| Budget Amount *help |
¥4,550,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥1,050,000)
Fiscal Year 2011: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2010: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000)
Fiscal Year 2009: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2008: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
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| Research Abstract |
The activity of Rubisco is a major limitation of photosynthetic CO_2 assimilation rate in C_3 plants. In order to find useful Rubisco for improvement of photosynthesis in rice under elevated CO_2, the catalytic turnover rate(k_<cat>) of Rubisco was analyzed in Poaceae including C_3 alpine plants, C_3 cold resistant plants and C_4 plants. Rubisco in these plants showed 1. 1-to 2. 8-fold higher k_<cat> than that in rice. Among plants analyzed, Rubisco in Festuca ovina, Phleum pratense and Sorghum showed relatively high k_<cat> to Kc. In our estimation, the expression of high k_<cat> Rubisco of F. ovina and S. bicolor in rice could significantly enhance CO_2 assimilation rates under elevated CO_2. We introduced the small subunit(RbcS) of Sorghum and it was found that Sorghum RbcS significantly enhances k_<cat> of Rubisco in transgenic rice(Oryza sativa). These results suggest that Rubisco in rice transformed with sorghum RbcS partially acquires the catalytic properties of sorghum Rubisco. Rubisco content in transgenic lines was significantly increased over wild type levels but Rubisco activation was slightly decreased. The expression of sorghum RbcS did not affect CO_2 assimilation rates under a range of CO_2 partial pressures. The J_<max>/V_<cmax> ratio was significantly lower in transgenic line compared to the nontransgenic plants. These observations suggest that the capacity of electron transport is not sufficient to support the increased Rubisco capacity in transgenic rice. Although the photosynthetic rate was not enhanced, the strategy presented in this study opens the way to engineering Rubisco for improvement of photosynthesis and productivity in the future.
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