Long-term impact of cadmium shows little damage in Scenedesmus acutiformis cultures

Long-term (30 days) responses of green alga Scenedesmus acutiformis to cadmium (Cd) excess (1 or 10 mu M) were studied under in vitro heterotrophic conditions (Milieu Bristol medium containing glucose and casein). No extensive changes of morphology were observed but Cd slightly depleted chlorophyll autofluorescence and some mineral content (K, Ca, and Mg). However, Cd (mainly at 10 mu M) stimulated increase in biomass and accumulation of ascorbic acid, non-protein thiols, and phenols. Signs of oxidative stress (elevation of ROS, depletion of nitric oxide and viability, changes in the activities of SOD, CAT and GR) were also observed. Total Cd reached only 17.3 and 45.2 mu g/g DW at 1 or 10 mu M Cd but bioaccumulation factor (BAF) was comparable with other species and cultivation/exposure conditions (BAF similar to 40 at 10 mu M Cd) indicating that rather inorganic compounds than glucose or casein affect Cd accumulation. Short-term (24 h) exposure of algae to identical Cd doses in HEPES buffer revealed higher absolute Cd content in comparison with 30 days of cultivation (8-and 17fold) and comparison with previous studies indicates that S. acutiformis is a better cadmium accumulator. The extensive use of fluorescence microscopy for oxidative stress detection in algae is also carefully discussed.