Genetic and fossil evidence for the origin of modern humans

The origin of living Homo sapiens has once again been the subject of much debate. Genetic data on present human population relationships and data from the Pleistocene fossil hominid record are used to compare two contrasting models for the origin of modern humans. Both genetics and paleontology support a recent African origin for modern humans rather than a long period of multiregional evolution accompanied by gene flow.     

African origin of modern humans in East Asia: a tale of 12,000 Y chromosomes

To test the hypotheses of modern human origin in East Asia, we sampled 12,127 male individuals from 163 populations and typed for three Y chromosome biallelic markers (YAP, M89, and M130). All the individuals carried a mutation at one of the three sites. These three mutations (YAP+, M89T, and M130T) coalesce to another mutation (M168T), which originated in Africa about 35,000 to 89,000 years ago. Therefore, the data do not support even a minimal in situ hominid contribution in the origin of anatomically modern humans in East Asia.     

光和硝酸盐对番茄硝酸还原酶转录和酶活的调控

氮素代谢在植物生长过程中起着非常关键的作用,它是植株体内最基本的物质代谢之一,是植物正常生长发育的物质基础[1]。一般认为,硝酸还原酶(NR,EC l.6.1.1-3)是植物氮代谢过程中的关键酶,也是限速酶[2~4],其活性高低对整个氮代谢的强弱起关键的调控作用[5]。硝酸还原酶水平上的     

复合氨基酸对叶萝卜硝态氮吸收和同化的影响

以叶萝卜为试材,采用水培法研究了外源复合氨基酸(由等浓度的丙氨酸、β-丙氨酸、天冬氨酸、天冬酰氨酸、谷氨酸、谷氨酰胺和甘氨酸组成)处理对叶萝卜NO3-吸收和同化过程的影响。研究结果表明,浓度为0.3 mmol/L的复合氨基酸处理对NO3-的吸收比对照低38%,浓度为3.0 mmol/L的复合氨基酸处理对NO3-的吸收比对照高305%,并且与NO3-同化相关的硝酸还原酶、亚硝酸还原酶和谷氨酰胺合成酶的活性都相应增加,氨基酸处理后NO3-成分也有所增加。说明高浓度的复合氨基酸处理能促进植物对NO3-的吸收和同化。     

Changes of Nitrate Reductase Activity in Cucumber Seedlings in Response to Nitrate Stress

In China, nitrogen fertilizer application rates in intensive agricultural systems have increased dramatically in recent years, especially in protected vegetable production systems. This excessive use of nitrogen fertilizer has resulted in soil secondary salinization, which has become a significant environmental stress for crops such as cucumber, in the protected farmland of China. So it is necessary to illuminate how crops respond to nitrate stress. The objective of this work was to examine the effects of increased nitrate concentration [14 （CK） and 140 mmol L^-1 （T）] on NO3- concentration, and in vitro and in vivo nitrate reductase activities in the roots and leaves of cucumber （Cucumis sativus L. cv. Xintaimici） seedlings with hydroponic culture. The results showed that the NO3- concentration in the roots and leaves of T seedlings significantly increased over treatment course, and at 12 d increased by 1.08 and 1.72 times with respect to CK seedlings, respectively; in vitro nitrate reductase activity of T was increased dramatically to 1.74 times of CK in the roots at 2 d and 1.56 times of CK in the leaves at 6 d, and then decreased. At 12 d, in vitro activity was still 24.3% higher in the roots and only 9.9% lower in the leaves than CK. Compared with in vitro nitrate reductase activity, in vivo activity responded differently to the increase of treatment time. At the beginning, in vivo nitrate reductase activity in the roots and leaves of T had no significant difference from CK, whereas with the increase of treatment duration, the activity decreased. At 12 d, in vivo activity in the roots and leaves of T lowered by 20.1 and 52.8% with respect to CK, respectively. This evidence suggests that posttranslational activation of nitrate reductase in cucumber seedlings may be seriously inhibited by nitrate stress.     

双氰胺对设施菜地土壤硝酸盐淋溶和苦苣硝酸盐累积的影响

在设施菜地条件下,研究了添加不同浓度双氰胺(DCD)对土壤和苦苣硝酸盐含昔及苦苣产量的影响.结果表明,添加2%和5%双氰胺可有效降低苦苣生长初期表层土壤硝酸盐含量,推迟硝酸盐含量高峰出现15 d左右,减少硝酸盐的深层淋溶,显著降低苦苣体内硝酸盐和业硝酸盐含量,提高苦苣产昔.添加10%双氰胺使土壤硝酸盐含量始终保持较低水平,对防止硝酸盐深层淋溶和降低苦苣硝酸盐和亚硝酸盐含量效果显著,对苦苣产量影响较小.     

土壤硝酸盐试纸条 反射仪测定法存在问题及其解决方案

针对浸提方法影响硝酸盐试纸条-反射仪法结果的问题,选择陕西关中的土娄土和渭南的黑垆土为供试材料,通过室内对比试验,对土壤硝酸盐浸提剂、振荡与沉淀时间及水土质量比等因素进行优化。结果表明,浸提剂类型、振荡与静置时间均对试纸条-反射仪法的土壤硝酸盐测试结果产生较大影响,而水土质量比对测定结果无显著影响,最终确定利用饱和硫酸钙作为浸提剂、振荡10 min、静置5 min为最佳前处理方法,在此条件下,硝酸盐试纸条-反射仪法测试结果准确,测试效率高。     

蔬菜硝酸盐污染及其防治途径的探讨

蔬菜是一种容易富集硝酸盐的作物,人体摄入的硝酸盐81.2%来自蔬菜, 而硝酸盐是强致癌物--亚硝胺的前体.为了获得高产,过量施用氮肥,导致硝酸盐积累、蔬菜品质下降.介绍了硝酸盐的国际国内的食用标准,硝酸盐在植物体内的同化以及积累机制;并探讨了蔬菜受硝酸盐污染的影响因素及控制对策.     

地下水硝酸盐污染的控制对策及去除技术

对地下水中硝酸盐的危害、来源进行了阐述,并就此提出了相应的修复和去除技术,比较了各种方法的优缺点,尤其是对今后的发展方向进行了探讨。     

甘蓝过量表达硝酸还原酶基因对硝酸盐积累的影响

为探索过量表达硝酸还原酶基因对甘蓝(Brassica oleracea L.var.capitata L.)硝酸盐积累的影响,以‘中甘11号’下胚轴为外植体,采用根癌农杆菌(Agrobacterium tumefaciens)介导法将烟草硝酸还原酶基因(NR)导入甘蓝,获得13株卡那霉素抗性植株。PCR和Southern blot检测证实,NR基因已经成功导入并整合到甘蓝的基因组。4个转基因株系硝酸盐质量分数明显低于非转基因供体株系,降幅为13.9%~23.0%。说明:将重组硝酸还原酶基因导入甘蓝且得到超量表达,创制低硝酸盐育种材料的方法可行。     

蔬菜中硝酸盐含量积累问题及其调控

不合理的施肥和环境因素等都可引起硝酸盐在蔬菜中的过量富集,从而影响蔬菜的品质,影响消费者的身体健康.综述了近年来国内外有关蔬菜中硝酸盐含量的影响因素及其调控措施的研究进展.     

植物对硝态氮的吸收及其调控

硝态氮不仅是重要的营养元素，而且作为信号物质调节植物的生长发育，土壤中硝态氮的含量变化很大，为适应不同环境，植物进化出多种获得氮素的途径，因此了解植物适应氮营养胁迫的生理遗传特性在理论和实践上都具有重要的意义，本文就近年关于植物对硝态氮吸收和调控的工作进行了综述。     

肉制品中亚硝酸盐含量超标原因分析

测定了潮州市面销售的8种品牌火腿的亚硝酸盐含量,结果显示,所测8份样品中有4份超标,抽检合格率为50%,其中亚硝酸盐残留量最高达29.77 mg/kg,超过国家标准(GB)规定1.49倍;超标检样主要集中在小型肉制品加工厂和个体食品加工者,提示消费者在选购火腿等肉制品时应注意品牌和生产厂家。     

反射仪-硝酸根试纸法现场速测蔬菜硝酸盐水平及其应用

通过结球甘蓝、白菜和黄瓜的田间试验,研究了用反射仪-硝酸根试纸法田间现场速测黄瓜、白菜和结球甘蓝叶柄汁液硝酸根含量与土壤硝酸根含量、施氮量、蔬菜食部硝酸盐含量和产量的关系。结果表明,结球甘蓝心叶外第3展开叶叶柄中段、白菜心叶外第2展开叶叶柄中段、黄瓜心叶下第3叶叶柄中段、叶柄汁液硝酸盐浓度与施氮量和产量都有极显著和显著相关性,灵敏地反映了蔬菜及其土壤的硝酸盐水平。用于3种蔬菜氮素营养诊断推荐追肥,氮肥用量比常规高产施氮量减少40.7%￣66.4%,从而最大限度地控制过量化肥对蔬菜和环境的污染。结球甘蓝播种后40d心叶外第1、2和3展开叶叶柄汁液硝酸盐浓度与土壤硝酸根含量极显著和显著线性相关。反射仪-硝酸根试纸法现场测定外叶叶柄汁液硝酸盐含量与按GB/T15401-94的方法实验室测定可食部分硝酸根含量极显著线性相关。反射仪-硝酸根试纸法快捷简便,是蔬菜氮素营养诊断和蔬菜硝酸盐含量监测的理想的现场速测技术。     

蔬菜硝酸盐污染及其防治

详细介绍了蔬菜硝酸盐、亚硝酸盐的国际公认的食用卫生标准;分析了当前不同地区各类蔬菜被硝酸盐污染的状况以及影响因素,并从选育硝酸盐含量低的品种、科学施肥、选择适宜采收期、做好食前处理等途径来控制蔬菜硝酸盐污染。