After Ripening and Abscisic Acid Mediated Changes in the Expression of Brassinosteroid and Ethylene Genes in Wheat Seeds

Seed dormancy is a trait that inhibits seed germination under optimal conditions. After ripening of a dormant seed leads to several physiological changes including changes in seed hormone level and responsiveness. Ethylene (ET) and brassinosteroids (BR) are implicated in the regulation of seed dormancy and germination. In this study, we examined the effect of after ripening and ABA on the germination of wheat seeds, and the expression of ET and BR biosynthesis and signaling related genes. While no seed dormant seed germinated within 24 h, the after-ripened seeds exhibit 95% of germination. This effect of after-ripening on germination is associated with the upregulation of specific BR-related genes including de-etiolated 2 and dwarf 4 (BR biosynthetic genes), related to ABI3/VP1 and BR signaling kinase (positive regulators of BR signaling), and BR insensitive 2 (negative regulator of BR signaling). Furthermore, upregulation of the ET biosynthesis gene, 1-aminocyclopropane-1-carboxylic acid oxidase, and the ET receptor gene, ET response sensor1 accompanied the germination of after-ripened seeds. ABA treatment delayed the germination of after-ripened seeds, and at the same time downregulated the expression of BR signaling kinase. No change in the expression of ET biosynthesis or signaling genes was induced by the ABA treatment.