Histological reorganization and spatiotemporal distribution of cell wall epitopes during somatic embryogenesis in oil palm (Elaeis guineensis Jacq.)

Abstract Somatic embryogenesis is a key strategy for the clonal propagation of elite oil palm ( Elaeis guineensis Jacq.) genotypes. Although several protocols have been established, the structural aspects underlying the induction of embryogenic callus in this species remain unknown. The present study aimed to elucidate the cellular aspects associated with the acquisition of embryogenic competence, with emphasis on callus ontogeny and cell wall dynamics. Immature leaf explants were cultured and analyzed at different developmental stages using light microscopy, scanning electron microscopy, histochemical assays, and immunocytochemistry. The results demonstrated that callus formation originates from procambial cells, with initial proliferation through periclinal divisions followed by the organization of globular structures. A heterogeneous callus was observed, comprising peripheral regions formed by vacuolated cells with thickened cell walls and internal regions composed of cells exhibiting embryogenic features, such as dense cytoplasm and a prominent nucleus. Histochemical analyses revealed a high protein content in the central zone of the callus, polysaccharide accumulation in the peripheral zone, and greater starch deposition in the peripheral zone. Furthermore, immunolocalization analyses indicated a dynamic reorganization of cell wall glycoproteins and pectins during the process, suggesting structural modifications associated with cellular reprogramming and somatic embryo formation. Taken together, these findings demonstrate that somatic embryogenesis in E. guineensis involves coordinated changes in cellular organization and cell wall composition, providing a structural framework for a better understanding of the cellular events underlying somatic embryogenesis in oil palm.