An Isotope Effect in Photosynthesis

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In the course of some kinetic studies on photosynthesis of barley seedlings, it has been found that plants utilize C{sup 12}O{sub 2} faster than C{sup 14}O{sub 2}. The plants were placed in a closed system containing an infra-red absorption-cell for the analysis of total CO{sub 2} and an ionization chamber for the determination of C{sup 14}O{sub 2} in the gas phase, both instruments recording continuously. Carbon dioxide, containing about 2% C{sup 14}O{sub 2}, was introduced in the dark and the specific activity at this point taken as unity. After a short dark period, the lights were turned on and photosynthesis ... continued below

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Weigl, J.W. & Calvin, M. November 23, 1948.

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In the course of some kinetic studies on photosynthesis of barley seedlings, it has been found that plants utilize C{sup 12}O{sub 2} faster than C{sup 14}O{sub 2}. The plants were placed in a closed system containing an infra-red absorption-cell for the analysis of total CO{sub 2} and an ionization chamber for the determination of C{sup 14}O{sub 2} in the gas phase, both instruments recording continuously. Carbon dioxide, containing about 2% C{sup 14}O{sub 2}, was introduced in the dark and the specific activity at this point taken as unity. After a short dark period, the lights were turned on and photosynthesis was allowed to take place. A figure shows the result of a typical experiment. During the initial dark period the specific activity fell because of dilution by inactive respired CO{sub 2}. However, as photosynthesis proceeded, the specific activity of the residual CO{sub 2} rose until, when only 1/6 of it remained, the specific activity reached a peak some 20% higher than it had been at the start of photosynthesis. At this point the steady respiratory dilution became an appreciable fraction of the total remaining CO{sub 2}, and the specific activity dropped rapidly.

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  • Report No.: UCRL--228
  • Report No.: AECU-55
  • Grant Number: DE-AC02-05CH11231
  • DOI: 10.2172/929395 | External Link
  • Office of Scientific & Technical Information Report Number: 929395
  • Archival Resource Key: ark:/67531/metadc901641

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  • November 23, 1948

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  • Sept. 27, 2016, 1:39 a.m.

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  • Nov. 3, 2016, 7:58 p.m.

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Weigl, J.W. & Calvin, M. An Isotope Effect in Photosynthesis, report, November 23, 1948; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc901641/: accessed September 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.