# Nanotechnology in Plant Metabolite Improvement and in Animal Welfare
## 2 Silver-Nanoparticles in Crop Improvement  
Plant tissue culture plays important roles in agrotechnology [2; 10; 38]. Plant micropropagation is one of the best alternatives for crop improvement and shows a special significance in multiplication through a vegetative approach. This minimizes the risk of pathogen accumulation and the slow proliferation rate in generative multiplication, which in turn, causes a loss in both crop quantity and quality [39; 40; 41; 42]. Several studies have shown the positive impacts of AgNP augmentation for callus induction, shoot generation, and growth (Table 1). Calli obtained from in vitro culture of _Caralluma tuberculata_ were compact and greenish in color. The water content, which is an important parameter for metabolic and physiological status, increased along with the callus biomass values [8; 37]. However, administration of AgNPs above the estimated optimum level (60 \(\upmu\)g/L) caused a significant decline in callus biomass [8]. In the sugarcane (_Saccharum officinarum_) [43], the addition of AgNPs resulted in significantly higher shoot multiplication and elongation at high concentrations of these nanoparticles while showing no effect on growth. This study exhibited the hormetic effect of AgNPs in plant tissue culture, as it was clearly shown that the application of AgNPs in the medium resulted in inhibition of shoot multiplication and elongation. This study also revealed that the accumulation of important nutrients in the medium, such as N, Mg, and Fe was also increased. Therefore, the increased levels of nutrients related to chlorophyll biosynthesis, may lead to higher photosynthetic activity, conversely, higher concentrations of AgNPs may lead to phytotoxicity. These results were similar to those of previous studies, such as those on _Cucurbita pepo_[44] and _Raphanus sativus_[45]. The addition of the same size of AgNPs to the MS culture medium of _Stevia rebaudiana_ [PERSON]. [PERSON] et al. [29] exhibited an increase in shoot number and length in all AgNP treatments compared to those in the control. However, the highest concentration of AgNPs showed a lower amount of shoot multiplication and elongation. The in vitro culture of _Prunella vulgaris_ L., which is known as self-healing, using a medium containing Naphthaleneacetic acid (NAA) + AgNPs alone or augmented with Gold-Nanoparticles (AuNPs) showed a very significant increase in callus proliferation as compared to that in the control [46]. In _Lavandula angustifolia_ shoot propagation, media enrichment with AgNPs and AuNPs showed significantly improved plant development compared to that in the control. Regardless of the components and concentration, the addition of those nanoparticles (NPs) was reported to enhance the formation of lateral shoots. Generally, the addition of AgNPs even at the highest level did not exhibit any visible toxic effects such as necrosis; however, higher levels of AuNPs exhibited a slight color change in the leaf blades to yellowish. The effect of AgNPs' was also investigated in callus induction of _Oryza sativa_ cv. IR64; where the highest callus induction was observed at a relatively low concentration of AgNPs [47]. The callus induction increased significantly as compared to that in the control medium. A study on the optimum concentration of AgNPs for three possible propagation methods of _Chrysanthemum morifolium_ was also investigated [48] in a solid and liquid medium, as well as microphonics. The addition of AgNPs to the culture medium improved dramatically the number of shoots as well as the plant height and biomass. It is also worth noting that callus cultures, as well as cell suspension culture (CSC), are used to enhance the accumulation of plant secondary metabolites. Callus which is derived from plant organs cultured in vitro can be defined as unorganized or undifferentiated cell mass that can serve as a potential plant biotechnological platform to manufacture significant bioactive compounds of pharmaceutical interests [10].