Search

Endophytic bacteria (EB) possess different beneficial traits. Endophytic microbes are often functional in that they may carry nutrients from the soil into plants, modulate plant development, increase stress tolerance of plants, suppress virulence in pathogens, increase disease resistance in plants, and suppress development of competitor plant species. They may enhance plant development by carrying nutrients from the soil into plants and protect plants against phytopathogens by synthesizing extra-/intracellular proteolytic enzymes, as well as releasing antimicrobial metabolites and competing with pathogens for habitation and nutrients. In this study, we investigated the ability to produce exo/endo-enzymes such as gelatinase, amylase, and catalase, and antagonistic activity of 77 EB strains isolated from lowland rice roots grown in Doan Ket commune, Thanh Mien district, Hai Duong province, Vietnam. Out of 77 isolates, 76 (98.71%) showed the ability to liquefy gelatin after 7 days with different rates of hydrolysis. The test of starch hydrolysis revealed 58 (75.33%) isolates that were able to hydrolyze starch. Fifty-one out of 77 isolates (66.24%) were able to produce catalase. The antagonistic activity of rice root endophytic bacteria was determined against bacterial leaf blight disease-causing pathogen Xanthomonas oryzae pv. oryzae (Xoo), strains X19.2 and VX41. We found that three isolates (TP5, TP7, TP11) showed the ability to inhibit the growth of strain VX41 and twelve isolates (TP3, TP7, TP8, TP9, TP10, TP11, TP12, TP13, TP15, TP17, TP21, TP23) were able to inhibit the growth of strain X19.2. These results are served as a venue for further investigation in planta under the conditions of net house and field trials in order to confirm the potential strains for the development of bioinoculant toward controlling the disease caused by Xoo.

Sweet potato Ipomoea batatas (L.) Lam is an important food crop in the world as well as in Vietnam. Despite its many benefits, the production of sweet potato is restricted in many areas of the world by diseases, weed, and, particularly, pests. As an alternative, genetic transformation provides the means for complementing conventional breeding to improve sweet potato to resistant to pest. In this study, shoot tip explants of KB1 sweet potato variety were infected with A. tumefaciens C58 carying pBI101/cry3Ca1 con-struct. The selection were occured on callus producing medium (SM) containing 0.5 g/L picloram, 50 mg/L kanamycin and 500 mg/L cefotaxime. Survival embryogenic calli were then transferred to embryo producing medium (EG2) supplemented with 1.0 mg/L ABA and 1.0 mg/L GA3 after 2–3 weeks. Putative transgenic shoots regenerated on medium (RM) adding 0.5 mg/L kinetin and 1.0 mg/L BAP were rooted on root producing medium (RR). The tentative transgenic lines were proved positively by PCR and finalized by Southern hybridization, and biotest in laboratory. Conclusionly, we obtained 62 tentative transgenic sweet potato lines resistant to kanamycin. Among these lines, five putative transgenic lines were proved positively by Southern hybridization and have one copies of the cry3Ca1 gene. Two of them have the lower degree of infestation by sweet potato weevil (Cylas formicarius) than that of untransformed lines.

Joint Research on Environmental Science and Technology for the Earth

Joint Research on Environmental Science and Technology for the Earth

Joint Research on Environmental Science and Technology for the Earth

Genetic modification from selfed progenies of 18 rice (Oryza sativa L.) plants regenerated from callus tissues which survived desiccation, were investigated at the DNA level using the random amplified polymorphic DNA (RAPD) method. Twelve 10-mer random primers were used to amplify DNA of progenies from the regenerated plants, and a total of 228 PCR products and 1780 DNA fragments were obtained by primers, generating between four to thirteen major bands. The size of the amplified fragments ranged from 0.2 to 2.55 kb. The results showed that 10 out of 12 primers produced polymorphic bands, two primers (RA31 and RA185) showed no polymorphism among plants tested. A dendrogram of the genetic distance was constructed based on their polymorphism, demonstrating that somaclonal variation exists in rice plants regenerated from callus which survived the desiccation treatment. Part of this variation can be useful in rice breeding.

Silver nanoparticles are useful for medical applications due to their strong antibacterial activity. The antibacterial activity can be tuned by controlling the size and shape of the prepared silver nanoparticles. In this work, silver nanoparticles with different sizes and shapes were synthesized by solution phase routes, and their interactions with Escherichia coli were studied. Triangular silver nanoprisms were prepared by the reduction of silver nitrate at room temperature in the presence of polyvinylpyrrolidone, sodium citrate, hydrogen peroxide and sodium borohydride. Spherical silver nanoparticles were also prepared using silver nitrate as metal precursor and sodium citrate as well as sodium borohydride as reducing agents. The morphologies and structures of the nanoparticles were characterized by transmission electron microscopy, UV-visible spectroscopy and X-ray diffraction. The results indicated that spherical silver nanoparticles were obtained with different average sizes of 4, 21 and 40 nm, respectively. The edged silver nanoprisms containing mainly {111} lattice planes were obtained in the range size of 25 to 400 nm. The antibacterial study revealed that the edged triangular silver nanoprisms with {111} lattice planes exhibited the strongest antibacterial property, compared with spherical nanoparticles. Our study demonstrated that triangular silver nanoprisms with sharp edges and sharp vertexes also display a good antibacterial activity in comparison to other shaped nanoparticles.

The impact of the University of Illinois at Chicago-based Vietnam-Laos International Cooperative Biodiversity Group (ICBG) Program "Studies on Biodiversity of Vietnam and Laos", which has been in operation for the period of 1998-2005, touches on five major areas of endeavor: (a) biodiversity inventory and conservation; (b) studies on medicinal plants; (c) drug discovery and development; (d) economic development; and (e) issues on intellectual property rights and benefit sharing in natural products drug discovery and development. Highlights are presented and the significance is discussed.

A marine Antarctic psychrotolerant bacterium (strain ANT/505), isolated from sea ice-covered surface water from the Southern Ocean, showed pectinolytic activity on citrus pectin agar. The sequencing of the 16S rRNA of isolate ANT/505 indicates a taxonomic affiliation to Pseudoalteromonas haloplanktis. The supernatant of this strain showed three different pectinolytic activities after growth on citrus pectin. By activity screening of a genomic DNA library of isolate ANT/505 in Escherichia coli, two different pectinolytic clones could be isolated. Subcloning and sequencing revealed two open reading frames (ORF) of 1,671 and 1,968 nt, corresponding to proteins of 68 and 75 kDa, respectively. The deduced amino acid sequence of the two ORFs showed homology to pectate lyases from Erwinia chrysanthemi and Aspergillus nidulans. The pectate lyases contain signal peptides of 17 and 26 amino acids that were correctly processed after overexpression in E. coli BL21. Both enzymes were purified by anionic exchange chromatography. Maximal enzymatic activities for both pectate lyases were observed at 30 degrees C and a pH range of 9 to 10. The Km values of both lyases for pectate and citrus pectin were 1 g l(-1) and 5 g l(-1), respectively. Calcium was required for activity on pectic substrates, whereas the addition of 1 mM ethylenediaminetetraacetic acid (EDTA) resulted in complete inhibition of the enzymes. These two enzymes represent the first pectate lyases isolated and characterized from a cold-adapted marine bacterium.

Polyadenylated RNA was isolated and a cDNA library constructed from seedlings of a chilling-tolerant rice cultivar (Oryza sativa L. subsp. Japonica cv Nipponbare). Four clones were isolated by differential screening. Northern blot hybridization using RNAs from chilling-tolerant (Nipponbare) and -sensitive (IR36) cultivars revealed higher steady-state levels of transcripts for the four genes in Nipponbare than in IR36 maintained at the same low temperatures. The accumulation of transcripts homologous to selected cDNA sequences during chilling were tissue-specific. The nucleotide and deduced amino acid sequences of three clones, pBC121, pBC442, and pBC591, were determined, and no homology was identified by comparison with the latest version of EMBL and LASL gene data bases. The deduced protein sequences from the longest open reading frame of the clones pBC121 and pBC442 are rich in leucine and serine, whereas that of the clone pBC591 contains arginine-rich basic domains.

Understanding the molecular mechanisms of desiccation tolerance in higher plants is an important goal of applied biology. Many efforts in plant breeding have been made to select for drought resistance. The selection has always been difficult because complex traits are involved. Using suitable experimental systems molecular biology offers the possibility to investigate drought resistance on the level of single genes. Two model systems (developing cereal embryos and resurrection plants) have been chosen to understand mechanisms of desiccation tolerance at the molecular level. Common to both these experimental systems is that they can experience protoplastic dehydration. This mechanism should be distinguished from biochemical or morphological adaptations which allow plants to withstand dry environments.

We have isolated a genomic clone encoding trichobakin (TBK), a type I ribosome-inactivating protein from the plant Trichosanthes sp. Bac Kan 8-98 (family Cucurbitaceae), by PCR using specific primers designed from the cDNA sequences of alpha-trichosanthin. The sequence encoding mature TBK was constructed in the pET-21d(+) vector for overexpression in Escherichia coli strain BL21(DE3). The recombinant protein was purified to homogeneity by CM-Sepharose chromatography on FPLC with a final yield of about 55 mg/l of culture. The protein has a molecular mass of about 27 kDa, as shown by SDS/PAGE and matrix-assisted laser-desorption ionization MS. It was found that the protein inhibited luciferase mRNA translation in the rabbit reticulocyte cell-free system with an IC(50) value (that which causes a 50% reduction of residual translational activity) of about 3.5 pM. The rRNA N-glycosidase activity of the protein was also proved at the above-mentioned concentration after rRNAs were treated with acid aniline.

Summary The formation of callus tissues from root segments of Zea mays seedlings was generally induced on synthetic media by 2, 4-D at concentrations ranging from 2 to 20 mg/1; the subcultures of this callus tissue, however, were successfully cultivated at lower auxin concentrations (1 — 4 mg/1). Studies on the uptake and incorporation of ( 3 H-methyl)-thymidine by root segments grown on a medium containing 5 mg/1 2,4-D have shown that the thymidine incorporation increased after a lag phase of 6 h and then reached two maxima: The first one after 24 h and the second one after 120 h. By treatment with specific inhibitors, actinomycin D (10 −5 and 10 −6 M), puromycin (10 −4 and 10 −5 M) or cycloheximide (10 −4 and 10 −5 M) the thymidine incorporation during the first period can be inhibited either partially or completely. The total nucleic acids prepared by phenol extraction were separated by MAK-column chromatography. In order to demonstrate the incorporation of 3 H-thymidine into DNA the nucleic acids from all fractions of the resulting DNA-RNA-peak were again precipitated and furtherly characterized. The nucleic acids from the DNA-RNA-peak show a very high specific activity and are the only one labelled with 3 H-thymidine. They are stable against RNase but not against pancreatic DNase I. Preparations from callusing roots show a higher 3 H-thymidine incorporation and a higher specific activity in comparison to normal roots. From these findings it was concluded that an additional DNA-synthesis is necessary in the early period of callus formation.