De novo ABA synthesis and expression of seed dormancy in a gymnosperm: Pseudotsuga menziesii

Seeds of dormant Douglas-fir seeds germinated poorly when they were cultivated at 20-23 degrees C while isolated embryos germinated fully within two weeks. Seed dormancy was therefore imposed on the embryo by its surrounding structures. This physiological behaviour was well correlated with changes in ABA level during culture. Indeed, the ABA level decreased in isolated embryos while it increased in both embryo and megagametophyte during culture of whole seeds. The origin of this increase was analysed and the different ways by which seed coats could interfere with ABA accumulation are discussed.