Mechanism of seed dormancy in Cynoglossum officinale L.
Roles of seed coat and methanol-extractable phenolic substances in regulation of Cynoglossum officinale seed dormancy were studied. Removal of the seed coat resulted in nearly complete germination of innately dormant seeds. The seed coat did not substantially retard water uptake nor did it contain any water soluble germination inhibitor, but the O2 uptake of seeds increased approximately six-fold upon removal of the seed coat. The increase in O2 uptake induced by seed-coat removal was due to both an increase in seed respiration (measured by CO2 evolution) 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 [catechol oxidase] activity. Analysis of the pattern of methanol-extractable phenolic substances, however, showed no significant quantitative or qualitative correlation between changes in specific phenolic compounds and seed germination induced by stratification or seed-coat removal. It is concluded from this study that C. officinale seed coats inhibit seed germination by controlling O2 availability to the embryo.