Pathways of CO₂ Fixation in the CAM Plant Kalanchoe daigremontiana. II* Effects of O₂ and CO₂ Concentration on Light and Dark CO₂ Fixation

Abstract

Steady-state fixation of CO*2 by leaves of K. daigremontiana was examined at O*2 concentrations of 4, 20 and 36%. Oxygen concentration had no effect on the rate of dark CO*2 fixation, whereas CO*2 fixation in the light was substantially inhibited by 20 and 36% O*2. Dark CO*2 fixation showed a high affinity for CO*2 (half-saturated at about 3 ¿M at 16°C) whereas CO*2 fixation in the light showed a much lower affinity for CO*2 (half-saturated at about 9 ¿M at 16°C and 37 ¿M at 29°C). The inhibition by O*2 of CO*2 fixation in the light was observed at intercellular CO*2 pressures up to 850 ¿bar. It was associated with a positive CO*2 compensation point which was abolished in 4% O*2, and a post- illumination burst of CO*2 evolution which was not modified by low O*2. The response of dark and light CO*2 fixation in K. daigremontiana to O*2 concentration is discussed in comparison with photosynthetic CO*2 fixation in C*3 and C*4 plants.