REDEFINING SEED DORMANCY - AN ATTEMPT TO INTEGRATE PHYSIOLOGY AND ECOLOGY

1 The paper reviews the literature on seed dormancy, with special rega rd to inconsistencies in terms and definitions used. It presents a con cept of seed dormancy in which physiology and ecology are integrated. Its aim is to increase the understanding of seed dormancy and germinat ion, and to help defining ecological research questions. 2 It is claim ed that seed dormancy should not be identified with the absence of ger mination. Seed dormancy should rather be defined as a characteristic, the degree of which determines the range of conditions in which a seed is able to germinate. Dormancy varies on a continuous scale, which is visualized by continuous changes in the range of conditions suitable for germination. If the conditions required by the seed are met by its environment, the seed will germinate. 3 The concept of dormancy that is described in the paper is partly based on a physiological model for the regulation of dormancy and the stimulation of germination. In thi s model dormancy is related to the amount of a hypothetical phytochrom e receptor in the seed. 4 It is argued that the process of dormancy re lease should be clearly distinguished from the germination process its elf. It is stated that as yet only temperature has been shown to alter the degree of dormancy in seeds. Factors like light and nitrate are o ften indispensable for germination, but only by promoting the germinat ion process itself, not by mitigating the requirements for germination . 5 It is suggested that seed dormancy prevents germination when condi tions are favourable for germination, at a time of the year when it ca n be expected that the plant originating from the seed will not surviv e and produce offspring. 6 It is concluded that dormancy should not be regarded as inactivity of seeds. At any degree of dormancy, seeds con tinuously react to their environment by adjusting their level of dorma ncy to the changing environment.