Table 9.2.

Advantages and Disadvantages of Different Plants as Transgenic Bioreactors

Plant/Fruit	Advantage	Disadvantage
Tobacco	•Good model for evaluating recombinant proteins •Low cost preserving system •Easy purification of antibodies stored in the seeds •Large harvests	•Produces toxic compounds* (toxic alkaloids incompatible w/oral delivery) •Potential for outcrossing in field
Potato	•Dominated clinical trials •Easily manipulated/transformed •Easily propagated from its “eyes” •Stored for long periods without refrigeration	•Relatively low tuber protein content •Unpalatable in raw form**; cooking may cause denaturation and poor immunogenicity of vaccine
Banana	•Does not need cooking •Proteins not destroyed even if cooked •Inexpensive •Grown widely in developing countries	•Trees take 2–3 years to mature and transformed trees take about 12 months to bear fruit •Fruits spoil rapidly after ripening and contain very little protein, so unlikely to produce large amounts of recombinant proteins
Tomato	•Grows quickly •Cultivated broadly •High content of vitamin A may boost immune response •Overcomes the spoilage problem by freeze-drying technology •Heat-stable, antigen-containing powders†, made into capsules •Different batches blended to give uniform doses of antigen	•Relatively low fruit protein content •Acidic fruit may be incompatible with some antigens or for delivery to infants •No in vitro system to test fruit expression
Rice	•Commonly used in baby food because of low allergenic potential •High expression of proteins/antigens •Easy storage/transportation •Expressed protein is heat stable	•Grows slowly •Requires specialized glasshouse conditions
Lettuce	•Fast growing •Direct consumption	•Spoils readily
Soybean and alfalfa	•Relatively efficient transformation system •High protein content in leaves •Leaves edible uncooked •Ideal system for animal vaccines	•Potential for outcrossing in field •Deep root system problematic for cleaning field
Legumes or cereals	•Production technology widely established •High protein content in seeds •Stable protein in stored seeds •Well suited for animal vaccines •Industrial seed processing well established	•Inefficient transformation systems •Heating or cooking for human use may cause denaturation and poor immunogenicity of vaccine (corn meal is exception) •Potential for outcrossing in field for some species

^*Currently, therapeutic proteins in tobacco are being produced.

^**Some kinds of South American potatoes can be eaten raw. Although some studies show that cooking does not destroy full complement of antigen in potatoes.

^†Freeze-dried tomato powder containing NV capsid and LT-B was found immunogenic.