Abstract
A study was conducted with 48 species of the amount of 14CO2 released during the first minute of dark following fixation of 14CO2 in the light. Light fixation periods varied from 5 to 60 seconds. The species examined included both monocots and dicots and represented C4, C3, and Crassulacean acid metabolism (CAM) photosynthetic types.
Total CO2 uptake was determined as the sum of soluble 14C (ethanol and water), insoluble 14C, and 14CO2 released during the first minute of dark. Insoluble 14C made up a very small percent of the total. The percent of soluble 14C increased with fixation time in C4 species, while the percent of 14CO2 released in the dark decreased. C3 species released a very small percent of 14CO2 in the dark, and this percent remained relatively constant with time of 14CO2 fixation whereas C4 species released a higher percent initially and this percent declined with time of fixation. CAM species were similar to C4 species.
The species are grouped according to the 14CO2 released during the first minute of dark with light labeling times of 5 and 60 seconds. These comparisons are shown to separate C3 from C4 and CAM species. Further, the data suggest that the origin of the CO2 in the dark release of C4 plants is quite different from that of C3 plants.
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Selected References
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