Photosynthetic Oxygen Exchange in Isolated Cells and Chloroplasts of C3 Plants

Abstract

Photosynthetic O2-production and photorespiratory O2-uptake were measured, using stable isotope techniques, in isolated intact leaf cells of the C3 plant Xanthium strumarium L. and isolated intact chloroplasts of Spinacia oleracea L. (cv. Yates 102). Considerable light dependent O2-uptake occurred in both systems, a proportion of which could be suppressed by CO2 (63% suppression in chloroplasts by 50 .mu.M CO2, 58% in cells by 100 .mu.M CO2 and 250 .mu.M O2). At low O2, O2-uptake was CO2 insensitive. At high CO2 up to 19% of total electron flow was to O2 in cells and up to 14% in chloroplasts. O2-uptake showed inhibition by KCN (61% in cells, 35% in chloroplasts by 0.2 mM KCN). O2-uptake half saturated at 75-85 .mu.M O2 in cells and 50-65 .mu.M O2 in chloroplasts, at low CO2. RuP2[ribulose 1,5-bisphosphate]-oxygenase reaction and direct photoreduction of O2 via a Mehler reaction are discussed.