DNA transfer by particle bombardment makes use of physical processes to achieve the transformation of crop plants. There is no dependence on bacteria, so the limitations inherent in organisms such as Agrobacterium tumefaciens do not apply. The absence of biological constraints, at least until DNA has entered the plant cell, means that particle bombardment is a versatile and effective transformation method, not limited by cell type, species or genotype. There are no intrinsic vector requirements so transgenes of any size and arrangement can be introduced, and multiple gene cotransformation is straightforward. The perceived disadvantages of particle bombardment compared to Agrobacterium-mediated transformation, i.e. the tendency to generate large transgene arrays containing rearranged and broken transgene copies, are not borne out by the recent detailed structural analysis of transgene loci produced by each of the methods. There is also little evidence for major differences in the levels of transgene instability and silencing when these transformation methods are compared in agriculturally important cereals and legumes, and other non-model systems. Indeed, a major advantage of particle bombardment is that the delivered DNA can be manipulated to influence the quality and structure of the resultant transgene loci. This has been demonstrated in recently reported strategies that favor the recovery of transgenic plants containing intact, singlecopy integration events, and demonstrating high-level transgene expression. At the current time, particle bombardment is the most efficient way to achieve plastid transformation in plants and is the only method so far used to achieve mitochondrial transformation. In this review, we discuss recent data highlighting the positive impact of particle bombardment on the genetic transformation of plants, focusing on the fate of exogenous DNA, its organization and its expression in the plant cell. We also discuss some of the most important applications of this technology including the deployment of transgenic plants under field conditions.

Most plastid transformation studies with tobacco, and all reports for other species (except tomato [G.D. Nugent, M. ten Have, A. van der Gulik, P.J. Dix, B.A. Uijtewaal, A.P. Mordhorst, Plastid transformants of tomato selected using mutations affecting ribosome structure. Plant Cell Rep. 24 (2005) 341-349]), have used biolistics for plastid transformation. However, nuclear transformation via biolistics has not been reported for any vegetable Brassica species so we used protoplast culture and PEG-mediated DNA uptake, to examine both nuclear and plastid transformation of cauliflower, an important vegetable Brassica. A vector containing genes for hygromycin resistance and b-glucuronidase activity (pGUS-HYG) was used for nuclear transformation, while plastid transformation utilised a vector (pZB1) containing accD-rbcL plastome targeting regions cloned from Brassica napus (oil seed rape), and the selectable marker gene aadA, conferring resistance to spectinomycin. Protoplasts were embedded in agarose and selected on media containing hygromycin or spectinomycin. From five experiments, a single plastid transformant of the commercial cultivar Thalassa was obtained, whereas nuclear transformants were obtained at an absolute transformation frequency up to 1.3 Â 10 À5. No spontaneous spectinomycin resistant mutants were observed in any plastid transformation experiments. PCR and Southern blot analysis confirmed the transgenic status of plants regenerated from the protoplast-derived calli. #

Silver chloride nanoparticles were prepared by the precipitation reaction between silver nitrate and sodium chloride in an aqueous solution containing poly(vinyl alcohol) as a stabilizing agent. Different characteristics of the nanoparticles in suspension and in lyophilized powder such as size, morphology, chemical nature, interaction with stabilizing agent and photo-stability were investigated. Biological tests showed that the obtained silver chloride nanoparticles displayed antibacterial activities against Escherichia coli and Staphylococcus aureus.

The stability of chitosan with a degree of deacetylation (DD) of 88 and 81% was investigated in solution during storage for 60 days at various temperatures (60, 28, and 58C) and acid concentrations (0.8M, 0.2M, and 0.1M). The first-order rate constant of chain hydrolysis of 88%DD chitosan at 608C was about 1.4 times higher than that of the 81%DD sample. At 288C, the rates of hydrolysis for both chitosan samples were four to five times lower than those at 608C and are similar. At 58C, chain degradation was not significant. Although acetic acid caused significantly higher (P 0.05) chain scission than formic acid, no significant difference of rate change was observed among three different acid concentrations. Reprecipitation of dissolved chitosan was applied for its purification and to transfer dissolved chitosan to the solvent used to measure its molecular weight. Reprecipitation resulted in slightly lower molecular weight (P 0.05) for both 88%DD and 81%DD samples. The molecular weight of chitosan before and after reprecipitation had good linear relationship (r 2 > 0.9).

Spatial manipulation of a precise number of viruses for host cell infection is essential for the extensive studies of virus pathogenesis and evolution. Albeit optical tweezers have been advanced to the atomic level via optical cooling, it is still challenging to efficiently trap and manipulate arbitrary number of viruses in an aqueous environment, being restricted by insufficient strength of optical forces and a lack of multifunctional spatial manipulation techniques. Here, by employing the virus hopping and flexibility of moving the laser position, multifunctional virus manipulation with a large trapping area is demonstrated, enabling single or massive (a large quantity of) virus transporting, positioning, patterning, sorting, and concentrating. The enhanced optical forces are produced by the confinement of light in engineered arrays of nanocavities by fine tuning of the interference resonances, and this approach allows trapping and moving viruses down to 40 nm in size. The work paves the way to efficient and precise manipulation of either single or massive groups of viruses, opening a wide range of novel opportunities for virus pathogenesis and inhibitor development at the single‐virus level.