Urease Metabolism in Citrullus

Abstract

SINCE the speculations by one of us¹ as to the function of urease in Citrullus seeds appear to have aroused interest, we feel we ought to report that further work has shown the original hypothesis (that urease is a reserve protein) to be untenable. We remain unconvinced that the metabolism of urease in Citrullus is connected with the metabolism of urea or its derivatives; but it does not appear to be a normal seed-reserve. First, we find that the protein content of the cotyledons of seedlings grown in a nitrogen-free culture medium may fall in eight days to about half its initial value; but the urease content may remain unchanged. Secondly, if seedlings are grown under optimal conditions in soil, we find in the cotyledons no appreciable change in major nitrogen fractions over ten days; but a reduction in urease begins to be apparent at about the fourth–sixth day, followed by a rapid fall almost to zero at about the eighth day. The rapid rise in water-content from about the fourth day shows that this is the time when cell-extension and vacuolation begin; and since Brown and Broadbent² have shown that this is a time of considerable metabolic activity, it seems likely that disappearance of urease is connected with its onset.