organelle membrane-bound cell compartment
Transgenesis in plants is technically challenging because the transgene must penetrate the tough cell walls, which are not present in animal cells. Instead of modifying plant genes in the nucleus, a method called transplas-tomics alters genes in the chloroplast, which is a type of organelle called a plastid. Chloroplasts house the biochemical reactions of photosynthesis. Transplastomics can give high yields of protein products, because cells have many chloroplasts, compared to one nucleus. Another advantage is that altered chloroplast genes are not released in pollen, and therefore cannot fertilize unaltered plants. However, it is difficult to deliver genes into chloroplasts, and expression of the trait is usually limited to leaves. This is obviously not very helpful in a plant whose fruits or tubers are eaten. The technique may be more valuable for introducing resistances than enhancing food qualities. Someday, transplastomics may be used to create "medicinal fruits" or edible vaccines.
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