| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2005: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Research Abstract |
We utilized ion beams as a mutagen to generate new ultraviolet B (UVB) hyper-resistant or hyper-sensitive rice or Arabidopsis mutant, and have isolated a new UVB hyper-resistant mutant of rice, UVB-tolerant Sasanishiki-5 (uvt-Sa5), a new UVB hyper-sensitive mutant of rice, UVB-sensitive Sasanishiki-3 (uvs-Sa2) and a UVB hyper-resistant mutant of Arabidopsis, UVB-insensitive 4(uvi4) We characterized these mutants in this study.
1. The fresh weight (FW) of uvi4 plants grown under supplementary UVB radiation was more than twice that of the wild-type (WT). No significant difference was found in their ability to repair the UVB-induced CPD, or in the amount of UV-absorbing compounds, both of which are well-known factors that contribute to UV sensitivity. We found that the hypocotyl cells in uvi4 undergo one extra round of endo-reduplication. The uvi4 mutation also promoted the progression of endo-reduplication during leaf development. UVI4 is necessary for maintenance of the mitotic state, and the loss of UVI4 function stimulated endo-reduplication. Therefore, enhanced polyloidization is responsible for the increased UVB tolerance of the uvi4 mutant.
2. The FW of uvt-Sa5 plants grown under supplementary UVB radiation was as similar as that of the wild-type (WT). No significant difference was found in the amount of UV-absorbing compounds. The uvt-Sa5 had increased CPD photorepair ability, although the transcript level of CPD photolyase gene was as similar as that of WT. On the other hand, UVB hyper-sensitive mutant of rice, uvs-Sa2, was deficient in dark repair ability, nucleotide excision repair (NER) ability. Thus, the systems used by rice plant to repair DNA damage are indispensable for their growth under UVB radiation, and the simultaneous enhancement of these systems may help generate a highly resistant rice plant.
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