Characterization of oxalate oxidase and cell death in Al-sensitive and tolerant wheat roots

Several genes including oxalate oxidase (Oxo) are upregulated in Triticum a estivum L, root tips exposed to Al. To better understand the function of Ox o during Al exposure, the protein level and enzyme activity were measured. The data indicate that both Oxo protein and activity are increased proporti onally to the level of root growth inhibition (RGI), A high level of Oxo ex pression may result in excess H2O2 production which could become toxic and induce cell death. However, the timing of H2O2 production (observed after 2 4 h) indicates that it cannot be the primary cause of cell death first obse rved after 8 h, Moreover, at Al concentrations resulting in 50% RGI, we did not observe any cell death in the sensitive cultivar while a punctated pat tern of death involving small groups of cells Tvas found in the tolerant cu ltivar, This pattern was maintained for several days in the tolerant cultiv ar, suggesting the involvement of a cell death mechanism aimed at replacing epidermal cells intoxicated with Al while root growth is maintained. The a ccelerated epidermal cell turnover may represent a new detoxification mecha nism helping to protect deeper cell layers of the meristematic and elongati on zone essential for root growth.