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

摘要

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.