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

The seed coat is a multifunctional tissue that plays an important role in dormancy and germination of sunflower seeds. In addition, abscisic acid (ABA) and gibberellins (GAs) are the primary phytohormones that antagonistically regulate seed dormancy, although other phytohormones such as auxins (AUX) and Jasmonates (JAs) also play a critical role in the modulation of these processes. Here, we investigated the role of the seed coat in imposition and release of sunflower seed dormancy. We evaluated the endogenous level of ABA, jasmonic acid (JA) and indol-3-acetic acid (IAA) in dry and imbibed seed coats of two inbred Helianthus annuus lines (B123 and B91), and analysed the seed coat anatomy of their dry cypselas. The results showed that the dormancy of B123 seeds is associated with a low content of ABA, JA and IAA in seed coat, and a high content of these phytohormones in the embryo. A dry storage period increased ABA and JA contents in the seed coat, although it decreased them in the embryo. Both the embryo and seed coat showed a reduction in IAA after the storage period. No relevant differences were registered in the histological analysis of the seed coat. Altogether, our results remark the relevance of the interaction between the seed coat and the embryo in the release of dormancy in sunflower seeds.