Temperature-mediated changes in the force balance of the micropylar region adjust overcoming of dormancy to seasonality in diaspores of the Neotropical palm Butia capitata

BACKGROUND AND AIMS: Butia capitata diaspores require years to germinate due to dormancy, determined by the association between an embryo with low growth potential and restrictive sites of a seminal and pericarpal nature. The species is endemic to the highly seasonal environment of the Cerrado biome. We evaluated the role of temperature in controlling the force balance of the micropylar region, aiming to characterize the relationship between overcoming dormancy and adaptation of germination to seasonality. METHODS: A wide range of thermal regimes was applied to isolated embryos, isolated seeds and diaspores (i.e. pyrenes = seeds enclosed by the endocarp). Pyrenes were subjected to thermal cycles: 11 alternating temperature regimes (90 days) + 30 °C (30 days), in association with moisture conditions (dry and moist) in freshly harvested pyrenes and pyrenes subjected to conditioning (1-year storage, burial in the greenhouse, burial in the natural environment and after-ripening), totaling 168 treatments. In each thermal cycle, germination and the force balance in the micropylar region (embryo growth potential vs. the resistance of adjacent tissues) were evaluated. KEY RESULTS: Thermal variation differentially affects the interaction sites of the micropylar region, which favors the maintenance of dormancy. The heterogeneity of diaspores makes the overcoming of dormancy dependent on thermal cycles, which results in germination being spread out over years. 35/20 °C regime contributes to overcoming dormancy (germination rates of 92%), at the end of the second thermal cycle. CONCLUSIONS: Temperature plays a crucial role in overcoming seed dormancy. The thermal regime occurring at the transition between the dry and rainy seasons promotes dormancy overcoming, synchronizing germination with ecological windows of opportunity for seedling establishment, during the wet season. These results broaden our understanding of the mechanisms involved in overcoming seed dormancy in palms and other species with woody, indehiscent endocarps, especially those from seasonal environments.