Extracts from ripe fruit and seeds of Sorbus aucuparia inhibit germination of other seeds, tested with Amaranthus caudatus and Lepidium sativum. The main compound of the “neutral fraction” of fruit extracts is the lactone compound parasorbic acid (4 -7 mg/g fresh weight) which inhibits germination at concentrations ≧ 5 × 10-4 ᴍ. The “acid fraction” contains abscisic acid (1.3-2.5 µg/g fresh weight) and isopropylmalic acid (1.0-1.5 µg/g fresh weight) as germination inhibitors. Whereas abscisic acid inhibits germination of L. sativum at concentration ≧ 5 × 10-7 ᴍ, germination of A. caudatus is inhibited only at concentrations ≧ 10-5 ᴍ. This is probably due to differences in uptake of the acid because abscisic acid methylester inhibits germination of both species at concentrations ≧ 5 × 10-7 ᴍ. Isopropylmalic acid belongs to a structural type of germination inhibitors which had already been detected in oat extracts.
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