Cations of Al and rare earth elements (REEs) are phyto-toxic.1 The toxicity of such cations has been summarized as followings: (1) metal cations induce the production of superoxide (O2) in plant cells; (2) the metal cations with higher valence induce greater oxidative burst (OXB); (3) with higher ion valence, the concentration required for maximal response is minimized; (4) the induced OXB is sensitive to inhibitors of NADPH oxidase.2 To date, non-redox metal cations such as those of Al,3 La,M Ce,5 and Gd, have been shown to induce OXB.
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