Abstract Titanium dioxide nanoparticles (TiO2NPs) are widely used and may impact the environment. Thus, this study used a high concentration of TiO2NP (1000 mg/L) to verify the defense mechanisms triggered by a plant system – an indicator of toxicity. Furthermore, this study aimed at completely characterizing TiO2NP suspensions to elucidate their toxic behavior. TiO2NPs were taken up by meristematic cells of Allium cepa, leading to slight inhibition of seed germination and root growth. However, severe cellular and DNA damages were observed in a concentration-dependent manner (10, 100, and 1000 mg/L). For this reason, we used the highest tested concentration (1000 mg/L) to verify if the plant cells developed defense mechanisms against the TiO2NPs and evaluated other evidences of TiO2NP genotoxicity. Nucleolar alterations and plant defense responses (i.e., increased lytic vacuoles, oil bodies and NP phase change) were observed in meristematic cells exposed to TiO2NP at 1000 mg/L. In summary, TiO2NPs can damage the genetic material of plants; however, plants displayed defense mechanisms against the deleterious effects of these NPs. In addition, A. cepa was found to be a suitable test system to evaluate the cyto- and genotoxicity of NPs.

Component Based Development (CBD) aims at constructing software through the integration, using interfaces and contracts, between pre-existing components. The main goal of this work is to provide access to component that can be published at the Web, retrieved, and reused in all phases of an application development within a given domain. We present an architecture for software components reuse by using a mediation layer that integrates the semantics of Web components with previously registered components from a virtual library of components. In our architecture, components are described through XML documents and published by local repositories or remote servers. The innovative aspect of our proposal is the combination of mediators and software agents for reusable component retrieval within a Domain Engineering context. Mediators can represent application domain as well as integrate the description of domain related components. Queries can be issued to the mediation layer and processed by the GOA Object Server, which presents the query results as a list of suggested components along with its repository link in XML. Software agents are responsible for web component discovery and filtering. Techniques such as user models (profiles), and recommendations are used for presenting a ranked list of links. Finally, resulting links from mediators and web post-processed results are combined and presented to the user.