The control of root growth by reactive oxygen species in Salix nigra Marsh. seedlings.

The production of reactive oxygen species (ROS) in specific regions of Salix seedlings roots seems essential for the normal growth of this organ. We examined the role of different ROS in the control of root development in Salix nigra seedlings, and explored possible mechanisms involved in the regulation of ROS generation and action. Root growth was not significantly affected by OH quenchers, while it was either partially or completely inhibited in the presence of H₂O₂ or O₂·⁻ scavengers, respectively. O₂·⁻ production was elevated in the root apex, particularly in the subapical meristem and protodermal zones. Apical O₂·⁻ generation activity was correlated to a high level of either Cu/Zn superoxide dismutase protein as well as carbonylated proteins. While NADPH-oxidase (NOX) was probably the main source of O₂·⁻ generation, the existence of other sources should not be discarded. O₂·⁻ production was also high in root hairs during budding, but it markedly decreased when the hair began to actively elongate. Root hair formation increased in the presence of H₂O₂ scavengers, and was suppressed when H₂O₂ or peroxidase inhibitors were supplied. The negative effect of H₂O₂ was partially counteracted by a MAPKK inhibitor. Possible mechanisms of action of the different ROS in comparison with other plant model systems are discussed.