The Influence of Embryo Restraint During Dormancy Loss and Germination of Fraxinus excelsior Seeds

Abstract

Evidence is presented which suggests that the embryo is constrained by its enclosing tissues, the endosperm and seed coat layers, and this constraint plays an important role in the control of germination in the deeply-dormant fruit of Fraxinus excelsior L. The puncture force required to penetrate the endosperm/seed coat layer opposing the radicle declined during the stratification treatment used to break dormancy. This change was independent of embryo growth and occurred in advance of dormancy loss during the cold (3°C) period of stratification, but it did not occur when seeds were kept at constant 15°C. The results suggest that a localized weakening of the seed coat/endosperm layers in front of the radicle is an essential part of the process of dormancy loss during cold stratification and subsequent germination of F. excelsior seeds.