Structural changes in the micropylar region and overcoming dormancy in Cerrado palms seeds

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Interaction between embryo growth and cytochemical changes in the micropylar endosperm promote the overcoming of dormancy in Cerrado palm seeds. Dormancy in palm seeds is modulated by structural components. However, changes in the structures that are responsible for permitting the conclusion of germination are still poorly understood. This study aimed to identify morphological, anatomical, physiological and cytochemical changes during germination in the micropylar region of seeds of Cerrado palms (Acrocomia aculeata, Attalea vitrivir and Butia capitata) with different levels of dormancy. The role of opercular components, the effect of exogenous GA3, and endo-β-mannanase activity on embryo growth and opercular resistance were evaluated. Changes in protein reserves and in the pectic profile of the cell walls of the micropylar endosperm were investigated using cytochemical techniques. Dormancy is determined by the inability of the embryo to displace the operculum, whose resistance decreases with imbibition, but is not influenced by GA3 or endo-β-mannanase activity. Embryo growth prior to the conclusion of germination is directly related to the displacement of the operculum and is stimulated by GA3 in seeds of A. aculeata and A. vitrivir. Initially, the displacement of the operculum occurs with the separation of cells in the region of weakness of the micropylar endosperm after mobilization of protein reserves. The cell walls in the region of weakness are rich in pectic compounds, the composition of which varies over time. Although the mechanical effect of embryo growth is a determinant in the completion of germination, the remodeling of the pectic profile of the middle lamella and cell walls in the micropylar endosperm can be considered important in its control in palm seed.