Zinc induced phytotoxicity mechanism involved in root growth of Triticum aestivum L.

This study investigated the inhibition mechanism of root growth in wheat seedlings when exposed to different zinc (Zn) concentrations. All applied Zn concentration did not affect seed germination, but reduced root length; in contrast, only Zn at 3 mM inhibited significantly the growth of shoot. The loss of cell viability and the significant increases of lignification as well as the increases of hydrogen peroxide (H2O2), superoxide radical (O2−) and malondialdehyde levels were observed in the root tissue exposed to Zn treatment. And also, Zn stress led to the inhibition of cell-wall bound peroxidase. Moreover, NADPH oxidase inhibitor diphenylene iodonium could block greatly the elevation of O2− generation in Zn-treated roots. Therefore, the increased H2O2 generation was dependent on the extracellular O2− production derived from plasma membrane NADPH oxidase. In addition, the loss of cell viability and the significant increases of lignification in response to the highest Zn concentration may be associated with the remarkable reduction of root growth in wheat seedlings.

► The inhibition mechanism of root growth in response to Zn was investigated.
► The increases of H2O2 and O2− levels were observed in the root under Zn treatment.
► Extracellular H2O2 generation dependent on plasma membrane NADPH oxidase.
► The loss of cell viability was responsible for root growth reduction due to Zn.
► The increase of lignification was responsible for root growth reduction due to Zn.