Photosynthesis, plant growth and N allocation in transgenic rice plants with decreased Rubisco under CO2 enrichment.
Ribulose-1,5-bisphosphate carboxylase (Rubisco) efficiency for CO2-saturated photosynthesis was examined in leaves of rice (Oryza sativa L.). The amount of Rubisco in a leaf was calculated to be 30-55% in excess for the light-saturated rate of photosynthesis at 100 Pa CO2. Long-term exposure to CO2 enrichment decreased the amount of Rubisco protein. However, N was not reallocated from decreased Rubisco to other components limiting photosynthesis, and the decrease in Rubisco was simply due to a decrease in total leaf-N content by CO2 enrichment. Thus, rice plants did not optimize N allocation into Rubisco at elevated CO2. Transgenic rice plants with decreased Rubisco were obtained by transformation with the rbcS antisense gene. The transformant with 65% wild-type Rubisco was selected as a plant with optimal Rubisco content for CO2-saturated photosynthesis at the level of a single leaf. This selected transgenic plant had 20% lower rates of photosynthesis at normal CO2 (36 Pa), but 5-15% higher rates of photosynthesis at elevated CO2 (100 Pa) for a given leaf N content. However, such transgenic plants did not necessarily show greater production of biomass even under conditions of CO2 enrichment. Although they had a higher N-use efficiency for plant growth under such conditions during the middle stage of growth, the growth rate was lower during the early stage of growth. Thus, improvement of N-use efficiency by a single leaf did not necessarily lead to greater production of biomass by the whole plant.
Graduate School of Agricultural Science, Tohoku University, Sendai, Japan. makino@biochem.tohoku.ac.jp
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Makino
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Nakano
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Mae
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Shimada
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Yamamoto
D002245:Carbon Dioxide / Q000378:metabolism*; D016373:DNA, Antisense; D009584:Nitrogen / Q000378:metabolism*; D012275:Oryza / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D010788:Photosynthesis; D030821:Plants, Genetically Modified; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism*
D016373:DNA, Antisense; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen