# Nanotechnology in Plant Metabolite Improvement and in Animal Welfare
## 2 Silver-Nanoparticles in Crop Improvement
In addition, callus culture coupled with nano-elicitation has been reported as a promising strategy for enhancing alkaloid [49], flavonoid, and phenolic compounds [50]. For instance, AgNPs have been reported to boost the concentration of different flavonoids including flavonoids, hydroxybenzoic and hydroxycinnamic acids in the CSC of bitter gourd [21]. An increase of total phenolic and flavonoid content had also been demonstrated in callus culture of _Caralluma tuberculata_ and _Prunella vulgaris_ after being elicited by AgNPs and AgAuNP, respectively [8; 41]. Along with their effects on growth improvement, AgNPs also possess anti-microbial properties since it was reported that the addition of AgNPs in culture media postponed the appearance of internal contamination of _Araucaria excelsa_[27]. According to this study administration of nanoparticles reduced bacterial contamination and, in addition, application of AgNPs on the medium was also reported to control pathogenic fungal proliferation [51]. Although several studies have shown the positive effects of AgNPs on plant propagation, its exact mechanism has not been understood in detail. From the data presented, the effect of AgNPs on plant growth in vitro and media decontamination was dependent on various factors, such as plant species, nature, explant type, and age, as well as the AgNP size and concentration [8; 27; 52]. Thus, the results of the examinations suggested that the effect of AgNPs is dose-dependent, in which application of high concentrations of these nanomaterials leads to growth inhibition and necrosis. It was suggested that the increase in callus biomass was due to AgNPs modifying the plant cell wall structure, possibly allowing the plant cells to uptake more water and nutrients from the medium [8]. This suggestion was based on the structural impact of the cell wall in plant cells, compared to that in animal cells [53]. In Section 5 of this review article, we discuss the potential use of different nanoparticles. However, the reader should consider that the sophistication of molecular carriers or cargo-nanoparticles, as they are often also defined, for the delivery of exogenous material within a living cell is highly diversified. Also, they have different purposes and become ever more numerous with different chemical features often designed to reach specific bio-targets. In this work, for the sake of conciseness, we briefly overview the nature and chemical-physical properties of cationic liposomes, cat-anionic vesicles, and graphene-based carbon nanotubes. With respect to this, drug absorption into a cell, organ, or whole organism, depends also on the chemical structure of the compound and on the hydrophilic/lipophilic balance of the tissue. This constitutes a major challenge. The goal in developing the features of the cargo supramolecular carriers is, in fact, endowing them with the possibility of reaching the appropriate site in a living organism. This means, in other words, that they should identify the appropriate receptor on the cell surface, alternatively, these supramolecular aggregates should be flexible enough to be assumed actively by the target cell or to freely assumed by passive diffusion. In any case, the ideal properties of a molecular cargo in drug delivery should assure the uptake of an efficacious amount of drug within the target tissue. This latter can have different chemical characteristics, such as polarity of the membrane or of the internal cytoplasmic matrix. These parameters play a crucial role in the optimal solution of the drug within an aqueous medium: with respect to this, molecules may be transformed into acid salts when target tissues are strongly polar, or they may form complexes with crown ethers. Sophisticated methods exist for the transport of an exogenous molecule such as gels and dendrimers carbon nanotubes. These latter are raising an enormous interest for their potential usage as cargo molecules both in cultured cells and in whole organisms but also in the extremely variegated field of applications.