Photosynthesis in enzymatically isolated leaf cells from the CAM plant Sedum telephium L.

A technique has been developed for the enzymatic isolation of leaf cells from the Crassulacean acid-metabolism plant Sedum telephium. The cells exhibited high activity in both ¹⁴CO₂ incorporation (30–70 mol CO₂ mg^-1 chlorophyll h^-1) and O₂ evolution in the presence of bicarbonate (60–110 mol O₂ mg^-1 chlorophyll h^-1). Half-maximum saturation of ¹⁴CO₂ incorporation occurred at a bicarbonate concentration of ca. 2 mM (20 M CO₂) at pH 8.4 and 30°C. Two types of light-dependent O₂ evolution are reported: O₂ evolution in the absence of exogenously supplied bicarbonate (endogenous O₂ evolution), and bicarbonate-stimulated O₂ evolution. Oxygen evolution in the presence of approximately ambient concentrations of CO₂ appeared to be a combination of the endogenous O₂ evolution and O₂ evolution from fixation of the exogenously supplied CO₂.Abbreviations CAM Crassulacean acid metabolism - cirlo chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PEP phosphoenolpyruvate - RuDP ribulose-1,5-diphosphate