无细胞分裂素培养基上高效的大豆下胚轴外植体器官再生

虽然已经有大豆下胚轴再生植株的很多报道，但再生率总是很低并且不定芽的再生都是在添加细胞分裂素的培养基上取得的。这种培养基使外植体形成大量愈伤组织且阻碍了再生芽的进一步生长。为此本实验将表面灭菌的成熟种子置2种培养基上萌发，一种添加2 mg/L苄基腺嘌呤（BA）而另一种不添加；6 d后将小苗的下胚轴切下作为外植体培养到两种诱导不定芽再生的培养基上，同样一种添加2 mg/L BA而另一种不添加。在9个当地、2个美国和1个巴西共12个供试品系中，最好的培养结果是在含2 mg/L BA的培养基上萌发、长 苗、切取下胚轴并在不含BA的再生培养基诱导不定芽。以此程序，不定芽的再生率和质量都得到了显著提高，其中一个当地品种“广大粒”的再生率达到了72%。     

Laboratory and on‐farm evaluation of low‐cost salt mixtures for use during salinity acclimation and the nursery phase of Pacific white shrimp (Litopenaeus vannamei)

The current study evaluates the efficacy of a low‐cost salt mixture (LCSM) to replace expensive reconstituted sea salt (RSS) in the salinity acclimation and nursery phase of Pacific white shrimp under laboratory and farm conditions. LCSM was formulated to yield sodium, potassium, calcium and magnesium concentrations closely comparable to that of diluted seawater. Laboratory‐based nursery trials were conducted at 2, 6 and 15 g/L salinities, incrementally replacing RSS with LCSM (25%, 50%, 75% and 100%) at four replicates per treatment. Thirty postlarvae were reared for 7 days in 24‐L aquaria during the 2 and 6 g/L trials, while the nursery trial for 15 g/L salinity was conducted for 21 days with 400 postlarvae stocked in 150‐L tanks. On‐farm evaluation of LCSM was carried out in two tank‐based systems installed on levees adjacent to shrimp production ponds. RSS was incrementally replaced with LCSM (0%, 50%, 75% and 100%) and 100 postlarvae stocked into each 800‐L tank. Salinity acclimation was done from 30 g/L to 6 or 1.5 g/L within 2–3 days by pumping water from adjacent shrimp production ponds. Following salinity acclimation, the S4 system maintained flow‐through at 1.5 g/L, while N10 system was maintained static at 6 g/L salinity. At the conclusion, no significant differences were observed for either survival or growth of shrimp postlarvae between RSS and LCSM treatments at all salinities examined. Results reflect the potential use of LCSM to replace RSS, which could be an excellent solution to bring down the cost of production in inland shrimp aquaculture.     

Expression and possible role of 20alpha-hydroxysteroid dehydrogenase in the placenta of the goat

20Alpha-hydroxysteroid dehydrogenase (20alpha-HSD) catalyzes the conversion of progesterone to its inactive form 20alpha-dihydroprogesterone (20alpha-OHP). 20Alpha-HSD is expressed in the murine placenta, suggesting a role, yet unidentified, played by this enzyme during the course of pregnancy. To elucidate the possible roles of 20alpha-HSD during pregnancy, 20alpha-HSD gene expression in the placenta was examined by Northern blot analysis, and progestin (progesterone and 20alpha-OHP) concentrations in the maternal and fetal sera and the amniotic fluid were measured by radioimmunoassay in pregnant Shiba goats. The expression of 20alpha-HSD mRNA was observed in the placenta and the intercaruncular part of the uterus during mid to late pregnancy. Analysis by in situ hybridization revealed that 20alpha-HSD mRNA was mainly localized in the endometrial epithelium of the caruncle side of the placenta. Considerable enzyme activity of 20alpha-HSD was also detected in the cytosolic fraction of the placenta and intercaruncular part of the uterus. Although concentrations of progesterone and 20alpha-OHP in the maternal serum showed similar profiles, progesterone levels in the fetal serum stayed extremely low throughout the pregnancy. The 20alpha-OHP concentration in the fetal serum was always higher than that in the maternal serum. In the amniotic fluid, the concentrations of both progesterone and 20alpha-OHP remained at very low levels throughout the pregnancy. These results support the notion that 20alpha-HSD protects the fetus from the cytotoxic effects of progesterone, and thereby maintains the normal development of the fetus.     

Evaluation of an alternative salt mixture to culture Pacific white shrimp (Litopenaeus vannamei) in inland aquaculture

Pacific white shrimp, Litopenaeus vannamei, exhibit a remarkable ability to tolerate low‐salinity environments, facilitating its culture far from coastal areas using various production systems at salinities less than 15 g/L. Recirculating aquaculture systems (RAS) and biofloc systems are usually operated using reconstituted sea salt (RSS), which is a considerable financial burden to commercial producers due to its higher price. Current study was carried out with the objective of testing the efficacy of a low‐cost salt solution to replace expensive RSS to grow shrimp under laboratory conditions. Low‐cost salt mixture (LCSM) was formulated to yield sodium, potassium, calcium and magnesium concentrations closely comparable to that of diluted seawater using agriculture grade sodium chloride, magnesium chloride, magnesium sulphate, potassium oxide, calcium chloride and sodium bicarbonate. Growth trials were conducted at three different salinities of 3, 6 and 15 g/L, incrementally replacing RSS with LCSM (0, 2.5, 25, 50, 75 and 100%) at four replicates per treatment. Twenty juvenile shrimp were reared for 42 days in 150 L polyethylene tanks. Ionic profile of water, ionic profile and osmolality of shrimp haemolymph were determined to justify growth and survival data through analysing ionic variations and osmoregulatory capacity of shrimp. At the conclusion, no significant differences were observed in survival, growth, osmoregulation and levels of cations in shrimp haemolymph between RSS and LCSM treatments at all salinities examined. Results reflect the potential use of LCSM to replace RSS which could be an excellent solution to bring down the cost of production in inland shrimp aquaculture.     

Decay of the GRB 990123 optical afterglow: implications for the fireball model

Broad-band (ultraviolet to near-infrared) observations of the intense gamma ray burst GRB 990123 started approximately 8.5 hours after the event and continued until 18 February 1999. When combined with other data, in particular from the Robotic Telescope and Transient Source Experiment (ROTSE) and the Hubble Space Telescope (HST), evidence emerges for a smoothly declining light curve, suggesting some color dependence that could be related to a cooling break passing the ultraviolet-optical band at about 1 day after the high-energy event. The steeper decline rate seen after 1.5 to 2 days may be evidence for a collimated jet pointing toward the observer.     

Developed microbial biofilms can restore deteriorated conventional agricultural soils

Nitrogen fixing bacteria play a key role in the growth and persistence of effective microbial communities in the soil by supplying N through biological nitrogen fixation (BNF). In the long run, chemical inputs, particularly N fertilisers are known to adversely affect N₂ fixers and hence maintenance of soil fertility and crop productivity. This study examined the effect of developed microbial biofilms with N₂ fixers on restoration of soils deteriorated by conventional agricultural practices in tea cultivation. Just reducing recommended chemical fertiliser use by 50% significantly increased soil microbial biomass and BNF, and decreased soil NO₃⁻ and pest infestation. The lower chemical fertiliser addition coupled with the biofilm-based biofertilisers known as biofilmed biofertilisers (BFBFs) further increased BNF significantly. The combined application significantly increased soil organic C by ca. 20%, and reduced leaf transpiration by ca. 40%. It also supported plant growth, rhizoremediation and soil moisture conservation in comparison to the 100% chemical fertilisation. Those improved performances were observed to be proportional to the increased density of soil bacteria, and have several agronomic and environmental implications. It is apparent from this study that replenishing the depleted soil microbial communities by applying such biofertilisers is likely to be beneficial in agroecosystems with chemical N fertiliser use, if they are to be sustained for crop production.     

Porous semiconductor chalcogenide aerogels

Chalcogenide aerogels based entirely on semiconducting II-VI or IV-VI frameworks have been prepared from a general strategy that involves oxidative aggregation of metal chalcogenide nanoparticle building blocks followed by supercritical solvent removal. The resultant materials are mesoporous, exhibit high surface areas, can be prepared as monoliths, and demonstrate the characteristic quantum-confined optical properties of their nanoparticle components. These materials can be synthesized from a variety of building blocks by chemical or photochemical oxidation, and the properties can be further tuned by heat treatment. Aerogel formation represents a powerful yet facile method for metal chalcogenide nanoparticle assembly and the creation of mesoporous semiconductors.     

Evaluation of soybean meal from different sources as an ingredient in practical diets for Pacific white shrimp Litopenaeus vannamei

Solvent extracted soybean meal (SBM) is generated using different varieties of soybeans grown under a range of conditions and then processed at different crushing plants. Due to its competitive cost and availability, it is a popular plant‐based protein source for shrimp feed formulations. However, there is limited information about effects of variations in the nutritional composition of soybean meal have on performances of shrimp. Hence, the present study was designed to determine the effects of different soybean sources on the growth performances of Litopenaeus vannamei. Two growth trials were conducted with iso‐nitrogenous and iso‐lipidic (350 g/kg protein and 80 g/kg lipid) test diets formulated with 25 sources of soybean meal. Trial one incorporated 14 treatments including a soy‐based diet containing 517 g/kg SBM (eight replicates) and this soy source was then replaced with 13 different soybean sources (four replicates per treatment). The second trial used the same basal diet and 11 different sources of soybean meal (Total 12 diets) with five replicates per treatment. Both growth trials were conducted with a stocking density of 10 shrimps/aquarium in a semi‐closed recirculating system and the initial weight of shrimps for trials 1 and 2 were 0.23 g ± 0.02 and 0.67 g ± 0.02 respectively. During the two trials, shrimp were fed four times/day assuming a FCR of 1.8, over 42 days for trial 1 and 35 days for trial 2. Results indicated that there are differences among sources of soybean meal for standardized percentage TGC. Diet 21 that contained SBM4550 had the largest value for TGC whereas the lowest value for TGC was observed for shrimp fed diet 17 that contained SBM45536. According to the statistical analysis that was used to interpret the growth performance data from the complete chemical profile of the SBM, phosphorous, phytate‐phosphorous and total phytic acid levels had positive correlations (p < 0.005) with TGC whereas raffinose (p = 0.086) had a negative correlation with TGC. Results of this work indicates phosphorous, phosphorous in phytic acid and total phytic acid and raffinose are important components in SBM that may have significant effects on the growth performances of pacific white shrimp.     

Adoption and failure rates of vaccinations for disease prevention in chicken farms in Jos,Nigeria

Vaccinations against diseases to prevent disease outbreaks are strategic to disease prevention, but vaccination failures may constitute a challenge in practice. This study was aimed at assessing the adoption and failure rates of vaccinations in 80 chicken farms in Jos, Nigeria. Data were obtained through a structured questionnaire validated by interviews and checking of farm and veterinary records. Vaccination score (0–1) from the vaccination checklist (5 for broilers and 12 for layers) and vaccination procedure score (0–1), based on scored adopted procedures, were calculated for each farm. Vaccine effectiveness was calculated for each vaccine using the odds ratio from the association of frequencies of disease outbreaks in vaccinated and unvaccinated flocks. Farmers used more of imported than local vaccines. Vaccination procedure and vaccination scores did not influence frequencies of disease outbreaks, but vaccination scores tended to non-robustly correlate (r = − 0.89, p > 0.05) with rates of disease outbreak. Vaccination rates were highest against Newcastle disease and infectious bursal disease, and their vaccinations also had the highest effectiveness. There was an association (p = 0.009) between composite vaccination rates and disease outbreaks with 2.1 odds of outbreaks in vaccinated than unvaccinated flocks. Vaccination failures occurred in the use of 11 out of 12 vaccines and the highest failure rate (47.9%) was in vaccination against coccidiosis. Therefore, vaccination failure is a critical factor in poultry vaccination practice within the locality. The adoption of poultry vaccinations needs to be strategised in the context of a national poultry vaccination policy in order to promote effective poultry disease prevention and control.