Hydration cycles and overcoming dormancy in Butia capitata (Arecaceae) diaspores

Key message Hydration cycles promote embryo physiological changes, favoring overcoming dormancy in Butia capitata seed banks. Abstract Dormant seeds can spend many years in soil seed banks while subject to successive hydration and dehydration cycles (HC). Our knowledge concerning the effects of HC on seed survival and on overcoming dormancy is still limited, especially among tropical species. We sought to evaluate structural and physiological aspects of the diaspores (pyrenes: seeds enclosed by the endocarp) of the neotropical palm Butia capitata submitted to HC (in association with thermal regimes) under laboratory conditions and in a simulated soil seed bank. Biometric, anatomical, histochemical, biomechanical (the resistance of restrictive structures to embryo growth), and physiological (viability, the potential for in vitro embryo elongation, germination, and endo-β-mannanase activity) evaluations were performed. HC, in association with thermal regime variations, positively affect the growth potential of the embryos, which is related to an increase in their water absorption capacity, increased cell division, embryo expansion, and endosperm reserve mobilization. Those changes result in a gradual decrease in dormancy intensity, allowing a gradual exit from the soil seed bank through germination. Diaspores of B. capitata present morphophysiological dormancy of a particular type that is characterized by restricted embryo growth inside the seed before germination, low levels of endosperm reserve mobilization, and the gradual overcoming of dormancy over several years. The ability to form soil seed banks is an important adaptive strategy when faced with a seasonal environment with irregular rainfall in which the species occurs.