## 4 Plant Tissue and Organ Cultures in Bioreactors
### Temporary Immersion System
The enzymes marked in red are expressed by plant species presented in Table 1.  
methylbut-2-enyldiphosphate synthase; HMGR: 3-hydroxy-3-methylglutaryl-CoA reductase; HMGS: hydroxymethylglutaryl-CoA synthase; HQT: hydroxycinnamoyl-CoA quinate hydroxycinnamoyltransferase; IPP: isopentenyl diphosphate; IRS: iridoid synthase; LAMT: loganic acid O-methyltransferasearse; LS: lupeol synthase; MCT: 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase; MDS: 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase; MK: mexulonate kinase; MVD: diphosphomevalonate decarboxylase; MVP: 5-phosphomevalonate; MVPP: mexulonate-5-pyrophosphate; P450: cytochrome P450; PAL: phenylalanine-ammonia-lyase; PMK: phosphomevalonate kinase; SE: squalene epoxidase; SGD: strictosidine \(\beta\)-D-glucosidaseidase; SLS: secologanin synthase; SS: squalene synthase; ST02C: terpene synthase; STR: strictosidine synthase; TDC: tryptophan decarboxylase  
Transgenic Plants as Green Biofactories for the Production of Recombinant Proteins Grown in Bioreactors  
Therapeutic recombinant proteins are exogenous proteins expressed in a producing organism and used for the treatment or prevention of various diseases in humans or animals [146; 147; 148]. Unlike artificially synthesized drugs, recombinant proteins are generally very large, complex molecules with specific mechanisms of action. Their size and complexity make the chemical synthesis of proteins very difficult, so these new drugs must be biologically produced using the protein synthesis machinery found in cells [146; 149]. More than 300 protein-based drugs have been approved in the US and Europe, with proteins accounting for almost a third of all drugs under development. Almost half of the market is made up of therapeutic proteins (e.g., enzymes, antibodies, vaccines, growth factors, and cytokines), followed by industrial proteins (e.g., technical enzymes) and reagents (e.g., antibodies for protein detection and purification) [150; 151; 152]. Advances in recombinant protein production technologies, including engineering of expression hosts, optimization of upstream culture (e.g., bioreactor design and nutritional and physical parameters), and the development of more efficient protein extraction and purification methods are important market developments [19; 153]. Production using a plant expression system is both profitable and scalable, and an interesting alternative for the pharmaceutical industry; in addition, therapeutic protein production in plants has proven to be an attractive alternative to other expression systems, such as transgenic animals, cultures of mammalian cells, yeasts, and bacteria [47; 154]. Plants have provided humans with useful bioactive compounds for many centuries, but it has only been in the last few decades that it has become possible to use plants to produce specific recombinant pharmaceutical proteins. Plant production systems are extremely attractive due to the lack of risk of contamination of the final product with human or animal pathogens (e.g., bacteria, viruses, and prions) as well as bacterial toxins. One of the first pharmaceutically important proteins produced in plants was human growth hormone, which was expressed in transgenic tobacco in 1986 [42; 43]. However, the structural authenticity of plant-derived recombinant proteins was confirmed in 1992, when plants were first used to produce an experimental vaccine--hepatitis B virus (HBV) surface antigen [149]. Recombinant proteins can be functionally expressed in a variety of plant systems; however, it is imperative to identify a platform that offers the best conditions for the expression and recovery of a particular protein [146; 153].