Photorespiration and the postillumination CO2 burst

Abstract

An open system of gas analysis was used to study the kinetics of the short postillumination CO2 burst (PIB) from soybean leaves. After correcting for the sample volume in the gas analyzer (IRGA), we found that the maximum measurable rate of CO2 evolution occurred within 8 s after the sudden reduction in light intensity, lasted for about 6 s, and then declined rapidly. The corrected rate was 45% higher than the rate indicated by the IRGA output. The maximum rate of the PIB was proportional to the effect of light intensity on the preceding apparent rate of photosynthesis in 21% O2 and 350 ppm CO2. A similar proportionality was found between the PIB and the light intensity in each of the five parts of the visible spectrum which were tested. No PIB was found when the O2 concentration was reduced to less than 2% O2. The effect of 21% O2 on the rate of CO2 evolution after 8 s in the dark relative to the rate in 2% O2 was about 20% greater than the effect of 21% O2 on apparent photosynthesis in the preceding light period. This difference may be ascribed to internal refixation during photosynthesis.The results supported the theory that photorespiration continues for a short period longer than photosynthesis after a sudden reduction in light intensity. This period is much shorter than previous papers have indicated. The action spectrum for the PIB provides no support for flavin-activation as the mechanism of the light effect.