The role of the sunflower seed coat and endosperm in the control of seed dormancy and germination: phytohormone profile and their interaction with seed tissues

The sunflower embryo is surrounded by a one-layered endosperm and a unitegmic seed coat, which are multifunctional tissues involved in dormancy and germination of sunflower seeds. Abscisic acid (ABA) and gibberellins (GAs), together with other phytohormones such as auxins (AUX) and Jasmonates (JAs), play an antagonist role in the regulation of seed germination and dormancy. Here, we investigated the role of the seed coat and endosperm in the imposition and release of sunflower seed dormancy in two inbred Helianthus annuus lines (B123 and B91), and evaluated the endogenous level of ABA, jasmonic acid (JA) and indol-3-acetic acid (IAA) in these tissues (either dry or imbibed). Histological analyses of these tissues were also performed in dry cypselas of both lines. The seed coat and endosperm, along with the embryo, displayed a relevant contribution in the imposition of seed dormancy in B123 line. B123 seed dormancy could be associated with a low content of ABA, JA and IAA in the seed coat and endosperm, and a high content of these phytohormones in the embryo. The release of B123 seed dormancy after a dry storage period showed increased ABA and JA contents in the seed coat and endosperm, but decreased levels in the embryo. The seed coat and endosperm, as well as the embryo showed a reduction in IAA after the storage period. Thus, the hormone metabolism and interaction between seed tissues play a relevant role in the release of B123 seed dormancy. The anatomy of the seed coat and one-layered endosperm showed no relevant differences between lines. Altogether, our results remark the relevance of the interaction between the seed coat, endosperm and embryo in the release of dormancy in sunflower seeds.