Does pro-vitamin A not occur naturally in rice?
Rice does contain pro-vitamin A. But unfortunately it is not found in the grains but in the leaves and roots. Scientifically speaking, grains do have the genes that are responsible for making pro-vitamin A but the genes are not expressed unlike in the case of leaves and roots. But is it true that some varieties of unpolished rice do contain pro-vitamin A? All rice cultivated has some pro-vitamin A in the outer layers. But it is extremely little and is lost when polished. The reason for polishing is to enable rice storage in tropical climate as otherwise it would turn rancid. How do you make the grains produce pro-vitamin A? Genes consist of DNA. To be functional, however, a gene needs a piece of DNA sequence in front of it that acts as a molecular switch, able to activate or to inactivate the gene. This switch is called a promoter. The promoter plus the structural gene associated with it is known as `expression cassette’. Only these two together will render a gene functional. Promoters
