Golden Rice: A bio-fortified food

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BIOFORTIFICATION ISthe idea of breeding crops to increase their nutritional value. This can be done either through conventional selective breeding, or through genetic engineering. It differs from ordinary fortification because it focuses on making plant foods more nutritious as the plants are growing, rather than having nutrients added to the foods when they are being processed. This is an improvement on ordinary fortification when it comes to providing nutrients for the rural poor, who rarely have access to commercially fortified foods. It has also overcome many health problems of human beings including vitamin deficiency as insufficiencies of different vitamins affect over one-half of the worlds population, children and pregnant women being at the highest risk. Shortage of dietary vitamin A is a major public health problem in the developing world affecting 190 million children under five particularly in Africa and South East Asia with India contributing to 85 per cent of cases in South East Asia. An estimated 250,000 to 500,000 vitamin A-deficient children become blind every year, half of them dying within 12 months of losing their sight. Pregnant women with insufficient levels of vitamin D are considered at increased risk of gestational diabetes, preeclampsia, and having infants small for their gestational age.

Scientific evidence shows that this technique is technically feasible without compromising agronomic productivity. Predictive cost-benefit analyses also supports biofortification as being important in the armamentarium for controlling micronutrient deficiencies. As such, biofortification is seen as an upcoming strategy for dealing with deficiencies of micronutrients in the developing world. The challenge is to get producers and consumers to accept biofortified crops and increase their intake of the target nutrients. With the advent of good seed systems, the development of markets and products, and demand creation, this can be achieved.

Golden rice is a variety of rice (Oryza sativa L.) produced through biofortification to biosynthesize beta-carotene, a precursor of vitamin A, in the edible parts of rice. It differs from its parental strain by the addition of three beta-carotene biosynthesis genes. The scientific details of the rice were first worked out in 2000. At that time, it was considered a significant breakthrough in biotechnology, as the researchers had engineered an entire biosynthetic pathway. It was created by transforming rice with only two beta-carotene biosynthesis genes:

1. psy (phytoene synthase) from daffodil (Narcissus pseudonarcissus)

2. crtI (carotene desaturase) from the soil bacterium Erwinia uredovora

The insertion of a lyc (lycopene cyclase) gene was thought to be needed, but further research showed it is already being produced in wild-type rice endosperm. The psy and crtI genes were transformed into the rice nuclear genome and placed under the control of an endosperm-specific promoter, so they are only expressed in the endosperm. The exogenous lyc gene has a transit peptide sequence attached so it is targeted to the plastid, where geranylgeranyl diphosphate formation occurs. The bacterial crtI gene was an important inclusion to complete the pathway, since it can catalyze multiple steps in the synthesis of carotenoids up to lycopene, while these steps require more than one enzyme in plants. The end product of the engineered pathway is lycopene, but if the plant accumulated lycopene, the rice would be red. Recent analysis has shown that the plants endogenous enzymes process the lycopene to beta-carotene in the endosperm, giving the rice the distinctive yellow color for which it is named.

The original golden rice was called SGR1, and under greenhouse conditions it produced 1.6 µg/g of carotenoids. Field testing provides a more accurate measurement of nutritional value and enables feeding tests to be performed. The first field trial of these golden rice cultivars was conducted by Louisiana State University Agricultural Center in 2004. Preliminary results from the field tests have shown field-grown golden rice produces 4 to 5 times more beta-carotene than golden rice grown under greenhouse conditions.

In 2005, a team of researchers at biotechnology company, Syngenta, produced a variety of golden rice called “Golden Rice 2”. They combined the phytoene synthase gene from maize with crt1 from the original golden rice. Golden rice 2 produces 23 times more carotenoids than golden rice (up to 37 µg/g), and preferentially accumulates beta-carotene (up to 31 µg/g of the 37 µg/g of carotenoids). In 2005, researchers were promoted to further improve golden rice by increasing the levels of or the bioavailability of pro-vitamin A, vitamin E, iron, and zinc, and to improve protein quality through genetic modification.

To receive the Recommended Dietary Allowance (RDA), it is estimated that 144 g of the most high-yielding strain would have to be eaten. Bioavailability of the carotene from golden rice has been confirmed and found to be an effective source of Vitamin A for humans. The research that led to golden rice was conducted with the goal of helping children who suffer from vitamin A deficiency (VAD). Vitamin A is supplemented orally and by injection in areas where the diet is deficient in vitamin A. As of 1999, there were 43 countries that had vitamin A supplementation programmes for children under 5; in 10 of these countries, two high dose supplements are available per year, which, according to UNICEF, could effectively eliminate VAD. However, UNICEF and a number of NGOs involved in supplementation note more frequent low-dose supplementation should be a goal where feasible.

As many children in countries where there is a dietary deficiency in vitamin A rely on rice as a staple food, the genetic modification to make rice produce the vitamin A precursor beta-carotene is seen as a simple and less expensive alternative to vitamin supplements or an increase in the consumption of green vegetables or animal products. Initial analyses of the potential nutritional benefits of golden rice suggested consumption of golden rice would not eliminate the problems of vitamin A deficiency, but should be seen as a complement to other methods of vitamin A supplementation. Since then, improved strains of golden rice have been developed containing sufficient provitamin A to provide the entire dietary requirement of this nutrient to people who eat about 75g of golden rice per day. In particular, since carotenes are hydrophobic, there needs to be a sufficient amount of fat present in the diet for golden rice (or most other vitamin A supplements) to be able to alleviate vitamin A deficiency. In that respect, it is significant that vitamin A deficiency is rarely an isolated phenomenon, but usually coupled to a general lack of a balanced diet. The RDA levels accepted in developed countries are far in excess of the amounts needed to prevent blindness. Moreover, this claim referred to an early cultivar of golden rice; one bowl of the latest version provides 60% of RDA for healthy children.

So, Golden rice is actually a revolution brought about by biotechnology/biofortification. It can seriously check the vitamin A deficiency, thus decreasing the death rate and improving the health of the people especially in developing countries.


Published in: Volume 05 Issue 10

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