Al3+ exclusion in macaúba palm diaspores: structural and cytological aspects

Abstract The oil palm macaúba ( Acrocomia aculeata ) maintains seed banks in soils rich in Al 3+ of the Cerrado biome. However, the interaction of this cation with complex diaspores such as those of Arecaceae is still poorly understood. We aimed to evaluate the role of diaspore structure and embryonic cytology in the tolerance of the species’ seeds to Al 3+ . Diaspores (seeds enclosed by the endocarp) were exposed to Al³⁺ (0, 500, 1000, 2000, 4000 and 8000 µM L − 1 ) for 60 days. The histolocalization of Al³⁺ in the seed was performed, and viability, cell membrane functionality, and embryonic respiratory activity were evaluated. Al³⁺ retention by diaspore components was evaluated using quantitative and histochemical methods. Isolated embryos were immersed in the same solutions, and the quantification and histolocalization of Al³⁺ were performed, evaluating its effect on cell structure. Embryo viability and in vitro development were evaluated. The pericarpal structures and the seed coat restrict the penetration of Al³⁺ towards the endosperm and embryo, which maintains the physiological status of the seeds. In embryos, Al³⁺ is retained in the cell walls and also compartmentalized in vacuoles at the periphery of the cotyledon, thus preserving the embryo axis. In vitro development is not affected, and only 8000 µM L − 1 of Al³⁺ reduces embryo viability. Macaúba diaspores are highly tolerant to Al³⁺, exhibiting exclusion mechanisms in both pericarpal structures and embryonic cells. These mechanisms preserve the embryo axis and favor the species’ adaptation to vast regions of the Cerrado biome.