Nutrients, antibodies, secondary metabolites and vaccines

A gene encoding the enzyme phytoene synthase, which condenses two molecules of geranyl geranyl diphosphate to get β-carotene (provitamin A) synthesis, was expressed in rice endosperm (Burkhardt et al. 1997). The biosynthetic pathway for regulating Vitamin C content has been investigated by Wheeler et al. (1998). Plants could also produce antibodies (Ma and Hein 1995) and vaccines (Arntzen 1998). Antibodies against bacteria associated with dental caries (Ma et al. 1998), antigens for certain forms of diabete (Ma et al. 1997), and some new vaccines (Arakawa et al. 1998) can be produced in fruits particularly banana.

At present there is active research on flavonoid biosynthesis which is thought to possess health-promoting properties such as antioxidant, vasodilatory actions which may protect against cardiovascular diseases, particularly for one group such as flavonols (e.g., quercitin and kaempferol) and pigmentary flavonoids known as anthocyanins which play an important role in flower and leaf colour in plant. Attention is directed toward calchone isomerase, an enzyme involved in flavonol biosynthesis. Tomato fruits over-expressing constitutively Petunia calchone isomerase gene contained high levels of quercitin glycosides and moderate levels of kaempferol (Muir et al. 2001). This gene may be used to transform many fruit crops, reinforcing their natural red colour e.g., plum, grape, strawberry, and some Citrus sp. (e.g., orange, grapefruit).