Reactive oxygen species, ABA and nitric oxide interactions on the germination of warm-season C4-grasses

Hydrogen peroxide (H2O2) as a source of reactive oxygen species (ROS) significantly stimulated germination of switchgrass (Panicum virgatum L.) seeds with an optimal concentration of 20 mM at both 25 and 35 degrees C. For non-dormant switchgrass seeds exhibiting different levels of germination, treatment with H2O2 resulted in rapid germination (< 3 days) of all germinable seeds as compared to seeds placed on water. Exposure to 20 mM H2O2 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 H2O2 treatment, indicating the universality of the effect of H2O2 on seed germination in warm-season prairie grasses. For switchgrass seeds, abscisic acid (ABA) and the NADPH-oxidase inhibitor, diphenyleneiodonium (DPI) at 20 mu M retarded germination (radicle emergence), stunted root growth and partially inhibited NADPH-oxidase activity in seeds. H2O2 reversed the inhibitory effects of DPI and ABA on germination and coleoptile elongation, but did not overcome DPI inhibition of root elongation. Treatment with H2O2 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 H2O2 as compared to seeds maintained on water or on ABA. These data demonstrate that seed germination of warm-season grasses is significantly responsive to oxidative conditions and highlights the complex interplay between seed redox status, ABA, ROS and NO in this system.