A silicon transporter in rice

Silicon is beneficial to plant growth and helps plants to overcome abiotic and biotic stresses by preventing lodging (falling over) and increasing resistance to pests and diseases, as well as other stresses. Silicon is essential for high and sustainable production of rice, but the molecular mechanism responsible for the uptake of silicon is unknown. Here we describe the Low silicon rice 1 (Lsi1) gene, which controls silicon accumulation in rice, a typical silicon-accumulating plant. This gene belongs to the aquaporin family and is constitutively expressed in the roots. Lsi1 is localized on the plasma membrane of the distal side of both exodermis and endodermis cells, where casparian strips are located. Suppression of Lsi1 expression resulted in reduced silicon uptake. Furthermore, expression of Lsi1 in Xenopus oocytes showed transport activity for silicon only. The identification of a silicon transporter provides both an insight into the silicon uptake system in plants, and a new strategy for producing crops with high resistance to multiple stresses by genetic modification of the root's silicon uptake capacity.     

Positional cloning of zebrafish ferroportin1 identifies a conserved vertebrate iron exporter

Defects in iron absorption and utilization lead to iron deficiency and overload disorders. Adult mammals absorb iron through the duodenum, whereas embryos obtain iron through placental transport. Iron uptake from the intestinal lumen through the apical surface of polarized duodenal enterocytes is mediated by the divalent metal transporter, DMTi. A second transporter has been postulated to export iron across the basolateral surface to the circulation. Here we have used positional cloning to identify the gene responsible for the hypochromic anaemia of the zebrafish mutant weissherbst. The gene, ferroportin1, encodes a multiple-transmembrane domain protein, expressed in the yolk sac, that is a candidate for the elusive iron exporter. Zebrafish ferroportin1 is required for the transport of iron from maternally derived yolk stores to the circulation and functions as an iron exporter when expressed in Xenopus oocytes. Human Ferroportin1 is found at the basal surface of placental syncytiotrophoblasts, suggesting that it also transports iron from mother to embryo. Mammalian Ferroportin1 is expressed at the basolateral surface of duodenal enterocytes and could export cellular iron into the circulation. We propose that Ferroportin1 function may be perturbed in mammalian disorders of iron deficiency or overload.     

Sodium-dependent uptake of inorganic phosphate by the intracellular malaria parasite

As the malaria parasite, Plasmodium falciparum, grows within its host erythrocyte it induces an increase in the permeability of the erythrocyte membrane to a range of low-molecular-mass solutes, including Na+ and K+ (ref. 1). This results in a progressive increase in the concentration of Na+ in the erythrocyte cytosol. The parasite cytosol has a relatively low Na+ concentration and there is therefore a large inward Na+ gradient across the parasite plasma membrane. Here we show that the parasite exploits the Na+ electrochemical gradient to energize the uptake of inorganic phosphate (P(i)), an essential nutrient. P(i) was taken up into the intracellular parasite by a Na+-dependent transporter, with a stoichiometry of 2Na+:1P(i) and with an apparent preference for the monovalent over the divalent form of P(i). A P(i) transporter (PfPiT) belonging to the PiT family was cloned from the parasite and localized to the parasite surface. Expression of PfPiT in Xenopus oocytes resulted in Na+-dependent P(i) uptake with characteristics similar to those observed for P(i) uptake in the parasite. This study provides new insight into the significance of the malaria-parasite-induced alteration of the ionic composition of its host cell.     

唐山市水稻田土壤施硅肥对作物产量的影响

唐山市各县区长期种植水稻 ,逐渐表现出缺硅现象 :群体植株高度下降 ,茎叶变软 ,叶片披垂 ,易感病 ,籽粒空秕率高 ,导致产量降低。水稻田灌溉水有效硅含量 :沿海地区平均 1 2 92mg/kg ;内陆地区平均 2 37mg/kg。水稻田土壤有效硅含量 :沿海地区平均 74 57mg/kg ;内陆地区平均 59 63mg/kg。水稻田施用硅肥的最佳施肥量 :沿海地区施有效硅 1 2 1 5kg/hm2 ;内陆地区底施有效硅 1 61 6kg/hm2 。水稻田施硅增产的因子有 4个方面 :1、促进根系发育 ,增加白根数量 ,减少红、黑根数量 ,提高根系的吸收能力 ;2、提高植株有效分蘖和成穗率 ,减少养分消耗 ;3、增加植株高度 ,使茎叶健壮 ,提高抗病性 ;4、从产量结构分析 ,穗数、穗粒数、千粒重均增加 ,从而增高单位面积产量     

Essential role for collectrin in renal amino acid transport

Angiotensin -converting enzyme 2 (ACE2) is a regulator of the renin angiotensin system involved in acute lung failure, cardiovascular functions and severe acute respiratory syndrome (SARS) infections in mammals. A gene encoding a homologue to ACE2, termed collectrin (Tmem27), has been identified in immediate proximity to the ace2 locus. The in vivo function of collectrin was unclear. Here we report that targeted disruption of collectrin in mice results in a severe defect in renal amino acid uptake owing to downregulation of apical amino acid transporters in the kidney. Collectrin associates with multiple apical transporters and defines a novel group of renal amino acid transporters. Expression of collectrin in Xenopus oocytes and Madin-Darby canine kidney (MDCK) cells enhances amino acid transport by the transporter B(0)AT1. These data identify collectrin as a key regulator of renal amino acid uptake.     

Second messenger role for Mg2+ revealed by human T-cell immunodeficiency

The magnesium ion, Mg(2+), is essential for all life as a cofactor for ATP, polyphosphates such as DNA and RNA, and metabolic enzymes, but whether it plays a part in intracellular signalling (as Ca(2+) does) is unknown. Here we identify mutations in the magnesium transporter gene, MAGT1, in a novel X-linked human immunodeficiency characterized by CD4 lymphopenia, severe chronic viral infections, and defective T-lymphocyte activation. We demonstrate that a rapid transient Mg(2+) influx is induced by antigen receptor stimulation in normal T cells and by growth factor stimulation in non-lymphoid cells. MAGT1 deficiency abrogates the Mg(2+) influx, leading to impaired responses to antigen receptor engagement, including defective activation of phospholipase Cγ1 and a markedly impaired Ca(2+) influx in T cells but not B cells. These observations reveal a role for Mg(2+) as an intracellular second messenger coupling cell-surface receptor activation to intracellular effectors and identify MAGT1 as a possible target for novel therapeutics.     

Expression cloning of a cocaine- and antidepressant-sensitive human noradrenaline transporter

At most synapses, chemical signalling is terminated by a rapid reaccumulation of neurotransmitter into presynaptic terminals. Uptake systems for the biogenic amines are the initial site of action for therapeutic antidepressants and drugs such as cocaine and the amphetamines. We have isolated a complementary DNA clone encoding a human noradrenaline transporter. The cDNA sequence predicts a protein of 617 amino acids, with 12-13 highly hydrophobic regions compatible with membrane-spanning domains. Expression of the cDNA clone in transfected HeLa cells indicates that noradrenaline transport activity is sodium-dependent and sensitive to selective noradrenaline transport inhibitors. Transporter RNA is localized to the brainstem and the adrenal gland. The predicted protein sequence demonstrates significant amino-acid identity with the Na+/gamma-aminobutyric acid transporter, thus identifying a new gene family for neurotransmitter transporter proteins. Analysis of its structure and function may lead to structure-based drug design for the treatment of human depression and could help determine whether transporter abnormalities underlie affective disorders.     

水稻高亲和力磷酸盐转运蛋白基因的克隆、表达及检测

以水稻（粳稻）cDNA为模板,设计一对特异性引物,获得编码水稻高亲和力磷酸盐转运蛋白基因的全序列,ORF区编码含535个氨基酸的蛋白,具有磷酸盐转运蛋白保守的蛋白激酶C作用位点、N端糖基化位点与酪蛋白激酶Ⅱ作用位点Southern blot分析显示此基因在水稻基因组中具有多个拷贝,与水稻基因组序列分析结果一致Westernblot预测目的基因表达的蛋白大小约为57．7ku．该基因的真核表达研究正在进行中．     

建立一个基于报告基因的靶标筛药系统筛选上调ABCA1基因转录的中药提取物

ATP结合盒转运蛋白A1(ABCA1)具有催化外周细胞过量胆固醇和磷脂外向流出的功能。本实验将ABCA1启动子序列克隆到含有荧光素酶报告基因和新霉素抗性基因的pGL3B-neo载体中,并将得到的重组质粒pGL3B-neo/ABCA1转染入人肝癌细胞(hepG2)。通过稀释培养法最终得到含有重组质粒的稳定细胞系SABCA1。利用这个报告基因为基础的药物筛选系统,筛选了100多种中药提取物。通过荧光素酶活性测试,相对活性达到180%以上的有4种中药提取物,并最终挑选能明显激活ABCA1基因启动子的鬼箭羽水提组分进一步研究,得出半数有效浓度(EC50)为48.06 mg/L。此外,利用基于apoA1基因的药物筛选系统验证得出鬼箭羽水提组分也能促进apoA1基因的表达。     

AtSNX1 defines an endosome for auxin-carrier trafficking in Arabidopsis

Polarized cellular distribution of the phytohormone auxin and its carriers is essential for normal plant growth and development. Polar auxin transport is maintained by a network of auxin influx (AUX) and efflux (PIN) carriers. Both auxin transport and PIN protein cycling between the plasma membrane and endosomes require the activity of the endosomal GNOM; however, intracellular routes taken by these carriers remain largely unknown. Here we show that Arabidopsis thaliana SORTING NEXIN 1 (AtSNX1) is involved in the auxin pathway and that PIN2, but not PIN1 or AUX1, is transported through AtSNX1-containing endosomes. We demonstrate that the snx1-null mutant exhibits multiple auxin-related defects and that loss of function of AtSNX1 severely enhances the phenotype of a weak gnom mutant. In root cells, we further show that AtSNX1 localizes to an endosomal compartment distinct from GNOM-containing endosomes, and that PIN2 accumulates in this compartment after treatment with the phosphatidylinositol-3-OH kinase inhibitor wortmannin or after a gravity stimulus. Our data reveal the existence of a novel endosomal compartment involved in PIN2 endocytic sorting and plant development.     

一个烟草Mlo基因的电子克隆及其序列特性分析

电子克隆并探讨了一个烟草Mlo基因的结构和功能．以GenBank公布的水稻Mlo基因序列为信息探针对烟草的EST数据库进行同源搜索,并将获得的同源性高的EST序列进行序列拼接,最后得到了一个烟草Mlo基因的cDNA序列．采用生物信息学方法分析该基因编码蛋白的一级、二级结构,并对其功能进行预测．结果表明,此烟草Mlo基因...     

生长素调控极性运输载体PIN2质膜丰度与降解

主要观察了外源生长素长时间(8 h)处理对拟南芥生长素极性输出载体PIN2-GFP质膜丰度的影响,低温、KCN处理和生长素受体突变对生长素调控质膜PIN2-GFP丰度的影响,以及液泡H+-ATPase抑制剂ConA对野生型和生长素受体四突变体tir1afb1,2,3液泡中PIN2-GFP积累的影响.结果表明:外源生长素通过其受体TIR1/AFB介导的信号途径下调质膜PIN2-GFP的丰度,促进PIN2-GFP的内吞、胞内运输和液泡降解.暗示生长素通过TIR1/AFB介导的信号途径反馈调控质膜PIN2-GFP的水平,从而阻止了胞内生长素的过多输出.     

施用氮硅肥对巨型稻生长、养分利用和产量的影响

该文采用田间随机区组设计,以巨型稻“丰超6号”为供试材料,以磷钾肥为基肥,设置氮肥或硅肥使用组合的4种处理:不施氮肥和硅肥(CK)、施氮肥(N)、施氮肥配施低量硅肥(NSi₁)和施氮肥配施高量硅肥(NSi₂).研究结果表明:相对于CK处理,施用氮肥和硅肥使水稻地上部和根系生物量分别增加了55.6%和67.0%,使水稻根冠比分别增加了30.8%和46.2%.与CK处理相比,施用氮肥和硅肥使巨型稻分蘖数分别增加了23.9%和45.0%; 与单施氮肥相比,氮、硅肥配施使分蘖数进一步增加了17.1%,施用氮肥和硅肥使巨型稻SPAD值(叶绿素相对含量)分别增加了9.7%和19.8%.氮、硅肥配施使土壤碱解氮和有效硅含量分别增加了19.2%～31.5%和9.2%～28.5%.NSi₂处理较NSi₁处理的氮肥利用率提高了16.5%.与单施氮肥相比,NSi₁处理使巨型稻产量提高了11.7%,而NSi₂处理使巨型稻产量显著增加26.1%.在巨型稻种植过程中以氮肥配施高量硅肥(NSi₂)处理效果最好.     

Glucose/galactose malabsorption caused by a defect in the Na+/glucose cotransporter

Glucose/galactose malabsorption (GGM) is an autosomal recessive disease manifesting within the first weeks of life and characterized by a selective failure to absorb dietary glucose and galactose from the intestine. The consequent severe diarrhoea and dehydration are usually fatal unless these sugars are eliminated from the diet. Intestinal biopsies of GGM patients have revealed a specific defect in Na(+)-dependent absorption of glucose in the brush border. Normal glucose absorption is mediated by the Na+/glucose cotransporter in the brush border membrane of the intestinal epithelium. Cellular influx is driven by the transmembrane Na+ electrochemical potential gradient; thereafter the sugar moves to the blood across the basolateral membrane via the facilitated glucose carrier. We have previously cloned and sequenced a Na+/glucose cotransporter from normal human ileum and shown that this gene, SGLT1, resides on the distal q arm of chromosome 22. We have now amplified SGLT1 complementary DNA and genomic DNA from members of a family affected with GGM by the polymerase chain reaction. Sequence analysis of the amplified products has revealed a single missense mutation in SGLT1 which cosegregates with the GGM phenotype and results in a complete loss of Na(+)-dependent glucose transport in Xenopus oocytes injected with this complementary RNA.     

Molecular cloning and characterization of an insulin-regulatable glucose transporter

A major mechanism by which insulin stimulates glucose transport in muscle and fat is the translocation of glucose transporters from an intracellular membrane pool to the cell surface. The existence of a distinct insulin-regulatable glucose transporter was suggested by the poor cross-reactivity between antibodies specific for either the HepG2 or rat brain glucose transporters and the rat adipocyte glucose transporter. More direct evidence was provided by the production of a monoclonal antibody (mAb 1F8) specific for the rat adipocyte glucose transporter that immunolabels a species of relative molecular mass 43,000 (43K) present only in tissues that exhibit insulin-dependent glucose transport, suggesting that this protein may be encoded by a different gene from the previously described mammalian glucose transporters. This antibody has been used to immunoprecipitate a 43K protein that was photoaffinity-labelled with cytochalasin B in a glucose displaceable way, and to immunolabel a protein in the plasma membrane of rat adipocytes, whose concentration was increased at least fivefold after cellular insulin exposure. Here we describe the cloning and sequencing of cDNAs isolated from both rat adipocyte and heart libraries that encode a protein recognized by mAb 1F8, and which has 65% sequence identity to the human HepG2 glucose transporter. This cDNA hybridizes to an mRNA present only in skeletal muscle, heart and adipose tissue. Our data indicate that this cDNA encodes a membrane protein with the characteristics of the translocatable glucose transporter expressed in insulin-responsive tissues.     

Diurnal and monthly variations of carbon dioxide flux in an alpine shrub on the Qinghai-Tibet Plateau

Long-term flux observation is an efficient approachto collect CO2 emission or assimilation data in an ecosys-tem. In cooperation with a series of international coopera-tion programs including those sponsored by IGBP (Inter-national Geosphere-Biosphere Program), WCRP (WorldClimate Research Program), IHDP (International HumanDimension of Global Environment Change), GCTE(Global Change and Terrestrial Ecosystem) and LUCC(Land Use and Land Cover Change), a lot of researchwork conce…