# Nanotechnology in Plant Metabolite Improvement and in Animal Welfare
## 3 Silver-Nanoparticles in Plant Secondary Metabolite Enhancement  
Plants are rich in secondary metabolites helping them to survive under challenging environmental conditions. Furthermore, plant secondary metabolites are also well known as an important source of pharmacological or industrial means. In vitro plant cell and organ, culture has been proven to be advantageous for plant secondary metabolite production [12]. The application of elicitors, such as AgNPs, also has a positive effect on secondary metabolite enhancement in several studies [43; 46; 55; 56; 64]. In _Caralluma tuberculata_, application of AgNPs in MS medium showed the highest result for total phenolic compounds (total flavonoid content), phenylalanine ammonia-lyase, and DPPH free radical activity. Even though no significant increase was observed from the augmentation of AgNPs and PGRs, data showed that application of AgNPs with PGR resulted in the second-highest secondary metabolite production in \(C\). _tuberculata_ culture [51]. This evidence suggests that the addition of AgNPs _per se_ in the medium was more supportive for secondary metabolite enhancement. An increase in total phenolic compounds on sugarcane after media elicitation with AgNPs was also demonstrated [43]. This study also reported that the optimum concentration for phenolic compound enhancement in sugarcane occurred at medium concentration; higher concentrations caused a decrease of phenolic compound and antioxidant production while the production of reactive oxygen species (ROS) continued to rise. Administration of differently sized nanoparticles at various concentrations to _Arabidopsis thaliana_ exhibited a significant change in camalexin content as compared to that in the control where the best result for camalexin accumulation was observed. Pathway network analysis on the AgNPs in _A. thaliana_ revealed increases in the TCA-cycle, sugar metabolism, and shiki-mate phenylpropanol metabolism, which are also associated with plant resistance to abiotic stress. Therefore, the ability of AgNPs to induce the production of phytoalexins and other secondary metabolites is promising for the enhancement of plant immunity against pathogens [57]. Capsaicin enhancement through Cell Suspension Culture (CSC) of _Capsicum_ spp. where higher than those in _Capsicum_ fruit was observed: capsaicin level raised up to two-fold after three to six days of culture [55]. It should be pointed out that the CSC approach was also adopted for the evaluation of important secondary metabolite production in bitter gourd. Total phenolic and flavonoid compounds were examined, and an increase of total phenolic and flavonoid contents was monitored. Ultra-HPLC assessment showed 20 different individual phenolic compounds among which hydroxybenzoic acid, hydroxycinnamic acid, and other flavanols [21]. Elicitation by AgNPs affected the pharmacological activity of the bitter gourd extracts since CSC, extracts thus obtained, showed a significantly higher inhibitory effect towards \(\alpha\)-amylase as compared to that of the non-elicited ones. This may represent a potentially improved therapeutic tool as bitter gourd extracts are used for postprandial hyperglycemia treatment in diabetes patients [21; 68]. These elicited extracts also showed higher antimicrobial and inhibitory effects on MCF-7 and HT-29 cell propagation. Studies performed on stabilized _Prunella vulgaris_ CSCs' yielded analogous results [46; 56]. The TPC and TFC of the suspended cell showed significantly higher results in the NP-elicited-CSC, with the highest result in the combined AgAuNP treatment; similarly, administration of nanoparticles to _E. purpurea_ cultures resulted in a significant increase in cichoric acid, an important specific secondary metabolite. Nanoparticle suspensions at different concentrations were added to cells in logarithmic growth: results showed that maximum level of cichoric acid was obtained from elicitation with 2 mg/L AgNPs at 72 and 48 h of exposure respectively, for leaf and root-derived callus.