The impacts of exogenous H2O2 on primary root horizontal bending of pea (Pisum sativum L.)

Root gravitropism makes plant roots maintain a definite growth toward gravity direction. In this study, the garden pea seeds were used to investigate the impacts of exogenous hydrogen peroxide on the primary root horizontal bending. The results showed that exogenous H2O2 inhibited primary root gravitropism and induced horizontal bending at the initial stage of the pea seed germination, and the curvature was more severe with the increase of H2O2 concentration. The horizontal bending emerged before the radicale broke through the seed coat, after which the bending could not appear, and the earlier H2O2 treated, the more obvious the effect showed. In accordance with cytohistological observations, an asymmetrical cell-elongation generated at the elongation zones of the bending root, in which the outer layer cells was remarkably wider than the inner layer cells. Besides, it was only found in Papilionoideae that the primary root horizontal bending was induced by exogenous H2O2. As the H2O2 concentrations raised, the content of gibberellin A(3) (GA(3)) increased, which stimulated the activity of alpha-amylase (EC3.2.1.1) and promoted the hydrolysis of root starch, so the root-cap parts were dyed much lighter with the raising concentrations of H2O2. Finally, the root tip lost gravisensing and horizontally bended.