Absence of Dominance of the B Gene in Influencing ,&glucosidase Activity in Melzlotus Alba'

N sweetclover (Melilotus alba Desr.) the allelic pair designated B/b was I originally thought to be concerned with coumarin biosynthesis. Extracts of BB plants were reported to contain substantial amounts of both free and bound coumarin, while extracts of bb plants contained only bound coumarin (GOPLEN. GREENSHIELDS and BAENZIGER 1957; HASKINS and GORZ 1957), more recently identified as coumarinic acid glucoside (P-D-glucosyl-cis-o-h ydroxycinnamic acid) (KOSUGE 1961 ; STOKER and BELLIS 1962). The bound-coumarin character behaved as a simple recessive in crosses between bb and BB plants (GOPLEN, GREENSHIELDS and BAENZIGER 1957). SCHAEFFER, HASKINS and GORZ (1960) reported enzyme preparations of leaves of the BB genotype to be high in ,&glucosidase activity but detected no activity in preparations of bb leaves. Inasmuch as the activity of BB leaf extracts was not reduced by the addition of bb preparations, the absence of activity in the latter preparations probably was not caused by soluble ,+glucosidase inhibitors. Plants of the Bb genotype were not included in this comparison. These authors suggested that the effect of the B gene on ,&glucosidase activity was responsible for the influence of this gene on coumarin formation. Thus, in BB plants a portion of the coumarinic acid glucoside was presumed to be hydrolyzed by P-glucosidase, yielding coumarinic acid ( cis-o-hydroxycinnamic acid) which lactonized spontaneously, producing coumarin. Other studies (RUDORF and SCHWARZE 1958; HASKINS and GORZ 1961a) have shown that the existence of free coumarin in sweetclover extracts is largely an artifact of the extraction procedure, and have therefore raised doubt as to whether /3-glucosidase actually has a role in coumarin formation in vivo. Regardless of whether ,&glucosidase has such a role, there is no apparent reason to doubt the influence of the B/b alleles on the activity of this enzyme in sweetclover leaf preparations. Accordingly, the present experiments were designed to furnish information on the degree of dominance of the B gene with respect to p-glucosidase activity.