甲醇对植物的作用及其生理机制

甲醇是植物生长发育和代谢过程中体内产生的最简单的一碳化合物之一,与植物的很多生理过程(如光合作用、C1-四氢叶酸和某些植物激素生物合成以及植物耐逆性等)密切相关。本文对近年来国内外有关植物中甲醇的产生与释放途径、体内代谢、外施甲醇对植物的效应及其生理机制等方面研究进行了综述,并提出存在的问题和今后研究方向。     

The fly factor phenomenon is mediated by interkingdom signaling between bacterial symbionts and their blow fly hosts

We tested the recent hypothesis that the"fly factor"phenomenon(food cur-rently or previously fed on by flies attracts more flies than the same type of food kept inccessible to flies)is mediated by bacterial symbionts deposited with feees or regur-gitated by feeding flies.We allowed laboratory-reared black blow flies,Phormia regina(Meigen),to feed and de fecate on bacterial Luria-Bertani medium solidified with agar,and isolated seven morphologically distinct bacterial colonies.We identified these us-ing matrix-assisted laser desorption/ionization mass spectrometry and sequencing of the 165 rRNA gene.In two-choice laboratory experiments,traps baited with cultures of Pro-teus mirabilis Hauser,Morganella morganii subsp.sibonii Jensen,or Serratia marcescens Bizio,captured significantly more flies than corresponding control jars baited with tryptic soy agar only.A mixture of seven bacterial strains as a trap bait was more attractive to flies than a single bacterial isolate(M.m.siboni).In a field experiment,traps baited with agar cultures of P:mirabilis and M.m siboni in combination captured significantly more flies than lraps baited with either bacterial isolate alone or the agar control.As evident by gas chromatography-mass spectrometry,the odor profiles of bacterial isolates differ,which may explain the additive effect of bacteria to the attractiveness of bacterial trap baits.As"generalist bacteria,"P mirabilis and M.m.sibonii growing on animal protein(beef liver)or plant protein(tofu)are similarly effective in attracting flies.Bacteria-derived airborne semiochemicals appear to mediate foraging by flies and to inform their feeding and oviposition decisions.     

Effects of nitrogen addition on photosynthetic characteristics of Leymus chinensis in the temperate grassland of Nei Mongol,China北大核心CSCD

Aims The increased atmospheric nitrogen (N) deposition due to human activity and climate change greatly causes grassland ecosystems shifting from being naturally N-limited to N-eutrophic or N-saturated, and further affecting the growth of grass species. The aims of this study are: 1) to evaluate the effects of different N addition levels on morphology and photosynthetic characteristics of Leymus chinensis; 2) to determine the critical N level to facilitate L. chinensis growth. Methods We conducted a different N addition levels experiment in dominant species in the temperate steppe of Nei Mongol. The aboveground biomass, morphological and leaf physiological traits, pigment contents, chlorophyll a fluorescence parameters and biochemical parameters of L. chinensis were investigated. Important findings Our results showed that aboveground biomass first increased and then decreased with the increased N, having the highest values at the 10 g N·m-2·a?1 treatment, but the 25 g N·m-2·a?1 still significantly increased the aboveground biomass relative to 0 g N·m-2·a?1. Leymus chinensis accommodate low N situation through allocating less N to carboxylation system and decreasing leaf mass per area (LMA) in order to get more light energy. Moderate N addition captured more light energy through increasing total chlorophyll (Chl) contents and decreasing the ratio of Chl a/b. Moderate N addition increased LMA, carboxylation efficiency, maximum car boxylation rate (Vcmax), maximum electron transport rate (Jmax) and decreased Jmax/Vcmax, thus allocating more N to carboxylation system to enhance carboxylation capability. Moreover, the photochemical activity of PSII was increased through higher effective quantum yield of PSII photochemistry, electron transport rate and photochemical quenching coefficient. Excessive N addition had negative effects on physiological variables of L. chinensis due to lower carboxylation capability and photochemical activity of PSII, further leading to decreased net photosynthetic rate, whereas increased non-photochemical quenching coefficient and carotenoids played the role in the dissipation of excess excitation energy. Overall, moderate N addition facilitated the photosynthetic characteristics of dominant species, but excessive N addition inhibited photosynthetic characteristics. The most appropriate N addition for the growth of L. chinensis was 5-10 g N·m-2·a?1 in the temperate steppe of Nei Mongol, China.     

Mutations at position 7445 in the precursor of mitochondrial tRNA(Ser(UCN)) gene in three maternal Chinese pedigrees with sensorineural hearing loss

We report here the clinical, genetic and molecular characterization of three Chinese pedigrees with nonsyndromic bilateral hearing loss. Clinical and genetic evaluations revealed the variable severity and age-of-onset in hearing impairment in these families. Strikingly, there were extremely low penetrances of hearing impairment in these Chinese families. Sequence analysis of the complete mitochondrial DNA (mtDNA) showed the known A7445C mutation in two pedigrees and the novel A7445T mutation in another pedigree, in addition to distinct sets of mtDNA polymorphisms belong to Asian haplogroups D4j and F4. Indeed, the A7445C or A7445T mutation in the CO1 and the precursor of tRNA(Ser(UCN)) genes was present in homoplasmy only in the maternal lineage of those pedigrees but not other members of these families and 164 Chinese controls. In fact, the A7445C or A7445T mutation results in a read-through of the stop condon AGA of the CO1 message on the H strand of mtDNA, thereby adding three amino acids (Ser-Gln-Lys) to the C-terminal of the polypeptide. However, the mutated polypeptide may retain a partial function. Alternatively, the A7445C or A7445T mutation is adjacent to the site of 3' end endonucleolytic processing of L-strand RNA precursor, spanning tRNA(Ser(UCN)) and ND6 mRNA. Thus, the A7445C or A7445T mutation may also cause a defect in the processing of the L-strand RNA precursor, thus causing mitochondrial dysfunctions. Furthermore, the occurrence of the mutations at position 7445 in these genetically unrelated subjects affected by hearing impairment strongly indicates that mutations at the position 7445 are involved in the pathogenesis of hearing impairment.     

Autophagy inhibition‐enhanced assembly of the NLRP3 inflammasome is associated with cisplatin‐induced acute injury to the liver and kidneys in rats

The nucleotide‐binding oligomerization domain‐like receptor family, pyrin domain containing 3 (NLRP3) inflammasome has a key role in the inflammatory response. We found that cisplatin (7.5, 15 mg/kg, IV) could induce acute injury to the liver and kidneys of rats. Western blot and immunohistochemical analyses showed that expression of NLRP3, caspase‐1 and interleukin‐1β was upregulated significantly in a dose‐dependent manner after cisplatin exposure. Autophagy could inhibit NLRP3 expression and assembly of the NLRP3 inflammasome. Expression of light chain 3 II/I and p62 suggested that autophagy was inhibited during injury to the liver and kidneys. These data suggested that cisplatin might activate NLRP3 by inhibiting autophagy in the liver and kidneys of rats.     

GPI-anchored CEA family glycoproteins CEA and CEACAM6 mediate their biological effects through enhanced integrin alpha5beta1-fibronectin interaction

Carcinoembryonic antigen (CEA) and CEA family member CEACAM6 are glycophosphatidyl inositol (GPI)-anchored, intercellular adhesion molecules that are up-regulated in a wide variety of human cancers, including colon, breast, and lung. When over-expressed in a number of cellular systems, these molecules are capable of inhibiting cellular differentiation and anoikis, as well as disrupting cell polarization and tissue architecture, thus increasing tumorigenicity. The present study shows that perturbation of the major fibronectin receptor, integrin alpha5beta1, underlies some of these biological effects. Using confocal microscopy and specific antibodies, CEA and CEACAM6 were demonstrated to co-cluster with integrin alpha5beta1 on the cell surface. The presence of CEA and CEACAM6 was shown to lead to an increase in the binding of the integrin alpha5beta1 receptor to its ligand fibronectin, without changing its cell surface levels, resulting in increased adhesion of CEA/CEACAM6-expressing cells to fibronectin. More tenacious binding of free fibronectin to cells led to enhanced fibronectin matrix assembly and the formation of a polymerized fibronectin "cocoon" around the cells. Disruption of this process with specific monoclonal antibodies against either fibronectin or integrin alpha5beta1 led to the restoration of cellular differentiation and anoikis in CEA/CEACAM6 producing cells.     

Enzymic properties of recombinant BACE2.

BACE2 (Memapsin 1) is a membrane-bound aspartic protease that is highly homologous with BACE1 (Memapsin 2). While BACE1 processes the amyloid precursor protein (APP) at a key step in generating the beta-amyloid peptide and presumably causes Alzheimer's disease (AD), BACE2 has not been demonstrated to be directly involved in APP processing, and its physiological functions remain to be determined. In vivo, BACE2 is expressed as a precursor protein containing pre-, pro-, protease, transmembrane, and cytosolic domains/peptides. To determine the enzymatic properties of BACE2, two variants of its pro-protease domain, pro-BACE2-T1 (PB2-T1) and pro-BACE2-T2 (PB2-T2), were constructed. They have been expressed in Escherichia coli as inclusion bodies, refolded and purified. These two recombinant proteins have the same N terminus but differ at their C-terminal ends: PB2-T1 ends at Pro466, on the boundary of the postulated transmembrane domain, and PB2-T2 ends at Ser431, close to the homologous ends of other aspartic proteases such as pepsin. While PB2-T1 shares similar substrate specificities with BACE1 and other 'general' aspartic proteases, the specificity of PB2-T2 is more constrained, apparently preferring to cleave at the NH2-terminal side of paired basic residues. Unlike other 'typical' aspartic proteases, which are active only under acidic conditions, the recombinant BACE2, PB2-T1, was active at a broad pH range. In addition, pro-BACE2 can be processed at its in vivo maturation site by BACE1.     

构建定向T载体用于基因克隆和表达

传统的T载体克隆方法需要烦琐的后续步骤来筛选和鉴定重组子,并且无法实现目的基因的定向克隆。为了克服这些问题,本研究在pET-23a(+)的基础上构建了定向T载体pETG,首先通过定点诱变消除pET-23a(+)上的两个BfuⅠ位点得到PET-23aM;设计一对引物在5端各引入一个BfuⅠ位点,下游引物紧邻BfuⅠ位点引入13 bp的部分LacO序列,用该引物从pHBM2002上扩增Prrn-gfp表达盒,插入PET-23aM的NdeⅠ和XhoⅠ位点,得到定向T载体pETG。PCR扩增的目的基因通过下游引物引入7 bp剩余的LacO序列,该基因片段与BfuⅠ酶切制备的定向T载体连接、转化大肠杆菌DH10β感受态细胞,通过补加了X-gal的平板筛选蓝色重组子。质粒酶切和PCR鉴定表明蓝色菌落全部为定向插入的重组子,重组效率100%,利用本方法成功地定向克隆了103个人类肝蛋白编码基因cDNA,克隆过程无需复杂的步骤筛选鉴定重组子。随机选择了其中的8个基因的克隆进行表达,结果显示8个克隆均在大肠杆菌中获得成功表达。该结果表明定向T载体构建成功,并且该载体非常适合基因的克隆和表达。