Toxic Effects, Oxidative Stress and Ultrastructural Changes in Moss Taxithelium Nepalense (Schwaegr.) Broth. Under Chromium and Lead Phytotoxicity

The effect of short-term Pb and Cr (0, 100 and 1000μM) stress in moss Taxithelium nepalense (Schwaegr.) Broth., the possible generation of oxidative stress, antioxidant metabolism and changes in the chloroplast and cell membrane ultrastructure were investigated. In moss cells, treatment of Pb and Cr for 12 and 24 h decreased the dry mass and total chlorophyll content with marked inhibition under Pb. Both Pb and Cr accumulated after 24 h of their treatment where highest accumulation of Pb was visible than that of Cr. The ultrastructural studies at 1000 μM of Pb and Cr showed distortion of the thylakoid, distortion of chloroplast membrane and changes in the chloroplast structure. Chloroplast distortion was highly visible under Pb than that of Cr. The distortion in the cell membrane was evident at high concentration of Pb, while under Cr, minor changes were visible as compared to controls. Both Pb and Cr significantly increased the production of ROS like H₂O₂ and O₂ ^? radical with marked production after 24 h under Pb than that of Cr. The alteration in metabolism of activated oxygen in moss cells was evidenced by the increase in the lipid peroxidation in moss cells, with pronounced effect after 24 h than that of 12 h after Pb and Cr treatment. The SOD activity showed an increasing trend followed by decrease in CAT, POX and GR activity after 12 and 24 h. Both ascorbate and glutathione showed higher accumulation under Pb followed by Cr. The results showed that at high concentration of metals, oxidative stress could be induced in moss cells characterized by the generation of ROS and initiation lipid peroxidation that inhibited the major antioxidant metabolism. Both physiological and ultrastructural studies suggested the possible induction of oxidative stress in Taxithelium nepalense (Schwaegr.) Broth. under Pb and Cr toxicity.