Aluminum toxicity recovery processes in root apices. Possible association with oxidative stress

Al inhibits root apex elongation with concomitant morphological injuries such as ruptures punctuated by the regions stained with Evans blue. The recovery can be investigated by transfer of Al-injured roots to a solution lacking Al. In the Al-injured root apex, superoxide anion, H2O2, Al, and lignin accumulate. During the recovery process, the central cylinder elongates leaving the region stained with Evans blue without marked disappearance. The obvious function of the region is not clear but may trigger the elongation of central cylinder during the recovery process. Thus the function of the region stained with Evans blue might be derived from the programmed cell-like idea. Oxidative stress concerns events induced under Al toxicity and the recovery process. The superoxide anion is primarily formed by plasma membrane-associated NADPH oxidase and is dismuted to H2O2 and O2 by superoxide dismutase. H2O2 provides the electrons for the polymerization of phenolics to lignin, which causes the stiffening of the cell wall. The distortion of the cell wall caused by lignin may induce the breaking and tearing of cells, which results in the formation of ruptures at the rhizodermis and outer cortex layers. The production of superoxide anion, H2O2, and lignin was reduced during the recovery process and thereby the elongation of the central cylinder may be induced.

► Al inhibits root elongation with ruptures, which are separated by the region stained with Evans blue.
► The central cylinder elongates primarily without the repair of ruptures at the early stage of recovery.
► These events are associated with oxidative stress.