Explain the adaptations that allow rice plants to grow with their roots beneath water.
Using Fig. 4.1, describe how submergence in water affects ethene production in rice.
Using Fig. 4.2, compare how ethene affects internode elongation in C9285 and T65.
The snorkel genes were expressed when the plant was exposed to ethene. Their expression leads to a greater production of gibberellin, GA. Fig. 4.3 shows the effect of submergence on GA production in C9285 and in T65. Using Fig. 4.3, together with your knowledge of GA function, suggest an explanation for the differences in the effects of ethene in C9285 and T65 shown in Fig. 4.2.
Cultivated rice has been bred from the wild rice species Oryza rufipogon, Oryza nivara. O. rufipogon shows a strong deepwater elongation response, whereas O. nivara shows only a slight elongation response. A third species, Oryza glumaepatula, shows a strong elongation response. • O. rufipogon possesses both snorkel genes, SK1 and SK2. • O. nivara has SK1, but an insertion mutation has created a stop triplet in SK2. • O. glumaepatula has SK2, but lacks SK1.
Describe what this information shows about the relative importance of SK1 and SK2 in the deepwater elongation response.
Explain how an addition mutation could create a stop triplet.
Deepwater rice is the staple food crop in many regions that experience flooding during the rainy season. Many deepwater rice varieties produce lower yields than varieties that are not deepwater rice. Suggest how a deepwater rice variety with high yield could be produced, using artificial selection.