MECHANISM OF SEED DORMANCY IN CYNOGLOSSUM-OFFICINALE L

Roles of seed coat and methanol-extractable phenolic substances in reg ulation of Cynoglossum officinale L. seed dormancy were studied. Remov al of the seed coat resulted in nearly complete germination of innatel y dormant seeds. The seed coat did not substantially retard water upta ke nor did it contain any water soluble germination inhibitor, but the O2 uptake of seeds increased approximately six-fold upon removal of t he seed coat. The increase in O2 uptake induced by seed-coat removal w as due to both an increase in seed respiration (measured by CO2 evolut ion) and a high level of non-respiratory O2 consumption. C. officinale seeds contained high levels of phenolic substances, and seed extracts showed high polyphenol oxidase activity. Analysis of the pattern of m ethanol-extractable phenolic substances, however, showed no significan t quantitative or qualitative correlation between changes in specific phenolic compounds and seed germination induced by stratification or s eed-coat removal. It is concluded from this study that C officinale se ed coats inhibit seed germination by controlling O2 availability to th e embryo.