# Nanotechnology in Plant Metabolite Improvement and in Animal Welfare
## 1 Introduction  
Plant in vitro culture is considered a biotechnological process that involved growing plant cells, tissues, or organs in an artificial nutrition media in a controlled environment and aseptic condition. Application of plant in vitro culture for plant propagation and crop improvement has been discussed [1; 2; 3; 4; 5]. In addition, it is also utilized for pharmacological purposes [5; 6]. As far as agriculture is concerned, cell propagation in vitro, has been widely used for massive production of low-proliferating crops, for improvement of crop varieties, and preparation of pathogen-free plants, as well as for maintaining stocks of endangered species as an ex-situ conservation approach [5; 6; 7; 8; 9; 10]. Plant cell culture can be applied to a wide range of botanical species through different methods and procedures and this assumes strategic importance considering the present concern about environmental issues [10]. Plant tissue culture has also been used as a major platform for the productionof secondary metabolites, which are widely used for pharmacological as well as industrial purposes [10; 11; 12]. Plant secondary metabolites contained in medicinal plants are the major reason why they have been used traditionally by society worldwide [13]. Many bioassays and phytochemical studies have been carried out to scientifically prove the pharmacological effect of the plant's natural constituents [14; 15]. The culture of plants in vitro is directed towards the aseptic growth of parts or whole plants under specific nutritional and environmental conditions [1; 12]. This technique depends on the concept of totipotency, which refers to the ability of plant cells to express a full genome through cell division [1; 2]. Several factors affect the success of in vitro culture, such as the genotype, physiological status, and type of explants, disinfection method employed in the preparation of the sample, culture medium, plant growth regulators (PGRs), light intensity, photoperiod, and temperature. Generally, medium composition strongly influences morphogenesis in explants [16; 17; 18]. Media are typically composed of macro- and micronutrients, amino acid organic supplements, vitamins, carbon sources, and PGRs, as well as solidifying agents [4; 7; 12]. Elicitors can be defined as molecules or agents known for their ability to induce a response in the organisms they are administered to. They are also added for some special purposes, such as enhancing phytochemical production in plants [19; 20]. These molecules are of biological or non-biological origin and can recognize cytoplasmic membrane receptors on the plant cells. Recognition and binding led to signal elicitation, which stimulates the expression of genes related to secondary metabolite production [20; 21; 22]. The elicitors work as plant stressors in a natural environment: they can be represented by fungi, bacteria, activated enzymes, and other biological compounds [22; 23]. Other forms of elicitors are constituted by physical agents such as temperature, salinity, heavy metals, and mineral stress [22; 23; 24]. With respect to this, nanoparticles/heavy metals conjugates show high potential as in vitro culture elicitors for their physiochemical properties and fall within the field of nanotechnology [22; 25]. Nanotechnology has rapidly become prominent in various scientific fields of application [26]. Nanobiotechnology has been widely utilized for drug and gene delivery, bio-detection of pathogens and proteins, disease control, and fluorescent biological labeling. Also, in plant tissue culture it has found use in seed germination, yield, and bioactive compound improvement, as well as a plant protection [12; 26; 27]. Nanomaterials exhibit unique properties such as low molecular, large surface-area-to-volume ratio, ability to engineer electron exchanges, special electronic and optical attributes, and surface reactive capability [26; 28].