Does integrative effects of glyphosate, gibberellin and hydrogen peroxide ameliorate the deleterious effects of the herbicide on sorghum seed through its germination?

Abstract

We investigated the interconnected roles of reactive oxygen species (ROS) generated upon seed exposure to glyphosate and/or gibberellic acid (GA₃), and the possible interaction between the herbicide and the plant hormone during germination of sorghum seeds. GA₃ decreased antioxidant enzyme activity in embryos, and the over accumulation of hydrogen peroxide (H₂O₂) in 1000 mM GA₃-treated seeds resulted in the lowest germinability among treatments. The deleterious effects of glyphosate on germination rate, in contrast, were not related to H₂O₂ accumulation, but to its interference with the mitochondrial electron transport chain. However, interactions among glyphosate, GA₃ and H₂O₂ during seed germination were observed. Similar to paclobutrazol, glyphosate appears to interfere with the de novo synthesis of gibberellin, which modulates seed germination through oxidative metabolism. Seeds experiencing increased oxidative status due to GA₃ (100 mM) or H₂O₂ (50 mM) applications had the effects of glyphosate on germination rate reversed. Since decreased ATP synthesis is a secondary effect of glyphosate, increased H₂O₂ concentrations in embryos must facilitate germination by decreasing the energy required by ATP-demanding metabolism. Our results showed that glyphosate affect seed germination of sorghum, and that the herbicide interacts with oxidative and gibberellin metabolisms.

Keywords: Antioxidants; Economic crops; Plant hormones; Reactive oxygen species; Shikimate.