Induction mechanism of and protection mechanism against the peroxidation of lipids in plant cells.

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Aluminum (Al) is thought to be a major factor to inhibit plant root growth in acid soils. Molecular mechanisms of Al toxicity and also of Al tolerance were investigated in cultured tobacco cells and pea roots.In tobacco cells in nutrient medium containing Fe ion (II, III), Al stimulated the Fe-mediated peroxidation of lipids which caused apoptosis-like cell death including internucleosomal breakage of DNA. Two-types of Al-tolerant tobacco cell lines were isolated and investigated specificity of the tolerance phenotype. Since they showed tolerance also to various kinds of reagents (HィイD22ィエD2OィイD22ィエD2, t-butyl hydroperoxide, A23187) which induce the peroxidation of lipids, it seems that they acquired a tolerant mechanism against the peroxidation of lipids. ON of the cell line accumulated phenolics, and the major one was identified as caffeoyl putresine by LC/MS and NMR. Caffeoyl putresine protected tobacco cells from the peroxidation of lipids cause by a combination of Al and Fe (II). This cell line also exhibit an enzymatic activity similar to glutathione peroxidase in animal systems.In pea roots, Al also enhanced the peroxidation of lipids, but did not require the coexistence of Fe. The peroxidation of lipids was one of the early events caused by Al. The Al-enhanced peroxidation of lipids was not cause of the inhibition of root elongation during Al treatment, but was partly a cause of the inhibition of root re-growth in Al-free medium.The results indicate that Al enhances the peroxidation of lipids in both cultured plant cells and roots, and suggest that antioxidants such as caffeoyl putresine and glutathione peroxidase seem to protect plant cells from the Al-enhanced peroxidation of lipids.