Trends in Plant Science
Volume 10, Issue 12, December 2005, Pages 586-593
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Biofortifying crops with essential mineral elements

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Humans require more than 22 mineral elements, which can all be supplied by an appropriate diet. However, the diets of populations subsisting on cereals, or inhabiting regions where soil mineral imbalances occur, often lack Fe, Zn, Ca, Mg, Cu, I or Se. Traditional strategies to deliver these minerals to susceptible populations have relied on supplementation or food fortification programs. Unfortunately, these interventions have not always been successful. An alternative solution is to increase mineral concentrations in edible crops. This is termed ‘biofortification’. It can be achieved by mineral fertilization or plant breeding. There is considerable genetic variation in crop species that can be harnessed for sustainable biofortification strategies. Varieties with increased mineral concentrations in their edible portions are already available, and new genotypes with higher mineral densities are being developed.

Section snippets

Mineral malnutrition in humans

Humans require various mineral elements (Table 1). Some are required in large amounts, but others, such as Fe, Zn, Cu, I and Se, are required in trace amounts because higher concentrations can be harmful 1, 2. Ultimately, these mineral elements enter the food chain through plants. Some essential mineral elements, such as K and Na, occur solely as soluble inorganic ions in plants. However, most mineral elements also occur in organic compounds or inorganic salts, in both soluble and insoluble

Variation within angiosperms

Although all flowering plants (angiosperms) probably require the same mineral elements, tissue concentrations of these elements can differ markedly between plant species, even when they are grown in the same environment (Figure 1) 25, 26. Much of the variation in the tissue concentrations of some mineral elements, such as K, Ca, Mg, Si, Ni and Zn, occurs at the ordinal level or above 25, 26, 27. This implies that the concentrations of these elements in plant tissues are constrained by an

Biofortification through biotechnology

Much is known about the molecular mechanisms effecting the accumulation of Fe 6, 17, 72, 73, Zn 17, 19, Ca 29, 60, Mg [74] and Se [21] in plants. This knowledge will be useful for developing functional (DNA-sequence) markers for conventional breeding and molecular targets for genetic engineering 2, 19, 44 to aid the development of crops with increased mineral concentrations.

Transgenic approaches to biofortification rely on improving mobilization from the soil, uptake from the rhizosphere,

Perspective

It is clear that mineral malnutrition presents a significant global challenge. In addition to the traditional interventions of supplementation and fortification of foods, several agronomic options are available to increase dietary minerals. The ultimate solution is dietary diversification, but this is not immediately practical. In the meantime, biofortification of edible crops is advocated through either mineral fertilization and/or plant breeding. It is evident that both these strategies can

Glossary

Antinutrient:
a substance that impairs the absorption of an essential element by the gut.
Bioavailability:
the amount of an element in a food constituent or a meal that can be absorbed and used by a person eating the meal.
Biofortification:
the process of increasing the bioavailable concentrations of an element in edible portions of crop plants through agronomic intervention or genetic selection.
Fortification:
the addition of an ingredient to food to increase the concentration of a particular element.

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