## 9 Influence of Microparticles Treatments on the Synthesis of Plant Metabolites
[164] show that treatments with alginate-based microparticles on lettuce (_Lactuca sativa_ L) had significantly stimulated the synthesis of plant metabolites, without significant impact on the lettuce morphology. The controlled release was achieved, and passive uptake of ions through the root system was active during the whole period of maturation. Using two types of cultivations (conventional and hydroponics) revealed interesting data. Generally, all treatments had a significant influence on plant metabolites synthesis, relative to the controls. Compared to the Cu-alginate microparticles, Ca-alginate microparticles had a significantly higher effect on synthesizing plant metabolites. Equal treatments in conventional and hydroponics cultivation yielded results with high correlation, which verifies the repeatability and feasibility of the experiment. Treatment with Ca-alginate microparticles resulted in the highest yield of total chlorophylls in the conventional cultivation of lettuce, with up to an impressive 76% relative to the control [164]. Ca\({}^{2+}\) is known to serve as a secondary messenger for cytokinin action in improving the synthesis of chlorophylls [106]. These results are in correlation with research on supplementation with Ca\({}^{2+}\), where higher chlorophyll values were also observed in chickpea leaves [19]. Treated lettuce resulted in an increase of up to 48% in total polyphenols content [164]. Generally, Ca-alginate-based microparticles had a stronger effect on synthesizing polyphenic compounds when comparing them to Cu-alginate-based. Ca-alginate microparticles (with and without _T. viride_ spores) treatments also resulted in a significantly higher accumulation of total flavonoids with an increase of up to 42%. Ca\({}^{2+}\) has an important role in polyphenic metabolism [169]. Application of Ca\({}^{2+}\) increases the phenylalanine ammonia-lyase activity, and a higher accumulation of polyphenic compounds occur. This can significantly increase the plants' resistance to the infections caused by the pathogens [170]. Regarding the antioxidant activity in treated lettuce plants, Ca-alginate-based microparticles again had the most pronounced effect [164]. Previously, [PERSON] et al. [19] revealed that supplementation with Ca\({}^{2+}\) significantly boosts antioxidant activity in plants. Cu-based microparticles had a lower effect, but some treatments in hydroponic cultivation were significantly higher than control (untreated). More data on this can be seen in [PERSON] et al. [164]. In conventional cultivation, non-encapsulated _T. viride_ spores (suspension) had less or even a negative influence on the plant metabolites synthesis when compared to the encapsulated ones. Equal treatment in hydroponic cultivation revealed significant influence, and this can be explained by the fact that this type of cultivation (hydroponic) is sterile compared to the conventional (soil). Furthermore, due to the lower survivability, as well as the need for the organism to uptake some of the nutrients from the surrounding media to survive, there will be fewer available nutrients for the plant. Also, temperatures on the open field and closed hydroponics system are not the same. These facts highlight the importance of biological agent encapsulation, since its survivability increases significantly in an environment that is perhaps not favorable when inoculating the latter. Increasing the number of plant metabolites as chlorophylls, carotenoids, polyphenols, and an overall increase in antioxidant activity contributes to the quality of food for both humans and animals. Future investigation should focus on the precise agriculture and metabolomics aspect to determine which mechanisms are responsible for synthesis stimulation and to quantify plant needs more precisely. Metabolomics is one of the fastest developing methods for the identification and quantification of changes happening in a sample based on a set of metabolites with low molecular mass [171].