Why the Rice We Eat Lacks Beta-Carotene

 

      Rice is the most important food crop in many Asian and South American countries (DellaPenna). Rice is easy to grow in these tropical climates, and this starchy food provides a large amount of calories per serving (242 calories per cup-cooked white rice)(Riceweb). It is often the bulk of dietary food for humans in densely populated countries. 

Figure 3: Anatomy of the rice plant. Rice is a semi-aquatic annual grass that grows in extremely moist areas, and the seeds sprout in water. The main stem of the rice plant has side shoots known as tillers that are able to grow roots and develop into new plants. Each tiller has a flowering head that produces the rice seed that we eat (Riceweb). This prolific seed producing and plant propagating capability contributes to the plants success as an agricultural crop.  These properties also facilitate the reliance on rice as a main food item in overpopulated countries.

 

 

Figure 4:  Anatomy of the rice seed.  The white rice we consume is actually the center of the seed and contains the caryopsis (brown rice) that is enclosed by the hull. The brown rice contains the embryo and the white endosperm. The endosperm is the nutritive tissue of the seed, and it is absorbed by the embryo during growth. Around the seed is a hull that contains the palea, lemma, and rachilla. The hull is removed upon processing to give the white rice endosperm for human consumption (Riceweb).

 

The rice plant contains the entire pathway to produce beta-carotene, yet all of the genes are expressed in other parts of the plant, but not in the endosperm. The hull surrounding the seed contains beta-carotene, but is shucked in processing brown and white rice. During the development of the endosperm and the embryo many of the genes for the beta-carotene pathway are expressed. However, the carotenoids are not produced in the endosperm because the genes are not expressed for enzymes that synthesize the necessary intermediates.

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Deficiencies in Vitamin A

 

Introduction Why the Rice We Eat Lacks Beta Carotene
Dietary Sources of Vitamin A Problems With Vitamin A Supplements
Deficiencies in Vitamin A Synthesis of Beta-Carotene and Vitamin A
Genetic Engineering of Rice Conclusion