Diaspore structure and germination ecophysiology of the babassu palm (Attalea vitrivir)

Both germination and seedling establishment in palm trees are strongly influenced by the morphoanatomy of the fruits, although the interactions of these processes with ecophysiological aspects are not yet well understood. The present work evaluated structural and physiological aspects of seed germination in Attalea vitrivir, a species living under the seasonal climate of the Cerrado (Brazilian savanna) biome. We studied morphology, anatomy and histochemistry of the fruits and seedlings, the effects on germination of the pericarp, of diaspore storage conditions, germination temperature, removal of the operculum, and of gibberellic acid (GA3) application, and characterized the imbibition process of the seeds. Germination depends on a series of complex interactions between structures and physiological processes. The pericarp protects the seed and also causes physical dormancy that, when interacting with the temperature regime, can delay germination until subsequent rainy periods. Some seeds demonstrated non-profound physiological dormancy associated with restricted germination imposed by the operculum. Germination and initial development result from the elongation of the cotyledon cells and are affected by the activities of two distinct meristems in the proximal region of the embryo. The haustorium develops an invaginated secretory epithelium and aerenchyma, and actively participates in seed reserve mobilization. The adaptation of A. vitrivir to the Cerrado environment, with a strongly seasonal climate, is favored by its diaspore structure, by the abundance of endosperm reserves that allow the seedlings to survive for a long period above soil level, and by a seedling development pattern that protects the vegetative axis by deep burial.