Date of this Version
The influence of the two genes, cu and b upon the level and form of coumarin in sweetclover leaf tissue was determined by assaying 25 sweetclover plants of each of the four homozygous genotypes, CuCuBB, CuCubb, cucuBB, and cucubb. An assay of alfalfa leaves provided an indication of the magnitude of fluorescence not ascribable to coumarin. Approximately 0.2 percent total coumarin (dry weight basis) was found in plants homozygous for cu, which is 11.5 times the amount found in alfalfa, but only about 1/20 of the level found in CuCu plants. Thus, the cu-effected block in coumarin synthesis is partial rather than complete. However. the action of the b gene in blocking the formation of free coumarin is virtually complete, as shown by the extremely low levels of free coumarin in bb plants. The probable relationship of bound coumarin, free coumarin and the cu and b genes is shown. Important implications in sweetclover breeding, and in other studies are indicated.