Nitrate Reductase in the Citrus Plant: Properties, Assay Conditions and Distribution within the Plant

A nitrate reductase enzyme preparation has been obtained from citrus plant tissue extract and the optimal assay conditions have been established. The enzyme has been found to be similar or even identical to those of many other annual plants, i.e., cysteine is required for its extraction in the active state, it is DPNH‐specific, and in some cases FAD‐dependent. Comparisons were made between the activity measured in fragments with that of the extracted preparation of the same plant tissues. The occurrence of the enzymes was demonstrated in germinating seeds, cotyledons, rootlets, shoots, leaves and fruit of citrus plants.