Control of seed germination in the shade

Seeds consist of encapsulated plant embryos in a highly resistant and desiccated state. Seeds enhance plant fitness by allowing plants to withhold their growth until the appearance of appropriate environmental conditions. Thereupon, seeds germinate, allowing the resumption of the plant’s life cycle. However, protection and propagation is not expected per se to confer fitness without germination control mechanisms avoiding potentially fatal starts such as germination in an inappropriate season or in the face of sudden environmental changes in light or water quality. It is therefore not surprising that multiple levels of germination control mechanisms have appeared during plant evolution. The first level, present in most plant species, including in the model plant Arabidopsis, is that of seed dormancy where the germination of newly produced seeds is blocked even under favorable germination conditions (i.e., presence of adequate water and light). Seeds must therefore first lose their dormancy in order to germinate. Dormancy is progressively lost over time (after-ripening) or following a cold treatment under wet conditions (stratification). Once seeds become post-dormant (i.e., able to germinate when exposed to adequate germination conditions), a second level of germination control unfolds, where the pace of germination is adjusted in response to the specific physical parameters of the seed’s environment. In Arabidopsis, as in many plant species, the seed coat is essential to prevent dormant seed germination, since its removal triggers embryonic growth. The Arabidopsis seed coat consists of an outer layer of dead tissue, the testa, and a single Control of seed germination in the shade