screened acid soil-tolerant wild soybean (Glycine soja Sieb. and Zucc.) accessions and evaluated their agronomic and tolerant performance under acid sulfate soil (ASS) conditions. Only three accessions, J-13, J-19 and J-55, among 381 G. soja accessions obtained from G. soja Germplasm Collection of Japan, were identified as having strong tolerance by the acid soil toxicity score (ATS) at soil pH 3.3. These three tolerant G. soja accessions showed significantly lower aluminum (Al), iron (Fe) and manganese (Mn) contents in the aboveground part than the intolerant ones in 0.25 lime requirement (LR) conditions (pH 3.8). Aboveground dry matter weights (DW) and seed yields of three tolerant G. soja accessions, except seed yield of a tolerant accession J-55, were also significantly higher than intolerant ones under the 0.25 LR condition. This clearly indicates that lower contents of toxic mineral in the ASS-tolerant G. soja led to higher macro-nutrient uptake, DW, and seed yields. We conclude that the three tolerant G. soja accessions identified in the present study possess high levels of tolerance to the soil acidity and Al-excess soil conditions, and could be valuable genetic resources for soybean improvement programs.

Acid sulfate soil (ASS) has an extremely low pH (3.0) and a high capacity to fix phosphate; symptoms of phosphate deficiency are commonly observed in many crop plants. Arbuscular mycorrhizal (AM) fungi form mutualistic relationships with plant roots, and improve uptake of phosphate from soil. However, there is little information on the actual situation of AM fungi in ASS in Thailand. The purpose of the present study is to determine the indigenous AM fungal density and species in ASS in Thailand. AM fungal spores were retrieved and identified by molecular approaches from ASS field at the central plain of Thailand. This study showed that AM fungal spore density in ASS was 0.232 spores per g dry soil. Among the plant species growing in the natural ASS, there was no AM fungal colonization in the roots of four plant species, i.e. Digitaria sp., Fimbristylis sp., Mimosa pudica L., and Sesbania sp.; however, AM colonization was found in Wedelia roots. Using phylogenetic analysis, four operational taxonomic units (OTUs), i.e., one Glomus, one Entrophospora, one Paraglomus and one unknown species were identified from the AM fungal spores. Five OTUs, i.e., two Glomus, one Acaulospora, one Entrophospora and one unknown Glomeromycota were indentified from Wedelia roots. To our knowledge, this is the first report of the actual situation of AM fungi in ASS in Thailand determined by using molecular approaches.

The present study aims to: 1) identify acid sulfate soil (ASS)-tolerant rice varieties from the genetic stock of Korean rice (Oryza sativa L.) varieties under ASS conditions; 2) to evaluate their yield performance, and elucidate the physiological mechanism for ASS tolerance with the identified tolerant varieties. Two hundred sixty-six rice varieties were screened for ASS tolerance, and we identified two japonica-indica hybrid varieties, Geumgang (GG) and Pungsan (PS), as having high tolerance under ASS paddy conditions (pH 3). We first conducted a yield trial of GG and PS grown in Wagner pots to determine their potential yields under ASS conditions. A yield trial under paddy field condition followed. In the pot experiment, the ASS-tolerant varieties, GG and PS, showed significantly higher yields than PT-1, which is a local reference variety in mildly improved soil pH conditions (pH 4.1–4.6). Al and Fe content in GG and PS were significantly lower than that of PT-1, so there might be some mechanism that inhibits the absorption of toxic metal ions in the tolerant varieties. In the paddy conditions, the grain yields more than 5 t ha−1 of the two tolerant varieties under mildly improved soil pH condition were significantly higher than PT-1. Dry matter weights of above ground parts also showed the same trend as grain yield. The study demonstrated that the ASS-tolerant japonica-indica rice varieties with high yielding potential could contribute to the improvement of rice yield in ASS regions, and will be good materials for the development of acid soil-tolerant rice varieties.

Arbuscular mycorrhizal fungi (AMF) improve the uptake of immobile mineral nutrients such as phosphate, thereby improving plant growth. In acid sulfate soil (ASS), AMF spore density is generally low which impacts root colonization and phosphate uptake. Thus, inoculation may help increase AMF colonization of crops grown in ASS. AMF spore density decreases after cultivation of a non-host crop or bare fallow. In addition, preceding crops affect the growth and yield of subsequent crops. The production of AMF inocula requires AMF-compatible plants. The objective of the present study is to elucidate the effect of preceding crops on the persistence of inoculated AMF and growth of succeeding maize under an ASS condition with lime application. Spore density of AMF after cultivation of preceding crops (soybean or job's tears) was maintained in comparison to fallow leading to higher AMF colonization of maize and improved plant growth. Thus, maintenance of AMF spore density, either through selection of preceding crops or application of AMF inoculum, may be a viable strategy to improve maize growth in limed ASS of Thailand.

The visual symptoms of damage by acid sulfate soil look quite similar to those due to soil moisture deficit. The present paper is to confirm if acid soil-tolerance is associated with drought tolerance in terms of leaf water potential, transpiration, and dry matter production. Seedlings of seven acid soil-tolerant (acid-tolerant), and three acid soil-intolerant varieties (acid-intolerant) were subjected to low pH conditions (pH 3.8) for 48 hours. The rate of water uptake was determined continuously by measuring radioactivity in the collar part (target area) of rice leaves exposed to 18F-labeled water (18F-water) using a Positron Emitting Tracer Imaging System (PETIS). The PETIS measurement showed that the radioactivity in the target position of leaves of acid-tolerant varieties increased faster than that of the intolerant varieties after the 18F-water was applied into the vial. In the plants subjected to low pH conditions, the transpiration rate (Tr) and leaf water potential (Ψ) decreased in both acid-tolerant and intolerant varieties. However, the extent of reduction was less in the acid-tolerant varieties than in the intolerant ones. Moreover, the dry matter production rate of the acid-tolerant varieties was significantly higher than that of the acid-intolerant ones in the low pH conditions. This study clearly shows that 18F-water uptake in a leaf was higher, and water relations were also better maintained in the acid-tolerant varieties compared with intolerant ones, resulting in higher growth rate in the acid-tolerant varieties, when plants were exposed to the acid solution conditions. We conclude that acid soil-tolerance is closely associated with leaf water relations in rice plants.

10Cr-1Mo-1W-VNbN steel forging was observed through TEM (Transmission Electron Microscope), SEM (Scanning Electron Microscope) with EBSD (Electron BackScattering Diffraction) pattern method and tested through nano-indentation tester to investigate the microstructural change during creep damage process. Long-term creep rupture and interrupted creep test samples were investigated and effective damage parameters were selected. Dislocation substructure through TEM thin foil method showed increasing block/lath width especially near grain boundary according to creep damage accumulation and the same feature was observed through EBSD IPF mapping more clearly and easily. Area averaged KAM (Kernal Average Misorientation) KAMave was shown to be effective for evaluating dislocation microstructural changes during creep. Nano-indentation tests were conducted at the same position in EBSD measurement, which showed a good correlation between hardness value and the square root of KAMave. The differential equation of dislocation density with creep time was applied to estimate the relationship between averaged KAMave and time through the relationship between hardness and dislocation density. The creep damage estimation curves were obtained by the integrated form of the equation. As the KAMave showed an apparent drop against time fraction in the primary creep stage near grain boundary followed by almost constant trend for later stage. The statistical distribution of KAMave during creep damage process suggested the localized recovery of dislocation substructure near grain boundary.

The microstructural changes during the creep damage process were investigated on 10Cr–1Mo–1W–VNbN steel forging and the weldment of Mod.9Cr steel–12Cr steel casting, using a scanning electron microscope equipped to take electron backscatter diffraction (EBSD) patterns, and by nano-indentation. Creep rupture and interrupted creep test samples were cut at mid-section along longitudinal direction and inverse pole figures (IPF) and Kernel average misorientation (KAM) maps were obtained from EBSD patterns. Grain size and block size were clearly identified by IPF maps and proved to be good measures of creep time fraction. Area-averaged KAM (KAMave) was shown to be effective for evaluating dislocation microstructural changes during creep and for creep damage evaluation of the forging material. Nano-indentation tests were conducted at the same position in EBSD measurement, which showed a good correlation between hardness value and the square root of KAMave. The creep damage estimation curves of KAMave were obtained as a function of creep time fraction. For the fine-grained, heat-affected zone, area fraction of creep voids and grain size measured by EBSD were good measures of creep damage, while KAMave was not such a good measure.

Microstructural change during creep damage process was investigated on the fine grained heat affected zone (HAZ) and the coarse grained HAZ of 12Cr steel casting base metal welded by 9Cr weld steel, using a scanning electron microscope with electron backscattering diffraction pattern (EBSD) equipment. Creep rupture and interrupted creep test samples were cut at mid-section along longitudinal direction and inverse pole figure, image quality and kernel average misorientation maps were obtained through EBSD observation. The measured quantities were creep void size, grain size, precipitation size, area averaged image quality value IQ ave and area averaged kernel average misorientation KAM ave. Micro Vickers hardness test was also conducted to investigate the hardness distribution across the weld joint. Among various creep damage evaluation parameters, hardness, area fraction of voids, KAM ave and area fraction of precipitates at each HAZ showed apparent changes with creep damage time fraction at HAZ p...

In this study, soil samples were collected from upland fields where maize and soybeans had been cultivated and the density of AM (arbuscular mycorrhizal) fungal spores and the percentage of soybean roots infected with AM fungi (infection ratio) were assessed to determine the factors of the soil chemical properties affecting the mycorrhizal infection. The roots and rhizosphere soil were sampled from 9 soybean fields and 8 maize fields in the summer of 2004. The soil samples were examined for chemical properties (pH, electric conductivity, total phosphate, available phosphate, and phosphate absorption coefficient) and the density of AM fungal spores. Soybean roots were stained with trypan blue to determine the infection ratio. There was a significant difference in soil pH and available phosphorus content with the sampling site. The phosphorus absorption coefficient markedly varied with the sampling site and there was a significant difference in the phosphorus absorption coefficient with the site. The spore density in the soybean and maize fields markedly differed with the sampling site and there was a significant difference spore density with the sampling site. The density of AM fungal spores in the soybean field was negatively correlated with the available phosphorus content, and showed a positive correlation with the phosphate adsorption. This means that an increase in the available soil phosphorus due to the application of phosphate fertilizers will lower the density of AM fungal spores in the soil and that the density of AM fungi spores is generally higher in soils with a higher phosphate absorption coefficient. It is considered that this tendency is marked in the soil with a low phosphate adsorption coefficient. The infection ratio was positively correlated with spore density, and negatively with the available phosphorus content. To increase mycorrhizal infection of soybeans, we need to decrease the amount of available soil phosphorus and simultaneously to increase the density of AM fungal spores. Excessive application of phosphorus fertilizers should be avoided.

The optimum distribution of leaf nitrogen (N) in the canopy of rice plants ( Oryza sativa L.) for maximum daily canopy photosynthesis (DCP) and the optimization effects on DCP were estimated during the grain filling period. The low- and high-density canopies (28.3 and 47.5 plants m −2 ) and isolated plants were established at heading using plants in pots grown up at the low density until heading to make the same canopy architecture except plant density and the same leaf N distribution at the start of treatment among the two canopies and the isolated plants. The simulation was conducted under two conditions of the upper limit of leaf N. Under condition 1, upper limit of leaf N content was 1.80 g m −2 . Under condition 2, upper limits were measured leaf N content in each leaf position at heading. The model indicates that if leaf N content in the upper leaves can be increased with reduction of N in the lower leaves, DCP will increase in any of the plant density, light conditions and under conditions 1 and 2. On a clear day, the estimated increase in DCP was 19–45 and 38–70% in the low- and high-density canopies under condition 1, respectively. Even under condition 2, which is more realistic than condition 1, the increase was up to 21 and 25% in the low- and high-density canopies. These estimates obtained by the present model that incorporates the shading effects of panicles and stems on DCP were higher than the previous reports which did not consider the effects of shading by panicles and stems. In the observed leaf N distribution, the higher the plant density was, the steeper the gradient of the leaf N remained. The gradient in the high-density canopy was closer to that of the predicted optimum leaf N distribution, and likely to contribute to maintaining higher DCP in the canopies. Compared with the hypothetical case in which gradient of leaf N distribution would be more gentle as observed in the isolated plants, the maintained steeper gradient of observed leaf N content in the canopies was estimated to increase DCP by 13 and 5% in the high- and low-density canopy, respectively.

Aluminum (Al) is a major phytotoxic mineral in the soil at low pH conditions (Jones and Kochian, 1996). Pellet et al. (1995) reported that Al would damage the roots by making the plants more sensitive to other abiotic stresses such as defi ciency of water and nutrients, and eventually reduce the crop yield. One of the Al-tolerance mechanisms in plants would be Al exclusion from the root apices. In several upland plants, Al tolerance is closely associated with an increased ability of roots to release organic acids, such as citrate (de la Fuente et al., 1997; Ma et al., 1997a; Pineros et al., 2002), malate (Osawa and Matsumoto, 2001; Tesfaye et al., 2001), and oxalate (Ma et al., 1997b; Wenzl et al., 2001), which may prevent Al uptake by chelating Al. Rice, a lowland plant, has been identifi ed as a high Al-excluder at root apex (Osaki et al., 1997), but the mechanism of Al exclusion in rice plants has not been fully elucidated. The purpose of the present study is to confi rm that the varietal difference of the Al tolerance in rice is associated with organic acid formation in the intact root apices when Al was added to the low pH nutrient solution, and furthermore, to identify the sort of organic acid formed in the root exposed to Al.

アマランサスやキノアについて地下水位が生育や収量へ及ぼす影響を明らかにした. 供試したアマランサスはA. caudatus L., A. cruentus L., A. hypochondriacus L.の3種でキノアの供試品種はBaer2とNL-6である. 地下水位は水を入れた深さの異なる容器にポットを浸して調整した. A. hypochondriacus L.はA. caudatus L.やA. cruentus L.に比べ, より高い地下水位でも出芽率や生育・収量の低下が少なかった. また, A. hypochondriacus L.は地下水位3 cmでも播種後70日目の枯死率が対照区と変わらなかった. このことから, 供試した3種のアマランサスの中でA. hypochondriacus L.は高地下水位における生育量の低下が他の2種に比べ少ないと考えられた. 一方, キノアはアマランサスのA. hypochondriacus L.より地下水位の上昇による生育量の低下が生じやすく高地下水位に対する耐性はA. caudatus L.やA. cruentus L.と同程度であると考えられた. さらに, これらを栽培するにあたってはダイズを栽培する時以上に地下水位を低下させる必要があると考えられた.

本研究は, 酸性硫酸塩土壌を有するタイ南部ナラチワ県を研究対象地とし, 酸性土壌地域でのイネ収量を向上させることを目的として行ったものである. 第1報として, まず, 人工的に作った強酸性土壌にイネ (Oryza sativa L.) 48品種を移植し, 4週間後の個体の生存率によって14品種を選抜した. なお, 参考として, 酸性土壌に強いとされるアフリカイネ (Oryza glaberrima Steud.) 29品種もイネと同様に栽培し, 耐酸性を調べた. その結果, イネ14品種とアフリカイネ10品種が選抜された. 選抜されたイネ品種14のうち, 強酸性土壌で最も高い生長速度を示した4品種と, タイ南部ですでに耐酸性があるとされている2品種, それに本研究で耐酸性がないとされた3品種を比較することによって, イネの耐酸性機構を生理学的側面から検討した. 対照区に対する酸性土壌区の相対根長は, 耐性品種で大きく, 非耐性品種で小さかった. 葉面積においても根長と同様な傾向が見られた. さらに, 酸性土壌条件下での作物生長の阻害は, アルミニウム (Al) に起因することから, 酸性土壌条件下で栽培された植物体の葉身Al濃度を調べた. その結果, 葉身Al濃度は耐性品種よりも非耐性品種の方で高くなっていた. そこで, 葉身の光合成速度を測定したところ, 葉身の光合成速度は耐性品種の方が非耐性品種よりも有意に高い値を示した. これらのことから, Alが葉身にまで移行しにくく, その結果高い光合成能力が維持されていることが, 酸性土壌耐性の大きな原因の一つと考えられた.

本研究はフェーン現象下の気象を風洞装置を用いて再現し, 高温乾燥風に対する耐性イネ品種と感受性品種との水分状態とクロロフィル含量の差を調べたものである. 耐性品種として韓国農村振興庁嶺南農業試験場の盈徳出張所で選抜した日本型Naepung-byeo (NP), 感受性品種として同定されたオーストラリア原産の日本型Ilabong (IB) を供試し, それぞれ水田土壌をつめた1/1250aポットに移植し, 屋外自然条件下の湛水状態で生育させた. 3時間の高温乾燥風処理は出穂後4日目に行った. 穂の水ポテンシャルの変化は処理終了直後から顕著に現れ, NPでは処理開始前の-0.25 MPaに比べ, -0.75 MPaと大きく低下した. 一方, IBではさらに著しく, 処理開始前の-0.34 MPaから-1.53 MPaに大きく低下した. NPの穂の水ポテンシャルは, 処理終了後2時間目までは低下したが, 処理終了後6時間目には回復する傾向を示した. 葉身における水ポテンシャルは低下する傾向があったものの, 高温乾燥風処理による差は小さく, 品種間で有意な差は認められなかった. また, 穂の相対水分含量は水ポテンシャルと同様, NPでは高温乾燥風処理による低下はほとんど見られず, 処理終了後6時間目には回復する傾向を示した. しかし, IBでは処理終了直後の相対水分含量は処理開始前に比べて大きく低下し, 処理終了後6時間目では22%と極めて低かった. 穂のクロロフィル含量もNPで高く維持され, IBでは顕著に低下し, 処理終了後6時間目にはほとんどが白穂となった. このことから, 耐性品種であるNPは高温乾燥風に対し, 頴花で水分損失を防ぐ何らかの防御機構を有し, 時間の経過とともに回復したと考えられた.

In order to develop life assessment techniques for aged components made of modified 9Cr–1Mo steel, specimens were artificially deteriorated by aging, creep and fatigue tests at elevated temperatures, and associated changes in the microstructure and mechanical properties were examined. It was observed that aging resulted in formation of Laves phase causing a decrease in toughness. The creep damage in base metal could be correlated with decrease in hardness, while creep damage in weldments could be correlated with the area fraction and density of creep voids. Creep rupture in weldments occurred in the fine-grained heat affected zone by the formation and growth of creep voids. The fatigue damage in base metal correlated to the maximum length of a crack among micro-cracks initiated during fatigue cycles.

Effect of W on creep strength of martensitic steels was investigated paying special attention to microstructural degradation during creep. Though tempered martensitic lath structure is stable at the elevated temperatures without stress, its recovery takes place substantially during creep. After the recovery, lath width and dislocation density in lath interior reached the stationary values determined by creep stress. There was no difference in the stationary values between the two steels with (TAF650 steel) and without (Mod.9Cr–1Mo steel) W. However, recovery processes of the lath structure are significantly different between the two steels. The growth of lath width and the annihilation of dislocations in lath interior are slower in W containing TAF650 steel than those in Mod.9Cr–1Mo steel. Accumulation of creep strain is suppressed in TAF650 steel because of the slow recovery of its lath structure. The retardation of the recovery of lath structure results in the lower creep rate and the higher creep rupture strength of the W containing steel. The slow recovery of lath structure in the W containing steel is ascribed to pinning effect of M23C6 and Laves phase (Fe2W) precipitated on lath boundaries.

Genetic challenge to express higher carbonic anhydrase (CA) activity in the cytoplasm of tobacco mesophyll cells was carried out by an improved promoter (El2 Ω) with a cDNA of partially modified mouse CA. In leaves of T1 progenies of transgenic tobacco (ffCA plant), the expressed mouse CA peptide was confirmed with 1, 5-3.2 times higher than the transgenic tobacco having foreign mouse CA controlled by simple CaMV 35S promoter (fCA plant). The ffCA plants manifested higher photosynthetic carbon assimilation (PCA) rate under ambient CO2 condition than wild type plants. The chlorophyll fluorescence measurement analysis revealed that the ffCA plant's improved PCA rate is related to the reduction of mesophyll CO2 transfer resistance (Rr) with little change in the stomatal resistance (Rs) or mesophyll CO2 fixation resistance (Rx). Moreover, ffCA plants showed a higher growth rate under high light condition.

It was reported that a supernodulating soybean mutant, En6500 derived from the variety of Enrei, could produce many root nodules, but the growth rate of the plant was not necessarily high. The purpose of this paper, therefore, is to examine the characteristics of nodulation and also of plant growth in En6500 for elucidation of the mechanism of its low growth rate. The relative growth rate was low in En6500 compared with Enrei. The dry weight of the nodules per unit root mass was greater in En6500 than in Enrei, suggesting that the root of En6500 is supporting too many or an excess of nodules, which presumably leads to a reduction of plant growth rate. Reduced growth rate was associated with low net assimilation rate and further with low leaf photosynthesis. Moreover, the reduced leaf photosynthesis was associated with low partitioning of nitrogen to the leaves in En6500. Much allocation of nitrogen to the plant organs besides the leaves resulted in low photosynthesis, and also in the reduced nitrogen-use efficiency for dry matter production, which might be a potential mechanism for the low growth rate of En6500, a supernodulating soybean mutant.

Summary Eleocharis vivipara Link alters its photosynthetic mode depending on the growth environment. It utilizes C4 photosynthesis when grown under terrestrial conditions (terrestrial form) and C3 photosynthesis when grown under submerged conditions (submerged form). The photosynthetic organ (the mature internodal region of the culm) of the terrestrial form shows typical Kranz anatomy with well-developed bundle sheath cells, while the bundle sheath cells of the submerged form are not developed. In the mature internodal region of the terrestrial form, expression of the genes encoding two carboxylases, the small subunit of ribulose 1,5-bisphosphate carboxylase (RbcS) and phosphoenolpyruvate carboxylase (Ppc), occurred mainly in bundle sheath cells and in mesophyll cells, respectively, as seen in a typical C4 leaf. In the submerged form, RbcS was expressed in both bundle sheath cells and mesophyll cells, and no expression of Ppc was observed. In the immature internodal region with undeveloped bundle sheath cells, both life forms showed the same expression pattern as in C3 plants: RbcS expression was localized in mesophyll cells and no Ppc expression was observed. The C4-type expression pattern was established concomitantly with the development of bundle sheath cells during tissue maturation in the terrestrial internode. In contrast to the terrestrial form, the submerged form maintains C3-type gene expression during tissue maturation. When the terrestrial culm was submerged, a region of transition from the terrestrial form to the submerged form was established in newly sprouting culms. In this transitional region, C4-type expression of the two carboxylase genes was still maintained even though the development of bundle sheath cells was repressed. This observation suggests that the C4-type cell-specific gene expression pattern does not depend on the formation of Kranz anatomy.

Tubifex eggs individually inherit a single maternal centrosome during the first mitosis (mitosis I), and thereby form an asymmetrically organized monastral mitotic apparatus for the unequal cleavage. This maternal centrosome does not duplicate itself at the transition to mitosis I but does so at the transition to the second mitosis (Shimizu T, 1996, Roux's Arch Dev Biol 205: 290-299). To examine whether the maternal centrosome duplication is under cytoplasmic control, we produced syncytial eggs by electric fusion of an early meiosis II egg with an early mitosis I egg in an equator-to-equator fashion. As suggested from the diffusion rate of microinjected Texas Red-dextran (10,000 MW), diffusible ooplasmic components in syncytial eggs appear to be intermingled within 20 min following fusion. At ∼120 min after fusion, the meiosis II spindle and the mitosis I nucleus in each syncytial egg complete respective meiosis and mitosis almost simultaneously. Shortly after completion of the meiosis/mitosis, s...

The influence of potassium (K) deficiency on leaf water and osmotic potentials, and concentrations of major solutes was determined to assess their contributions to the leaf growth of soybean plants grown in solution cultures containing 5.0 and 0.2 mM KCl. A deficient supply of K restricted leaf growth due to decreased mesophyll cell numbers and cell enlargement, though water content, water and osmotic potentials of the expanding leaves were not affected by the treatment. The osmolarity of the expanding leaves showed very similar values in both treatments, though the K+ concentration in the K-deficient plants was remarkably lower than that of the control. In response to the K-deficiency, some cations, anions, sugars and amino acids accumulated in the expanding leaf, compensating the decrease in K concentration approximately 92%. These findings suggest that the leaf growth depression observed in the K-deficient plant occurred when the water relations of the K-deficient leaves are maintained close to that of the control.

We found in a previous study that Brazilian tall cultivars of spring wheat (Triticum aestivum L.) were more resistant to drought in respect of photosynthesis as compared to Mexican and Japanese semidwarf cultivars. In this study, a yield trial was performed with the same 20 cultivars to elucidate the yield and yield component responses to the soil water conditions in Cerrados, a semiarid region of Brazil. Under dry conditions, the dry matter yield of the Brazilian cultivars was significantly higher than the yields of the Mexican and Japanese cultivars. The grain yield of the Brazilian cultivars was also 34-46% greater than those of the Mexican and Japanese cultivars. Under fully-irrigated conditions, however, the Mexican and Japanese cultivars showed higher harvest indices and 18-21% greater grain yield than the Brazilian cultivars, although no practical difference was found among the cultivar groups in terms of dry matter yield. An analysis of yield components showed that the Brazilian cultivars had a larger 1000 kernel weight than the Mexican and Japanese cultivars under dry conditions, while the Mexican and Japanese cultivars had a higher kernel number than the Brazilian cultivars under fully-irrigated conditions. The reverse rotation of yield ranking among the cultivars under non-irrigated and fully-irrigated conditions is due to the fact that the Mexican and Japanese cultivars are more sensitive to soil moisture than the Brazilian cultivars.

Our previous paper showed that cultivar difference of flag leaf photosynthesis (LPS) in rice (Oryza sativa L.) was attributed to the difference in mesophyll resistance (rm). In this paper, we tried to divide rm into CO2 transfer resistance (rr) and CO2 fixation resistance (rc) for further analysis of rm by means of 3C determination of photosyntheti c products. In the heading time, rr, and rc occupied 14, and 58% in the total resistance, respectively, in average through 31 cultivars. This suggests that cultivar difference of LPS is mainly caused by the difference of r c. The percentage ratios of each resistance to the total one were maintained comparatively constant through the senescing process of the flag leaves. Moreover, the CO2 concentration in CO 2 fixating site showed almost the same values in different cultivars in a whole life span of a flag leaf. The rc showed a close correlation with ribulose-l,5-bisphosphate carboxylase/oxygenase (RubisCO) content. Carbonic anhydrase (CA) activity showed no correlation with rr, but showed positive correlation with rc. It was suggested that a mutual regulation system between CA activity and RubisCO activity could exist.

Although many studies have shown cultivar differences in photosynthetic response to water deficit, the understanding of detailed mechanisms is not sufficient. We examined the mechanisms of water stress-resistance in terms of photosynthetic performance under low soil water potential (Ψsoil) with sixteen cultivars of wheat (Triticum aestivum L.) from different habitats, which had shown different drought resistance on a grain yield basis. Cultivar differences in photosynthetic maintenance in response to decrease of Ψsoil (water stress resistance), were found at ail seedling, booting, and grain filling stages. Cultivars with high drought resistance based on grain yield also showed high water stress resistance in photosynthetic performance. Water stress resistance (Rws) was caused more by tolerance (Tws, maintenance ability of photosynthesis in response to decrease of leaf water potential, ΨL)in some cultivars, which maintained relatively high photosynthesis (PN) in spite of decreases in ΨL, while it was caused more by water stress avoidance (Aws, maintenance ability of ΨL in response to decreases in Ψsoil) in other cultivars, which showed a relatively high PN by maintaining a relatively high ΨL under the same low Ψsoil. However, there was a positive correlation between Rws and Tws or between Rws and Aws. It is suggested that avoidance and tolerance usually occur simultaneously in adaptation to low Ψsoil, although water stress resistant cultivars varied in the water stress resistance mechanism.

The mechanism of cultivar difference in salt tolerance was investigated with Korean rice cultivars, paying special attention to the relationship between sodium (Na) and potassium (K) ions in various organs. Three tolerant and three sensitive cultivars, with Nipponbare and IR8 as the reference cultivars, were cultured in solutions containing different concentrations of NaCl. The Na ion concentration in the leaf blade, leaf sheath and root increased with increasing NaCl in the culture solution in all cultivars. Furthermore, with increasing Na ion, the K ion concentration decreased in the root and leaf sheath. Conversely, in the leaf blade, the K ion concentration increased with increasing Na ion. No relationship between thc extent of accumulation of Na and K ion in the leaf blade and salt tolerance was observed, hence, these findings do not support the hypothesis that salt tolerance is related with the exclusion of K ion by absorbed Na ion in the leaf blade. However, exclusion of K ion by Na ion in the root was round in all the cultivars tested, and extent of the K exclusion might be related to the salt tolerance in rice plants.

Intergeneric hybrid plants were obtained by the sexual crossing of Diplotaxis muralis DC, a C3 species, and Moricandia arvensis (L.) DC, a C3-C4 intermediate species. The morphological characteristics and chromosome numbers showed that these plants were true hybrids. The hybrid had a CO2 compensation point of 27 μl/ L, nearly as low as that of M. arvensis (20 μl/L). A C3-like value of 45 μl/L for this point was found in somatic hybrids produced in our laboratory by protoplast fusion between red cabbage (Brassica oleracea L. var. capitata) or cauliflower (Brassica oleracea L. var. botrytis) and M. arvensis. However, significant differences were not found among the sexual and the somatic hybrids in the concentration or total activity of ribulose-l,5-bisphosphate carboxylase/oxygenase. The results showed that the expression, of a C3-C4 intermediate character of photosynthesis from M. arvensis appears to depend on the combination of other characters of the parental species.

The first cleavage in the freshwater oligochaete Tubifex hattai is unequal and meridional, and produces a smaller cell AB and a larger cell CD. This study traces the process of furrow formation, reorganization of cortical F-actin and the assembly of a mitotic apparatus during this unequal division. Cleavage furrow formation consists of two stages: (i) when eggs are viewed from the animal pole, meridionally running furrows emerge at two points of the egg's equator that are 90° apart from each other and approach the egg axis as they deepen; and (ii) at the midpoint between the equator and the egg center, the bottoms of these furrows link to each other on the animal and vegetal surfaces of the egg and form a continuous ring of constriction in a plane parallel to the egg axis. Egg cortices, isolated during the first step and stained with rhodamine-phalloidin, show that the bottoms of recently formed furrows are underlaid by a belt of tightly packed actin bundles (i.e. a contractile arc). The transition to the second stage of furrow formation coincides with the conversion of these actin belts into a continuous ring of F-actin. Whole-mount immunocytochemistry of microtubules reveals that the first cleavage in Tubifex involves an asymmetric mitotic spindle, which initially possesses an aster at one pole but not the other. This ‘monastral’ spindle is located at the egg's center and orients itself perpendicular to the egg axis. During anaphase, astral rays elongate to reach the cell surface, so that the array of astral microtubules in the plane of the egg's equator covers a sector of 270–300°. In contrast, it is not until the transition to telophase that microtubules emanating from the anastral spindle pole approach the cell margin. If eggs are compressed along the egg axis or forced to elongate, they form monastral spindles and divide unequally. In living compressed eggs, mitotic spindles, which are recognizable as bright streaks at the egg's center, appear not to shift their position along the spindle axis during division, suggesting that without eccentric migration of spindles Tubifex eggs are able to divide unequally. These results suggest that mechanisms that translocate the mitotic spindle eccentrically do not operate in Tubifex eggs during the first cell cycle. The mechanisms that generate asymmetry in spindle organization are discussed in the light of the present results.