Respiratory Mechanisms in the Aroid Spadix

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Abstract
The flowers of Skunk-cabbage ( Symplocarpus foetidus ), like the spadix tissues of other Aroids, have a rapid, carbon monoxide and cyanide (HCN) resistant respiration; oxygen uptake is independent of the oxygen partial pressure over a wide range. Cell fractions were isolated by differential centrifugation and their oxidative activities studied. Oxidation of succinate and citrate by mitochondria can be inhibited 50 to 60 per cent. by 1 X 10 −3 M. HCN, and antimycin A (AA) causes partial inhibitions. An active mitochondrial cytochrome-c oxidase is present, and it shows a typical sensitivity to cyanide. The mitochondria possess an active reduced diphosphopyridine-nucleotide (DPNH) oxidase system, which is inhibited roughly 80 per cent. by 1 X 10 −3 M. HCN and 1.7 μg./ml. AA. The microsomal DPNH oxidase, which is less sensitive to inhibitors, is less active per gramme of tissue than that on the mitochondria. The final supernatant shows little DPNH oxidase. With all fractions, reduced triphosphopyridine nucleotide (TPNH) is oxidized much more slowly than DPNH. DPNH-cyto-chrome-c reductase activity was measured; the mitochondrial system is partially blocked by AA, whereas the microsomal activity is AA-insensitive. Spectro-photometric examination of a preparation of solubilized mitochondria showed that cytochromes a, b, and c are present. The results are discussed with reference to the pathway and localization of hydrogen and electron transport in the Aroid spadix.