The Rht gene is an inhibitor which stops a plant from growing. In a normal pathway, a gibberelin protein binds to the Rht gene and throws it away for degredation. Therefore, the plant is able to grow because gibberelin stops the inhibitor gene from inhibiting growth. When it comes to dwarfism, there is a defect or mutation in wheat that actually causes gibberelin to be ineffective. In dwarfs, because gibberelin is now inneffective, the Rht gene does not become inhibited and will thus be able to stop the wheat from growing. This is how dwarfism results in wheat
In rice however, there is a gene that is similar to Rht with the same function: it inhibits growing. With rice dwarfism, however, it is not that the gibberelin is ineffective, but that there is simply no gibberelin at all. This can be fixed however, by simply adding gibberelin which will then bind to the inhibitor and allow the rice to grow again. In wheat, this is not possible because the issue with the mutant is that gibberelin is rendered useless.
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