Interaction between embryo and adjacent tissues determines the dormancy in macaw palm seeds

The macaw palm is an American oleaginous plant of great agro-industrial interest. The present study examined the effects of seed structures on the in vitro germination of zygotic embryos and the development of plantlets to increase our knowledge about the pronounced seed dormancy in this species and contribute to improving its propagation. To evaluate the existence of inhibitory substances, we tested the effects of contact of the embryo with the endosperm and the tegument, as well as the effects of aqueous extracts of these structures on lettuce seed germination. The mechanical restriction to germination and access to reserves were evaluated by the cultivation of isolated embryos and embryos enveloped by the endosperm and operculum. The treatments were combined with culture media with or without sucrose and different concentrations of gibberellic acid (GA(3)). Chemical inhibition of germination by the tegument or endosperm was not demonstrated. The germination of isolated embryos was 87%, while only 14% of the embryos in contact with endosperm and operculum germinated. Germination was promoted by GA(3) and sucrose only when the embryos were enveloped within the endosperm and operculum and the phytoregulator facilitated the access to endospermic reserves. Dormancy in A. aculeata seeds is related to failure of the embryo to overcome the resistance of the adjacent tissues. The methodology proposed can be used for investigation of the causes of dormancy in palm seeds.