无机营养对春小麦抗旱适应性的影响

本文研究了无机营养对春小麦一些抗旱适应性的影响,主要包括:渗透调节的大小和变化过程、可溶性糖的积累、脯氨酸的积累、叶片导度的变化、离体叶片的失水速率、叶面积和耗水量的变化、根系生长和根/植冠值,并且分析了各个处理植株的水分利用效率(WUE)和产量的变异。认为,在干旱条件下,无机营养对于春小麦不同器官、不同生理功能,并不都具有一致的作用。有的利于提高植株的抗旱性,有的可以改变一些适应性产生的时间和发展过程,有的则不利于植株的抗旱性。通过综合分析,提出旱地施肥使作物增产的主要原因是,营养元素满足了作物生长所需,促进了根系发育,利于吸收水分、维持水分平衡和正常生理功能,但对作物自身的耐旱性并没有产生显著影响。     

Nucleotide sequence of the Escherichia coli cad operon: a system for neutralization of low extracellular pH.

Lysine decarboxylase of Escherichia coli has been the subject of enzymological studies, and the gene encoding lysine decarboxylase (cadA) and a regulatory gene (cadR) have been mapped. This enzyme is induced at low pH in the presence of lysine and achieves maximal level under anaerobic conditions. The induction of lysine decarboxylase increases the pH of the extracellular medium and provides a distinctive marker in tests of clinical strains. We report the sequence of the cad operon encoding lysine decarboxylase, a protein of 715 amino acids, and another protein, CadB, of 444 amino acids. The amino acid sequence of lysine decarboxylase showed high homology to that of the lysine decarboxylase of Hafnia alvei with less homology to the sequence of speC, which encodes the biosynthetic ornithine decarboxylase of E. coli. The cadA and cadB genes were separately cloned and placed under the control of lac and tac promoters, respectively, to facilitate independent study of their physiological effects. The cadB gene product had a mobility characteristic of a smaller protein on protein gels, analogous to that found for some other membrane proteins. The CadB sequence showed homology to that of ArcD of Pseudomonas aeruginosa, encoding an arginine/ornithine antiporter. Excretion studies of various strains, the coinduction of cadB and cadA, and the attractive physiological role for an antiport system led to a model for the coupled action of cadA and cadB in uptake of lysine, the reduction of H+ concentration, and excretion of cadaverine.     

Regulation of the Escherichia coli cad operon: location of a site required for acid induction.

The cad operon encodes lysine decarboxylase and a protein homologous to amino acid antiporters. These two genes are induced under conditions of low pH, anaerobiosis, and excess lysine. The upstream regulatory region of the cad operon has been cloned into lacZ expression vectors for analysis of the sequences involved in these responses. Deletion analysis of the upstream region and cloning of various fragments to make cadA::lacZ or cadB::lacZ protein fusions or operon fusions showed that cadA was translated more efficiently than cadB and localized the pH-responsive site to a region near an upstream EcoRV site. Construction of defined end points by polymerase chain reaction further localized the left end of the regulatory site. The presence of short fragments bearing the regulatory region on high-copy-number plasmids greatly reduced expression from the chromosomal cad operon, suggesting that titration of an essential activator protein was occurring. With nonoptimal polymerase chain reaction conditions, a set of single point mutants were made in the upstream regulatory region. Certain of these altered regulatory regions were unable to compete for the regulatory factor in vivo. The locations of these essential bases indicate that a sequence near the EcoRV site is very important for the activator-DNA interaction. In vivo methylation experiments were conducted with cells grown at pH 5.5 or at pH 8, and a difference in protection was observed at specific G residues in and around the region defined as important in pH regulation by the mutation studies. This work defines essential sequences for acid induction of this system involved in neutralization of extracellular acid.     

In vivo metabolism of a mutant apolipoprotein, apoA-IIowa, associated with hypoalphalipoproteinemia and hereditary systemic amyloidosis.

Apolipoprotein (apo) A-I is the major protein constituent of plasma high density lipoproteins (HDL). A kindred has been identified in which a glycine to arginine mutation at residue 26 in apoA-I is associated with hypoalphalipoproteinemia and hereditary systemic amyloidosis. We isolated the mutant protein, termed apoA-IIowa, from the plasma of an affected subject and studied its in vivo metabolism compared to that of normal apoA-I in two heterozygous apoA-IIowa subjects and two normal controls. Normal and mutant apoA-I were radioiodinated with 131I and 125I, respectively, reassociated with autologous plasma lipoproteins, and simultaneously injected into all subjects. Kinetic analysis of the plasma radioactivity curves demonstrated that the mutant apoA-IIowa was rapidly cleared from plasma (mean fractional catabolic rate [FCR] 0.559 day-1) compared with normal apoA-I (mean FCR 0.244 day-1) in all four subjects. The FCR of normal apoA-I was also substantially faster in the heterozygous apoA-IIowa subjects (mean FCR 0.281 days-1) than in the normal controls (mean FCR 0.203 days-1). Despite the rapid removal from plasma of apoA-IIowa, the cumulative urinary excretion of its associated radioactivity after 2 weeks (44%) of the injected dose) was substantially less than that associated with normal apoA-I (78% of injected dose), indicating extravascular sequestration of radiolabeled apoA-IIowa.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic and physiological response of the rabbit to continuous and intermittent treadmill exercise

Our knowledge of the effects of exercise on the heart is limited by the predominant use of rats as an animal model. The rabbit has many advantages over the rat as an animal model to study. However, little work has characterized its capacity to exercise. The purposes of the present study were to determine if the rabbit could (i) learn to run on a motor-driven treadmill at relatively high speeds using different exercise protocols, and (ii) characterize the various physiological and metabolic responses of the rabbit to acute bouts of exercise. We found that female New Zealand white rabbits had the capacity to run continuously on the treadmill for up to 21 min at 20 m/min until exhausted. Continuous, endurance-type exercise resulted in significant elevations in body temperature, heart rate, and plasma lactate levels. Plasma triglyceride concentration decreased as a function of this type of running whereas plasma glucose levels were unchanged. Twenty-four hours after a bout of running, plasma creatine phosphokinase activity was significantly elevated. The rabbits also had the capacity to learn to run using an intermittent, higher speed protocol. These physically untrained animals could achieve speeds of up to 70 m/min for 10 bouts of 15 s run/30 s rest. Their metabolic and physiological responses to this protocol were similar to those of continuous running with the following exceptions. The decrease in plasma triglyceride was less marked and the increase in plasma lactate was greater after intermittent exercise. Glycogen content of the rabbit vastus lateralis muscle was also significantly depleted after exhaustive, intermittent exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

气候变化下中国主要生物燃油树种分布与变迁

生物燃油树种是发展生物质能源,实现化石能源替代战略的重要物质基础,明确当前和未来气候变化下我国生物燃油树种适生区分布,对保护和利用生物燃油树种,促进林业生物能源产业发展,保障能源安全和实现“双碳”目标具有重要意义。基于我国10个主要生物燃油树种的1037条树种分布数据和20个环境变量,利用最大熵模型(MaxEnt)预测了各树种当前和未来气候情景下(2050年和2070年的RCP4.5情景)的潜在适生区,得到了影响各树种分布贡献率最大的环境因子,并对我国各区域主要种植树种进行了区划。结果表明：(1)MaxEent模型预测效果较好,各树种模拟结果AUC值均在0.9以上。(2)影响各种分布的贡献率较高的环境因子因树种而异,最暖季度降水量和温度季节性变化标准差的相对贡献率较高。(3)10个生物燃油树种极高适生区面积范围在43.38万km²—117.74万km²之间,可根据模拟结果将树种分布划分为北部、中东部、东南部和西南部4个亚区,北部亚区主要树种为文冠果(Xanthoceras sorbifolium)和欧李(Cerasus humilis),中东...     

乳酸菌胆盐水解酶和共轭脂肪酸产生及对宿主脂代谢影响的研究进展

乳酸菌是一类影响宿主脂代谢的人体肠道益生菌。乳酸菌对脂代谢的影响作用与其产生胆盐水解酶(bile salt hydrolase,EC3.5.1.24,BSH)及共轭转化多不饱和脂肪酸(polyunsaturated fatty acids,PUFAs)关系密切。菌株差异、菌群分布和饮食差异是影响BSH及共轭脂肪酸产生的重要因素。本文重点阐述了两类物质对宿主脂代谢的影响机制,以期为后续研究提供借鉴。BSH能够降解肝脏分泌的胆汁酸(bile acids,BAs),降低脂类物质的吸收。BAs的降解产物胆汁酸脱氧胆酸(deoxycholic acid,DCA)和石胆酸(lithocholic acid,LCA)能够通过机体信号通路法尼类X受体(farnesoid X receptor,FXR)、小异二聚体伴侣(small heterodimer partner,SHP)及肝脏X受体(liver X receptor,LXR)等信号通路进行调控,促进胆固醇转运及向BAs转化。此外,BSH还能够通过下调固醇调节元件结合蛋白1c (sterol regulatory element binding protein 1c,SREBP-1c)、上调5ʹ-腺苷单磷酸激活蛋白激酶α(5ʹ-AMP activated protein kinase,AMPKα)和过氧化物酶体增殖物激活受体α (peroxisome proliferator-activated receptor α,PPARα)抑制脂质合成,促进脂质的分解。PUFAs可被乳酸菌转化产生共轭脂肪酸,如共轭亚油酸(conjugated linoleic acid,CLA)和共轭亚麻酸(conjugated linolenic acid,CLNA),CLA/CLNA能够促进机体产生瘦素(leptin,LP),抑制食欲、促进能量消耗;CLA/CLNA还可以通过激活PPARα进行调控,促进人体脂质的氧化分解。乳酸菌通过以上多种途径共同作用调节宿主的脂代谢,对深入理解乳酸菌调控脂代谢机制及临床应用有着重要意义。     

贝莱斯芽孢杆菌RJW-5-5的分离鉴定及细菌素、抗菌肽基因簇挖掘

[背景]化学防治污染日益严重,作物抗性、农药残留、病害再生现象越来越普遍,因此筛选新型生防菌株及研究其抗菌物质已成为热点.[目的]筛选出一株对禾旋孢腔菌等植物病原菌具有生防功能的贝莱斯芽孢杆菌,挖掘其调控合成细菌素、抗菌肽(RiPPs)的基因簇.[方法]通过分离筛选、对峙培养等方法筛选出菌株,通过全细胞脂肪酸和Biol...