Genetically Improved Crops - The Oxford Topic of Food, Politics, and Society - page 77

Table 3.2 Continued

Class/Components Source2 Potential Health Benefit

Sulfides/Thiols

Diallyl sulfide Onions, garlic, olives, leeks,

scallions

May lower LDL cholesterol; helps
to maintain healthy immune
system

Allyl methyl trisulfide,
Dithiolthiones

Cruciferous vegetables May lower LDL cholesterol; helps

to maintain healthy immune
system

Tannins

Proanthocyanidins Cranberries, cranberry products,

cocoa, chocolate, black tea

May improve urinary tract health
May reduce risk of CVD and high
blood pressure

1 Examples are not an all-inclusive list.
2 U.S. Food and Drug Administration approved health claim established for component.
Modified from ILSI, 2004.

breeding strategies. Research to improve the nutritional quality of plants has histori-
cally been limited by a lack of basic knowledge of plant metabolism and the challenge of
resolving complex interactions of thousands of metabolic pathways. A complementar-
ity of techniques both traditional and novel is needed to metabolically engineer plants
to produce desired quality traits. Metabolic engineering is generally defined as the redi-
rection of one or more reactions (enzymatic and otherwise) to improve the production
of existing compounds, to produce new compounds, or to mediate the degradation of
undesirable compounds. It involves the redirection of cellular activities by the modifica-
tion of the enzymatic, transport, or regulatory functions of the cell. Significant progress
has been made in recent years in the molecular dissection of many plant pathways and
in the use of cloned genes to engineer metabolism.
Although progress in dissecting metabolic pathways and our ability to manipulate gene
expression in GM plants has progressed apace, attempts to use these tools to engineer plant
metabolism have not quite kept pace. Since the success of this approach hinges on the abil-
ity to change host metabolism, its continued development will depend critically on a far
more sophisticated knowledge of plant metabolism, especially the nuances of intercon-
nected cellular networks, than currently exists. This complex interconnectivity is regularly
demonstrated. Relatively minor genomic changes (point mutations, single-gene inser-
tions) following metabolomic analysis are regularly observed to lead to significant changes
in biochemical composition (Bino et al. 2005; Davidovich-Rikanati et al. 2007; Long et al.
2006). Giliberto et al. (2005) used a genetic modification approach to study the mecha-
nism of light influence on antioxidant content (anthocyanin, lycopene) in the tomato cul-
tivar Moneymaker. However, other genetic changes, which on the surface appear to be
more significant, unexpectedly yield little phenotypical effect (Schauer and Fernie 2006).