ADDITIONAL INDEX WORDS. enzymatic activity, image analysis, staining, Brassica oleracea, Spinacia oleracea, Allium cepa ABSTRACT. 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.
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