For non-dormant switchgrass seeds exhibiting diVerent levels of germination, treatment with H 2 O 2 resulted in rapid germination (<3 days) of all germinable seeds as compared to seeds placed on water. Exposure to 20 mM H 2 O 2 elicited simultaneous growth of the root and shoot system, resulting in more uniform seedling development. Seeds of big bluestem (Andropogon gerardii Vitman) and indiangrass [Sorghastrum nutans (L.) Nash] also responded positively to H 2 O 2 treatment, indicating the universality of the eVect of H 2 O 2 on seed germination in warm-season prairie grasses. For switchgrass seeds, abscisic acid (ABA) and the NADPH-oxidase inhibitor, diphenyleneiodonium (DPI) at 20 M retarded germination (radicle emergence), stunted root growth and partially inhibited NADPH-oxidase activity in seeds. H 2 O 2 reversed the inhibitory eVects of DPI and ABA on germination and coleoptile elongation, but did not overcome DPI inhibition of root elongation. Treatment with H 2 O 2 appeared to enhance endogenous production of nitric oxide, and a scavenger of nitric oxide abolished the peroxide-responsive stimulation of switchgrass seed germination. The activities and levels of several proteins changed earlier in seeds imbibed on H 2 O 2 as compared to seeds maintained on water or on ABA. These data demonstrate that seed germination of warm-season grasses is signiWcantly responsive to oxidative conditions and highlights the complex interplay between seed redox status, ABA, ROS and NO in this system.