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Abstract
Effects of potassium cyanide (KCN), salicylhydroxamic acid (SHAM), and oxygen concentrations on mitochondrial respiration were investigated in purified mitochondria of a typical phosphoenolpyruvate carboxykinase (PCK) crassulacean acid metabolism (CAM) plant Ananas comosus (pineapple) and a typical malic enzyme (ME)-CAM plant Kalanchoë daigremontiana. Mitochondria of A. comosus oxidized succinate and NADH faster than that of K. daigremontiana. Succinate and NADH oxidations in mitochondria of both species were partially inhibited by KCN and SHAM, indicating that these oxidations were connected to cytochrome and alternative pathways in their electron transport chain (ETC). NADH oxidation was more sensitive to KCN than succinate oxidation, suggesting that the ETC from NADH oxidation was less connected to the alternative pathway than that from succinate in mitochondria of both species. Concurrent oxidation of succinate and NADH resulted in much higher rates of cytochrome and alternative respirations than each individual oxidation alone in both species. NADH oxidation in A. comosus mitochondria was more connected to the cytochrome pathway, so A. comosus could produce much more ATP than K. daigremontiana. This capacity might be one of the fitting mechanisms of A. comosus to produce a sufficient amount of ATP for cytosolic PCK in the daytime. In addition, the reduction of oxygen concentrations decreased not only the cytochrome respiration, but also the alternative respiration on succinate oxidation in mitochondria of both species, and the decrease was greater in K. daigremontiana than in A. comosus.
