盐胁迫下野大麦耐盐生理机制初探

以盐生植物野大麦、甜土植物中国春小麦为材料,研究了NaCl胁迫对野大麦、小麦幼苗叶片质膜透性、含水量、地上和根部离子含量、脯氨酸含量、磷酸烯醇式丙酮酸羧化酶(PEPCase)活性的影响。结果表明,随盐胁迫浓度增加,野大麦的细胞膜透性、Na 含量、脯氨酸含量、Na /K 、PEPCase活性增加,含水量、K 含量下降;但在相同盐胁迫条件下野大麦地上部和根部Na 含量明显低于小麦,而根中K 含量高于小麦,表明野大麦可能具有拒绝吸收Na 和维持高K 含量的能力;野大麦的脯氨酸含量增加幅度小于小麦,表明在盐胁迫下野大麦不是通过脯氨酸的积累来达到体内渗透平衡的;野大麦PEPCase活性增加明显高于小麦,说明提高光合效率可能是野大麦实现盐适应的主要措施之一。     

低温和NaCl对玉米叶片离体PEPCase活性及其调节特性的影响

对玉米叶片磷酸烯醇丙酮酸羧化酶(PEPCase)的低温失活现象的研究结果表明,低温贮存期间,玉米叶片离体PEPCase活性随贮存时间的延长而明显降低.对效应剂G6p、Gly和2.4—D的敏感性也减弱.甘油对低温贮存期间酶的活性和对2.4—D的敏感性均有保护效应;G6p单独存在时对酶的活性和2.4—D的敏感性均无保护效应,但同一浓度的G6p在与Gly和甘油同时作用时对酶的活性和2.4—D的敏感性均有保护效应,其保护程度优于同浓度的甘油.NaCl对PEP-Case活性有抑制作用.对酶对效应剂的敏感性影响较小.对低温贮存期间酶的活性和对效应剂的敏感性均无保护效应,并能加速酶的低温失活和对效应剂敏感性的减弱.上述试剂对低温贮存期间酶对效应剂敏感性的保护程度与对其活性的保护程度相一致,表明低温贮存期间酶对效应剂敏感性减弱与其低温失活有直接关系.     

翘嘴红鲌PEPCK基因的克隆和序列分析

采用RT-PCR和RACE（Rapid Amplification of cDNA Ends）法,分离和克隆翘嘴红鲌（Erythroculter ilishaeformis）磷酸烯醇式丙酮酸羧激酶（PEPCK）基因的全序列,得到2 564bp[不含poly（A）]的全长cDNA,包括111bp5′非翻译区,1 911 bp阅读框以及含Poly（A）信号AATAAA的542 bp3＇非翻译区[不包括Poly（A）].阅读框共编码636个氨基酸,计算的分子量为69.65 kD.该序列含有PEPCK特有的结合草酰乙酯的结构域以及与GTP三磷酸链和Mg^2＋结合的激酶1和2基序.与其他鱼PEPCK的相似性高达83%～96%,和爪蟾、变形虫等其他动物的相似性为50%～69%.[中国水产科学,2006,13（3）：389 396]     

荧光抗体在热带作物小粒种咖啡的C_3/C_4属性鉴别中的应用

用从烟草提纯的 1,5-二磷酸核酮糖 ( Ru BP)羧化酶制备兔抗 Ru BP羧化酶抗体 ,并以异硫氰酸盐荧光素 ( FITC)标记抗体 .采用直接免疫荧光法对典型 C3植物水稻、C4 植物甘蔗和小粒种咖啡等进行了 Ru BP羧化酶的组织化学定位 .结果表明 :C3和 C4 植物叶切片中 Ru BP羧化酶的分布明显不同 ,C3植物的特异荧光位于叶肉细胞 ,C4 植物的特异荧光绝大部分位于维管束鞘细胞 ;小粒种咖啡的特异荧光仅分布在叶肉细胞 .因此认为 ,小粒种咖啡应属 C3植物     

Methionine sulfoximine suppressed the stimulation of dark carbon fixation by ammonium nutrition in wheat roots

To evaluate the role of NH₄ ⁺ assimilates in dark carbon fixation in roots in providing carbon skeletons expended for NH₄ ⁺ assimilation, the rate of dark carbon fixation in roots was measured using NaH¹⁴CO₃. The ¹⁴C-metabolites were analyzed in wheat (Triticum aestivum L.) plants grown in NH₄ ⁺ media for various periods of time with or without methionine sulfoximine (MSX) treatment. The dark carbon fixation rate in the roots of wheat plants that had been grown with NH₄ ⁺ for 1 d was approximately 6-fold higher than the rate in control roots. The stimulation of dark carbon fixation in NH₄ ⁺-grown plants, however, was not observed in MSX-treated roots. In the roots of NH₄ ⁺-grown plants, the concentration and ¹⁴C-Iabeling of acidic metabolites such as citrate and malate considerably decreased whereas those of basic metabolites, especially asparagine, increased noticeably. With MSX treatment, the incorporation of ¹⁴C into basic metabolites was negligible. In response to NH₄ ⁺, phosphoenolpyruvate carboxylase (PEPC) activity increased, and PEPC proteins accumulated in wheat roots. Neither activity nor amounts of PEPC in roots increased in the presence of MSX. These findings suggest that primary assimilation of NH₄ ⁺ in roots is essential for the stimulation of dark carbon fixation, which coincides with the increased activity of root PEPC, to sufficiently replenish carbon skeletons necessary for NH₄ ⁺ assimilation.     

Dietary biotin requirement determined for Indian catfish, Heteropneustes fossilis (Bloch), fingerlings

Triplicate groups of Indian catfish, Heteropneustes fossilis (Bloch), fingerlings (average wet weight 3.55 ± 0.03 g) were fed semi-purified diets containing six levels of biotin (0, 0.086, 0.26, 0.86, 2.5 and 4.3 mg kg⁻¹ diet) for 15 weeks. After 42 days of feeding, fish fed the control (no biotin) diet had developed severe deficiency signs characterized by convulsions, heavy mortality, listlessness, poor feed conversion and feed intake, dark skin colour, tetanus and weight loss. None of these signs was seen in fish fed biotin-supplemented diets. Among all the biotin-supplemented diets, percentage weight gain was significantly highest for fish fed the diet supplemented with 0.26 mg of biotin kg⁻¹ and significantly lowest for fish fed the diet supplemented with 0.086 mg of biotin kg⁻¹. Feed conversion ratio (FCR) and protein efficiency ratio (PER) patterns were similar to that of percentage weight gain. The carcass protein and lipid contents were influenced by the dietary biotin up to fish fed 0.26 mg of biotin kg⁻¹. Significantly higher body biotin content, liver pyruvate carboxylase and acetyl CoA carboxylase activities were observed in fish fed biotin-supplemented diets than in fish fed the control diet. Broken-line analyses showed that the optimum dietary requirement for biotin for maximal weight gain, body biotin content, liver pyruvate carboxylase and acetyl CoA carboxylase activities was about 0.25 mg kg⁻¹. Associated liver pyruvate carboxylase and acetyl CoA carboxylase activities for normal growth ranged from 105 to 120 units mg⁻¹ protein and from 9 to 11 units mg⁻¹ protein respectively.     

关于甜菜光合特性的研究

本试验探讨了不同类型甜菜品种在不同生育时期的光合特性，结果表明：在甜菜生育前期，高糖型品种的ＲｕＢＰ羧化酶活性较高，到生育中、后期丰产型品种的ＲｕＢＰ发化酶活性则表现较高的趋势；叶绿素含量亦呈这一趋势；在甜菜繁茂期丰产型品种的光合速率最高，糖分积累期高糖型品种光合速率高于其它处理；不同类型品种的光合速率每天中午均有降低现象，高糖型品种生育前期“午休”现象弱于其它类型品种。     

Distribution characteristics and diversities of cbb and coxL genes in paddy soil profiles from southern China

The Calvin-Benson-Bassham cycle and Wood-Ljungdahl pathway are two well-known ones in the six carbon sequestration pathways, but the current knowledge of their occurrence in different layers of agricultural soil profiles is poor. In this study, the diversities of three genes encoding ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), i.e., genes encoding the green-like (cbbLG) and red-like (cbbLR) forms of RubisCO I and encoding RubisCO II (cbbM), and the gene encoding carbon monoxide dehydrogenase large subunit (coxL) from five paddy soils in southern China were investigated by real-time quantitative polymerase chain reaction, restriction fragment length polymorphism (RFLP) analysis, and clone library. The abundances of the four genes ranged from 10⁷ to 10⁹ copies g^-1 soil, and the cbbLR gene outnumbered the other three genes in all soil samples, suggesting important roles they play in carbon dioxide (CO₂) fixation. In addition, it was found that the copy numbers of cbbLR and cbbLG decreased with increasing soil depth, while the copy numbers of cbbM and coxL decreased in the shallow depths but increased with increasing soil depth. The results of RFLP showed a larger Shannon index (H) in the deeper soil layers among the four gene clone libraries, indicating that the community diversity in these soil layers was greater. The cbbLG gene had relatively low diversity (at genus level), and most of the sequences were classified as Sideroxydans and Thiobacillus. In contrast, the highly diverse groups were found in the other three gene clone libraries (cbbLR, cbbM, and coxL), most of which were distantly related to known sequences, even forming separate clusters. In summary, this study provides a new insight into CO₂ fixers along agricultural soil profiles by comparing four bacterial genes.