Quantifying the dietary biotin requirement of the catfish,Clarias batrachus

Asian catfish, Clarias batrachus, were fed semi-purified basaldiets containing 0, 0.1, 0.5, 1, 3 and 5 mg biotin kg^–1diet for 60 days. Fish fed the control diet (no biotin) showed(P < 0.05) higher mortality, lower weight gain, specificgrowth rate (SGR), feed efficiency ratio (FER) and protein efficiencyratio (PER) than in fish fed diets supplemented with biotin. The highestweight gain, SGR, FER and PER were noticed in fish fed 1 mg biotinkg^–1, followed by 0.5, 5, 3 and 0.1 mg biotinkg^–1, except for PER (followed by 0.5, 5, 0.1 and 3 mgbiotin kg^–1). Quadratic analysis showed that the optimumdietary biotin requirements for maximal weight gain, PER and PER were2.49, 2.54 and 2.52 mg kg^–1, respectively. Liver biotinconcentrations were influenced by levels of biotin in the diet.Concentration of liver biotin increased as level of dietarysupplementation increased and no biotin was detected in the liver of thecontrol fish. Liver pyruvate carboxylase and acetyl CoA carboxylaseactivities were higher in fish fed biotin-supplemented diets than incontrols. Biotin concentrations, pyruvate carboxylase and acetyl CoAcarboxylase activities in liver associated with normal growth rangedfrom 10.59 to 10.66 g g^–1, 147.97 to 148.18 units mgprotein^–1 and 12.76 to 12.78 units mg protein^–1, respectively. Biotin deficiency symptoms such as anorexia, darkskin colour and convulsions were observed in fish fed the control diet.The optimum dietary biotin requirement for maximal growth of C.batrachus is about 2.49 mg kg^–1 diet.     

Design and development of a geothermal temperature control system for broodstock management of channel catfish Ictalurus punctatus

A control system was designed to raise and maintain water temperatures within 0.03-ha earthen ponds to a range conducive for spawning (24–30 °C) channel catfish Ictalurus punctatus. Heating was done during February 2001 to April 2001, when temperatures would have otherwise prohibited spawning (<24 °C). Temperature was increased from 10 °C (ambient) by 2 °C per day, and maintained at 27 °C, by the addition of geothermally warmed water (36 °C). The control system substantially increased the controllability and precision of heating ponds compared to manual operation. Systems were designed to control sets of four ponds. In designing this control system, consideration of biological constraints was essential. Reproduction in channel catfish is most strongly influenced by temperature. Because cold fronts are common during the winter and early spring (January–March), it was essential to ensure that pond temperatures did not fall below the range for spawning. Constraints on the heating rate and temperature variability to maintain fish health and stimulate spawning behavior were considered. Components of the control system included temperature measurement devices (type-T thermocouples), a central electronic control unit, electronic switches and electrically actuated ball valves. In response to the temperature sensed by each thermocouple, the controller sent a message to close or open the valve. When the valve was opened, warm water was added to the pond to increase the average pond temperature. Hardware and algorithm design and initial system testing were the major components of this project. The final design incorporated information on relevant biological parameters and safety features including peak pond temperature, independent aeration and water pressure control mechanisms. Initial results indicate successful control of this biological system, and ongoing studies suggest similar mechanisms may be used for additional control objectives. In particular, this system could be used to vary pond temperatures to study biological responses and to cool ponds by addition of well water during summer months.     

In vivo activity of native GnRHs and their analogues on ovulation in the African catfish, Clarias gariepinus (Burchell)

Four distinct forms of native gonadotropin‐releasing hormone (GnRH) and two newly designed analogues were tested for their in vivo activity to induce ovulation in African catfish. The effects of these peptides on ovulatory parameters were compared with those of carp pituitary and [d ‐Ala⁶, Pro⁹‐NEt]‐mammalian GnRH analogue (mGnRHa), two tested ovulation‐inducing agents in African catfish. Assessment of ovulation was carried out by determining the ovulation ratio and the relative quantity of egg produced. From the results of the experiments, the order of potency of the native GnRH peptides is summarized as chicken GnRH‐II (cGnRH‐II) >salmon GnRH (sGnRH) >mammalian GnRH >chicken GnRH‐I (cGnRH‐I). Chicken GnRH‐II was as potent as mGnRHa while cGnRH‐I was totally ineffective. The new d ‐Orn⁶‐cGnRH‐II and d ‐Orn⁶‐sGnRH with a substitution at position 6 with d ‐isomer residue were as potent as the most extensively used mGnRHa, indicating that the position 6 modification might be more crucial than the substitution at the C‐terminal. On the basis of our results, the potential use and incorporation of cGnRH‐II and sGnRH for the development of more generic spawning induction therapies are suggested.     

Action of Clathrodin and Analogues on Voltage-Gated Sodium Channels

Clathrodin is a marine alkaloid and believed to be a modulator of voltage-gated sodium (Na_V ) channels. Since there is an urgent need for small molecule Na_V channel ligands as novel therapeutics, clathrodin could represent an interesting lead compound. Therefore, clathrodin was reinvestigated for its potency and Na_V channel subtype selectivity. Clathrodin and its synthetic analogues were subjected to screening on a broad range of Na_V channel isoforms, both in voltage clamp and patch clamp conditions. Even though clathrodin was not found to exert any activity, some analogues were capable of modulating the Na_V channels, hereby validating the pyrrole-2-aminoimidazole alkaloid structure as a core structure for future small molecule-based Na_V channel modulators.     

Calcium Signaling is Involved in Negative Phototropism ofRice Seminal Roots简

Calcium ions(Ca2+) act as an intracellular second messenger and affect nearly all aspects of cellular life. They are functioned by interacting with polar auxin transport, and the negative phototropism of plant roots is caused by the transport of auxin from the irradiated side to the shaded side of the roots. To clarify the role of calcium signaling in the modulation of rice root negative phototropism, as well as the relationship between polar auxin transport and calcium signaling, calcium signaling reagents were used to treat rice seminal roots which were cultivated in hydroculture and unilaterally illuminated at an intensity of 100–200 μmol/(m2·s) for 24 h. Negative phototropism curvature and growth rate of rice roots were both promoted by exogenous CaCl2 lower than 100 μmol/L, but inhibited by calcium channel blockers(verapamil and LaCl3), calcineurin inhibitor(chlorpromazine, CPZ), and polar auxin transport inhibitor(N-1-naphthylphthalamic acid, NPA). Roots stopped growing and negative phototropism disappeared when the concentrations increased to 100 μmol/L verapamil, 12.500 μmol/L LaCl3, 60 μmol/L CPZ, and 6 μmol/L NPA. Moreover, 100 μmol/L CaCl2 could relieve the inhibition of LaCl3, verapamil and NPA. The enhanced negative phototropism curvature was caused by the transportation of more auxin from the irradiated side to the shaded side in the presence of exogenous Ca2+. Calcium signaling plays a key role as a second messenger in the process of light signal regulation of rice root growth and negative phototropism.     

钙信号抑制剂加剧低钾胁迫对烟草幼苗光合特性及钾吸收的影响

  【目的】  研究低钾胁迫抑制钙信号传导对植株幼苗叶片光合特性及钾吸收的影响,为缓解作物的低钾胁迫提供理论依据。  【方法】  以烟草品种K326为试验材料进行了室内水培试验。烟草幼苗先在营养液正常钾(K+ 5 mmol/L)和缺钾(K+ 0.15 mmol/L)营养液中生长8 天,然后在营养液中分别施加钙通道有机阻断剂Vp、钙通道无机阻断剂LaCl₃和钙离子螯合剂(EGTA)钙信号抑制剂,继续生长4天后取样,测定植株干鲜重、电导率、活性氧含量、叶片抗氧化酶活性、叶片光合特性等指标和植株地上、地下部钾素浓度及钾离子吸收相关基因表达量。  【结果】  1)不添加钙通道抑制剂或螯合剂条件下,低钾胁迫的烟株地上部和根系干重较常钾水平显著降低了59.29%、39.82%,鲜重显著降低了51.58%、48.19%,除水汽压饱和亏外的其余5项光合特性指标显著降低,植株地上部和根系钾含量分别显著降低了39.31%和77.05%,而叶中可溶性蛋白、相对电导率、过氧化氢含量则显著增加,NKT2、NtKC1、NtHAK1、NtHAK5基因的相对表达量分别增加了2.09、3.32、3.23、12.34 倍。2)常钾水平下,3个钙抑制剂处理未明显影响地上部和根系干鲜重,而低钾水平下,钙抑制处理的地上部鲜重和干重显著高于无钙抑制剂对照。两个钾水平下,与各自对照相比,3个钙抑制剂处理的叶片相对电导率、活性氧积累量均显著增加,抗氧化酶SOD和POD活性、叶绿素含量显著减少,光合特性指标(除水汽压饱和亏外)明显降低。3)两个钾水平下,3个钙信号抑制剂处理的烟株地上部和根系钾含量均显著低于其对照,低钾胁迫下平均降低幅度分别达到25.54%和53.36%。低钾胁迫下,钾离子通道基因NKT2、NtKC1和转运蛋白基因NtHAK1、NtHAK5在根系中的相对表达量分别平均降低了60.60%、50.62%、38.61%、69.79%,钙通道相关基因NtCNGC1和NtCNGC11在根中的相对表达量分别平均降低了95.36%和87.04%。  【结论】  低钾胁迫明显影响烟株幼苗生长、光合作用及对钾素的吸收和积累。低钾水平下,外施钙通道抑制剂或螯合剂可进一步降低烟草叶片抗氧化酶活性,减弱烟株叶片光合作用,并抑制根中钾吸收相关基因的表达和烟株对钾素的吸收。     

饲料蛋白含量对稻-黄颡鱼共作模式气态氮排放、黄颡鱼生长和氮利用率的影响

【目的】明确饲料蛋白含量对稻-黄颡鱼共作模式下N₂O和NH₃挥发特征及黄颡鱼生长的影响,有利于稻-黄颡鱼综合种养的高效、绿色发展。【方法】采用盆栽模拟试验,以常规单养黄颡鱼模式为对照,系统研究了不同饲料蛋白含量对稻-黄颡鱼共作模式下N₂O和NH₃的排放特征、水体和底泥的氮含量以及黄颡鱼生长的影响。【结果】在相同蛋白含量下,稻-黄颡鱼共作模式的N₂O和NH₃挥发分别比单养黄颡鱼模式降低18.3%和76.20%,水体总氮和无机氮含量降低41.30%和48.85%,黄颡鱼蛋白累积量增加20.00%,氮利用率增加171.50%。在稻-黄颡鱼共作模式下,提高饲料蛋白含量会显著增加N₂O排放量和水体残留氮含量,但对NH₃挥发无显著影响;黄颡鱼特定生长率和蛋白累积量与饲料蛋白含量呈二次曲线关系。饲料氮利用效率随饲料蛋白含量增加呈线性降低趋势。【结论】综合考虑黄颡鱼生长和N₂O排放以及养殖水体氮残留等因素,确定稻-黄颡鱼共作模式饲料蛋白含量不宜超过43.04%。     

农村专业合作经济组织资金问题研究

根据当前我国农村专业合作经济组织发展的实际情况,分析了我国农村专业合作经济组织资金的现状,指出农村专业合作组织资金存在的问题,提出了相应的措施,以期为农村专业合作经济组织更加健康的发展提供借鉴。     

宁夏西干渠滚钟口水库调度研究

灌溉供水渠道普遍存在时段性供水困难现象,调度或处理不当,容易造成农业损失和水事纠纷。西干渠管理处利用渠道节制闸壅高水位向滚钟口水库注水,在用水高峰期补充下游灌溉,提高了灌溉保证率,较好地解决了灌溉困难。并通过水库滞纳雨洪资源,提高水资源的利用率和保证渠道运行安全。提出平原灌区利用适宜地形条件修建调节水库的建议。