How To Grow Tobacco At Home
Variety of genetically engineered organisms. The first among these that are currently being evaluated under phase I II clinical trials are Id proteins produced in transfected mammalian cells grown in tissue culture (26) and plant-derived single-chain variable region (scFv) Id fragments (27). It has been shown that Id proteins from lymphoma patients' specimens can be produced in recombinant bacteria and that DCs pulsed with these proteins (secreted as Fab fragments) can stimulate Id-specific cytotoxic T lymphocytes (CTLs) in vitro (28). Furthermore, the tobacco mosaic virus has been exploited as a vector for engineering protein production in tobacco plants. In a preclinical study, vaccination of mice with plant-derived Id scFv was able to elicit tumor protection equivalent to that of Id-KLH plus adjuvant (29). On the basis of these results, a phase I II clinical study has been initiated to evaluate the efficacy of plant-derived Id scFv vaccine in patients with follicular lymphoma (27).
Human haemoglobin as well as blood coagulation factors have been synthe-sised in GM tobacco plants. Glucocerebrosidase, an enzyme that is deficient in patients with Gaucher's disease, is an expensive drug since 10-12 tons of human placentas are used to isolate and purify the enzyme each year for a single patient. The enzyme has now also been obtained from GM tobacco,where it is expressed after harvesting the plants in order to limit accidental environmental exposure to pharmaceuticals.
Significant progress has been made since 1990 to produce antibodies in plants (Ma and Hein, 1995, 1996). A murine monoclonal antibody k chain, a hybrid immunoglobin A-G heavy chain, a murine joining chain, and a rabbit secretory component were produced in different transgenic tobacco plants sexual crosses between these plants resulted in plants that produce all four proteins simultaneously. A surprisingly high molecular weight secretory immunoglobin was assembled from these four chains and bound the antigen in this case, the native streptococcal antigen I II cell surface adhesion molecule (Ma et al., 1995).
The story of genetic modification in plants started 1980, when it was demonstrated that a soil bacterium, Agrobacterium, caused tumours in plants after transferring a small but distinct DNA fragment to a plant cell, where it would be incorporated in the nucleus and change the physiology of the local tissue. In 1983 the system was put to use and GM Agrobacteria were used to transfer an antibiotic resistance gene into a tobacco plant. Today advanced methods for the genetic transformation in a wide range of plants have been developed that are based on this natural phenomenon.
Boron is thought to have a direct effect on sugar synthesis. In cowpeas (Vigna unguiculata Walp), acute boron deficiency conditions increased reducing and nonreducing sugar concentrations but decreased starch phosphorylase activity (21). Under boron deficiency, the pentose phosphate shunt comes into operation to produce phenolic substances (22). Boron-deficient sunflower seeds showed marked decrease in nonreducing sugars and starch concentrations, whereas the reducing sugars accumulated in the leaves (23). This finding indicates a specific role of boron in the production and deposition of reserves in sunflower seeds. High concentrations of nonreducing sugars were also found in boron-deficient mustard (Brassica nigra Koch) (24). Camacho and Gonzalas (19) also found higher starch concentration in boron-deficient tobacco plants. In low-boron sunflower leaves, starch decreased, but there was an increase in sugars and protein and nonprotein nitrogen fractions (25). In
There is a great interest in expressing recombinant proteins in plants, either as an approach to improve food quality (Sun et al., 1996) or as bioproduction systems for proteins (Cramer et al, 1996). A methionine-rich 2S protein (18 methionine and 8 cysteine) in the Brazil nut (BN2S) gene was cloned (Altenbach et al., 1987), expressed in transgenic tobacco plants by the seed-specific phaseolin promoter, and enhanced the methionine content of transgenic tobacco seeds by up to 30 (Altenbach et al., 1989). A similar enhancement of the methionine content was later observed in rapeseeds (Altenbach et al., 1992). Similar approaches can be used to increase the lysine content by lysine-rich proteins or sweetness by using the sweet protein mabinlin (Sun et al., 1996). (Cramer et al., 1996), including large-scale biomass production at low cost, efficient and low-cost procedures to produce and maintain transgenic plants, similarity of posttranslational protein modification in plants and animals,...
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