title: Exogenous hydrogen peroxide reversibly inhibits root gravitropism and induces horizontal curvature of primary root during grass pea germination.
abstract: During germination in distilled water (dH(2)O) on a horizontally positioned Petri dish, emerging primary roots of grass pea (Lathyrus sativus L.) grew perpendicular to the bottom of the Petri dish, due to gravitropism. However, when germinated in exogenous hydrogen peroxide (H(2)O(2)), the primary roots grew parallel to the bottom of the Petri dish and asymmetrically, forming a horizontal curvature. Time-course experiments showed that the effect was strongest when H(2)O(2) was applied prior to the emergence of the primary root. H(2)O(2) failed to induce root curvature when applied post-germination. Dosage studies revealed that the frequency of primary root curvature was significantly enhanced with increased H(2)O(2) concentrations. This curvature could be directly counteracted by dimethylthiourea (DMTU), a scavenger of H(2)O(2), but not by diphenylene iodonium (DPI) and pyridine, inhibitors of H(2)O(2) production. Exogenous H(2)O(2) treatment caused both an increase in the activities of H(2)O(2)-scavenging enzymes [including ascorbate peroxidase (APX: EC 1.11.1.11), catalase (CAT: EC 1.11.1.6) and peroxidase (POD: EC 1.11.1.7)] and a reduction in endogenous H(2)O(2) levels and root vitality. Although grass pea seeds absorbed exogenous H(2)O(2) during seed germination, DAB staining of paraffin sections revealed that exogenous H(2)O(2) only entered the root epidermis and not inner tissues. These data indicated that exogenously applied H(2)O(2) could lead to a reversible loss of the root gravitropic response and a horizontal curvature in primary roots during radicle emergence of the seedling.
authors.affiliation: School of Life Sciences, Lanzhou University, Lanzhou 730000, China.
authors.forename: Jinglong
authors.initials: J
authors.lastname: Jiang
authors.forename: Miao
authors.initials: M
authors.lastname: Su
authors.forename: Liyan
authors.initials: L
authors.lastname: Wang
authors.forename: Chengjin
authors.initials: C
authors.lastname: Jiao
authors.forename: Zhengxi
authors.initials: Z
authors.lastname: Sun
authors.forename: Wei
authors.initials: W
authors.lastname: Cheng
authors.forename: Fengmin
authors.initials: F
authors.lastname: Li
authors.forename: Chongying
authors.initials: C
authors.lastname: Wang
mesh_terms: D002374:Catalase / Q000378:metabolism; D016166:Free Radical Scavengers / Q000494:pharmacology; D018525:Germination / Q000187:drug effects*; D018522:Gravitropism / Q000187:drug effects*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D027807:Lathyrus / Q000187:drug effects* / Q000502:physiology; D016877:Oxidants / Q000494:pharmacology*; D010544:Peroxidases / Q000378:metabolism; D018517:Plant Roots / Q000033:anatomy & histology / Q000187:drug effects* / Q000502:physiology; D012639:Seeds / Q000187:drug effects / Q000502:physiology*; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D016166:Free Radical Scavengers; D016877:Oxidants; C038983:1,3-dimethylthiourea; D006861:Hydrogen Peroxide; D010544:Peroxidases; D002374:Catalase; D013890:Thiourea