Iron-dependent oxidative stress in Chlorella vulgaris

The role of iron as catalyst for oxidative stress was studied during the development of Chlorella vulgaris cells. Increases on iron availability beyond 200 muM led to a decrease in the growth rate of the cultures of C. vulgaris. Quantification of the EPR signals of POBN/lipid radicals adducts indicated that iron addition increased lipid radical content in the membranes (more than three-fold at 500 muM Fe). The ratio of ascorbyl radical content/ascorbate content was increased in cells exposed to 500 muM iron as compared to standard conditions (90 muM Fe). beta -Carotene content was not affected by iron addition, however, alpha -tocopherol, ascorbate and total thiol content in C. vulgaris is cells was increased when iron supply was higher than 90 muM. The morphology of the cells developed under 500 muM iron showed a decreased number of ribosomes and alterations in the cellular starch deposits as compared to the cells grown at 90 muM iron. Exposure to UV-B increased the content of lipid radicals and affected cellular internal structure as compared to non-irradiated cells developed at 500 muM iron. Even though results from model systems cannot be directly used to predict ecological effects, these data suggest that oxidative stress triggered by an excess of iron could affect cellular growth and have a negative impact to phytoplankton. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.