Genetic, Developmental, and Within-Plant Variation in Free and Bound Coumarin Content of Sweetclover

Seeds of sweetclover contained a low level of both free and bound coumarin. An increase in both forms of coumarin occurred when seedlings were grown in the light, but no increase was found when they were kept in the dark. First- and second-year plants of Evergreen (CuB phenotype), W-7 (Cub), and W-31 (cu-) were sampled in the field at intervals throughout the 1959 growing season. Leaves, stems, and roots were assayed for free and total coumarin content. The level of free coumarin was highest in the leaves of plants of the CuB phenotype, with a small amount in stems and virtually none in roots. Bound coumarin was found in appreciable quantities in leaves, stems, and roots of CuB and Cub plants, although leaves had an appreciably higher level than stems, and stems contained a higher percentage than roots. The low content of free and bound coumarin in roots tended to remain constant throughout the season, whereas in leaves and stems a sharp drop in both forms was noted toward the end of the first season of growth and as the plants approached maturity in the second year. Plants of the Cu- phenotype were low in both forms of coumarin throughout the entire life cycle