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.

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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 ° C and a pH range of 9 to 10. The K m 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.

A procedure for rapid propagation of Agave (A. eantala Roxb., A. fourcroydes Lem. and A. sisalana Perrine, (Agavaceae) have been developed. The explants were excised from stolon plantlets, sterilized and cultivated on Murashige and Skoog (MS) basal medium containing 2% sucrose, 10% coconut water and 0.8% agar. The addition of following combination of growth substances --0.075 mg l 1 naphthalenacetic acid (NAA) + 0.1 mg 1-~ indolylbutyric acid (IBA) + 0.5 mg 1-l kinetin (KIN) caused an extensive proliferation of multiple shoot primordia. Subcultures of these on the same medium were successful for the multiplication with an index of 3-4 times per 4 weeks subculture period. Shoots were rooted on hormone free MS medium and then transferred into a sand bed for acclimation before field planting.

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.Rice is cultivated worldwide under diverse ecological conditions. The common environmental stress affecting growth and development of rice is the irregular exposure to low temperatures. Thus, the ability of crop plants of tropical and subtropical origins to resist a period of low temperature during growth is an agriculturally important trait. The cultivars of Indica subspecies of rice in particular are often injured by cooler temperatures (around 100C) (12). To date, the mechanism of chilling tolerance is not sufficiently understood to effectively improve resistance either by conventional or by genetic engineering techniques. Therefore, numerous plants have been studied to discover the molecular mechanism responsible for cold tolerance (for reviews, see refs. 5 and 6).In general, plants respond to low temperature exposure by inducing the synthesis of several proteins (4,8,12,14) that may lead to cold hardening and cold tolerance (5, 13). These proteins are products of a gene or genes whose expression is differentially regulated by exposure to low temperature (1,4,(6)(7)(8). Several of these cold-regulated genes have been cloned and characterized (2,9,15,21).Our previous study (12) showed that cold temperatures induced the novel synthesis of several proteins in rice seed-' L.T.B. was supported by a fellowship of the Matsumae Intemational Foundation, Japan (from April to October, 1989) and a fellowship of the Science and Technology Agency, Japan (from September 1990 to March 1991).lings of tolerant cultivars due to differential gene expression. In the present study, we focused on the molecular cloning and characterization of four cDNAs of transcripts that accumulate in seedlings of the chilling-tolerant cultivar Nipponbare at low temperatures. MATERIALS AND METHODS Plant MaterialsSeeds of two rice cultivars (Oryza sativa L. subsp. Japonica cv Nipponbare and 0. sativa L. subsp. Indica cv IR36) were dehusked and sterilized in 1% sodium hypochlorite for 15 min. After three washes with autoclaved water, the sterilized seeds were placed in a vesse...