Cytochrome c Oxidase as a Cause of Variation in Oxygen Uptake Rates Among Vegetables

The effect of cytochrome c oxidase, the terminal oxidase in the respiratory chain, on O 2 uptake by vegetables was investigated. Broccoli florets ( Brassica oleracea L. var. italica Plenck), spinach leaves ( Spinacia oleracea L.), and onion bulbs ( Allium cepa L.), which were expected to show rapid, moderate, and slow O 2 uptake rates, respectively, were used in the current study. The order of O 2 uptake rate measured by a closed method with a gas chromatograph was broccoli florets > spinach leaves > onion bulbs. Cytochrome c oxidase activity of mitochondrial preparations from onion bulbs was lower than that of the other vegetables, as was the O 2 uptake rate. The higher O 2 uptake rate of broccoli florets compared to spinach leaves was caused by higher cytochrome c oxidase activity of the floral buds. Grayscale luminance was used to determine the extent and distribution of staining in the tissues due to cytochrome c oxidase activity. Active O 2 uptake by floral buds of broccoli florets was caused by the high concentration of cytochrome c oxidase in the pistil and petal. The absorbance of stems of broccoli florets at 823 nm, possibly derived from absorption by copper in cytochrome c oxidase, was higher than that of onion scale leaves, which agreed with the results of cytochrome c oxidase staining. We concluded that cytochrome c oxidase contributed to the O 2 uptake rate by vegetables and that cytochrome c oxidase was one of the important causes for variation in O 2 uptake rates among vegetables.