Pollutant-induced cell death and reactive oxygen species accumulation in the aerial roots of Chinese banyan (Ficus microcarpa)

Industrial pollutants induce the production of toxic reactive oxygen species (ROS) such as O(2)(.−), H(2)O(2), and (·)OH in plants, but they have not been well quantified or localized in tissues and cells. This study evaluated the pollutant- (HSO(3)(−), NH(4)NO(3), Al(3+), Zn(2+), and Fe(2+)) induced toxic effects of ROS on the aerial roots of Chinese banyan (Ficus microcarpa). Root cell viability was greatly reduced by treatment with 20 mM NaHSO(3), 20 mM NH(4)NO(3), 0.2 mM AlCl(3), 0.2 mM ZnSO(4), or 0.2 mM FeSO(4). Biochemical assay and histochemical localization showed that O(2)(.−) accumulated in roots in response to pollutants, except that the staining of O(2)(.−) under NaHSO(3) treatment was not detective. Cytochemical localization further indicated that the generated O(2)(.−) was present mainly in the root cortex, and pith cells, especially in NH(4)NO(3)- and FeSO(4)-treated roots. The pollutants also caused greatly accumulated H(2)O(2) and (·)OH in aerial roots, which finally resulted in lipid peroxidation as indicated by increased malondialdehyde contents. We conclude that the F. microcarpa aerial roots are sensitive to pollutant-induced ROS and that the histochemical localization of O(2)(.−) via nitrotetrazolium blue chloride staining is not effective for detecting the effects of HSO(3)(−) treatment because of the treatment’s bleaching effect.