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Plant Physiology 68:1253-1256 (1981)
© 1981 American Society of Plant Biologists

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Effects of O2 Tension and Temperature during Light Uptake of 14CO2 on the Dark Release of 14CO2 by Excised C3 and C4 Leaves 1

Tommy Wynn

Department of Botany, North Carolina State University, Raleigh, North Carolina 27650

A study was conducted on a C4 (Panicum maximum) and a C3 (Panicum bisulcatum) species to determine the nature of the dark release of 14CO2 with respect to its responses to changes in temperature and O2 tension during light CO2 uptake of 14CO2.

The total one minute uptake of 14CO2 increased with increased temperatures up to 30°C for both species at all O2 tensions.

The total release of 14CO2 during the first four minutes of dark by the C4 species was 5 to 10 times greater than the C3 species; however, there was no consistent pattern in the C4 species as a function of temperature or O2 tension. In contrast, the dark release by the C3 species was similar to that of light uptake as a function of temperature or O2 tension. The percentage of the one-minute 14CO2 fixation that was released as 14CO2 during the first four minutes of dark increased with O2 tension for the three highest temperatures (20, 30, and 38°C) and remained, though reduced, after a 10-minute dark chase in 12CO2 for the C3 species.

It was concluded that: (a) the source of the dark CO2 release in C3 species is different from that of C4 species; (b) the dark CO2 release in C3 species likely is derived from intermediates of photorespiration and is similar to the postillumination burst of CO2; and (c) the source(s) of the dark CO2 release in C4 species is not photorespiration.

1 Supported by Cooperative Agreement 12-12-7001-1049 between United States Department of Agriculture, Science and Education Administration and North Carolina Agricultural Research Service. Paper No. 6295 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, Noth Carolina.






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Copyright © 1981 by the American Society of Plant Biologists