July 22, 2009 According to the World Health Organization, approximately two billion people suffer from iron deficiency. They tire easily, experience problems in metabolizing harmful substances in their bodies and eventually suffer from anemia. Women and children are particularly affected in developing countries, where rice is the major staple food. Peeled rice, also called polished rice, does not have enough iron to satisfy the daily requirement, even if consumed in large quantities. For many people, a balanced diet or iron supplements are often unaffordable.
Rice actually has a lot of iron, but only in the seed coat. Because unpeeled rice quickly becomes rancid in tropical and subtropical climates, however, the seed coat - along with the precious iron - has to be removed for storage. Researchers working with Christof Sautter and Wilhelm Gruissem in the laboratory of plant biotechnology at ETH Zurich have now succeeded in increasing the iron content in polished rice by transferring two plant genes into an existing rice variety. Their work was published July 21 in the online edition of Plant Biotechnology Journal.
Genes help to mobilize and store iron
The rice plants express the two genes to produce the enzyme nicotianamin syn-thase, which mobilizes iron, and the protein ferritin, which stores iron. Their synergistic action allows the rice plant to absorb more iron from the soil and store it in the rice kernel. The product of nicotianamine synthase, called nicotianamin, binds the iron temporarily and facilitates its transportation in the plant. Ferritin acts as a storage depot for iron in both plants and humans. The researchers controlled the genes introduced in such a way that nicotianamin synthase is expressed throughout the rice plant, but ferritin only in the rice kernel. Together, the expression of the genes has a positive impact on iron accumulation in the rice kernel and increases the iron content more than six-fold compared to the original variety.
No negative impacts anticipated
The ETH scientists are excited about the new rice variety. The prototypes behave normally in the greenhouse and show no signs of possible negative effects. "Next we will have to test whether the rice plants also perform well in the field under agronomical conditions", says Wilhelm Gruissem. The ETH Professor does not expect the plants to have a negative impact on the environment. It is unlikely that they will deplete the soil of iron, as iron is the most abundant metallic element in it.
Distribution to farmers still many years away
The rice plants will have to undergo many greenhouse and field tests for bio-safety and agronomic performance before the high-iron rice varieties eventually become available to farmers. The current prototypes are unsuitable for agricultural production yet. Although the new rice variety already has an iron content that is nutritionally relevant, Gruissem wants to increase it further. After all, many people who suffer from iron deficiency can only afford one meal per day. If the scientists manage to increase iron in the rice kernel up to twelve-fold, one rice meal will be sufficient to satisfy the daily iron requirement.
The experience with the high-vitamin A "Golden Rice", which was developed at ETH Zurich in collaboration with researchers at the University of Freiburg (Germany), has shown that it takes years before genetically engineered rice can actually be planted by farmers. The regulatory hurdles and costs involved in making genetically modified plants available to agriculture and consumers are very high. The ETH scientists aim to make their high-iron rice plants available to small-scale and self-sufficient farmers free of charge.
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- J. Wirth et al. Rice endosperm iron biofortification by targeted and synergistic action of nico-tianamine synthase and ferritin. Plant Biotechnology Journal, 7: in press
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