Iron-dependent oxidative stress in Chlorella vulgaris

The role of iron as catalyst for oxidative stress was studied during the de velopment of Chlorella vulgaris cells. Increases on iron availability beyon d 200 muM led to a decrease in the growth rate of the cultures of C. vulgar is. Quantification of the EPR signals of POBN/lipid radicals adducts indica ted that iron addition increased lipid radical content in the membranes (mo re than three-fold at 500 muM Fe). The ratio of ascorbyl radical content/as corbate 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 co ntent in C. vulgaris is cells was increased when iron supply was higher tha n 90 muM. The morphology of the cells developed under 500 muM iron showed a decreased number of ribosomes and alterations in the cellular starch depos its as compared to the cells grown at 90 muM iron. Exposure to UV-B increas ed the content of lipid radicals and affected cellular internal structure a s compared to non-irradiated cells developed at 500 muM iron. Even though r esults from model systems cannot be directly used to predict ecological eff ects, these data suggest that oxidative stress triggered by an excess of ir on could affect cellular growth and have a negative impact to phytoplankton . (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.