Positive correlation between the number of root nodule primordia and seed sugar secretion in soybean (Glycine max L.) seedlings inoculated with a low density of Bradyrhizobium japonicum

Sufficient rhizobium population in the rhizosphere of legume seedlings is required for early and enough setting of root nodules. Potential of seed and seedling root exudates for proliferation of Bradyrhizobium japonicum PNT119 was evaluated in the soybean cvs. Enrei and Tachinagaha. In both cultivars, seed exudates showed a higher potential than root exudates. In the seed exudates, a low-molecular high-polarity fraction including sugars and amino acids showed a higher potential than both high-molecular fraction and low-molecular low-polarity fraction. The correlations between the sugar or amino acid contents of seed exudates and the number of root nodule primordia at 7 d after sowing were investigated among 12 soybean cultivars. When seeds were inoculated with a low rhizobium density, a high correlation coefficient was detected between them. However, there was no positive correlation in the plants inoculated with a high rhizobium density. These results suggest that the amount of low molecular substances in the seed exudates determines the number of root nodule primordia through rhizobium proliferation around seed and young roots when the rhizobium density is the limiting factor. The genetic trait relating to seed coat secretion should be considered as a possible key factor contributing to adequate root nodulation in soybean seedlings cultivated in fields with a low rhizobium density.     

Molecular detection of human periodontal pathogens in oral swab specimens from dogs in Japan

Periodontal diseases are known to be major diseases in humans, and are also common in dogs. The purpose of the present study was to analyze the distribution of periodontitis-related bacterial species using oral swab specimens collected from 26 pet dogs. The distribution of an animal gingival organism Porphyromonas gulae, in addition to 10 human periodontitis-related bacterial species, including Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia, Capnocytophaga ochracea, Capnocytophaga sputigena, Prevotella intermedia, Prevotella nigrescens, Aggregatibacter actinomycetemcomitans, Campylobacter rectus, and Eikenella corrodens, were evaluated by polymerase chain reaction with species-specific sets of primers. Porphyromonas gulae, Tannerella forsythia and Campylobacter rectus were detected in almost all dogs analyzed, all of which should be regarded as common members of oral flora in dogs. Then, isolation and identification of the Porphyromonas species in swab specimens were performed. There were 35 strains isolated from 22 dogs, and broad-range polymerase chain reaction and sequencing methods revealed that approximately 70% of them were Porphyromonas gulae. In contrast, the frequency of Porphyromonas gingivalis was extremely low. These findings indicate the presence of specific periodontitis-related pathogens in pet dogs, especially Porphyromonas gulae.     

Non-CpG methylation occurs in the regulatory region of the Sry gene

The Sry (sex determining region on Y chromosome) gene is a master gene for sex determination. We previously reported that the Sry gene has tissue-dependent and differentially methylated regions (T-DMRs) by analyzing the DNA methylation states at CpG sites in the promoter regions. In this study, we found unique non-CpG methylation at the internal cytosine in the 5'-CCTGG-3' pentanucleotide sequence in the Sry T-DMR. This non-CpG methylation was detected in four mouse strains (ICR, BALB/c, DBA2 and C3H), but not in two strains (C57BL/6 and 129S1), suggesting that the CCTGG methylation is tentative and unstable. Interestingly, this CCTGG methylation was associated with demethylation of the CpG sites in the Sry T-DMR in the developmental process. A methylation-mediated promoter assay showed that the CCTGG methylation promotes gene expression. Our finding shows that non-CpG methylation has unique characteristic and is still conserved in mammals.     

Compositions of Xylem Fluid of Arsenic-Stressed Barley Seedlings: A Measurement with PIXE System and HPLC

Compositions of the xylem fluid of arsenic (As)-stressed hydroponic barley (Hordeum vulgare L. cv. Minorimugi) were investigated. The seedlings were treated with 0, 6.7, 33.5, and 67???M As in the form of arsenite. The xylem fluids were collected from the cut surface of plants 14?days after treatments and analyzed. Arsenic toxicity reduced the flow rate of xylem fluid. Mineral concentrations of the xylem fluid were measured with particle-induced X-ray emission system, but organic solutes were measured with high-performance liquid chromatography. Arsenic did not influence the concentrations of phosphorus (P), potassium (K), magnesium (Mg), and iron (Fe) very much. However, the concentrations of manganese (Mn), zinc (Zn), and copper (Cu) increased resulting in fairly stable translocation of the elements. The concentration and translocation of Ca decreased in the xylem fluid with increasing As concentrations in the medium. Arsenic concentration increased with increasing As in the nutrient solution, but its translocation decreased. Arsenic treatments did not affect phytosiderophore concentration very much, but their translocation decreased. The concentration of citrate increased but that of malate and succinate decreased in 33.5???M As-treated plants.     

Presence of a Temperature Gradient Among Genital Tract Portions and the Thermal Changes Within These Portions Over the Estrous Cycle in Beef Cows

The aim of the present study was to describe the temperature of the different portions of the female genital tract and their relation to rectal temperature and to investigate the effect of steroid hormones profiles on these variables over the estrous cycle in cattle. Four nonpregnant Japanese Black cows were investigated daily over two successive estrous cycles using a digital thermometer with a long probe and rounded-end sensor to record the temperature of the rectum (RT), vagina (VT), cervix (CT), uterine body (UBT) and uterine horns (UHT). Blood samples were collected immediately before temperature recording to assay peripheral levels of progesterone (P₄) and estradiol-17β (E₂). Moreover, transrectal ultrasonography was carried out after temperature recording to monitor the ovulatory follicle and track ovulation. During the experiment, the ambient temperature and relative humidity were recorded for further calculation of the temperature humidity index (THI). The temperature within the genital tracts in these cows progressively increased towards the uterine horns from the vagina. The VT, CT, UBT and UHTs were significantly higher in association with peripheral P₄ concentrations greater than 4 ng/ml (mid-luteal phase) when compared with lower peripheral P₄ concentrations. The VT was more significantly (P<0.01) correlated to the CT, UBT and UHTs than RT. In conclusion, a temperature gradient was present among the vagina, cervix and uterus over the estrous cycle, and changes in peripheral P₄ concentrations were associated with the thermal variations within these portions. The VT could be more beneficial than RT in monitoring temperature of deeper portions of the female genital tract in bovine.     

Fiber digestion in various segments of the hindgut of horses fed grass hay or silage

We studied in vivo fiber digestibility and fermentation parameters such as volatile fatty acid concentration and in vitro degradation in each segment of hindgut of horses fed timothy hay or silage made from the same sward. Six Thoroughbred horses were fed timothy hay or silage in equal amounts (1.6% of bodyweight per day, bodyweight mean 572 kg) every 3 h per day, then slaughtered. There were no differences between hay and silage in the concentration of the total volatile fatty acids, the apparent digestibility of dry matter, organic matter, and fiber, and in vitro neutral detergent fiber (NDF) disappearance rate in each segment. The total volatile fatty acid concentration and the apparent digestibility of dry and organic matter and fiber differed ( P  < 0.01) depending on the digestive segments. Both for hay and silage, the concentration of total volatile fatty acids in the digesta liquid phase largely increased ( P  < 0.01) from the cecum to the right ventral colon, and kept a constant value from the right ventral colon to the right dorsal colon, and then decreased from the right dorsal colon to the small colon. For dry and organic matter and fiber components, the apparent digestibility changed in the same manner from former to hinder segments of the hindgut. Regardless of diet, dry and organic matter and fiber components showed lower values in the cecum and the right ventral colon and increased ( P  < 0.01) largely from the right ventral colon to the left dorsal colon, then kept constant values in segments to the rear of left dorsal colon. There were no differences in in vitro NDF disappearance among cecum, ventral colon and dorsal colon.     

Increase in phosphorus availability of upland Andosol under different fertilization conditions measured by isotopic techniques

In Japan, since about 50% of upland fields are covered with Andosols, in which phosphorus (P) supplied by fertilizer is likely to be immobilized, there is a large accumulation of P in upland soil (Agriculture, Forestry and Fisheries Research Council 1991). However, information on the changes in the availability of accumulated P under long-term field conditions is very limited.

In order to analyze the effect of continuous application of compound fertilizer and farmyard manure on the changes in P compounds and their availability to crop plants in the plow layer of an upland Andosol, a long-term field trial has been carried out in an experimental field of Tokyo University of Agriculture and Technology, Tokyo, Japan since November, 1982. The results obtained in the field trial demonstrated that although crop growth in the plot without P fertilizer application was more reduced than that in the plot with P fertilizer application during each stage of the trial, the differences in crop growth between the plots became attenuate as time passed. These findings suggest that in the plot without P fertilizer application, soil P that accumulated before the start of the trial became available for the growth of crops as time passed (Hirata 1997).

While Truog and Bray No.2 methods have been traditionally used for routine analysis of available soil P in Japan, it has been recently reported that P extraction by these methods led to an overestimation of the amount of available soil P (Kato et al. 1995b). It was reported that the L-value measured by the isotopic dilution method and E-value measured by the isotopic exchange kinetic method were more suitable for estimating the amount of available soil P (Russel et al. 1957; Dalal and Hallsworth 1976; Tran et al. 1988; Kato et al. 1995a, b), and that isotope techniques could become valuable tools for understanding the P dynamics in soil-plant systems (Di et al. 1997).

In the present report, we carried out investigations on P availability in soils taken from plots differing in P fertilizer application in the above trial over a period of 13.5 y by using the ³²P isotopic dilution method and the isotopic exchange kinetic method.     

Effect of continuous application of farmyard manure and inorganic fertilizer for 9 years on changes in phosphorus compounds in plow layer of an upland Andosol

The changes in total phosphorus (P) accumulation in the plow layer and in the contents of several P compounds in an upland Andosol with time and the effects of these changes on biomass production at the field level were investigated in relation to the continuous application of farmyard manure and compost (referred to as “farmyard manure”) and inorganic P for 9 y. 1) Inorganic P applied continuously without farmyard manure accumulated only in the plow layer of the upland Andosol, whereas the combined application of inorganic P and farmyard manure P led to the leaching below the plow layer, with a constant level (3.3–3.5 g kg^-1) of P accumulation in the plow layer within several decades. In order to reach a constant P accumulation level, higher application of P shortened the time required for the accumulation. 2) Bray No. 2-P value in the plow layer increased with time and tended to become maximum only under the application of both inorganic P and farmyard manure. 3) Aluminum (AI) bound-P (AI-P) fraction in the plow layer of the Andosol increased continuously and quadratically with the cultivation, along with an accelerated decrease in the amount of iron bound-P (Fe-P) and residual-P fractions (Res-P) during the 9-y period. 4) Continuous application of farmyard manure accelerated the decrease in the organic P (Org-P) fraction, presumably due to promoting microbial activity in the plow layer. 5) During the 9-y period, differences in crop growth with and without continuous application of P became attenuated, suggesting that the availability of accumulated P in the plow layer of the Andosol farm field before the experiment increased for the subsequent crop cultivation. Continuous increase in the AI-P fraction with time was closely correlated with the increase in P availability of accumulated P for crop growth.     

Adequate range of boron nutrition is more restricted for root nodule development than for plant growth in young soybean plant

A pot experiment was conducted under growth chamber conditions to determine the lower and upper critical levels of boron (B) for plant growth, nodule development, and nodule acetylene reduction activity (ARA) in young soybean plants. Plants of a soybean cultivar, Tachinagaha, were grown in pots containing river sand to which a nutrient solution with different B levels was added and were inoculated with Bradyrhizobium japonicum A1017. At 8, 12, and 16 d after sowing (DAS), among the plants supplied with the solution at 0, 1.0, and 2.0 mg B L^-1 , plants with 1.0 mg B L^-1 showed the highest values for dry shoot and fresh root weight, root length, total number of developing nodules and meristematic nodules (DMN), and ARA. At 20 DAS plants grown with 11 B levels (0-2.0 mg L^-1) were compared. The B critical deficiency levels for soybean dry shoot weight, fresh root weight, root length, DMN, number of complete nodules, and ARA were approximately 46, 35, 34, 57, 60, and 50 mg B kg^-1 dry matter, and the critical toxicity levels were approximately 114, 137, 134, 97, 104, and 89 mg B kg^-1 dry matter, respectively. The optimum B levels for the growth characters were approximately 34 to 137 mg B kg^-1 dry matter. The optimum range of B levels for nodule formation and function was more restricted than that for the growth characters. Based on the results of treatments with various B concentrations, 0.4 mg B L^-1 was found to be the concentration most beneficial for all the growth characters including nodule formation at the early stage (20 DAS) of development of soybean plants.