Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: January 3, 2008
Publication Date: February 13, 2009
Citation: Bethke, P.C. 2009. Rebirth and Death: Nitric Oxide and Reactive Oxygen Species in Seeds. In: Foyer, C., Faragher, R., Thornalley, P., editors. Redox Metabolism and Longevity Relationships in Animals and Plants. Vol. 62. New York, NY:Taylor and Francis Group. p. 17-30. Technical Abstract: Most seeds are dormant at maturity, and dormancy must be lost before germination can occur. The emergence of the embryo and its early growth depend on the coordinated activities of the embryo itself and the tissues surrounding it. We have used Arabidopsis seeds and barley grains to study the roles of plant hormones, nitric oxide (NO), and reactive oxygen species in dormancy loss, germination and post-germinative growth. Our data support the following sequence of events for dormancy and germination in these species. NO produced by the seed is perceived by the aleurone layer, a tissue that surrounds the embryo, and NO-perception promotes dormancy loss. NO perception leads to the transcription of genes in the embryo for the biosynthesis of the plant hormone GA. GA produced by the embryo up regulates the conversion of stored lipid to sugar in the embryo and aleurone. Cell wall degrading hydrolases weaken the aleurone cell wall and allow the embryonic root to break through. Hydrogen peroxide is generated as a by-product of lipid breakdown. In barley, GA represses the production of enzymes that metabolize reactive oxygen species. Aleurone cell death occurs as a result of reactive oxygen species damage, but NO acts as an antioxidant and delays death.