Elevated CO2 leads to a decrease in potential net photosynthesis in long-term experiments and thus to a reduction in potential growth. This process is known as photosynthetic downregulation. There is no agreement on t...Elevated CO2 leads to a decrease in potential net photosynthesis in long-term experiments and thus to a reduction in potential growth. This process is known as photosynthetic downregulation. There is no agreement on the definition of which parameters are the most sensitive for detecting CO2 acclimation. In order to investigate the most sensitive photosynthetic and molecular markers of CO2 acclimation, the effects of elevated CO2, and associated elevated temperature were analyzed in alfalfa plants inoculated with different Sinorhizobium meliloti strains. Plants （Medicago sativa L. cv. Aragon） were grown in summer or autumn in temperature gradient greenhouses （TGG）. At the end of the experiment, all plants showed acclimation in both seasons, especially under elevated summer temperatures. This was probably due to the lower nitrogen （N） availability caused by decreased N2-fixation under higher temperatures. Photosynthesis measured at growth CO2 concentration, rubisco in vitro activity and maximum rate of carboxylation were the most sensitive parameters for detecting downregulation. Severe acclimation was also related with decreases in leaf nitrogen content associated with declines in rubisco content （large and small subunits） and activity that resulted in a drop in photosynthesis. Despite the sensitivity of rubisco content as a marker of acclimation, it was not coordinated with gene expression, possibly due to a lag between gene transcription and protein translation.展开更多
The nifA gene is an important regulatory gene and its product, NifA protein, regulates the expression of many nif genes involved in the nitrogen fixation process. We introduced multiple copies of the constitutively ex...The nifA gene is an important regulatory gene and its product, NifA protein, regulates the expression of many nif genes involved in the nitrogen fixation process. We introduced multiple copies of the constitutively expressed Sinorhizobium meliloti (Sm) or Enterobacter cloacae (Ec) nifA gene into both the nifA mutant strain SmY and the wild-type strain Sm1021. Root nodules produced by SmY containing a constitutively expressed Sm nifA gene were capable of fixing nitrogen, while nodules produced by SmY containing the Ec nifA gene remained unable to fix nitrogen, as is the case for SmY itself. However, transfer of an additional Sm nifA gene into Sm1021 improved the nitrogen-fixing efficiency of root nodules to a greater extent than that observed upon transfer of the Ec nifA gene into Sm1021. Comparative analysis of amino acid sequences between Sm NifA and Ec NifA showed that the N-terminal domain was the least similar, but this domain is indispensable for complementation of the Fix? phenotype of SmY by Sm NifA. We conclude that more than one domain is involved in determining functional differences between Sm NifA and Ec NifA.展开更多
基金supported by Ministerio de Ciencia e Innovación (MICINN BFU2008-01405)Ministerio de Economia y Competitividad (BFU2011-26989)+1 种基金Fundación Universitaria de Navarra (PIUNA-2008)Fundación Caja Navarra
文摘Elevated CO2 leads to a decrease in potential net photosynthesis in long-term experiments and thus to a reduction in potential growth. This process is known as photosynthetic downregulation. There is no agreement on the definition of which parameters are the most sensitive for detecting CO2 acclimation. In order to investigate the most sensitive photosynthetic and molecular markers of CO2 acclimation, the effects of elevated CO2, and associated elevated temperature were analyzed in alfalfa plants inoculated with different Sinorhizobium meliloti strains. Plants （Medicago sativa L. cv. Aragon） were grown in summer or autumn in temperature gradient greenhouses （TGG）. At the end of the experiment, all plants showed acclimation in both seasons, especially under elevated summer temperatures. This was probably due to the lower nitrogen （N） availability caused by decreased N2-fixation under higher temperatures. Photosynthesis measured at growth CO2 concentration, rubisco in vitro activity and maximum rate of carboxylation were the most sensitive parameters for detecting downregulation. Severe acclimation was also related with decreases in leaf nitrogen content associated with declines in rubisco content （large and small subunits） and activity that resulted in a drop in photosynthesis. Despite the sensitivity of rubisco content as a marker of acclimation, it was not coordinated with gene expression, possibly due to a lag between gene transcription and protein translation.
文摘The nifA gene is an important regulatory gene and its product, NifA protein, regulates the expression of many nif genes involved in the nitrogen fixation process. We introduced multiple copies of the constitutively expressed Sinorhizobium meliloti (Sm) or Enterobacter cloacae (Ec) nifA gene into both the nifA mutant strain SmY and the wild-type strain Sm1021. Root nodules produced by SmY containing a constitutively expressed Sm nifA gene were capable of fixing nitrogen, while nodules produced by SmY containing the Ec nifA gene remained unable to fix nitrogen, as is the case for SmY itself. However, transfer of an additional Sm nifA gene into Sm1021 improved the nitrogen-fixing efficiency of root nodules to a greater extent than that observed upon transfer of the Ec nifA gene into Sm1021. Comparative analysis of amino acid sequences between Sm NifA and Ec NifA showed that the N-terminal domain was the least similar, but this domain is indispensable for complementation of the Fix? phenotype of SmY by Sm NifA. We conclude that more than one domain is involved in determining functional differences between Sm NifA and Ec NifA.
