Genetically Improved Crops - The Oxford Topic of Food, Politics, and Society - page 83

nourished are able to grow, learn, and prosper. They achieve more in school, are bet-
ter able to survive illnesses, and tend to earn more as adults (Kraemer 2012). The
clinical and epidemiological evidence is clear: select minerals (iron, calcium, sele-
nium, and iodine) and a limited number of vitamins (folate and vitamins E, B6, and
A) play a significant role in maintenance of optimal health and are limiting in diets
(Asensi-Fabado 2010).
As with macronutrients, one way to ensure an adequate dietary intake of nutri-
tionally beneficial phytochemicals is to adjust their levels in plant foods. Using vari-
ous approaches, including genomics, vitamin E levels are being increased in several
crops, including soybean, maize, and canola. In addition, rice varieties are being
developed with the enhanced vitamin A precursor β-carotene to address this vitamin
deficiency that leads to macular degeneration and impacts development. Golden
Rice II accumulates up to 37 μg β-carotene per gram of rice (23-fold more than the
original). This β-carotene has been shown to be bioavailable in sufficient amounts
that 100 to 200 g per day can provide adequate provitamin A to ameliorate against
deficiency (Tang et al. 2009). A number of other staple crops on which many depend
almost exclusively for calories have been produced enriched in β-carotene, including
maize and cassava (Harjes et al. 2008; Welsch et al. 2010; Yan et al. 2010). The latter is
being field tested in Nigeria.
Ameliorating another major deficiency common in LDCs—iron—has also been
addressed. Iron is the most commonly deficient micronutrient in the human diet, and
iron deficiency affects an estimated 1 to 2 billion people. Anemia, characterized by low
hemoglobin, is the most widely recognized symptom of iron deficiency, but there are
other serious problems such as impaired learning ability in children, increased suscep-
tibility to infection, and reduced work capacity. Drakakaki et al. (2005) demonstrated
endosperm-specific co-expression of recombinant soybean ferritin and Aspergillus
phytase in maize, which resulted in significant increases in the levels of bioavailable
iron. A similar end was achieved with lettuce (Goto et al. 2000).
A rather interesting approach was taken by Connolly et al. (2008) to increase the lev-
els of calcium in crop plants by using a modified calcium/proton antiporter known as
short cation exchanger 1 (sCAX1) to increase Ca transport into vacuoles. They also dem-
onstrated that consumption of such Ca-fortified carrots results in enhanced Ca absorp-
tion. This demonstrates the potential of increasing plant nutrient content through
expression of a high-capacity transporter and illustrates the importance of demon-
strating that the fortified nutrient is bioavailable. Other targets include folate-enriched
tomatoes and isoflavonoids (DellaPenna 2007; Yonekura-Sakakibara and Saito 2007).
Micronutrients: Phytochemicals
The primary evidence for the health-promoting roles of phytochemicals comes from
epidemiological studies, and the exact chemical identity of many active compounds