Testa structure in Erythrina speciosa (Leguminosae): the role of the mucilaginous stratum in the acquisition of physical dormancy

Abstract

Seeds of Erythrina speciosa (Papilionoideae) exhibit physical dormancy, but evidence has suggested that the proportion of impermeable seeds increases with storage. There are no records of structural variation in the testa of E. speciosa that justifies the difference in the percentage of seeds with physical dormancy. Therefore, the present study investigated the difference in permeability between mature seeds of E. speciosa that were freshly collected and those stored for 12 months. Seeds were examined for changes in testa structure that could result in differences in the percentage of seeds in physical dormancy. Thus, imbibition curves and water gaps were determined, and surface micromorphology, anatomy, and histochemistry of the testa were described. Our results revealed that the proportion of seeds with physical dormancy was higher in stored than in freshly collected seeds, with no anatomical changes in the testa to cause this difference. The analysis of surface micromorphology revealed that, in the lateral region of the seed (the water gap), the mucilaginous stratum was discontinuous in the freshly collected seeds and continuous in stored seeds. These results revealed that the mucilaginous stratum plays an important role in the acquisition and establishment of physical dormancy in E. speciosa.