Seed dormancy is a dynamic state: variable responses to pre- and post-shedding environmental signals in seeds of contrasting Arabidopsis ecotypes

Seeds have evolved to be highly efficient environmental sensors that respond not only to their prevailing environment, but also their environmental history, to regulate dormancy and the initiation of germination. In the present work we investigate the combined impact of a number of environmental signals (temperature, nitrate, light) during seed development on the mother plant, during post-shedding imbibition and during prolonged post-shedding exposure in both dry and imbibed states, simulating time in the soil seed bank. The differing response to these environments was observed in contrasting winter (Cvi, Ler) and summer (Bur) annual Arabidopsis ecotypes. Results presented show that environmental signals both pre- and post-shedding determine the depth of physiological dormancy and therefore the germination response to the ambient environment. The ecotype differences in seed response to ambient germination conditions are greatly enhanced by seed maturation in different environments. Further variation in response develops following shedding when seeds do not receive the full complement of environmental signals required for germination and enter the soil seed bank in either dry or imbibed states. Species seed dormancy characteristics cannot therefore be easily defined, as seed dormancy is a dynamic state subject to within-species adaptation to local environments.